Leonardo Times Januari 2016

LEONARDO TIMES

20 Journal of the Society of Aerospace Engineering Students ‘Leonardo da Vinci’

1996

Interview

Rick Tumlinson Page 37

Year 20 | N°1 | January 2016

2016

Stratos II+

One-fifth way to Space Page 44

NASA’s

Asteroid Grand Challenge Page 64

A little more room, a lot more comfort You’ll be amazed what extra legroom and a seat that reclines more can do for your journey. Get comfortable with Economy Comfort, available on all KLM ights.

Visit klm.com/economycomfort for more information.

I have learned so much at the Leonardo Times. A special thanks to all my colleagues who have made it possible to put together a professional effort every single time. After over 2 years of being the Editor-in-Chief, I hand over the reins to Victor Gutgesell.

Maybe he can explain the irony in Swiss being called neutral while the country has the world’s most positive flag!

Vliegtuigbouwkundige Studievereniging ”Leonardo da Vinci”

Asteroidal Gravitational Fields Aviation Safety Program 3D-deformation of the Earth's crust after earthquakes

Computer models for Glare material research

Periodiek van de Vliegtuigbouwkundige Studievereniging ‘Leonardo da Vinci’ - 10e jaargang - nummer 1 - maart 2006

PAGINA 24

AIR TRAFFIC Development of an Air Traffic COMPLEXITY Complexity Framework

Sushant Gupta Micro UAV Design Synthesis Exercise ‘Delfly’ to compete in first US-European MAV Competition

Editor-in-Chief

TailorMate: Tail plane design The perfect mate in tail optimisation and redesign

Galileo, European navigation system

September 2011

Europe’s own Global Navigation Satellite System

Leonardo Times Journal of the Society of Aerospace Engineering Students ‘Leonardo da Vinci’

number 3

The Leonardo Times has come a long way from its inception in 1996 when a bunch of students decided it was time that the college magazine moved from stapled printed pages and be a professional effort. The journey has been shaped by lots of talented editors through the years. As I was flipping the pages of our old editions, it gave me a sense of belonging to an organization which always thought ahead of its times and we picked out some interesting stories the journal has reported on over the years. Flip over to the centerfold of this edition to take a peek into

As I have been promising in previous editions, we have launched our brand new website: www.leonardotimes.com. Along with the print edition, you can track latest news from the world of aerospace engineering on-the-go on your mobile devices.

As an experiment, we have included some QR codes with video links to News that we have reported on in this edition as an extension of the content in print. So, go check out the website and write back to us with your comments on how we can improve the experience.

Year 15

EDITORIAL First of all, I wish you a very happy and a prosperous 2016! With the turn of the year, there is a special occasion to celebrate. The Leonardo Times Journal has completed 20 years and we celebrate this feat with this special Lustrum edition. We decided to indulge a bit and present to you this somewhat extravagant “golden” cover. As you can gauge by the thickness, there is extensive content spanning 80 pages, twice the normal content for this journal.

We feature Interviews of two stars in the Space Engineering. Rick Tumlinson, a wellknown space advocate and a pioneering visionary, talks candidly about the commercial space industry. Jason Kessler, Program Executive at NASA’s Asteroid Grand Challenge talks about how new ideas are streaming into NASA and how budding aerospace engineers can contribute. Also featured in this issue is a new series in the journal on the history of the famed “Space Race” We start from the year 1957. As always, cutting edge research from the world over is included along with articles on Balloon-powered internet, self-destructible unmanned aircraft and the very ambitious Stratos II+ rocket, fully designed and launched by student team DARE.

5e Jaargang, nummer 4, december 2001

Dear Reader,

Previous Lustrum Editions

the history of the journal.

cover september 2011.indd 1

06/09/2011 14:51

LEONARDO TIMES N°1 2016

03

FRONT FEATURES 03 Editorial 07 Leonardo's Desk 08 In the News 12 Life After Graduation

20

AERODYNAMICS

AP PHOTO/JON SHENK

CONTENTS

14 HEROES – A Helicopter analysis tool 52 Wave Drag

Project Loon

Project Loon aims to bring the technologies of access to everyone, using helium balloons that float in the stratosphere.

AEROSPACE STRUCTURES AND MATERIALS (ASM) 16 Non-conventional laminates 58 A Topology optimized airfoil 72 Continuous ultrasonic welding 74 Damage tolerance of stiffened structures

AVIATION DEPARTMENT 18 Self-destructible unmanned aircraft

CONTROL & OPERATIONS (C&O) 20 Project Loon

THE SPACE RACE 23 1957 – Sputnik and the Space Race

INTERNSHIP 28 Power Effects in airplane design

TIME FLIES 30 The hidden runway

SPACE DEPARTMENT 32 Launching space entrepreneurship

FLIGHT PERFORMANCE AND PROPULSION (FPP)

26

40 20 Years of the Leonardo Times The Leonardo Times, conceived in 1996 celebrates its 4th Lustrum. The student journal, now in its 20th year, takes a look down the memory lane.

34 Swirl recovery vanes 55 Dutch designs internationally recognized 60 Formation flight 76 Propeller with boundary layer inflow

SPACE ENGINEERING 37 Interview: Rick Tumlinson 64 NASA’s Asteroid Grand Challenge

STUDENT PROJECT S. RAMADIER/AIRBUS S.A.S.

44 STRATOS II+

WIND ENERGY 50 Can wind turbines act on what they “see”?

ADVERTISMENTS 02 KLM 06 European Patent Office 48 De Delftse Bedrijvendagen 71 ASML 79 NLR 80 Fokker

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Formation Flight

Formation flight is an operational method to reduce fuel consumption. By flying in formations, the induced drag can be reduced significantly, additionally lowering the fuel consumption.

Interview with Rick Tumlinson

TEDXESA

COLOPHON

37

Inspirational space visionary, with the motto: “those who reach for the stars have no fear of the night” and founder of several space companies sits down for a candid interview.

Year 20, NUMBER 1, JANUARY 2016 The ‘Leonardo Times’ is issued by the Society for Aerospace Engineering students, the VSV ‘Leonardo da Vinci’ at the Delft University of Technology. The magazine is circulated 4 times a year with a circulation of around 5000 copies per issue.

EDITOR-IN-CHIEF: Sushant Gupta

S. RAMADIER/AIRBUS

FINAL EDITOR: Victor Gutgesell EDITORIAL STAFF: Eleonoor van Beers, Joris Stolwijk, Lyubo Hristov, Mannat Kaur, Martina Stavreva, Nicolas Ruitenbeek, Nithin Kodali Rao, Ramya Menon, Raphael Klein, Rosalie van Casteren, Stevan Milosevic and Thijs Gritter.

THE FOLLOWING PEOPLE CONTRIBUTED: Matys Voorn, Srikar Yadala Venkata, Peyman Mouri Sardar Abadi, Jelle Westenberger, Dennis van Dommelen, Sieglinde Goossenaerts, Tom Stokkermans, Ashim Giyanani, Roy Veldhuizen, Dennis Berckmoes, Christian Alba, Dr. ir. Roelof Vos, Evert Windels, G.B. Spirlet, Martijn van Beurden, Nando van Arnhem DESIGN, LAYOUT: SmallDesign, Delft PRINT: Quantes Grafimedia, Rijswijk

NASA’s Asteroid Grand Challenge Interview with Jason Kessler, Program Executive of NASA’s Asteroid Grand Challenge. The program is focused on finding all asteroid threats to human populations and knowing what to do about them.

BORDER SESSIONS

Articles sent for publishing become property of ‘Leonardo Times’. No part of this publication may be reproduced by any means without written permission of the publisher.

‘Leonardo Times’ disclaims all responsibilities to return articles and pictures. Articles endorsed by name are not necessarily endorsed editorially. By sending in an article and/or photograph, the author is assured of being the owner of the copyright. ‘Leonardo Times’ disclaims all responsibility. The ‘Leonardo Times’ is distributed among all students, alumni and employees of the Aerospace Engineering faculty.

VSV ‘Leonardo da Vinci’ Kluyverweg 1, 2629HS Delft Phone: 015-278 32 22 Email: VSV@tudelft.nl ISSN (PRINT) : 2352-7021 ISSN (ONLINE): 2352- 703X Visit our website www.leonardotimes.com for more content. Remarks, questions and/ or suggestions can be emailed to the Editor-in-Chief at the following address:

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LeoTimes-VSV@student.tudelft.nl

LEONARDO TIMES N°1 2016

05

Join Europe’s top

engineers and scientists In 2016 the European Patent Office plans to recruit more than 200 engineers and scientists to work as patent examiners.

Our engineers and scientists – drawn from over 30 different European countries – work at the cutting edge of technology, examining the latest inventions in every technical field in order to protect and promote innovation in Europe.

If you have a diploma of completed university studies at Master’s level in physics, chemistry, engineering or the natural sciences, a good

working knowledge of at least two of our official languages (English, French and German) and the willingness to learn the third, you too could be part of our team of patent examiners in Munich, The Hague and Berlin.

We offer a competitive net basic salary (EUR 5 150.08 -7 293.53 per month, depending on experience) as well as various benefits and allowances.

To find out more about working as a patent examiner, and for details of our benefits package, visit our website at www.epo.org/jobs

LEONARDO'S DESK

A VIEW FOR 2016 Dear reader, I would like to start this first edition of Leonardo Times of 2016 by wishing you a wonderful year. For the board of the VSV ‘Leonardo da Vinci’, the turn of the year marks the midpoint of our journey that started on September 1 last year. This is a moment of reflecting on, for example, the successful Belgium Beer Drink on December 15, but most of all a point of looking at the great events that will take place over the course of this year.

I would like to congratulate the Leonardo Times editorial staff, for once again coming up with an outstanding issue. Furthermore, the Leonardo Times celebrates its 20th anniversary with a special edition, filled with 80 pages of exciting articles and memories of the magazine’s rich, two-decade long history.

Besides all these highlights and festivities, some thoughts on the contemporary state of the aviation industry should also be addressed.. The tragic events in Paris and Egypt in November, have had their effect on aviation. In the weeks followed by these incidents, the aviation industry has been scarred by bomb threats. It is a major challenge for the whole industry to make sure that aviation remains the safest mode of transport and that, in particular, civil aviation is not pressed down by the radical actions of a handful of

individuals. The accomplishment of this goal depends largely on a close collaboration between the acting parties and their combined strengths. It is in these collaborations that Europe should take lead and the Netherlands can be the perfect nation to exhibit this.

looks forward to the long awaited results. Or as in the CEO Interview that was held at our faculty on October 14, Franco Ongaro, the director of ESA-ESTEC said, “in these times of crisis, Europe can be proud of missions like Rosetta.”

One solution that will make aviation safer (and cleaner) is the regeneration of an airline’s fleet. In this light, the news of KLM’s addition of the latest flagship Boeing 787 Dreamliner amongst its fleet is received with excitement. With a total of 23 of these aircraft, KLM embraces the new, more economical and environmentally cleaner way of flying.

The board of the VSV ‘Leonardo da Vinci’ was honored to be a guest at the welcoming flight of the new Dreamliner ‘De Zonnebloem’ above the Netherlands and be amongst the first to experience the future of aviation.

I hope that the message of Ongaro, a message of hope and optimism, will resonate.

As a board, we also look optimistically at the coming six months. They will be months filled with great activities, like our Space Symposium, with the theme New Space: Launching Entrepreneurship. Furthermore, we will continue our mission to strive for an international society at an international faculty.

I would not be doing justice to this magazine’s great content and diversity if I do not address the novelties in Space. In September, NASA was able to confirm one of their longstanding hypotheses: liquid water flows on present day Mars. The space missions to Mars, like the Mars Reconnaissance Orbiter and the Mars Science Laboratory, should be considered amongst the greatest things that humanity was ever able to achieve. It is with sheer admiration that the scientific community watches the successes of the American and European Space missions and eagerly

A message of hope is also what Europe, the aviation- and the space industry need. Because hope and optimism connects people and it drives humanity forward on a positive course, in the direction of knowledge and progress. Our society’s namesake knew that already in the 15th century: The natural desire of good men is knowledge.

With winged regards, Matys Voorn President of the 71st board of the VSV ‘Leonardo da Vinci’

LEONARDO TIMES N°1 2016

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NASA, ESA, HUBBLE HERITAGE TEAM

Yves Rossy & Vince Reffet soar the skies with an Emirates A380

Final report of flight MH17 Dutch Safety Board October 13, 2015, Gilze-Rijen, The Netherlands The final report of the Dutch Safety Board claims that a “9N314M” warhead hit the Boeing 777 on July 17, 2014, as it flew at 10,000m above eastern Ukraine.

The warhead was fitted to a “9M28” Russian-built Buk missile system. The shrapnel in the debris, amongst other evidence, was the clue that led to this conclusion. The incident had resulted in tragic loss of life of 298 people, bulk of them originating from Netherlands. Ukrainian authorities claim that Russian-backed rebels were responsible but Russia in turn points the finger at Ukrainian forces. In July 2015, Malaysia proposed that the UN Security Council would organize an international tribunal to prosecute those responsible, which was vetoed by Russia. The report remains therefore inconclusive as to who is responsible for bringing down flight MH17. N.R. 08

N°1 2016 LEONARDO TIMES

EMIRATES, JETMAN.COM

IN THE NEWS ...

Virgo’s heartbeat cfa.harvard.edu November 16, 2015, Cambridge, MA, U.S.A.A team of astronomers and scientists at the Harvard-Smithsonian Centre for Astrophysics (CfA) measured the “pulse” of Messier 87, a massive elliptical galaxy in the Virgo constellation. Research included intense observation of M87 along with the examination of a unique series of images taken by the Hubble Space Telescope in 2006. The images were taken over a period of three months and revealed the galaxy to be “shimmering” as one in every four pixels changed with time. This was due to the presence of giant pulsating stars within the galaxy. Near the end of their lives, stars vary their brightness every few hundred days. By detecting and measuring these stellar “pulses”, astronomers believe to have found a new way to evaluate the age of a galaxy. This technique alongside previous findings, estimates the M87 galaxy to be 10 billion years old. M.K.

Skigull first flight IRWIN

The search for Earth’s twin cfa.harvard.edu

Flyingmag.com November 24, 2015 Coeur d' Alene Airport, Idaho, USA Famous American aerospace engineer Burt Rutan's SkiGull completed its first flight. The unusual airplane, which is designed to take-off and land from water, snow and land, flew for 1.8 hours with test pilot Glenn Smith at the controls. Rutan built the SkiGull in his garage, a 20-month project that he described as "grueling." S.G.

Parallel universe

face temperatures lower than 1000 degrees.

A search oriented towards the discovery of Earth-like worlds outside our Solar System, led to the “unearthing” of this planet. GJ1132b is 16% larger in size, 60% greater in mass and has a 20% higher gravitational field when compared to the Earth’s. It also has a rocky composition, which makes this planet a remarkable subject to study in the coming years. M.K.

Boeing December 08, 2015, Everett, WA, U.S.A PW

PurePower turbofan Bloomberg Business October 15, 2015, Hartford, U.S.A After being in the making for 30 years, Pratt & Whitney’s new Pure Power Turbofan is off to a propulsive start and expected to enter service before 2016. A gearbox located within the shaft of the engine permits the compressor to run at a different regime than the fan.

Conventional turbofans have both components attached to each other, and hence, run at the same velocity. The Pure Power engine allows them to be dissociated and operate at their optimal speeds. Consequently, the turbofan consumes 15% less fuel, pollutes less and is 75% quieter. With already 70 buy-

A ringed Mars ers located across 30 different countries, the $10 billion project just might be worth it.

N.R.

NASA

Earth, an early bloomer? HubbleSite

October 20, 2015, Baltimore, MD, U.S.A. According to a recent study conducted at the Space Telescope Science Institute (ST-

737-8max Coming out

BOEING

November 11, 2015, Cambridge, MA, U.S.A. A Venus-like planet dubbed GJ-1132b, has recently been found 39 light years away from Earth. One-fifth the size of our Sun, this planet orbits its own “Sun” every 1.6 earth days at a distance of 2.3 million kilometers. Its proximity to its star causes this rocky planet’s surface temperature to be roughly 230 degrees Celsius. While too hot to sustain water, it is cool enough to host an atmosphere. No previously known worlds have shown sur-

Inverse October 29, 2015, CalTech, CA, U.S.A. Cosmologist Ranga-Ram Chary from CalTech believes to have found a fingerprint possibly left by a parallel universe. 300,000 years after the Big Bang, recombination occurred giving rise CMB (cosmic microwave background), which encompasses all of space. The fingerprint is an evident “bruise” in the background, which was discovered whilst analyzing the CMB. It could be left by a parallel universe that bumped into ours during the recombination event. There is however, a 30% chance that this bruise just noise. M.K.

ScI), the Earth has evolved to its current state relatively early. The study suggests that only 8% of the total potentially habitable planets existed when the universe was born around 4.6 billion years ago. Our Sun will burn for another 6 billion years, before its life cycle comes to an end. However, there’s sufficient time for the remaining 92% of the potentially habitable planets to evolve. The data also illustrates that 10 billion years ago, the universe was producing stars at a much greater rate than it is now. With more than enough matter still remaining from the Big Bang, the universe will continue to create an abundant number of stars for billions of years to come.

M.K.

The Guardian November 23, 2015, University of California, Berkeley, CA, U.S.A. The death of Phobos, Mars’s mini moon, will leave Mars with a ring for millions of years. Phobos is believed to be doomed, as it will disintegrate into rubble roughly 20 to 40 million years from now.

As Phobos begins to crumble, scientists predict that within a timeframe of just 6 weeks, a ring will be formed around Mars. Mars could be the first rocky planet to wear a ring in our Solar System, the other four being all gas giants. M.K.

KLM’s new ride

KLM November 14, 2015, The Netherlands KLM celebrates the arrival of “Zonnebloem” (Sunflower), its first Boeing 787-9 Dreamliner amongst another 20 to come. Over the coming years, the 787 will play a key role in the Dutch carrier’s fleet renewal and expansion.

All of KLM’s Dreamliners will be named after flowers. N.R. LEONARDO TIMES N°1 2016

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The lonely galaxy ESA

November 13, 2015, MD, U.S.A. A recent study suggests that during the impact that caused the creation of the Earth and the moon, our blue planet might have conveniently taken all the moon’s elements such as water, zinc, and potassium. Until now, the consensus has been that this gambit occurred when the initial crash occurred. A team at the Southwest Research Institute in Colorado now believes that the speed required would need to be too high for these molecules to escape the moon’s gravity.

M.K.

November 17, 2015, HST If you think you’re lonely, the story of MCG+01-02-015 will put things in perspective…. MCG+01-02-015 is a galaxy located in a massive “void” in the direction of the constellation Pieces. Being quite alone in a spatial void, which is millions of light-years wide, it was termed “the loneliest of galaxies”

by ESA. The structure of the universe, trivially described, is a cluster of galaxies spread out in a vast 3D space where there exists more than a few voids. Such voids are empty, of course, but there are “void galaxies” which are sometimes present. It is however unknown how these galaxies end up within these colossal voids. Speculations go from past gravitational turmoil to being born from an island of gas within the void. Regardless, when you name a galaxy “MCG+01-02-015”, how do you expect it to have any friends?

M.K.

airbus.com

November 24, 2015, France Equipped with Pratt & Whitney’s new PurePower engines, Airbus’ A320neo (new engine option) is set provide unbeatable comfort and efficiency.

The new aircraft has an increased range, reduced engine noise, and lower emissions.

With already 4,300 orders, the newly certified jet is off to a tremendous start. N.R.

Cygnus is back spacenews.com

NASA

December 6, 2015 Cape Canaveral, FL, U.S.A.

Time is money!

Aviation Week November 19, 2015 Nevada, U.S.A. Aerion has begun the search for a site for final assembly and testing of its AS2. The $120 million supersonic private jet will travel at a top speed of Mach 1.5 and be able to cross the Atlantic is just over 4 hours. Perfect for those with a bulged bank account and no time to lose. N.R.

The Halloween comet

Discovery News November 10, 2015, NEO 2015 TB145, or “Spooky”, was the asteroid (or an extinct cometary nucleus) whose flyby was anticipated only 21 days before its occurrence on October 31st. In this day and age, such an event seems quite improbable. However, it’s quite difficult to spot asteroids, especially comets. There is continuous professional and amateur research for near-Earth objects (NEOs). NEOs are objects which enter the Earth’s orbital vicinity. We currently know of 13,280 NEOs and hope that we have spotted all the bigger ones. M.K. 10

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Comac’s C919 Comac November 11, 2015, Shanghai, China Comac has unveiled its first large passenger aircraft in an effort to mount a challenge to the duopoly held by Boeing and Airbus. The C919 seats 168 passengers and has a range of 5,540 km. Boeing’s latest World Market Outlook estimates that China’s total demand for civilian aircraft over the next 2 decades is worth $780 billion. The C919 will compete in the market for single-aisle passenger jets currently dominated by Airbus’ A320 and Boeing’s 737. It is an important step for the Chinese economy, where they are moving beyond low-cost manufacturing to hightech manufacturing. Comac already has orders for 517 aircraft from 21 customers, most of which are Chinese airlines. N.R.

Star’s weight loss technique space.com November 11, 2015, Shanghai, China Stars are born, they live and they die. Nearing the end, they expand profoundly to become colossal gas giants. They also lose a significant amount of their mass during this time before their supernova salvation sequence. However, it is unclear as to at causes such rapid weight-loss? Pictures of the YV Canis Majoris from the SPHERE instrument onboard the Very Large Telescope at ESO have provided an explanation for this phenomenon. The star has extremely large grains of dust which are pushed away by starlight. It’s estimated that the star expels a quantity of dust, which is 30 times the mass of Earth, every year from its surface. The photo shows the color tone caused by the massive dust particles around YV Canis Majoris.

This image is taken from the Very Large Telescope in Chile, and the SPHERE instrument is blocking out the star to better observe the dust. M.K.

ESO

A320neo certified

COMAC

space.com

IRWIN

Sneaky Earth

LOCKHEED MARTIN

November 17, 2015, Bethesda, MD, U.S.A. The FAA has approved Lockheed Martin’s Hybrid Airship for commercial transportation.

The gentle giant can carry cargo and personnel in and out of the most remote areas.

No need for airports, roads, or infrastructure of any kind. An Air Cushion landing system allows the airship to land on any type of surface, including water. The tri-lobe-hull combines aerodynamic lift with buoyant lift, significantly reducing fuel consumption and transport costs rendering it far more efficient than any fixed or rotor wing aircraft. Lockheed’s futuristic design has the potential to invigorate and expand global transportation networks. It is expected to enter service by 2018. N.R.

The New Shephard Blue Origin

BLUE ORIGIN

BLUE ORIGIN

Hybrid airship Lockheed Martin

November 23, 2015, West Texas Blue Origin, a private spaceflight company, launched and landed their reusable rocket, the “New Shephard”, during a successful unmanned sub-orbital test flight. Post launch, the rocket separated from the space capsule, and made its way back towards the launching pad where its engines reignited and the rocket hovered back down to Earth. This astonishing feat was accomplished by prudently steering the rocket. Its physical design helped it glide, air breaks brought down its terminal velocity to 622 km/h, and fins on the outside steered it through high crosswinds. This allowed the rocket to perfectly align over the landing pad, deploy its landing gear and touch down. New Shephard’s space capsule went on to successfully complete an unmanned suborbital test flight, and safely floated back to Earth.

M.K.

GOOGLE

The Internet race The Guardian November 11, 2015, CA, U.S.A. Facebook and Google are investing in rival efforts to beam the Internet down to the ground from flying objects in the stratosphere. Zuckerberg’s company is creating a network of solar-powered drones, called “Aquila”. The carbon-fiber flying wings have a wingspan of 43m and are powered by four electric motors. Data is then sent from the ground to the drone using lasers, which is then passed-on to the other drones up to distances of 11km. Aquila can then transmit internet signals to ground users via radio signals. Google’s “Project Loon” uses high-altitude balloons that use advanced software and wind currents to direct them into position, at which point they beam an Internet connection to a ground antenna. Both companies have a big financial incentive to get more people online, so which one will be the first to do so? N.R.

LEONARDO TIMES N°1 2016

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TU DELFT

ALUMNI INTERVIEWS

LIFE AFTER GRADUATION

Interviews with Aerospace Engineering graduates of TU Delft LEONID PAVLOV

Graduated in 08-2012

Which MSc track did you take and what was your thesis about?

The MSc track I took was Aerospace Structures and Computational Mechanics, my studies concluded with a thesis on the topic of designing, manufacturing and testing of grid-stiffened structures for aircraft fuselages. I did my thesis at Airborne Composites in Den Haag and it was an absolutely amazing experience due to its intense analysis/design focus and almost daily hands-on manufacturing and testing work.

When you started studying Aerospace, what were your expectations for your future career?

Before I started my studies, I always thought I wanted to work with aircraft engines, which is something I am still fascinated by and I hope I will at some point in the future. But during my studies, the charisma and enthusiasm of Christos Kassapoglou changed the way I saw aircraft structures and in the end since I wasn’t terrible at this topic and I really liked the people working at the ASCM chair, I decided to follow the structures MSc track.

At that point I wanted to work on some hardcore analysis of aircraft structures.

Did it work out? What are you doing now, and where?

It kind of partly worked out, as the work I get to do is rather advanced and I also get to work on aircraft structures sometimes. I 12

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currently work as a development engineer in the Projects department of ATG Europe in Noordwijk. The company does a lot of work for ESA, so we mainly deal with Space engineering projects, but we get to do lots of exciting work in other fields as well! The atmosphere in our department is start-up like so the motivation of all the colleagues is extremely contagious. The work is demanding, but in return one gets to work on all sorts of things from systems engineering to manufacturing technology and structural analysis methods development.

Describe a typical day at your current position There is no such thing as a typical day at ATG and that keeps it extremely interesting.

Normally the activities include brainstorm sessions with colleagues and interns related to technology and business development, often a lot of days would go into building advanced structural analysis models using CAD and FEM software for a broad range of analyses: static and dynamic, vibro-acoustic, thermal, etc. We also apply fully parametric modeling approaches at ATG and often get to develop methods and approaches on how to actually parameterize different structures, which is exciting and innovative work!

Sometimes manufacturing of composite structures and activities related to that take a significant part of the day, if not days in a row.

How are you applying your Aerospace knowledge at your current position?

I am very happy to be working exactly in the

field I have studied. So in general all of the things I have learned during my studies are applied in the daily life, on a much grander scale of course. Courses on mechanics of composites, dynamics, FE analysis, manufacturing, system and space engineering are all a great starting point for the activities I get to do.

Which aspects of student life do you miss, and which aspects do you not miss at all?

The thing I miss the most is the possibility of spending a significant amount of time on gaining fundamental understanding of a physical or mathematical problem. In the current dynamic environment I often do not have this possibility and hence I need to invest some of my own time in order to get a better understanding of particular methods or phenomena.

JOHN NAAKTGEBOREN

Graduated in 06-2013

Which MSc track did you take and what was your thesis about?

When I first started with MSc courses it was called Airline Management and operations (AMO) but later on it was called Air Traffic Operations (ATO). My thesis was about creating a performance model for an air cargo carrier from a belly cargo perspective. In the research, I have tried to find product attributes which influence the demand for cargo (Price, type of aircraft etc.).

When you started studying Aerospace, what were your expectations for your future career?

The most obvious choice was KLM because at that time I thought KLM was an amazing company to work for (I still do). However, during my study I got in touch with consulting which got me even more excited. Then at the end of my graduation project I started to think, why not combining consulting and working in the airline industry.

position

Did it work out? What are you doing now, and where?

My day always starts with a stand-up meeting of 15 minutes in which we discuss what we have achieved the previous day, the issues we encountered and what are trying to achieve that day. After the stand-up meeting, I’ll have to attend meetings like team lead meetings in which we discuss the progress, the risk and issue meeting. Also, I often perform business process mappings and I organize and facilitate workshops with the business.

Yes, it all worked out perfectly. After graduation I joined Accenture consulting and started working at an international airline.

How are you applying your Aerospace knowledge at your current position?

Describe a typical day at your current

During my study I learned a lot about the business processes in an airline (Passenger,

Cargo, Engineering and Maintenance). I try to apply this knowledge in my day to day operations (presentations, workshops).

Which aspects of student life do you miss, and which aspects do you not miss at all?

FREEDOM obviously!! Besides the fact that I do have freedom of managing my time, it is still required that I am present at the client the most of the time. During your study you can say: “studying can wait, I am going to the beach” which you obviously cannot when you are working (e.g. the day that I wrote this it was 30+ degrees). What I do not miss at all is an easy question: the exams definitely!!

LAKSHMI R SABBAPATHY

Graduated in 11-2014

Which MSc track did you take and what was your thesis about?

MSc Track: Controls and Simulation. Thesis title: Global Optimization using Interval analysis on FPGA. The thesis was about implementing an Interval Optimization algorithm used in the C&S group on a hardware called FPGA to speed up the algorithm execution.

When you started studying Aerospace, what were your expectations for your future career?

I had no expectations when I started. But as I progressed with my studies, I got interested into doing a PhD on advanced flight control.

Did it work out? What are you doing now, and where?

I am currently working as Simulation software engineer at Lockheed Martin Commercial Flight training, Sassenheim, The Netherlands. As part of the Engineering Product support team, I get to work on a wide range of issues on an aircraft from Engines to simulation of onboard systems such as APU etc.

Describe a typical day at your current position I reproduce the customer issue, study the schematics involved in the cockpit, identify software bugs and test the debugged code

in flight simulators.

How are you applying your Aerospace knowledge at your current position?

I work on the product support for A320/330.

I enjoy working on the Simulink Flight model, ground reaction model, the landing gear model etc. and I believe it’ll help me with my future aspirations.

miss, and which aspects do you not miss at all?

Something that dawned on me around graduation was that I would miss working with one of the awesome professors at C&S’, as his presence itself is so intense. I also miss attending lunch lectures, availing student privileges at events like the Paris Airshow, hot chocolate on the 3rd floor and being an editor for the Leonardo Times!

Which aspects of student life do you LEONARDO TIMES N°1 2016

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CHRISTIAN JILG

AERODYNAMICS

HEROES - A HELICOPTER ANALYSIS TOOL To linearize or not to linearize Srikar Yadala Venkata, MSc. Student, Aerodynamics & Wind Energy, Faculty of Aerospace Engineering, TU Delft A large number of physical and control parameters need to be considered for the analysis of helicopters. However, its compactness and flexibility make it a lucrative mode of, both military and domestic, transport. The HEROES toolbox is used here to compare the results of the linear and non-linear computation techniques.

However, the rotor brings in different complexities. Unlike the wings of an aircraft, the rotating blades behave differently when subjected to different physical conditions and control parameters. The sheer number of flight conditions this brings into picture is enough to explain the difficulty. The inherent instability of a helicopter adds to this making the analysis and research of helicopters rather tough but quite important.

The numerical analysis of the main rotor requires three parameters to define translational velocity, three parameters to define the angular velocity and three control parameters.

These nine parameters with the atmospheric data are solved by five equations. These include the law of conservation of momentum (or momentum theory), three flapping relations and an equation to formulate the thrust coefficient. The results of this computation 14

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are the three parameters of flapping, the induced velocity and the thrust coefficient.

The five equations can be solved non-linearly or can be linearized by neglecting higher order terms and solved as a linear set of equations. Apart from understanding the basic working of a helicopter, this article also tries to show the difference in the results from these two computation techniques and how much of a difference the linearization makes.

To do this, two cases will be considered.

Firstly, a case of a helicopter in hover mode will be taken up, followed by a case when

SRIKAR YV

H

elicopter is an aircraft that uses rotating wings to produce lift and control.

The wings rotate along a vertical axis generating aerodynamic forces. The rotating blades impart momentum onto the air in the vicinity thus accelerating it downwards. This motion of air applies an equal and opposite force on the rotor blades, producing lift. This helps the helicopter achieve vertical flight without any translational motion in contrast to fixed wing aircrafts thus making vertical take-off or landing and heavier-than-air hover possible.

the helicopter moves forward. For both the cases, an articulated rotor (stiffness of rotor blades is assumed to be zero) and a rigid rotor will be considered. The linear and non-linear analysis of the rotor is incorporated in the HEROES toolbox. HEROES stands for Helicopter and Rotor Equilibrium and Stability toolbox. It is an open source MatLab toolbox developed by the professors and students of Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio (Faculty of Aerospace Engineering) from Universidad Politécnica de Madrid. The key features of HEROES include construction of helicopter models, performance analysis, mission, trim and stability of helicopters and to act as a computer aid for design helicopters. It is being developed to act as an alternative to experimental research and also help professors in teaching.

El Hangar Lab, ETSIAE, Universidad Politécnica de Madrid.

were neglected in the linear computations.

CASE 2 This case tries to demonstrate the behavior of the main rotor of the helicopter when the helicopter is moving forward with some velocity. HEROES first converts the velocity into a non-dimensional form by dividing it by the product of the angular velocity and the radiETSIAE

The results of the two cases are obtained by varying the input parameters to HEROES as required. It is to be noted that the values being considered here are not always realistic but have been used to understand the variations and rotor behavior better. Furthermore, the data of the MBB Bo105 helicopter is used for the analysis.

The drawback of the linear model is that the rotor never stalls. This however, is not true as the rotor wings do stall after a certain velocity. As velocity increases, one can see that the coning angle increases. After a certain value of the coning angle, parts of the blade will stall due to the increase in the effective angle of attack. This is one of the errors due to linearization. When the results of the non-linear model are considered, the stall is clearly visible after a non-dimensional velocity value of 0.3.

Here too, the stiffness of the rotor only brings about a slight difference in the results, especially before the blade stalls. The major difference due to stiffness is seen in the variation of the lateral flapping angle, which is the combined effect of the inertia of the blade ETSIAE

Figure 1 - Variation of coning angle, lateral and longitudinal flapping angle with the lateral pitch angle.

ing effect). The rotor of the helicopter always exerts a force opposing the motion of the helicopter thus damping the motion. This tries to get the system back to equilibrium, thus improving the stability of the helicopter as a whole. The lateral flapping angle is also seen to decrease by about 2° due to the inertia of the blades.

CASE 1 In this case, the helicopter is allowed to hover and the lateral pitch angle of the blade is varied from zero to three degrees. The result is shown in Figure 1. Observable from the graphs is the fact that the coning angle does not really vary with the lateral pitch angle. This is because it depends only on the collective pitch angle and the blade stiffness.

The change due to blade stiffness is however very small. It is worth noting that the thrust coefficient and the induced velocity show similar results with the changing lateral pitch angle.

However, the longitudinal flapping angle is seen to increase. This is due to the pitch-flap lag. For the articulated rotor, the pitch-flap lag is 90°. Thus we see that the increase in the lateral pitch angle leads to an increase in the longitudinal flapping angle. The lateral flapping angle however remains 0°.

On the other hand, when blade stiffness is introduced, a slight fall in the values of longitudinal flapping angle is seen. More importantly, the lateral flapping angle is also seen to increase now, even though by about just a degree. This is because the pitch-flap lag is inversely proportional to stiffness. Thus an increase in stiffness reduces the pitch-flap lag slightly which leads to the increase in both lateral and longitudinal flapping angles.

There is not much difference between the linear and non-linear computation results in this case. This helps one conclude that the results obtained are accurate. The small difference seen in the results is obviously due to the effect of the higher order terms that

Figure 2 - Variation of coning angle, lateral and longitudinal flapping angle with the velocity as the helicopter moves forward. us of the main rotor. This is the reason why the variation is seen until 0.4 only. Here, the collective pitch is fixed at 15° while the lateral and longitudinal pitch angles are assumed to be zero. The results are as shown in Figure 2.

Considering the results of the articulated rotor from the linear computations first, it is seen that the coning angle increases with increase in velocity. The longitudinal flapping angle is seen to decrease. This results in the rotor cone bending backwards exerting a net force which pulls the helicopter rearwards, exactly opposite to the direction of the velocity vector. The same kind of behavior is seen when the helicopter moves backward, pitches or rolls.

and the pitch-flap lag.

Thus, in conclusion, the linear computation models do provide good results but only when the computation does not involve the stalling of the rotor. The non-linear models, though more complicated with a higher computation cost leading to better results, are more synchronous to reality.

References [1] Bramwell, A.R.S., “Bramwell’s Helicopter Dynamics (Second Edition, 2001)” [2] Tejero, A.C., Granado J.L.E., Garcia, O.L., Ruiz, J.M., Andrés, A.S., “Teoría De Los Helicópteros (First Edition, 2009)” [3] Johnson, W. “Rotorcraft Aeromechanics (2013)

This is due to the flap back effect (or dampLEONARDO TIMES N°1 2016

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ASM

NON-CONVENTIONAL LAMINATES Characterization, Design and Optimization of Dispersed-ply Laminates Ir. Peyman Mouri Sardar Abadi, Graduate Aerospace Engineering, Engineer at TANIQ B.V. Most aeronautical composite parts are made out of conventional laminates (combination of 0°, 90°, and ±45° fiber directions). Dispersed-ply laminates are one type of non-conventional laminates which are not limited to the aforementioned fiber angles. This leads to a higher degree of freedom while tailoring the structure for a specific loading case.

D

ispersed-ply laminates can be assembled using plies in any direction limited by the manufacturing equipment (interval angle of 2° or 5°). Based on the loading condition, the dispersion of ply angles can improve the damage tolerance of a laminate by maintaining its stiffness properties (Lopes, 2008). Compression after impact (CAI) is also strongly a function of the laminate stacking sequence (Dost, 1991).

Furthermore, based on the load case the direction of the fibers can be selected such that the laminate withstands the required load with less number of plies (Fuoss, 1998) resulting in a lighter structure.

Figure 1 - Short beam shear (SBS) test.

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N°1 2016 LEONARDO TIMES

Impact is the most common cause of damage, which gives rise to the utmost concerns regarding laminated composites. Delamination as a result of impact, is one of the most prominent failure mechanisms. In the aeronautical industry, damage tolerance under compression after impact (CAI) is a critical condition in designing the composite structures. Therefore, this research investigates the potential of dispersed-ply laminates in improving damage resistance under impact and damage tolerance during CAI. Many parameters affect the behavior of a

laminate under impact and CAI. To focus on the influence of dispersion of fiber orientation (different interface angles and stacking sequences) on the behavior of a laminated composite, the field of study has to be narrowed down. In this work, a quasi-isotropic (QI) laminate is studied, which has the same stiffness in any direction in its plane. Therefore, by focusing on only one of these directions for a plate, a laminated beam can be considered to simplify the problem to a 2D delamination case. Furthermore, in this work a low velocity impact (LVI) is studied, which can be approximated as a quasi-static load to reduce the computational complexity.

Therefore, impact of a plate is simplified to a short beam shear (SBS) test (see Figure 1), which measures the interlaminar shear strength (ILSS).

During this work, some experiments are performed to find a relation between interface angles and fracture toughness in mode II loading which is required in modeling delamination. Based on the simplified problem, a 2D finite element (FE) model, as shown in Figure 2, is created to simulate delamination initiation and propagation through the thickness of the laminate beam. This model is also used to reproduce buckling of the delaminated beam under CAI. Such a simple 2D model is required to minimize the computational time in order to be employed in an optimization. Note that besides simplicity of the Finite Element (FE)model, it is able to capture crack initiation and propagation between every two adjacent plies.

Although Genetic Algorithm (GA) is the most commonly employed heuristic method in the optimization of composite laminates, several authors (Bloomfield, 2010 and Hudson, 2010) concluded that for different load cases for the optimization of a laminate stacking sequence with a large design variables (more fiber directions), Ant Colony Optimization (ACO) algorithm performs better in terms of the computational time. Therefore, to improve the load carrying capability under compression of a damaged laminated composite, an ACO algorithm is used for designing dispersed stacking sequences. This optimization technique is explained in detail below.

ACO ALGORITHM

In this work, it is decided to design a dispersed-ply laminate including sixteen plies with orientations that are multiples of 5°. In addition, the laminate is symmetric and balanced. To design a symmetric laminate, it is just enough to design half of the stacking sequence, which is repeated on the other side of the symmetry plane. On the other hand, designing a balanced laminate is more challenging since the number of unbalanced laminates is much higher than the number of balanced ones in a set of 16-layer laminates made out of fiber angles between −85° to 90°, with a step of 5°.

Since the goal of this project is to investigate the effect of full dispersion of the fiber angles, placing plus and minus angles next to each other may not result in finding the best optimum solution. On the other hand, searching for the balanced laminates using all plus and minus angles (in total 36 fiber directions) needs more computations. Sebaey et al. (Sebaey, 2013) used a two-pheromone ACO technique to design a fully dispersed stacking sequence without only paring θ and − θ fibers. In this modified ACO method, the pheromone matrix defined previously is responsible for selection of fiber orientations for every design variable, which are one quarter of the total number of layers. Another pheromone matrix (Π) is responsible for shuffling of the layers. Therefore, in the first phase the fiber angles for a quarter of laminate are selected using only θ angles, in the second phase − θ angles are added to the available layers, and they are shuffled in different patterns. Since it is not feasible to use all of the shuffling patterns, limited number of said patterns is chosen.

WIKIPEDIA

The ACO algorithm is a search technique that mimics the behavior of ants in finding the shortest path between the nest and the food source. Each ant marks the path it passed between the food and the nest by depositing volatile chemical (pheromone) on the ground. Every time an ant passes the same path or part of the same path, more pheromone would be added to that area. In this way, the probability of choosing these paths by the other ants becomes higher.

After a while, the shortest way can be found when the amount of pheromone on a specific path is large enough (Dorigo, 1996). In the first step when an ant leaves the nest for food (the first optimization iteration), all the paths (stacking sequences) have equal probability to be chosen by any ant. Therefore, in this step the path is picked randomly. After that, the result of every ant (the objective function) is compared with each other. The path with the shortest distance gets the highest amount of pheromone and the longest one receives the smallest amount. The information related to the pheromones is collected in pheromone matrix (τ). After the first step, ants are more likely to choose paths with the largest amount of pheromone. This procedure continues until all the ants choose the same path, which is the shortest path (optimum solution) (Rao, 2009). Figure 3 illustrates this searching process.

Figure 2 - A 2D FE model of a laminated beam under: (a) impact (b) CAI.

Figure 3 - Left: Marking the path from the food (F) to the nest (N) by one ant, Middle: Other ants choose the paths, Right: The shortest path has the highest pheromones.

In order to decrease the computational time for each iteration of the optimization, the FE analysis of stacking sequences designed by every ant are run in parallel. This way the optimization model finds the optimum design in a shorter time period. The results of the optimization represented an improvement in damage resistance and damage tolerance employing dispersed-ply laminates.

Although no decisive conclusion could be drawn from the effect of interface angles, the results showed the potential of dispersion of fiber directions. Furthermore, considering a higher number of layers is recommended to find a simple design rule regarding the interface angles, it needs more time for optimization.

References [1] C. Lopes, O. Seresta, M. Abdalla, B. Thuis, P. P. Camanho, Z. Gurdal, B. Thuis, and P. P. Camanho, “Stacking Sequence Dispersion and Tow-Placement for Improved Damage Tolerance”, AIAA J., vol. 1735, pp. 1–11, 2008 [2] E. F. Dost, L. B. Ilcewicz, W. B. Avery, and B. R. Coxon, “The effects of stacking sequence on impact damage resistance and residual strength for quasi-isotropic laminates”, Composite Materials: Fatigue and Fracture, vol. 3, pp. 476–500, 1991 [3] E. Fuoss, P. V. Straznicky, and C. Poon, “Effects of stacking sequence on the impact resistance laminates – Part 2: Prediction method”, Composite Structures, vol. 41, pp.

177–186, 1998.

[4] M.W. Bloomfield, J.E. Herencia, and P.M. Weaver. “Analysis and benchmarking of metaheuristic techniques for lay-up optimization”, Composite Structures, 88:272–282, 2010 [5] Craig W. Hudson, Joe J. Carruthers, and A. Mark Robinson, “Multiple objective optimisation of composite sandwich structures for real vehicle floor panels”, Composite Structures, 92(9):2077–2082, 2010 [6] M. Dorigo, V. Maniezzo, and A. Colorni.

“The Ant system: optimization by a colony of cooperating agents”, IEEE Transactions on Systems, Man and Cybernetics Part B, 26(1):1–13, 1996 [7] Singiresu S. Rao, “Engineering Optimization Theory and Practice”, John Wiley & Sons, New Jersey, 4th edition, 2009 [8] T. A. Sebaey, C. S. Lopes, N. Blanco, J. A. Mayugo, and J. Costa, “Two-pheromone Ant Colony Optimization to design dispersed laminates for aeronautical structural applications”, Advances in Engineering Software, 66:10–18, 2013 LEONARDO TIMES N°1 2016

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DARPA

AVIATION DEPARTMENT

SELF-DESTRUCTIBLE UNMANNED AIRCRAFT DARPA’s new quest Jelle Westenberger, Student Aerospace Engineering & member, Aviation Department, VSV

GREEK MYTHOLOGY One might know the name Icarus (Ikaros) from Greek mythology. Icarus was the son of Daedalus, and together they escaped imprisonment by implementing the principles of flight with self-made wings. Unfortunately, Icarus flew too close to the sun, causing the wax in his wings to melt and thereby losing all the feathers attached to it. As a result, Icarus plunged into the sea and drowned.

from falling into the wrong hands, thereby handing over critical intelligence to hostiles forces. This means that the military teams have to put an extra effort in dismantling and transporting the supply vehicle. This process is time-consuming and can be hazardous to MARTYN WILLIAMS

Transporting supplies to emergency personnel and military teams that are operating in difficult-to-access areas has been possible for quite some time.

However, contemporary solutions require extra logistical efforts to realize the cleanup and disposal of the unmanned aircraft that comes along with the supplies. In order to eliminate this extra labor, the Defense Advanced Research Projects Agency (DARPA) has started the ICARUS program.

The tragic story of Icarus inspired DARPA to name their new project ICARUS (Inbound, Controlled, Air-releasable, Unrecoverable Systems). The goal of this project is to design single-use supply drones that automatically vanish after their job objective has been achieved and thereby mimicking the disintegrating wings of young Icarus that led him to his death.

DISPOSAL OF SUPPLY VEHICLES During military operations in hostile areas, it is critical for the military personnel to ensure that no supply vehicles are left behind. The main reason for this is to prevent technology 18

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Figure 1 - An electronic chip, designed by PARC, that will shatter when a laser beam hits the black dot.

the outcome of the operation. Furthermore, not only the military but also medical personnel and rescue teams who are stationed in disaster-prone areas are currently required to put in extra effort in cleaning up the supply vehicles.

This is why DARPA started ICARUS program.

This program should result in the development of supply drones that can deliver payload to military or medical teams and then swiftly disintegrate, without leaving a visible trace. This will lead to military operations progressing more rapidly and thus having a higher chance of success. Furthermore, emergency personnel will no longer have to be responsible for the disposal of the supply vehicles.

COOPERATION WITH OTHER PROJECTS

TRANSIENT REQUIREMENTS DARPA is looking for cooperation with external organizations and has therefore published a broad agency announcement in October 2015, intended to bring in some engineering teams having innovative concepts. In this document, the main purpose of the project and the minimal system requirements of the aircraft are described. It also includes some demanding requirements for the disintegration (transient) processes of the aircraft.

As an objective, DARPA requires the aircraft to “physically” disappear within four hours after payload delivery or within thirty minDARPA

ICARUS can actually be seen as an application of one of DARPA’s other projects: VAPR (Vanishing Programmable Resources), where researchers are developing self-destructing electronics for medical and military purposes. The VAPR program has already led to astonishing results e.g. small polymer panels have been developed that decay

led to the initiation of the ICARUS program which is indicated to consist of two phases, each lasting fourteen and twelve months respectively. The first phase includes the development of an aircraft that will meet the mission requirements, but without disintegrable (transient) materials. Subsequently, phase two consists of integrating transient materials with the design from phase one.

The program already has approximately eight million dollars in funding (DARPA, 2015).

designed in such a way that it ensures that the materials complete the transient process, even when there is no communication possible between the operator and the aircraft.

This guarantees the protection of critical intelligence that may be aboard the aircraft.

AVIONIC REQUIREMENTS The mission of the aircraft is to deliver the payload to a predetermined location. Besides disintegration, this is also an important mission. The idea is to release the supply aircraft from a larger aircraft that will be loitering at an altitude of about 35,000ft. When released, the supply-aircraft must be able to travel at least 150km horizontally against an average headwind of 25m/s. This represents the wind conditions at the launch and landing zone, respectively. The aircraft will most likely be gliding because having a motor requires extra design effort in order to meet the transient requirements. Furthermore, the payload must be delivered to its target destination with an accuracy of at least ten meters and it should be able to do so fully autonomously, see Figure 3.

Moreover, the aircraft must be designed in such a way that its proportions are less than three meters at maximum along its longest dimension. It must hold a payload that weighs at least three pounds and its dimensions must meet a set of different form factors. The latter will ensure that different types of military and medical equipment can be transported.

OTHER PURPOSES

Figure 2 - The aircraft must be able to traverse 150 km and deliver the payload within 10 meters of its destination. from a solid to a gas phase. These could be used as PCB’s or even as structural elements of the aircraft that immediately decay after being triggered to do so. Furthermore, another one of VAPR’s findings is the development of electronics bearing glass strips that can be triggered to shatter into minuscule particles. Moreover, DARPA has sponsored a team of engineers from the Palo Alto Research Center who created a chip that can explode on demand, either by radio signals, heat or mechanical triggering.

To increase the collaboration between VAPR and ICARUS, Troy Olsson has been appointed as the project manager of both projects.

Olsson believes that, with the progress made in VAPR, it becomes plausible to imagine building larger, more robust structures leading to using these materials for an even wider array of applications (Olsson, 2015). This has

utes after morning civil twilight (when the sun is above 5° below the horizon), whichever comes first. Physical disappearance is defined as the decomposition into particles that are smaller than 100 micrometers in the longest dimension. These particles are barely visible to the naked eye. Furthermore, the transient materials that will be used are not allowed to produce severe damage to the environment and the decomposition process must not be noticeable from a small distance. This means that burning or using explosives to get rid of the aircraft is out of the question.

Although ICARUS is mainly initiated to fulfill military uses, the technology that may result from it could also serve other purposes. Think of bio-degradable civilian drones, tracking devices for endangered animals or even biomedical devices that can serve a certain purpose within the human body and subsequently dissolve once its job has been done. The possibilities can be deemed endless.

References [1] http://www.darpa.mil [2] http://www.techinsider.io [3] Broad Agency Announcement, DARPA-BAA-16-03, https://www.fbo.gov, DARPA, October 9, 2015 The Aviation Department The aviation department of the Society of Aerospace Engineering Students ‘Leonardo da Vinci’ fulfills the needs of aviation enthusiasts by organising activities like lectures and excursions in the Netherlands and abroad.

A frequently used keyword related to triggering the disintegration is “fail-sure”. This may sound very counterintuitive to an engineer at first, but it actually describes the necessary mechanism of the triggers that activate the disintegration. The trigger system must be LEONARDO TIMES N°1 2016

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C&O

PROJECT LOON

Balloon-powered Internet for all

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GOOGLE

Stevan Milošević Student Aerospace Engineering & Editor, Leonardo Times

Two-thirds of the world still lacks access to the Internet. Project Loon is trying to change that, using a network of balloons that float at an altitude of 20km.

The team behind this project hopes to bring Internet connectivity to rural and remote areas, as well as to help fill coverage gaps, in case of a natural disaster, for example.

G

oogle[x] (the skunkworks team of Google) is a research lab with an interesting portfolio. They have started projects such as the self-driving car and Google Sunroof, which uses satellite data to determine the size and output one can receive by installing solar panels on one’s roof. They are also the people behind Project Loon – the goal of which is to project a swarm of helium balloons into the stratosphere, which communicate wirelessly with each other and with a ground station that connects the whole network to the Internet.

These helium balloons can reach an altitude of around 20km, above all commercial flight paths and weather perturbations. When launching, however, the airspace around the launchpad must be cleared. Once the balloons reach their ‘cruising’ altitude, they experience an air pressure of around 5.5% of sea level pressure, and are fully exposed to solar radiation that would normally be blocked out by the atmosphere by the time it reached the ground. While the solar panels aboard the balloons use this direct source of energy for all the onboard electrical components, the balloon itself (with a surface area of 500m2) experiences stress from the rapid temperature changes as it floats in the stratosphere.

Another current issue is the coverage per balloon - in order to form a stable network there need to be enough of them to form a moving belt around the globe, requiring thousands of balloons.

The balloons are controllable to a certain degree, since the airflow changes direction depending on the altitude and location. These airflow changes are openly published by the National Oceanic and Atmospheric Administration, and from this data the direction of the air movement at a certain location (latitude, longitude, and altitude) can be determined.

Navigation is performed by pumping air either in or out of the balloon, which changes the altitude, thereby changing the balloon’s course of direction.

As the project itself has minimal commercial market as of yet, the use of off-theshelf components is quite limited. The hardware, software, as well as the balloon itself have been mostly made from scratch. A lot of issues had to be resolved, such as the thermal control of the battery (which uses space-grade reflective blankets to keep the heat from the computer around the battery in a -50°C environment), the micro holes that appear on the balloon due to solar radiation, and the control software (Figure 1) that ensures LEONARDO TIMES N°1 2016

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The primary goal of the Loon project is to provide Internet to remote locations, but the possible use cases of this technology stretch far beyond that– imagine everyone on this planet having access to the Internet!

This is, obviously a very amitibous goal, but so is everything else done at Google[x]; they call their projects ‘moonshots’ for a reason.

The technology used on each balloon is still relatively expensive – long range Wi-Fi antennas are needed to reach the ground from an altitude of 20km, the solar panels are space-grade, and the hardware necessary for the mesh network structure needs further optimization (a mesh network is a network in which access points or nodes connect to multiple other ones nearby, creating a spider-web-looking network structure). Following Moore’s law (an observation that the average computing power of electronic devices doubles every 2 years) these electronic components will soon be of more reasonable cost, which will help expand the Loon network further.

The potential applications of this technology are seemingly endless, although currently they are specific to the communications field. Loon is targetting developing parts of the world with a lacking infrastructure, such as some parts of central Africa, the southeastern part of Asia and Oceania. Although a widespread grid of submarine cables exists around the world, some locations are still offline. Since the cost of balloon launches is decreasing rather quickly, while installing a long distance submarine cable is still as expensive as it always has been (usually in the range of billions of USD [2]), the most cost-effective solution might soon be the airborne Loon network.

Another significant application of the Loon network would be in case of natural disasters, 22

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Figure 1 - Tracking software used to monitor individual balloon’s position. such as an earthquake, where the ground lines might have been damaged, and no viable access to the outside world is possible.

A network of only a few balloons could be used to temporarily restore the connectivity of a whole medium-sized city, which would make search-and-rescue easier, and also help the general public to recover from the catastrophes quicker.

Global Internet connectivity can also be used for inflight Wi-Fi, since the current inflight Internet technology used relies on satellite Internet. With the balloons being positioned in the line of sight from a typical cruise altitude of a commercial airliner, the connection would be easy to attain. If the Loon project becomes a commercial success, it can be used as a worldwide innovation platform, out of which, currently inconceivable things can emerge.

The project has already been ongoing for three years, and in this time-frame, the team has ironed out many imperfections. The he-

a day. The stratosphere wind data has also been improved, allowing the Loon control centre to directs the balloons to where they are required – meaning the connection delivered by the network can be stabilized and maintained over longer periods of time.

Thus, the current barriers for the Loon project can be seen in the technological area although this problem will diminish over time, as with most of electronics -, and the sheer volume of production required for proper functionality. Thankfully, Google is very open-sourced with most of their projects, so as more people with an entrepreneurial mindset find out about the idea, the expansion will surely be quick.

In the grand scheme of things, some people will dismiss this idea as absurd, or that it is too far-fetched, but the global implications of creating a worldwide network infrastructure are far from that and could bring a positive change to a large fraction of civilization, most of whom are not even aware of it.

GOOGLE

What started off as a concept in 2013 is now almost ready for mass production. This is required, since a lot of balloons are necessary to provide good coverage. Project Loon plans on creating a whole belt around the equator, with balloons deflating in the stratosphere after 100 days (due to helium depletion), then are navigated to land for reusing and recycling purposes. This also becomes a logistics problem once you consider that thousands of balloons are necessary to create a continuous belt around the globe, as well as the airspace that needs clearing whilst the balloons travel in the paths of commercial flights. That is why the project started beta testing in New Zealand, where the circulating time is shorter than around the equator. Currently the beta test has expanded to Sri Lanka, Indonesia and India, with further expansion planned in the near future.

GOOGLE

that the balloons cover the right area (a complex Airborne Separation Assistance System is used, with the software developers taking the inspiration from a flying flock of birds).

Symbolic ground antenna used to connect to the Loon network. lium would initially leak from balloons, causing them to last only a few hours, instead of the initially planned 100 days – this has been fixed with automated, precise manufacturing plants that can output dozens of balloons

References [1] Project Loon, https://www.google.com/ loon/, Google, 2015.

[2] Submarine Telecoms Industry Report (3rd issue), Terabit Consulting, 2014.

THE SPACE RACE

1957 Sputnik and The Space Race

Victor Gutgesell Student Aerospace Engineering & Editor Leonardo Times LEONARDO TIMES N째1 2016

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October 4, 1957, the first man-made Earth satellite sends a steady beeping signal on radio for everyone to hear. While its creator Sergei Korolev, his team and the whole Soviet Union celebrate this success, the people of the western world are stunned and terrified. With the technology to deliver satellites into space, the Soviet Union had an advantage over the United States. Although it looked like they had won, the race was not over yet. This battle of technology soon became a battle of ideology and a fight for prestige. Nonetheless without the Space Race, many technologies would not have been developed. First article of the series where we take a look back at the famed 'Space Race'.

At the beginning of the 20th century, scientists started to look at rocket technology and its potentials. Inspired by the first science fiction books like “From the Earth to the Moon”

by Jules Verne or “In the Days of the Comet”

by H. G. Wells, the dreamers amongst the scientists began to wonder if space travel was an actual possibility. The pioneers in the field were Konstantin Tsiolkovsky and Robert H. Goddard. Tsiolkovsky, who was a teacher of mathematics, published his paper “The Exploration of Cosmic Space by Means of Reaction Devices” in 1903 and became famous within the Soviet Union. He described 24

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the physical laws that govern a rocket’s motion. In his honor, the equation that describes the velocity change acquired by a rocket was named the “Tsiolkovsky Equation”.

Robert H. Goddard on the other hand took

an engineering approach to rockets and became famous for his three improvements to rockets. He significantly improved the rocket’s performance by introducing a combustion chamber, an exhaust nozzle and the arrangement of the rocket into stages. Both men concluded that a rocket propelled by liquids would have a great amount of power and potentially enough to go to space.

WERNHER VON BRAUN When in 1923 Hermann Oberth published his book “By Rocket into Planetary Space”, he inspired many fellow Germans to do research in rocketry with the dream of spaceBUNDESARCHIV

ROCKETS? Rocket technology is older than one would think. Already around 300B.C, Chinese used gunpowder, stuffed in bamboo tubes, sealed at one end as fireworks. Whereas this was firstly used for rituals, it soon became a part of their military strategies. The Mongols brought this technology to the West. The first documentations in Europe about rockets are dated to around 1250 A.D., and the European armies used small ballistic rockets to augment their artillery from that point onwards.

The technology, however, was underestimated until World War II.

NASA

A Bumper V-2 test in the United States.

Before creating their own rockets, both, USSR and the United States, reconstructed German V-2s to study the technology.

Wernher Von Braun (1912-1977) in Peenemünde with high rank Nazi officials, General Dr. Dornberger, General Olbricht, Major Brandt.

When WWII ended, von Braun and his team had to decide what to do. Both USSR and U.S. authorities had taken an interest in German know-how and technology. Von Braun, together with his team, decided that their knowledge would be best used across the Atlantic. Since they were afraid of being forced to work in the Soviet Union and their workplace was close to the Russian front, von Braun took his whole personnel and equipment south to Austria, where he surrendered to the U.S. army. Shortly after him, his team from Peenemünde and his equipment were shipped to the United States.

SERGEI KOROLEV

NASA

At the same time, the Red Army were trying to find the Germans who were responsible for the V-2. Impressed by German technol-

Portrait of Sergei Pavlovich Korolev (1907-1966).

FLY.HISTORICWINGS.COM

flight. Thus followed the foundation of many rocketry clubs in Germany, one of which was “Verein für Raumschiffahrt” (Society of Spaceship Travel), and it was soon joined by a young Mechanical Engineering student, Wernher von Braun. Von Braun was ever since fascinated by rockets and after reading Oberth’s book, the dream of going to space did not leave him. After his graduation in 1932, he dedicated his time to developing new rockets and he soon managed to convince the military of his capabilities and became the director of the German military rocket program. Under the Nazi regime and throughout the war, he continued his work on rockets. Therefore, he moved to Peenemünde, a city at the coast of the German Baltic Sea. This period of his life remains controversial to this day, as it is unclear to what extent he was supporting the Nazi regime. During the war, he produced his most famous rocket, the V-2. Von Braun claimed that his research was only concerned with space travel. Therefore, after hearing about the V-2 strikes on London, he said, “the rocket flew perfectly, except for landing on the wrong planet”.

Robert H. Goddard next to his liquid fueled rocket in 1926. ogy, the Soviets decided to take whatever they could and incorporate it into their own technology. Sergei Korolev was one of the many experts assigned for this task.

Korolev, born in 1907 in Ukraine, and who was originally an aircraft designer, took an interest in rocketry in the 1930s. He had previously made a name for himself amongst space enthusiasts in Russia, with his publications and the co-foundation of a rocketry organization called GIRD. The group lasted for two years until the military saw its potential and merged it with their Gas Dynamics Laboratory. Korolev was assigned deputy chief of the institute and from then on dedicated his research to rocket technology. In 1937, during the Great Purge, Korolev was denounced for dislocating funds and thus sentenced to imprisonment in a Gulag camp.

He was sent to eastern Siberia to work in a gold mine. A change in leadership in the secret police got Korolev out of the Gulag just a year later. He was moved to a “sharshka”, a slave-labor camp for intellectuals, where he worked on engineering projects, assigned by the communist leadership. After working on two bomber airplanes, Korolev was moved to a sharshka under Valentin Glushko, where he worked on a rocket assisted booster for aircraft. His imprisonment was a primary reason why the Russian rocket technology fell behind the German’s, which was now in American hands.

A government decree discharged Korolev and many other scientists in 1944. As a decoration for his work, Korolev was awarded the badge of honor in 1945. Shortly after, he was commissioned into the Red Army and ordered to go to Germany and recover German rocket technology.

Korolev and the Red Army were not able to find any scientists responsible for the V-2s.

In a great effort to find them, the Red Army hung wanted posters, drove through cities and villages with megaphones and questioned surviving workers. They did not know about von Braun’s surrender to the U.S. In the end, they retrieved some 150 German scientists and pieces of the V-2 project and brought them back to Russia.

THE WEST The end of WWII marked the beginning of the Cold War; a war fought with propaganda and espionage, rather than soldiers. The Cold War was a battle of ideologies and technologies. It was the USA against the USSR, East against West, and somewhere in between those worlds, von Braun was pitted against Korolev.

Both Superpowers developed the nuclear bomb and concluded that the optimum carrier system for its delivery was a rocket. In case of an attack, a rocket or a missile would be the perfect means of a counter attack.

Neither the White House nor the Krem LEONARDO TIMES N°1 2016

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lin were interested in going to the Moon or sending anything into orbit. After WWII ended in 1945, this remained the great dream that von Braun and Korolev shared. Individually both nations developed their rocket technology further. However, with von Braun and his team, the United States had a technological advantage over the Soviet Union.

Upon arriving in the United States, the scientists were further interrogated and later moved to Fort Bliss, an army installation north of El Paso, Texas. These scientists were so valuable to the U.S., that they cleared out the history of their involvement with the Nazi party in Germany and kept their existence within the U.S. a secret to the public for some time. With their new fake documents and fake history, the scientists were ready to get back to their work. Nonetheless, they were not allowed to do so. In Fort Bliss, they were kept under constant surveillance and apart from demonstrating some V-2s and teaching Americans about rocketry, the Germans were more or less doomed to do nothing.

Von Braun sent out many appeals to continue his work and all were denied until the Cold War became hot for the first time.

When the Korean War broke out, the need for missiles surged once more. In the military, it was clear that the best way to satisfy this need was to use the Germans. The instructions from Washington said to ‘please build

Von Braun used this military base for his dreams of civilian space flight. He published magazines and illustration books about the possibilities of spaceflight and involved the larger public with his dreams. He even played with the idea of a retaliation weapon in space, which would take the form of an armed space station and in the event of a Soviet attack it would launch a nuclear missile. Another space enthusiast, Walt Disney, jumped the gun on promoting spaceflight.

Together with von Braun, he paved the way for the U.S. public to fantasize about a flight to outer space.

As the director of the Development Operation Division of the Army branch, which was in charge of the rockets, von Braun modified a Redstone to a sounding rocket and created the Jupiter-C; the first rocket to have the capabilities to bring a satellite to space.

This was proven in a flight test, which was surveyed by the army, so von Braun and his team would not accidentally launch into space. In 1954, the U.S. government agreed that a research satellite would be sent to space in the International Geophysical Year, 1957. In Washington, however, von Braun remained a controversial character. Many believed that the first satellite should be an American achievement, without German help. Thus, the Navy was granted the first go for a satellite launch. Their system, however, relied on too many new technologies, whereas von Braun’s philosophy was to test, test and test again before even considering a launch.

Korolev began working on an R-2 rocket in 1947. Besides being a revolutionary designer, he was also a good manager and had a talent in organizing and planning. This made his career advance rapidly and soon he became so important to the Russian rocket program and the USSR Military that his very identity was kept a state secret. Many people working for him did not even know his name from then on; they simply called him ‘Comrade Chief Designer’.

With the R-2 missile, Korolev was able to double the range and precision of the V-2.

The next development, the R-3 topped that range again, however due to engine problems the program was shut down in 1952.

This was followed by a short-range missile, the R-5. Already then, Korolev was dreaming of larger carrier systems and so was the Kremlin. In 1952, he was assigned the task to build an intercontinental ballistic missile with the capabilities of delivering a 5-ton warhead to the United States. This seemed ludicrous to many rocket engineers back then, mainly because of the required thruster size. Korolev, however, took the job and said it could be done. For him this rocket was the ticket to space, indeed the R-7 certainly had the payload capabilities to do so. Yet the thrust required for this rocket remained a problem. Korolev had an idea – he approached Glushko, a specialist in rocket engine design and suggested clustered thrusters and a multi-stage rocket. Glushko agreed after some arguing under the condition that the engines were his department only.

Already in 1953, the first ground tests were carried out. The revolutionary design posed many problems and the test failures put a lot of pressure on Korolev. Besides from having clustered engines and several stages, the ALEX ZELENKO

WIRED4SPACE.COM

Redstone rocket at take-off.

a rocket like your V-2, just bigger and better’.

Thereafter the team was moved to Huntsville, Alabama, to the Redstone Arsenal of the U.S. Army. With new funding for his projects, von Braun was able to develop the Redstone rocket in 1953. The rocket was a short-range nuclear missile, the first of its kind.

Then – the shock; a steady beeping sound on radio, for everyone to hear. It was the Russian Sputnik sending its signals as it was in orbit around Earth.

THE EAST In 1947, the first R-1 rocket was tested. After two years of gathering information and reconstructing V-2 blueprints, the R-1 was built. It was in fact a Russian made V-2 missile with only few modifications. In total eleven tests were made with the R-1 which proved to be as imprecise as the V-2. With such poor precision and short range, the pressure increased on Korolev, who had been assigned Chief Designer of long-range missiles. He soon decided that rebuilding German technology would lead them nowhere without von Braun himself. Therefore, the German rocketry group in Russia was soon dissolved and sent back to Germany. Nonetheless, the Russians learned some valuable lessons from the tests.

An R-7 rocket in exhibition in Moskow

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RUSSIATREK.ORG

rocket was the first rocket ever to use thrust vectoring as means of stabilization. Already while testing the rocket, Korolev tried to persuade his military officials to use to rocket to launch a satellite. However, the military was only interested in sending warheads to the United States. A visit by Nikita Khrushchev marked a positive change – while showing him a mockup of the R-7, Korolev took a bold approach and showed the leader of the USSR his ideas for a satellite and managed to convince Khrushchev to investigate spaceflight further.

August 7, 1957 was the date that Korolev had waited for so long, the first successful test of his R-7 rocket. Now they had to prepare a second launch and replace the dummy warhead of the test with the satellite.

The original idea was to send a satellite with scientific experiments and cameras to space.

The satellite was called Object-D. Object-D had to undergo a major makeover because it turned out to be too heavy and too large for a launch. The Russian scientists stripped it to its bones until only a sphere with a radio transmitter and four antennas was left. This sphere was named the Sputnik-1.

On October 4, 1957, the satellite was launched from Baikonur Cosmodrome. After lifting off perfectly and ascending to space, the team had to wait 90 long minutes to hear the signal that Sputnik sent from space. The signal did come 90 minutes later, as expected. The first man made Earth satellite had successfully been sent to space!

SPUTNIK SHOCK When the first people heard the signal in America, they could not figure out what it was. It worried them, with all their technology they could not understand how this signal is coming from space. It did take them a while, but finally they figured out it was being emitted by a Russian satellite. The Ideological enemy of the Cold War had apparently beaten them in technology. For von Braun, the news was an absolute shock. With his rocket, he would have been able to beat the Russians by a year but the Americans did not allow him. Then he was ordered by Congress to testify on the technological gap between the Russians and the Americans. He made it clear that he was blocked from using his full potential as an engineer.

The U.S. was under pressure to launch a satellite too. In a rushed attempt to close the technological gap, the U.S. Navy prepared one of their untested Vanguard rockets with a satellite on top. What should have been a media spectacle turned into a shaming disaster. The rocket lifted off one meter from the pad only to crash back on the ground and blow up in a ball of fire. Even though von Braun was sorry for the scientists, he was also happy to have a chance to finally launch a satellite. Within 60 days von Braun

USSR propaganda poster from a space campaign between 1958-1963. The poster displays Sputnik 1,2 and 3 on their way to space. The text reads: “Motherland! You lighted the star of progress and peace. Glory to the science, glory to the labor! Glory to the Soviet regime!” was supposed to launch.

Then came another shocking news from Russia. Only four weeks after Sputnik-1, the Russians have sent a living dog, Laika, to space. To celebrate the anniversary of the October revolution on November 4, 1957 the Soviet Union announced this worldwide.

Now the Americans began to worry. If the Russians could do that, they could easily shoot a hydrogen bomb on American soil.

All eyes were on von Braun now.

et took off with the satellite Explorer-1. The United States were back in the Space Race.

References A Brief History of R ocketry, solarviews.com/ eng/rocket.htm Wernher von Braun: Dreamer of Space, Engineer of War, Michael J. Neufeld The Red Rockets' Glare: Spaceflight and the Russian Imagination, 1857-1957, Asif A. Siddiqi Sputnik and the Soviet Space Challenge, Asif A. Siddiqi

On January 31, 1958, 22:48 ET a Juno rockLEONARDO TIMES N°1 2016

27

DARCORPORATION

INTERNSHIP

POWER EFFECTS IN AIRPLANE DESIGN Design, Analysis and Research Corporation (DARcorporation) in Kansas, USA Dennis van Dommelen, MSc. Student Flight Performance and Propulsion, Aerospace Engineering, TU Delft Propeller power affects aircraft performance significantly. Incorporating these effects in a preliminary design stage leads to more efficient aircraft designs and reduces time spent on redesigning the aircraft. These effects were addressed and new prediction methods were to be developed during a six-month-long internship at DARcorporation in Lawrence, Kansas. semi-empirical relations from research done on propeller aircraft in ‘60s and ‘70s (Hoak & Finck, 1960 and Wolowicz & Yancey, 1972).

The relations are based on existing theory and experimental data. The benefit of these methods is that they are accurate for the computational effort they require. However,

According to the subsequent research on the propeller wing interaction (Veldhuis, 2005), the use of the semi-empirical relations is restricted due to approximations of the DARCORPORATION

D

esign, Analysis and Research Corporation is an aeronautical engineering services company; the headquarters are located in Lawrence, Kansas, USA. Dr. Jan Roskam and Dr. Willem Anemaat co-founded the company in 1991. The core business of the company is aeronautical consulting, and besides that, the company distributes software and sells aircraft design books. It develops a preliminary aircraft design tool: Advanced Aircraft Analysis (AAA).

The project work focused on improving the power effects module and development of new methods for this particular module.

these methods have restrictions on certain parameters such as the aspect ratio of the wing. Developments lead to the usage of more efficient, higher aspect ratio wings. This way the empirical relations are less accurate as they require extrapolations. To improve this, new alternative (sub)methods are found and tested.

PROJECT WORK Propeller-powered aircraft still offer a high propulsive efficiency. Together with the development of the prop fan/open rotor fan, there is a need for a design tool for multiple configurations. The accuracy of the current method is determined first to see how accurate the prediction capabilities of the tool are. of the tool are. Current methods are based on 28

N°1 2016 LEONARDO TIMES

Figure 1 - Streamlines from a CFD analysis for a Cessna 210 Centurion.

aerodynamic characteristics of individual components or based on a simple combination of different components. In this research, a Vortex Lattice Method (VLM) with a Full Interaction Mode (FIM) is developed for propeller wing interaction. The FIM incorporates the interaction of the propeller on the wing, but also the interaction of the wing on the propeller. This method is further extended for use when analyzing complete aircraft by adding other aerodynamic surfaces to the model.

The results of the VLM with a FIM are compared to wind tunnel data for several aircraft.

It was found that the lift coefficient lined up well with the different lift curves obtained from NASA research reports. The pitching moment coefficient was less accurate, which is probably caused by the drag force contribution, as VLM is less accurate for drag predictions. A different method for drag estimations can improve the accuracy of the method. Besides the data obtained from AAA and wind tunnel data, different design tools, such as OpenVSP and CFD software (Figure 1), are used to compare accuracy and computational effort with the new method.

The VLM with a FIM is written in a paper for APISAT 2015 (Van Dommelen, Carroll & Anemaat, 2015), an international symposium on aerospace technology held in Cairns, Queensland, Australia. Dr. Willem Anemaat presented the paper in November 2015.

Writing a paper for the conference was not only exciting, but also a very valuable experience during the internship.

WORKING AT DARCORPORATION

The work experience is not the only useful part of working at the company; it is also very useful for networking. Dr. Jan Roskam still visits the company for an hour every day.

His experience in the aerospace engineering business is well known and his design methods are used in the TU Delft Aerospace Engineering curriculum. The conversations with Dr. Jan Roskam about his design experiences were very interesting and he gives tips and tricks in aircraft design that one might not have come across. Although the company is small in terms of the number of employees, it is well known in the aerospace industry.

During the six-month internship, Dan Raymer visited the office and gave a very interesting presentation about his tailless aircraft design.

DARcorporation has a close collaboration with The University of Kansas as well, which gave the opportunity to meet different researchers and professors. The University of Kansas is also located in Lawrence, where the aerospace engineering department of the University consists of thirteen professors.

ROCK CHALK JAYHAWK! During a visit to Lawrence, Kansas, you are most likely to hear “Rock Chalk Jawhawk” multiple times. This is the slogan of The University of Kansas. Rock Chalk refers to Mount Oread, where the university is located. Mount Oread consists of a coccolith-bearing chalk, similar to the white cliffs of Dover. The Jayhawk is an imaginary bird, which is the mascot of the university. Lawrence is situated in the north-east of Kansas. Population-wise it is as big as Delft, however, the city is spread out across an area twice the size of Delft, which is usual in the States. The sports culture is very different compared to the Netherlands; the university teams are very competitive and play in the national leagues. Kansas University is known for its basketball team.

American Football is also very popular, although the university is struggling to recruit

good football players. Nevertheless, the football stadium of The University of Kansas has a capacity of over 50,000 people. Baseball is another popular sport in the USA and in Lawrence; the majority supports the Kansas City Royals. During the internship, the Royals won the World Series for the second time in history, which was celebrated by over 800,000 people.

THE AMERICAN EXPERIENCE During the weekends, there is plenty of free time to get a feeling of the true American experience. As Lawrence is situated in the middle of the USA, it is a good location to start your road trips. Colorado and the Rocky Mountains are accessible by car and are definitely worth visiting. Float trips, camping and hiking are activities that are also popular.

This is a good way to explore the USA. Besides travelling, the American experience is not complete without holidays like Independence Day, Halloween and Thanksgiving.

Halloween in Lawrence was a completely new experience, where everyone dresses up in costumes and attends parties. Everything together made the six months an unforgettable experience. If you ever get the chance to do an internship abroad, do not hesitate and take the opportunity!

References [1] Hoak, D.E. and Finck, R.D., USAF Stability and Control Datcom, Flight Control Division, Air Force Flight Dynamics Laboratory, WPAFB, Ohio, 1978 [2] Wolowicz, Chester H. and Yancey, Roxanah B., Longitudinal Aerodynamic Characteristics of Light, Twin-engine, Propeller-Driven Airplanes, NASA TN D-6800, June 1972.

[3] Veldhuis, L.L.M., Propeller Wing Aerodynamic Interference, Delft, The Netherlands, 2005.

[4] Van Dommelen, D.M., Carrol, J.D., Anemaat, W.A., Semi-Empirical Propeller Power Effects in Airplane Preliminary Design, APISAT 2015.

VAN DOMMELEN

DARcorporation is a company that offers the opportunity to work on a broad spectrum of subjects. Besides the aircraft design projects, the company is also working on wind turbine designs and drag reductions for e.g. pick-up trucks. Within aircraft design, the engineers have their own contributions in their field

of knowledge, such as Aerodynamics and Structural design.

Road trip to the Rocky Mountains, Colorado.

LEONARDO TIMES N°1 2016

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PETRA/ PEDAL POWER TOURING

TIME FLIES

THE HIDDEN RUNWAY Vietnam’s successful air attack on the U.S. Navy Joris Stolwijk, MSc Student Aerospace Engineering, Editor Leonardo Times In the wake of World War II, Vietnam had become the next major battleground of the 20th century. It started with a battle for independence against the French, led by Ho Chi Minh and backed by the communist nations. Along with Laos and Cambodia, Vietnam finally became independent, but the country was split up in a communist northern and a democratic southern part. After attempts to reunite the country through elections failed, the southern part sunk deeper into political instability.

P

rime Minister Diem had failed to sustain peace and unity among its citizens, and as a consequence, the pro-communist National Liberation Front, better known as the Viet Cong, started guerrilla attacks from within South Vietnam. As the South Vietnamese army proved incapable of dealing with this disturbance, the US first got involved in the matter out of concern that the communist regimes would spread further. John F. Kennedy, US president at that time, was convinced that through air superiority, the conflict could be resolved within a short amount of time.

The power of the U.S. Air Force was indeed far superior to the more or less improvised group of aerial combat forces of North Vietnam- the Vietnamese People’s Air Force.

The VPAF only started to take shape several years into the Vietnam War, while the USAF already had decades of experience. However, once aided by the Soviet Union and China, Vietnam was quickly able to acquire a sizeable fleet and trained pilots. Still they never owned more than 200 aircraft [1], which was a fraction of the USAF's fleet. Over the course of the war, there were several events 30

N°1 2016 LEONARDO TIMES

that depicted how Vietnamese aircraft were still able to significantly impact the air domination by the US, eventually helping them to force the retraction of the US troops from Vietnam. One of these events took place on April 19, 1972.

stories told by local Vietnamese people, and has not been completely documented. Still, there may be enough evidence to claim that this must be one of the most impressive feats of the VPAF and Nguyen Van Bay. The preparation of the mission was supported by the clever ground troops of the North Vietnamese Army (NVA), who took advantage of the fact that they had far superior knowledge of their environment compared to the US troops, who were in a very unfamiliar territory. The USAF’s massive presence in Vietnam’s airspace meant that during the

Nguyen Van Bay (Figure 1), currently known to still be alive, is a veteran MiG-17 pilot, and one of the most heroic Vietnamese figures of the VPAF. He was born in Saigon (now known as Ho Chi Minh City) and fought against the French in his teens, yet he stayed in the communist Northern half after the separation took place and lost contact with his entire family. He was among the first pilot trainees for the VPAF, and was trained in China by Russian instructors. In 1966, after 200 training hours, he went into his first of many combats. In the following two years, he managed to shoot down seven USAF fighter aircraft, which was a remarkable achievement, although the US only acknowledges five of them [2]. It was only several years later when he would get to lead the mission that would make him a true national hero.

This particular event is partially based on

Figure 1 - Nguyen Van Bay.

BINH GIANG

Figure 2 - Nguyen Van Bay’s MiG-17, with registration 2047, in its current state.

Neither of the ships sank, and in absolute terms, the damage done did not critically affect the capabilities of the U.S. Navy. However, the psychological impact was significant for both sides. The Vietnamese hailed it as a great moral victory, as they finally achieved a feat that had been in planning for years- a successful attack on a U.S. Navy warship.

For the United States, it was the first air strike suffered by the U.S. Navy’s 7th fleet since the end of World War II [1], and it was a warning that they could not lower their guard, even at times when there was no apparent threat nearby. They were forced to use more men and resources for the protection of their ships at a time when the number of US troops had already begun to reduced.

Of course, the US hit back hard by attacking the cities Dong Hoi and Vinh directly afterwards. A few days later, they also found the location of the improvised runway at Gat. With a force of 33 aircraft, the runway and the stationed MiGs were completely destroyed,

and the VPAF had to abandon it [3]. For the North Vietnamese, it was all worth it, and Nguyen Van Bay made headlines. He was a favorite of Ho Chi Minh, and they dined together often. Soon after this successful mission, he was grounded from air combat service, such that his status could inspire future generations. After the retraction of US’s troops and the reunification of both halves of Vietnam, Van Bay’s heroics were permanent national pride. He became a farmer afterwards [1].

References [1] North Vietnamese Aces, http://acepilots. com/vietnam/viet_aces.html [2] Nguyen Van Bay and the Aces from the North, http://www.airspacemag.com/military-aviation/nguyen-van-bay-and-the-acesfrom-the-north-1606486/?no-ist=&page=1 [3] Boniface, Roger, MIGs Over North Vietnam: The Vietnam People's Air Force in Combat, 1965-75. Stackpole Books, 2010

US NAVY

daytime, when the USAF’s aircraft could be used to observe and control the activity on the ground, the Vietnamese were virtually powerless. In no way would they stand a long-term chance in direct confrontation.

The Vietnamese tactics where thus based around a typical game of hide-and-seek: as soon as the night fell, and the USAF couldn’t see what was happening on the ground anymore, the ground troops came into action to make things happen. Close to the Demilitarized Zone (DMZ), at Gat in the Quang Binh province, construction of a runway commenced by converting the road that was already there (see visual). However, every night before sunrise, they would cover their progress again with soil, such that from the air it would still appear to be a normal road.

This process was repeated for months until completion, when two MiG-17 fighter jets (Figure 2) were being assembled from their parts transported in the night for a milestone mission in the Vietnam War: the first ever bombing of US Navy warship. The makeshift runway was particularly short for the MiGs, and booster rockets had to be attached to the aircraft to make them take-off in time [3], whilst having to fly very low to stay unnoticed by radar. The targets were two US Navy warships, the USS Oklahoma City and the USS Higbee, which were attacking the Northern Vietnamese city Vinh from the Gulf of Tonkin.

The MiGs’ element of surprise proved very effective, as the aircraft were only discovered

by US radar when they were already nearing them at full-throttle. Using 250kg bombs, Van Bay managed to impose minor damage on the USS Oklahoma City, while his companion Le Xuan Di hit the USS Higbee in the rear and destroyed its gun mount (Figure 3).

They managed to escape from heavy gunfire and returned to the makeshift runway with little damage. The mission only took 20 minutes [3].

Figure 3 - The USS Higbee (DD-806), under repair in the Philippines after the attack by the VPAF. LEONARDO TIMES N°1 2016

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NASA

SPACE DEPARTMENT

LAUNCHING SPACE ENTREPRENEURSHIP The NewSpace industry Sieglinde Goossenaerts, Student Aerospace Engineering & member, Space Department, VSV Space exploration has always been funded by government organizations.

However as times are changing, the need for an open space policy is growing.

Nowadays, data is power and entrepreneurs are thinking ahead to create a variety of services to meet the growing demand for easy and reliable access to space.

The driving force behind these missions has traditionally been a government agency, allowing engineers and scientists to fulfill their dreams and feed their curiosity. While certain questions can now be answered, even more arise as data is analyzed. This data is of essential value to a growing amount of companies. There is a gap between the public demand for this data and the supply that space organizations provide. This gap has been growing for the past years and is further growing day by day.

Since several years, relatively new compa32

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nies are filling this gap: entrepreneurs who are not bound by conservative procedures and focus on the possible profits, rather than being governmentally funded. The capabilities of currently orbiting satellites are being maximized and new ones are sent to space in order to fulfill the customer’s demands.

This increased demand, coupled with a low

LIFT-OFF Some of the largest players in the field operate in the lift-off segment, providing launchers and launch bases. The launcher industry still has many established companies such as Astrium and ESA, but they are being chalSATELLITETODAY

A

lmost 60 years ago, engineers made history by launching Sputnik into orbit. This was the first milestone in the history of space exploration. Governments engaged in a race for the power over space, launching a wide variety of spacecraft throughout the years: satellites, manned orbiters, interplanetary and deep space mission probes, lunar landers, re-entry vehicles etc. fueled by the desire to showcase their technological superiority. They made discoveries about both the universe and Earth and are still doing so today.

supply that is heavily regulated and generally expensive, creates a market for space entrepreneurs dreaming to offer easy and reliable access to space. This has led to lowcost launchers, satellites, and data services.

The possibilities of opening space are endless, ranging from extremely precise and relatively cheap data services to space tourism.

Figure 1 - "Constellation flying" is multiple satellites flying in such patterns that they can continually cover the surface of the earth.

high-speed access to internet, even in the most remote areas of the globe. The system could be used to accommodate worldwide access to education, disaster management, or even an interupted internet connection while you are on an airplane. The satellites used would be easy to manufacture, lightweight and thus cheaper to launch [5]. The best of it all is that contrary to the traditional approach, all satellites can be mass-produced, reducing their cost even further.

Not only the supply of launchers itself, but also our entire vision on spaceflight and its accessibility is challenged. Quoting Spaceport America’s website [2], “enable affordable, efficient and effective access to space by developing and operating the world’s first purpose-built commercial spaceport aimed at inspiring and delighting the next generation.” It is safe to say that ambitions for this business are sky-rocketing.

This mass production is perhaps the largest asset of the new approach in satellite use.

Until recently, almost every vehicle sent to space has been individually designed for its dedicated mission purpose. A large disadvantage of this approach is that small damages to single components are often catastrophic. Constellation flying prevents these large-scale losses: when sending 648 individual micro-satellites to space, losing one can hardly be called catastrophic. This holds VIRGIN

lenged by the likes of SpaceX. These private companies strive to launch space missions at a fraction of the current costs. There is a high demand for cheaper rockets capable of shooting a variety of small satellites into orbit; both from the academic and private field.

This demand is being met by conducting revolutionary experiments, such as developing fully reusable rockets, which promise to launch more frequently, being cheaper and more reliable than ever [1].

getting more advanced. Considering ESABIC, that brings several space entrepreneurs under the ESA banner, some noteworthy applications are sports monitoring, city parking and decision support for ICT businesses [7].

Dedicated software can turn any image into a pattern of behavior and make conclusions from this data; you name it, you design the necessary software and satellite observations can tell you anything you want to know.

Though it might not seem glamorous, data management is the most direct way in which the space business influences our daily life through the nearly infinite amount of directions you can go with the data. Whether you’re interested in agriculture, sports or behavioral science, space could offer you the solutions you need.

Interested in hearing more about space entrepreneurship? Make sure to join the VSV symposium on March 1, 2016. The VSV symposium exists to inspire and stimulate aerospace students and any other student or professional that takes interest in entrepreneurship in space. The aim of this symposium is to offer insight into the possibilities the entrepreneurial approach offers, its foundations and current limitations. This involves discussions about new applications developed by the private sector to meet the demands of the general public. More info can be found at: http://vsv-symposium.com/.

References

Figure 2 - The Virgin Galactic vehicle.

IN-ORBIT But what should be launched into space?

In terms of satellites, some inspiring projects are currently going on. For example, Planet Labs having developed a system of satellite constellation flying (Figure 1) offer a photographic mapping system with great prospects. By 2016, the constellation could map our entire globe every day, which could be extremely useful for monitoring agricultural areas, climate programs and a wide variety of other interests. [3] Another example Skybox Imaging, which started out as a graduate project from Stanford. Only four years later, the company was bought by Google for no less than 500 million dollars and is looking at a bright future with data services through satellite constellations. [4] Big data is a true goldmine, and entrepreneurs are seeing its possibilities.

Incredible data can be acquired from satellites meant for imagery, but this is just a fraction of the possibilities: another exciting application of constellation flying is the project ‘OneWeb’. The goal is to send 648 micro-satellites in a constellation, enabling worldwide

an enormous advantage over the traditional one-satellite approach. Instead of concentrating all the resources and systems in one single satellite, the power of many small, easily manufactured and relatively systems is winning over company after company.

Soon, satellites will not be the only vehicles orbiting our companies like Virgin Galactic and XCOR have their sights set on sub-orbital manned flights. The Virgin Galactic sub-orbital vehicle is shown in Figure 2. This means that in the near future, space could literally be accessible for not only trained professionals, but for anyone wishing to at least partly fulfill their childhood dream of becoming an astronaut. That is, if you are willing to pay for it; the current prices are in the $250,000 range [6], and chances are low that this price will decrease in the near future.

[1] SpaceX Mission, http://www.spacex. com/about , SpaceX, 2015 [2] Spaceport America’s mission, http:// spaceportamerica.com/about-us/ , Spaceport America, 2015 [3] Planet Labs applications, https://www. planet.com/applications/ , Planet Labs, 2015 [4] Skybox imaging history, http://www. skyboximaging.com/company , Skybox imaging, 2015 [5] OneWeb solution, http://oneweb. world/#solution , OneWeb, 2015 [6] Virgin Galactic Spaceflight prices, http:// www.virgingalactic.com/human-spaceflight/fly-with-us/ , Virgin Galactic, 2015 [7] ESA-BIC companies, http://www.esa-bic. nl/ , ESA BIC Noordwijk, 2015 The Space Department The Space Department promotes astronautics among the students and employees of the faculty of Aerospace Engineering at Delft University Technology by organizing lectures and excursions.

DATA MANAGEMENT Compared to sub-orbital manned flight, data acquisition might seem like a down-to-earth thing, though millions are currently earned of data that is acquired from satellite observations. The applications are growing and LEONARDO TIMES N°1 2016

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SWIRL RECOVERY VANES Design and analysis for an isolated and a wing mounted tractor propeller Tom Stokkermans, PhD Candidate, Flight Performance and Propulsion

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In October 1973, the Organization of Petroleum Exporting Countries (OPEC) enforced an embargo on shipments of oil to, amongst others, the United States and the Netherlands. This was a response to supporting Israel in the Yom Kippur War. This embargo combined with the subsequent crisis in Iran, resulted in steep rises of the fuel prices, and one of the consequences was a renewed interest in advanced turboprop concepts.

I

The objective of this master thesis research is to improve the understanding of the aerodynamic interaction between a propeller and swirl recovery vanes in an isolated arrangement and a typical wing-mounted tractor arrangement, like a Fokker 50. This is realized by performing a series of transient RANS CFD simulations.

SRV DESIGN The swirl recovery vanes for these simula-

Vswirl

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n the light of this energy crisis, NASA initiated the Advanced Turboprop Project.

Propeller propulsion was investigated for improved propulsive efficiency, offering the potential to save 15 to 30 percent in aircraft block fuel with respect to turbofan engines (Whitlow and Sievers, 1984). Part of this project explored the idea of swirl recovery vanes (SRV). The torque applied to turn a propeller results in rotation of the fluid behind the propeller, the tangential or swirl velocity component. A part of the shaft power is transferred to the angular momentum of the fluid and does not result in useful propulsive power.

The principle of SRV is to generate a net thrust from the residual swirl in the propeller slipstream. These static vanes, as depicted in Figure 1, are placed under an incidence with respect to the oncoming swirling flow and produce a resultant aerodynamic force.

When the swirl angle- the angle spanned by the swirl and axial velocity component- is large enough, the resultant force may have a component in the thrust direction. This increase in thrust without change in the required shaft power results in an increase of the overall propulsive efficiency.

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Figure 1 - At the top, a sketch of the configuration with SRV Design 1 and wing including a definition of the swirl angle and SRV thrust is shown. At the bottom the wing lift and drag distributions defined with undisturbed conditions is plotted for the wing only and the wing with propeller and nacelle configurations with and without SRV in the cruise condition. tions are designed by a low-order analysis tool. First the slipstream flow field of the propeller for which the SRV are designed must be known, for instance by simulating the isolated propeller. By extracting the flow field behind the isolated propeller and providing that to the tool, it can analyze the thrust of a particular SRV design. The SRV are represented by lifting lines composed of horseshoe vortices, coupled with

parameters. An important assumption of this method is that the swirl recovery vanes do not influence the generated thrust or required shaft power of the upstream propeller.

Two different designs are chosen, each with a different objective. Design 1 is optimized for the cruise condition with a constraint on stall for a set high-thrust condition, representative of the climb phase, whilst Design 2 is optimized for the high-

thrust condition with a constraint on the cruise condition for zero or positive efficiency benefit. These are the designs where the SRV have a fixed pitch in flight. a subsonic airfoil analysis tool for the airfoil properties.

ISOLATED PROPELLER-SRV SIMULATIONS

An optimization routine subsequently finds the SRV design that generates the most thrust by varying the planform and airfoil

These two SRV designs are placed behind the propeller in the CFD analysis. In general the simulation results show that the SRV lead to an increase in propulsive efficiency by in LEONARDO TIMES N°1 2016

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A

C

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Vorticity magnitude isosurface with a contour plot of the axial vorticity component in [s-1] -350

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Figure 2 - Four isosurfaces of the vorticity magnitude behind the propeller are shown, including a contour plot of the axial vorticity component in the cruise condition: A. without SRV and without wing, B. with SRV and without wing, C. and D. with SRV and with wing side and rear view respectively. creasing the total thrust over a wide range of propeller rotational speeds, with minor effect on the propeller thrust and required shaft power, thereby satisfying the major assumption of the tool. For Design 1 and 2, gains in propulsive efficiency of 0.4% and 0.2% are found in the cruise condition and 2.6% and 3.1% in the high-thrust condition, respectively. The swirl angle and thus the SRV thrust is low in the cruise condition since this is an operating point chosen close to the maximum propeller propulsive efficiency. Therefore, only small gains in propulsive efficiency are found. In the high-thrust condition more swirl can be recovered.

The effect of SRV on the slipstream is also investigated. It is found that upstream of the SRV the effect on the velocity and total pressure in the slipstream is very small, in line with the small effect of the SRV on the propeller performance. Downstream of the SRV, somewhat less than half of the swirl remains compared to, when no SRV are present.

The regular helical structure of the propeller blade tip and root vortices is disturbed by the addition of vane tip of root vortices, see Figure 2. These vortices of the propeller and SRV interact with each other, resulting in a radial displacement of the vortex structure outside the slipstream boundary when no SRV are present.

WING-MOUNTED PROPELLER - SRV SIMULATIONS In order to investigate SRV in an installed propeller condition, the wing of a Fokker 50 is introduced behind the propeller and SRV Design 1. The loading on the wing induces an upwash upstream of the wing, resulting in a change of the inflow field for the SRV 36

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compared to the design inflow. This inflow is different for each vane by such a degree that flow separation degrades the SRV performance to a large extent. Therefore, a change in the SRV design is made by turning each vane over an angle to obtain the time- and radial-average design inflow in the cruise condition. For the cruise condition the increase in propulsive efficiency by the addition of SRV without considering differences in wing drag is found to be 0.9%. This is considerably higher than without the wing configuration, mainly due to the increased propeller propulsive efficiency and partly by increased SRV thrust . For a medium-thrust condition a gain of 2.1% is found, very similar to the value without wing.

For a wing-mounted tractor-propeller, conclusions on SRV performance can only be drawn from the complete force balance of thrust/drag and lift of the propeller, SRV, wing and nacelle. Considering the drag of all components, the net increase in propulsive efficiency by the addition of SRV is found to be 0.1% for the cruise and 1.0% for the medium-thrust condition with a net increase in lift of 0.4% and net decrease in lift of 0.6% respectively. The propeller slipstream greatly affects the wing lift and drag distribution by its increased axial velocity and introduced swirl, as seen in Figure 1. It is concluded that SRV reduce some of the effects of the propeller on the wing lift and drag distribution by a reduction of the swirl, resulting in a smaller deviation from the wing loading without propeller, including a higher drag. A design procedure for SRV should include the wing, for instance by an additional lifting line and optimize for combined SRV and wing maximum thrust, with a constraint on the net lift. This

may lead to SRV designs more focused on providing the optimal inflow for the wing, in order to reduce the wing drag. Furthermore, designing SRV with variable pitch may be mandatory for a wing mounted tractor propeller, due to a large inflow variability, which depends, amongst other things, on propeller thrust and wing loading.

The regular helical vortex structure of the propeller blade tip and root vortices is further disturbed by the addition of the wing, as seen in Figure 2: First of all, the larger velocity above the wing is clearly visible in the more downstream displaced vortex structure compared to below the wing. An upward motion of the vortex structure upstream of the wing and a downward motion downstream of the wing is also visible. This is due to the upwash and the downwash induced by the wing, respectively. In the rear view, the vortex structure above the wing is sheared more inboard with respect to the vortex structure below the wing. This shearing of the slipstream boundary is also indicated by Samuelsson (Samuelsson, 1990) and is a result of the spanwise flow over the wing by its loading.

References [1] J.B. Whitlow, Jr. and G.K. Sievers, “Fuel Savings Potential of the NASA Advanced Turboprop Program”, Aviation Fuel Conservation Symposium, Washington D.C., 1984 NASA TM-83736 [2] I. Samuelsson, “Experimental investigation of low speed model propeller slipstream aerodynamic characteristics including flow field surveys and nacelle/wing static pressure measurements” In 17th ICAS Congress, Stockholm, Sweden, pages 71–84, 1990.

SPACE ENGINEERING

RICK TUMLINSON INTERVIEW Eleonoor van Beers, Victor Gutgesell, Editors Leonardo Times, Sushant Gupta, Editor-in-Chief, Leonardo Times

“Those who reach for the stars have no fear of the night”. These are the profound words from Rick Tumlinson, a space visionary, founder of several successful private ventures and a great spokesperson for humanity’s desire to venture out into space.

What inspired you to go to Space?

I grew up reading science fiction by Isaac Asimov, Arthur C. Clarke and Robert A. Heinlein, the three gods of my church of science fiction! They created a future that I could live into and dream about. I was watching science fiction like Star Trek. I would be sitting there watching Star Trek in hostile space and flipping the channel and there were the real people doing the real thing. I flipped the channel again and there was the Vietnam War. So as a creature of my imagination, I went for what seemed hopeful and I wanted to be Captain Kirk and Hahn Solo. And the fact that it was occurring at a time, where we were sending out these probes: Galileo and Voyager, we could do anything, we could go to the moon. And here it was in glorious color and I looked at it and if I could do what they could do, I would do it.

I was a terrible student. That was a real problem for me in the beginning was that unlike Elon Musk or Paul Allen, I didn’t translate my education into creating a proper business, it took me a little longer than them to get around with this.

I was naïve enough to go for the cause, while they were going out for the money to do the cause. I wish sometimes I had become a billionaire first and then gone into Space. I’d be driving a better car. So I am little slow in getting there but I am doing alright. I have an asteroid mining company and a space suit company. It’s not hugely profitable yet but it’s still very much alive!

Rick Tumlinson is one of the world's top space visionaries.

What is the driving force for entrepreneurs to venture out into space? Is it at all profitable or is it for prestige?

First of all, you have to acknowledge that most of those who are doing it right now are not doing it for money. We like to pretend we are doing it for money, we try to make business plans but that’s not what is driving us. That’s why it has taken billionaires, because they don’t need the money. It is interesting because there is this divide, this Catch-22 moment: “Ok, how do I make money in Space?” Because I know I want to create an economy. If you create an economy, you create a culture and that means civilization is moving to Space. But I don’t know how

to do that. I certainly can’t do it, leveraging off the governments space program because it is too expensive to get into space. And if I can’t get into Space, I can’t create an economy. Along come the billionaires and in the meantime, a bunch of us have been working really hard to change the purchasing rules of the government, so the government has to buy what it needed from private companies.

We actually did several projects where we were trying to get the government to buy several vehicles as an example.

This occurred in the 90s and again in the 2000s. In 1995, I testified in front of the Congress and I said that all transportation to the space station should be com LEONARDO TIMES N°1 2016

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BIO

Rick Tumlinson is a space advocate and gives voice to critiques & discussions of current national space policies, the presentation of a "Frontier" ideology for opening space, the reasons and means of returning to the Moon, a spiritual reasoning of our place in the universe, the search for other life and the reasons why humans are reaching for the stars.

As a leading space visionary, he has appeared numerous times on American and International TV programs on CNN, BBC, CBS, ABC etc., written books and articles for Space News and renowned publications like New York Times, The Economist, Wall Street Journal. He lobbied to help pass the Space Settlement Act of 1988 and was called as a witness

mercially provided, preferably by several providers. That is very important because if you want an economy you need competition. If we are going to spend the tax dollars for going into space for some ‘crazy’ reasons, let’s at least do it in a way that catalyzes a new industry. That was our argument for many years.

quite reach the take-off point. They couldn’t break free of the gravity of the current situation – shall we say – the cultural reality where they were trapped in. They would fall back

er money in a way that enables companies to get started could meet in the middle with people that could invest enough money and they start to take off.

RICK TUMLINSON

Along came these people in the same period of time when the activists were working in Washington to change the laws. We had several false starts by small companies that were trying to pull it off. But they just couldn’t

"If you create an economy, you create a culture and that means civilization is moving to Space" to earth. Then, along come the billionaires, they can pour real money into it and get it to a point where it can start to take off. Now the catalyzing effect of spending the taxpay-

An artist's concept of Deep Space Industries' Dragonfly picker to capture asteroids for mining operations.

It took 20 years of fighting and trying to get people to understand, and at the same time, creating existence proves that it can happen. For example, we took over the Russian space station at one point and people were like: “Oh my god, these people are just some regular people with some money and they are renting a space station”. The right people heard that story and at the same time, they were reading that some people are trying to change the law. These are insiders, this is not everybody, but there is some guy sitting out there, maybe Elon Musk or Paul Allen who were paying attention.

Then we were doing the X-Prize and people were paying attention. The X-Prize actually failed, it didn’t work in its original idea.

I was on the board. If you look at it in a very hard-core way, now it’s more than 10 years later and no vehicle that was created by the X-Prize ever made it. What the X-Prize did was a partially intended consequence of exciting people and drawing cultural attention towards the idea of people going to Space.

You had to have the X-Prize, Dennis Tito fly to space, MirCorp and a shift in the government policy in the US. All four of those things were necessary to create an environment where these people who had grown up watching Apollo and Star Trek and Star Wars could go “Uh, I am coming in”.

People like to simplify and say: “Elon Musk changed the universe all by himself.” No! If a lot of people whose names you don’t ever hear hadn’t spent hours working in Congress so that NASA could have the rules changed, so they could actually purchase the right from them, it would not have happened.

The illustration depicts Deep Space Industries' Harvestor class spacecraft for asteroid mining 38

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That’s why I get a little upset when people say it was Elon Musk, it was Peter Diamandis.

No, it wasn’t, it was a bunch of people who did it. It is like changing the language for a contracting law for a bureaucrat. It says: “We

Corp (that aimed to send a rover to the Moon to confirm the existence of ice on its poles). MirCorp was one of his most impressive feats, as it utilized the aging Russian space station Mir for many firsts in commercial space exploration, such as having the first commercial space tourist (millionaire Dennis Tito, whom Mr. Tumlinson had personally signed up), a

SPACEX

in six congressional hearings on the future of NASA, the US Space program and Senate Committee on the Moon, Mars and beyond. He also played a key role in instituting the X-Prize as a founding trustee. Tumlinson co-founded many space ventures in the past including the Lunar Prospector (which discovered hints of water on the Moon) and Luna-

privately funded spacewalk, and a cargo resupply mission). The story of MirCorp was described in the documentary Orphans of Apollo. Amongst his numerous roles, he is currently involved as a visionary and founding entrepreneur of Deep Space Industries, Orbital Outfitters, and the Space Frontier Foundation to name a few.

engineering and the understanding of what it is they are trying to do. I think there needs to be more sophistication in the development of the business model, the concept itself. I think the idea of a group of people pooling their resources in a way that is building towards a future possibility is a valid idea.

With Deep Space Industries, what are the materials you want to mine?

The idea is to mine materials that will be used in space. It is not the idea to bring them back to earth, at least in the early stages. The first thing we are after is water. Other materials could be Iron and Nickel. We believe there are certain asteroids out there that are just packed with materials. You have to extract them. But extraction in many cases is just heating it up and capturing the steam.

A SpaceX Dragon spacecraft lands on Mars in this artist illustration of the possibilities for the privately built spacecraft. are going to pay you for delivering a payload rather than how much money you spend to build a rocket.” Cost plus contracting. That’s very obscure, not glamorous, not as cool as Iron Man Elon Musk standing there but you had to have that so he could succeed. And you needed a guy like Dennis Tito to go to space. Now it starts to click; now it starts to happen, and now we are looking at people like Elon Musk and Paul Allen and they are all going. And now we have NASA starting to look at it like: “Wow, maybe we should purchase some technologies from the private sector”. As all that starts to play together in another sort of complex matrix, we now have got the possibility to say, “Let’s get out there and sell them something”. Now we ask what is next. We know they are going to Disneyland and we sell them gas and cheeseburgers on the way.

Do you think that private enterprises will send the first person to Mars?

I think the private companies will get to Mars before the governments, unless the governments and the public entities stop them.

So, they are more of a hindrance than be-

ing the facilitators? What further problems do you see in private space exploration?

Unfortunately, I think that somebody might declare that: “Oh my god, Elon Musk is going to Mars and kill the bacteria”. Those we don’t even know are there yet. So the planetary protection people would kick in, he’ll be caught in the system, and in the meantime the government will slowly move in that way.

A lot of the biggest problems come from our own industry, where people promise too much and deliver too little. In terms of technology and in terms of making promises like “we are going to fly tourists into space by 2008”. That makes it hard to commit the next time you make this promise.

Elon Musk has plans for Mars. Do you think that is too ambitious?

I think he wants to put a robot on Mars. If it weren’t Elon Musk or Paul Allen, I would say yes. If Richard Branson said that I wouldn’t believe it.

What do you think about Mars One? I think Mars One is a valiant idea. I think they need some very serious work in terms of the

And the moon plays a role in this as a stop?

Not really. If people want to go to the moon, it is because they want to go to the moon. It is not because it by itself holds any economic promise in terms of opening space. It is a place to practice. The people who are planning on mining on the moon are going to have to raise the money to invest on creating an industrial infrastructure at the bottom of a gravity rock. They are going all the way down to the bottom of a crater where ice is a hard as steel and steel is as fragile as glass. They are going to have to extract those materialsand here is the fun part- if you are moving through time now, let’s say that it takes them 10 years. During that same 10 years, we are going straight out and we are going to learn how to use dirty nasty rocks and turn them into cool stuff. They are going to be pulling that nasty dirty stuff out and they are going to ship it to us. We are already going to be there. So, in other words, the second phase of their business plan is the first phase of our business plan. There are great reasons to go to the moon though.

References [1] House Report 104-233 - National Aeronautics And Space Administration Authorization Act, Fiscal Year 1996.

[2] Testimony of Rick Tumlinson, Founder, Space Frontier Foundation before the senate committee on commerce, science and transportation, October 29, 2003.

[3] RickTumlinson.com [4] “Musk: SpaceX Making 'Progress' Toward Mars Colony”, Tariq Malik, Space.Com, May 20, 2014.

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TIMES 20 years

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1996 2001 Asteroidal Gravitational Fields

5e Jaargang, nummer 4, december 2001

Vliegtuigbouwkundige Studievereniging ”Leonardo da Vinci”

2006

Aviation Safety Program 3D-deformation of the Earth's crust after earthquakes

Periodiek van de Vliegtuigbouwkundige Studievereniging ‘Leonardo da Vinci’ - 10e jaargang - nummer 1 - maart 2006

PAGINA 24

In 1996 students of the VSV ‘Leonardo da Vinci’ decided that it was time to come out with a publication to bring members up to speed with the latest ‘reilen en zeilen'.

1997 ‘Het Appelzuurtje, onze vliegende trots’ Lambach HLII flies for the first time in history

1999 ‘A3XX gevaar in de lucht’ In September 1999, LT reported on design of very large commercial aircraft in development, which later became the A380.

2000 ‘ISS’ First Crew’

Computer models for Glare material research

AIR TRAFFIC Development of an Air Traffic COMPLEXITY Complexity Framework

Micro UAV Design Synthesis Exercise ‘Delfly’ to compete in first US-European MAV Competition

In 2001, the Leonardo Times cele- brated its first ‘Lustrum’, five years since the journal came into being. At the end of the first lustrum, the circulation had doubled from 2000 for the first edition to an impressive 4000.

2002 ‘Ruimterace door de woestijn’ In March 2002, LT reported about the first solar car built by TU Delft, Nuna 1

2002 ‘Fokker Aerostructures is building a brand new factory in Papendrecht’ Fokker built a facility dedicated to GLARE

TailorMate: Tail plane design The perfect mate in tail optimisation and redesign

Galileo, European navigation system Europe’s own Global Navigation Satellite System

Year 10 of the LT was celebrated in golden colors coinciding with the naming of the KLM Hangar, as it was named after the VSV’s namesake Leonardo da Vinci. The journal had truly become a professional effort with a new layout and higher number of pages.

2009

2003 ‘Simona, a cooperation between Boeing and TUDelft’

In December 2000, the Leonardo Times reported about the first ISS crew, which has since been permanently manned.

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SIMONA research simulator coop- erated with Boeing to undertake a series of piloted simulation experiments.

From 2005 to 2010, the Leonardo Times featured cartoons, based on contemporary events in the aerospace industry

2009 ‘How to become European record holder for amateur rocketry’ Student team Delft Aerospace Rocket Engineering (DARE) broke the European record for amateur rocketry by reaching 12.5 kilometer altitude with their Stratos I rocket launching from Esrange, Sweden. A record DARE still holds today.

2010 ‘The first Dutch human powered aircraft’ A 19 year old TU Delft student completed the first human powered flight in the Netherlands.

2012 ‘Losing your Space ight Virginity’ Richard Branson discusses the future of Virgin Galactic in an interview with the Leonardo Times.

2012 ‘The First Supersonic Free Fall’ The 20th Aviation Departmen reports about Felix Baumgartner’s supersonic free fall from the stratosphere.

2013 ‘Mission to Mars’ We reported on the successful Mars and Moon programs of of the Indian Space Research Organization.

September 2011

2011 Leonardo Times Journal of the Society of Aerospace Engineering Students ‘Leonardo da Vinci’

2016 LEONARDO TIMES

20 Journal of the Society of Aerospace Engineering Students ‘Leonardo da Vinci’

Year 15

number 3

1996

cover september 2011.indd 1

06/09/2011 14:51

The LT celebrated its 3rd Lustrum in 2011 featuring all the past covers with leading figures in the aerospace industry writing testimonies about the journal. At this point in the history of the publication, the DSE was given a special place with articles from student groups showcasing their projects.

2012 ‘Losing your Space flight Virginity’ Richard Branson discusses the future of Virgin Galactic in an interview with the Leonardo Times.

2012 ‘The First Supersonic Free Fall’ The 20th Aviation Departmen reports about Felix Baumgartner’s supersonic free fall from the stratosphere.

Interview

Rick Tumlinson Page 37

2016

Stratos II+

One-fifth way to Space Page 44

NASA’s

Asteroid Grand Challenge Page 64

Year 20 | N°1 | January 2016

LEONARDO TIMES Journal of the Society of

Aerospace Engineering

Students ‘Leonardo da

Vinci’

After 20 years, its time to celebrate again. The LT celebrates its 20 years this issue with a 80 page edition in golden colors.

We thank all the people who have contributed to the Leonardo Times over the years and all the previous committees who have spent long hours putting together a professional effort.

The Faculty of Aerospace Engineering in TU Delft is recognized as a top educational and research institution and the deserves a publication that showcases the top quality work done in the field of Aerospace Engineering.

25 YEARS HUBBLE

VSV Lustrum ‘Up, Up and Away’ Page 06

The V 22 Osprey A failed tiltrotor Page 38

Interview AELS Page 56

Year 19 | N°3 | July 2015

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HALLAK

STUDENT PROJECT

STRATOS II+

One Fifth Way to Space Victor Gutgesell, Student Aerospace Engineering & Editor Leonardo Times In October 2015, DARE launched their Stratos II+ rocket to 21.5km; a great success for a team of students.

The launch is the product of a project that has lasted for more than five years and is just a part of a greater mission; reaching space. The 100km altitude is the ultimate goal of the TU Delft students and with Stratos II+, they achieved one fifth of it.

DARE stands for Delft Aerospace Rocket Engineering, and the guys and girls at DARE really do take that name seriously. Usually, DARE conducts about three launch days a year, where they launch several smaller rockets up to an altitude of 2km. Before Stratos, DARE managed to stand out in the Aerospace world with their CanSat campaign and set the “World Altitude Record Among Student Rocketry Programs” [3] with Stratos I. In 2001, DARE was founded as a part of the VSV. Soon they became a D:DREAM Team, and now they are the biggest of them all. With more than 150 members, DARE features a variety of projects such as the three propulsion teams: SolidSix (solid rocket engines), Deimos (liquid rocket engines) and Hybrids (hybrid rocket engines). In 2009, DARE set the first student altitude record in rocketry with Stratos I. This rocket was launched in Sweden and reached an altitude of 12.9km.

This enabled DARE to conceive Stratos II, with which they intended to go halfway to space. At first, the rocket was meant to be a two-stage solid fuel rocket, but with the development of the DHX-200 Aurora engine, the team altered the design to become the rocket it is today. Stratos II was meant to hit the 50km altitude mark in October 2014.

Sadly, a multitude of errors led to a failure of the launch campaign. Since then, the rocket went under a complete makeover. From the outside it looks more or less the same but the rocket is not Stratos II anymore; it is Stratos II+. Stratos II+ went back to Spain, which was also the Stratos II launch site, and on October 16, it was finally launched to 21.5km.

This launch marked a great relief and success for the team and caused a commotion in the press, all praising the students and their achievements. Nonetheless, their mission goal of reaching the 50km altitude was not reached.

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INTERVIEW Bastiaan Bom, Commissioner of External Affairs, DARE & BSc Student Aerospace Engineering, AND Christ Akkermans, PR Department, Stratos II+ & MSc Student Aerospace Engineering In general, the project was technically a lot more mature than it was in 2014. This was also because we had been to Spain before and knew what sorts of ground operations were awaiting us.

Bastiaan Bom

Christ Akkermans

Since Stratos II, what changes have been implemented?

Since the failure of Stratos II, our main course of action was to look at what really went wrong and what could be improved. We did some forensic engineering on the failed launch. We tried to identify the root causes of the failure, for example why the valve did not open. The valve not opening was why the rocket did not launch, and the valve did not open because it was frozen due to a fuel leak.

The fuel leak in question was there because something went wrong with the assembly of the rocket. So we traced this whole line back to the root causes and there we had to improve. In the end, we formulated a list of recommendations for the domains that we thought could be done better.

The base design of the rocket is the same.

Stratos II+ is in essence Stratos II; still aiming for 50km with the same engine and the same rocket size. But beyond that, it was more or less a new rocket. This made us rethink the name and we were inspired by naming schemes of smartphones like the iPhone 6 Plus.

Before you went to Spain, how confident were you that this time the rocket would launch?

Compared to last year, we were way more confident. We finally tested all the sub systems-like the flight termination system, which we were extremely confident about. An extra motor test assured us that the motor would deliver a 23s thrust as it was designed to do.

What was the most challenging task for you in the last year?

For the team in general, the most challenging task was to work with a real hard deadline, which Stratos II was not bound to. Now it was clear, after last year’s the failure, the launch site operators said: “If you want, you can come back next year”, so we had a clear deadline. This, on one hand, was really good.

It made us work hard, but on the other hand, it put a lot of pressure on the team. We really needed to accelerate this forensic analysis and come to our conclusions. Just the whole pace has been a lot faster. For both our positions in particular, it was challenging because we needed to get the funding covered in just a year, whereas earlier we had three years for the entire project. Eventually we managed to get the funding and even acquire new sponsors; for example we now have a sponsor for our fuel.

The goal of Stratos II+ was 50km, but you only reached 21.5km; what went wrong?

It is a combination of factors we are still looking into, but we have some clear leads already. First of all, the engine performance deviated just a bit from its original designed performance, as it was set four or five years ago. We actually knew about the uncertainty of the Stratos II+ reaching the 50Km altitude.

The decimal margin there was not correct.

JANSSEN

Some significant design changes were made , for instance the accessibility of the components. Servicing was much easier with Stratos II+ compared to Stratos II. The flight termination system was completely redesigned, as we only had very little time to design it for Stratos II. We even conducted another engine test campaign to improve the propulsion.

We carried out vibration tests on the capsule, to ensure that the flight electronics would withstand the extreme vibrations of the launch. We even changed the launch protocol to make ground operations go smoother than a year before.

So why did you decide to call the rocket Stratos II+ instead of Stratos II?

Stratos II+ taking off LEONARDO TIMES N°1 2016

45

WILLIGEN

A 5 or 10 percent deviation from the original performance gives a huge difference in altitude. That is the first thing. It was known that there was a slim chance to actually get to 50km.

From the videos and the flight data, we concluded that we flew a much lower parabola than we intended to. We needed to launch the rocket at a small angle, to get above the ocean since that is where we needed to land. Due to the passive stabilization however, the real path depends on the wind and there was wind current from the sea. What can be seen from the video is that it takes off fine and at some point it deviates a bit from its path. That is probably because there were stronger winds higher up in the atmosphere, which caused the rocket to fly a lower trajectory. And thus, a larger part of the flight was in a dense atmosphere, which gave a huge amount of extra drag and cut down the maximum altitude. Furthermore, the fuel tank was probably overfilled with nitrous oxide from the start on. We are suspecting that we were carrying quite a bit of extra nitrous oxide, and that bit of extra mass massively impacted the achieved altitude. Lastly, there are some general unknowns like the exact drag. It is really hard to estimate this on a supersonic vehicle with a shape like the Stratos II+. We used several methods to estimate this drag and the range we got for the solutions was huge. If the flight regime was on the high side of this estimated drag, we could only ever reach an altitude of 21km.

You were talking about an underperformance of the engine, was it not adjusted?

In fact it was, but just like with aircraft, if you aim for 22 tons and you end up at 24, a completely new design is needed. At some point however, we just wanted to launch the rocket. So in that regard, it was something to be expected. Nonetheless, from the measurements which we have obtained, we actually found that the engine performed perfectly fine from a technical perspective.

On the video feed you could see that quickly after lift-off the rocket started spinning and wobbling, do you know how that happened?

The fins were mounted at a small angle of 2 degrees. So we predicted the rocket to spin at a rate of 2 to 3 hz. The wobble probably has to do with the aerodynamics of the rocket. We are still analyzing it, since it was also unexpected for us.

Are you considering giving Stratos II+ another try or maybe making a Stratos II++?

We are definitely considering it because there are a lot of improvements to be made.

There are also possible weight reductions, with which we could go higher and actually get to 50km. But that’s still up to the next team to decide if they want to re-launch it. I think there is a high possibility.

Stratos II+ at apogee, picture taken by on-board camera Are you already working on a Stratos III? Yes. Currently, we are developing a new rocket motor, which will be for a Stratos III. This motor will be a liquid rocket motor. What we have now is a hybrid motor. If we simply decided to scale that up to go to 100km, we had to redesign the whole engine and start from scratch. For this, we would need a new conceptual design, a new prototype, new test campaigns and so on. Instead we decided that if we want to do something new, we will do something that we have not done before.

Our goal for 2016 is to design a battleship version of the cryogenic rocket motor, which we want to use for future missions. Once this is working, we want to fly it. We think this could happen within the next five years, provided that nothing major goes wrong.

The engine is not the only challenge though.

For instance the wind effect, which we discussed, is one of the key manifestations of why we need an active control on the rocket.

We have already had a project on that for a while, as we knew that this problem would come up one day.

Would you consider Stratos II+ as a fail-

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N°1 2016 LEONARDO TIMES

ure or as a success?

It is a great success. It is just amazing that you can, as a student, design all these systems and just have them work and launch.

We did not make it to 50km but the engine performed fine, the capsule performed fine and the rocket launched. The capsule was completely recovered intact. It was thoroughly watertight. When it arrived back at the base four or five hours later, it was still running. Even from an operational perspective, everything was smooth. So, it is definitely a big success. First we had a little problem with the ignition and on the launch day, we had some problems with a fuse on the power supplies of the radar building, which wasn’t even related to our system. Technically, it all went well and that’s just the amazing thing: You can achieve something like this, only with students!

References [1] Stratos II, The Story Behind The Rocket, Leonardo Times Magazine, January 2015 [2] en.wikipedia.org/wiki/Delft_Aerospace_ Rocket_Engineering (Yes! they have a Wikipedia page) [3] https://en.wikipedia.org/wiki/Amateur_ rocketry

HALLAK

LEONARDO TIMES N째1 2016

47

APPLICATION TRAININGS 9th, 10th and 11th of February

PRESENTATION DAYS 16th and 17th of February

IN-HOUSE DAYS 14th of March until 1st of April

SIGN UP: WWW.DDB.TUDELFT.NL

INTERVIEW DAYS 9th until 20th of May

KICK START YOUR CAREER! Every year ‘De Delftse Bedrijvendagen’ (DDB) leads 2500 students to the start of their career. If you want to hit the ground running this year, make sure you do not miss this event.

Whether you are job hunting or in need of an internship or graduation project, DDB offers an unique opportunity to get to know a wide variety of high-profile companies.

DDB is the largest technology oriented career event in the Netherlands, and takes place each year in the Aula Conference Centre of the TU Delft. This career event is specifically aimed at the students of Delft University of Technology and offers them a wide range of national and international companies and institutions.

For all information considering the event as well as registration you can visit our website on: www.ddb.tudelft.nl

1

2

APPLICATION TRAININGS 9th, 10th and 11th of February PREPARE YOURSELF FOR YOUR JOB INTERVIEW AND THE FAIR

PRESENTATION DAYS 16th and 17th of February GET TO KNOW 130 NATIONAL AND INTERNATIONAL COMPANIES

On the 9th, 10th and 11th of February DDB offers Application Trainings. The companies will provide you with both general tips and tricks as well as detailed personal advice. During the Application Trainings you can also have your résumé checked, so that it is up to date when visiting the Presentation Days.

On the 16th and 17th of February DDB hosts its best known event, the Presentation Days in the Aula Congress Centre. This technical career fair gives you the opportunity to get to know 130 different national and international companies!

There are several ways of meeting these companies: you can visit their information stand or view their company presentation.

Each day ends with an informal drink with the recruiters.

Note that it is only possible to have your résumé checked during the Application Trainings!

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4

IN-HOUSE DAYS 14th of March until 1st of April TAKE A LOOK BEHIND THE SCENES AT THE COMPANIES

INTERVIEW DAYS 9th until 20th of May TAKE PART IN ONE-ON-ONE INTERVIEWS WITH THE COMPANIES

From March 14th until the 1st of April the In-house Days offer an opportunity to form a better, more complete idea of the companies you are interested in. Your résumé will be forwarded to the companies of your choice.

Based on the résumés the companies will select the participants. As the name suggests, the In-House Days are a great way to learn about the culture of a company and the projects they work on at their location.

On March the 24th an In-House Day will be held in the Aula Congress Centre in Delft for companies situated far away from Delft.

You can sign up for the In-house Days until the 24th of February - the Wednesday after the Presentation Days.

From the 9th until the 20th of May DDB will be completed with the Interview Days. During this period, there are two different kind of interviews possible: Orienting interviews or even the first step in an application process. For the Interview Days your résumé will be sent to companies you are interested in, but also to companies that are specifically interested in your degree. You will receive an overview of which companies are interested in meeting you, and from these you can make a selection.

PARTICIPATION All activities described above are included in a single price when participating in DDB. On top of this, you also receive a full-color magazine with tips and tricks for a successful start of your career. You can participate by signing up via our website, www.ddb.tudelft.nl, or by coming to the Aula Congress Centre on the 19th, 20th or 21st of January. Until January 21st it is possible to register for a reduced fee. Hence we advise you to register before January 22nd. All personal information will be treated strictly confidentially.

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IMPORTANT DATES 21st of January: Deadline reduced entree fee 24th of February: Deadline registration for In-House Days and Interview Days

WIND ENERGY

40m Blind zone

200m forward looking

CAN WIND TURBINES ACT ON WHAT THEY “SEE”?

Predicting wind speeds at the wind turbine rotor using LiDARs Ashim Giyanani, PhD candidate, Wind Energy Research Group, Faculty of Aerospace Engineering, TU Delft Turbulence has puzzled scientists and researchers for decades now. In the wind energy industry, state of the art wind turbines are designed under the assumption that the turbulence in the wind is constant. In reality, a wind turbine faces varying turbulence. LiDARs (a portmanteau of "light" and "radar") can now track the wind in front of a turbine, thus enabling turbulence evolution to be studied.

W

ind turbine design and control strategies often assume Taylor’s frozen turbulence, where the fluctuating part of the wind is assumed to be constant.

In practice, a wind turbine faces higher turbulence in case of gust and lower turbulence in other cases. In order to increase the energy production and durability of a wind turbine, it has to measure the wind speed in real time and react accordingly. A LiDAR is such a measurement instrument. It measures the wind speed by transmitting laser beams of a known frequency. These transmitted laser beams are reflected by the nanoparticles in the air, moving with the same speed as that of the wind, which cause a frequency shift (also known as a Doppler shift) in the reflected beams. Using a nacelle mounted LiDAR, as shown in Figure 1, measurements can be taken in front of a wind turbine up to a certain distance. The changes in the wind speed and its turbulent structure can thus be tracked. However, it is not possible to predict the wind speed at the rotor since the wind changes its structure before it reaches the rotor. If the evolution of turbulence towards the rotor could be understood using the LiDAR, the gap between measurements and an efficient wind turbine control could be 50

N°1 2016 LEONARDO TIMES

fulfilled.

To understand the evolution of wind, either a fundamental approach or an engineering empirical solution approach can be taken.

The fundamental approach involves re-

Taylor’s frozen turbulence

Wind speed at 185m a

Process (Black box model)

solving the Navier-Stokes equation for the entire evolving field, which is mathematically difficult and computationally expensive.

Empirical solutions, on the other hand, provide accurate system estimation models based on LiDAR measurements. The use of Autoregressive moving average exogenous (ARMAX) estimation models provide insights into the evolution of wind upwind of the wind turbine between two points, a and b (Riahy & Abedi, 2008). The evolution of wind along these 15m distances is considered as a black box system (process), with the wind

Turbulence in reality

b Wind speed at 170m

Figure 1 - Nacelle mounted LiDAR experimental setup within LAWINE project, illustrating the presence of turbulence in oncoming wind towards the wind turbine. The black box process is modelled with the input at point a and the output at point b.

Disturbances/Noise e(t)

Input u(t) 10 min data Ts = 0.25s (4 Hz) Wind speed (185m)

Process

Ouput y(t) 10 min data Ts = 0.25s (4 Hz) Wind speed (170m)

Figure 2 - The black box process model specifications with the wind speeds at 185m and 170m from the wind tunnel as input and output respectively. The disturbances are inherently present in the wind speed due to stochastic behavior of turbulence. The time series of 10-minute data with sampling time period of 0.25 seconds is considered.

The ARMAX model as shown in Equation 1 predicts the future values based on past values along with an assumption of a stationary stochastic process output. It can be described by a deterministic part and a stochastic noise part (Ljung, 1987). The A, B and C in the ARMAX differential equation represent the estimated transfer functions, y(t) represents the process output, u(t) represents the process input, e(t) is the stochastic noise in the system and τ represents the time delay in the system. The deterministic part is determined using the Autoregressive exogenous (ARX) model, while the stochastic part is modeled using the Moving average (MA) model within the ARMAX model.

The predictions thus obtained are analyzed for residual correlations based on training data, which contains information regarding the time lag between the time series, step and impulse response. This forms the deterministic testing of the model. The stochastic testing of the model compares the residuals using the Autocorrelation and Partial autocorrelation functions, where the confidence limits are defined according to the time series statistics. The order of the ARX and the MA model are determined using the results from the deterministic and stochastic testing.

The final test includes the cross validation of the results using a fresh dataset of the time series.

Deterministic Input

Ay(t) =

Output

Bu(t − τ )

Stochastic Noise

+

Ce(t)

(1)

=

1 − 0.93q −1 y(t) + 0.28q −2

B

=

0.64q −5 u(t) − 0.56q −6

C

=

1 − 0.05q −1 − 0.17q −2 1 − q −1

(2)

The ARMAX estimation model bridges the gap between the measurements and the wind turbine control. The results are therefore useful in developing the transfer function for efficient wind turbine control, thereby reducing the fatigue and extreme loads in the wind turbine. ARMAX models with better estimation capabilities for the stochastic part could decrease the prediction error even further. However, it has to be studied and applied in the near future. Future stages involve looking at the evolution in the estimation pa-

0.3 3 Observed Predicted

2 0.2 0.11

Output

speeds at 185m and 170m defined as the input and output of the system respectively, and with a sampling time of 0.25 seconds as shown in Figure.2. The disturbance, or the noise input, is already present in the wind speed measurements as a result of the varying turbulence. Since part of the output is actually a derivative of the input, the model becomes a differential equation as shown in Equation 1. This equation conveys the physical behavior of the turbulence evolution of the wind towards the wind turbine. Various characteristics such as the linearity of the system, the bias and the random stochastic behavior are determined using the ARMAX model.

A

0 1 -0.1 2 -0.2 -0.3 3 4 -0.4 2400

2420

2440

2460

2480

2500

Time(samples) Figure 3 - The predicted data from the ARMAX(2,2,0,5) model based on the past measurements. The deterministic part is well followed, while the stochastic part hast to be modeled into the estimation so that the predictions are accurate. Correlation achieved: 90%.

It is necessary to predetermine the order of the A, B and C in the Equation 1 by fitting the data with a polynomial curve. Here, the orders of A, B and C are considered to be 2,2 and 0 based on the residuals obtained from the polynomial curve fitting and subsequent fitting iterations. Considering the evolution statistics, a time delay of 5 samples (1.25 seconds) is calculated. This is based on the peak of the correlation between the input and output time series, and as the correlation decreases steadily towards the wind turbine, the time delay increases. The predictions obtained from the ARMAX(2,2,0,5) models with second order polynomials then provide a good fit (90%) to the measured wind speed at the next measurement distance, i.e. 170m upwind of the turbine, as shown in Figure 3.

Based on Equation 1, the predicted input, output and the noise parameters A, B and C are defined as shown in Equation 2 (Tangirala, 2014).

rameters as the black box model is moved step by step towards the wind turbine.

References [1] L. Ljung, System Identification Theory for User.pdf, vol. 25. 1987.

[2] G. H. Riahy and M. Abedi, “Short term wind speed forecasting for wind turbine applications using linear prediction method,” Renew. Energy, vol. 33, no. 1, pp. 35–41, Jan. 2008.

[3] J. M. Lujano-Rojas, J. L. Bernal-Agustín, R. Dufo-López, and J. A. Domínguez-Navarro, “Forecast of hourly average wind speed using ARMA model with discrete probability transformation,” 2011 International Conference on Electric and Electronics, EEIC 2011, vol. 98 LNEE, no. VOL. 2. pp. 1003–1010, 2011.

[4] A. Tangirala, Principles of System Identification: Theory and Practise. CRC Press, 2014.

LEONARDO TIMES N°1 2016

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JASON BLADD

AERODYNAMICS

WAVE DRAG The battle against computation time ir. Roy Veldhuizen, R&D Engineer - Aerodynamics, WABCO Rotterdam Current methods to estimate wave drag in early design stages include fast and crude handbook methods, or slow and accurate computational methods.

There is a need for a method that combines the best of both worlds: fast and accurate calculations. Can meta-modeling be this method? ed as it leads to long calculation times.

PROPOSED SOLUTION Ideally, one wants both fast and accurate calculations. In order to achieve this, a meta-modeling method is proposed. This is, in essence a model of model. Thus, several cal-

First, several methods are investigated to find the best aerodynamic model. This investiga-

With the availability of computers, computational methods appeared. These methods solve simplified Navier-Stokes equations in order to predict the wave drag. However, with these computations come significant computation times.

Especially in early design stages, where many iterations are common, this is unwant52

N°1 2016 LEONARDO TIMES

METHOD SELECTION

cd w 20

×10

−4

ROY VELDHUIZEN

In the early days of transonic flight, the prime method for wave drag prediction was using handbook methods. These methods rely on trends obtained from numerous wind tunnel experiments. They express the wave drag as a function of general characteristics, such as the thickness of the airfoil, the Mach number.

As these methods use general trends, they are rather crude but very simple to apply and quick.

2D drag coefficient, cd [−]

PROBLEM STATEMENT Wave drag is the drag an airfoil experiences as a result of compressibility effects.

This drag component increases rapidly at a certain Mach number, called the drag divergence Mach number, MDD. Typically, commercial aircraft cruise at a Mach number a little higher than MDD and will experience wave drag.

culations of a model are performed, and from these calculations trends are recognized.

Based on these trends, a new model is developed, the meta-model. This meta-model is orders of magnitude quicker than a direct application of a computational method, but as it is a mathematical model care should be taken to ensure accurate results.

15 10 5 0 −5

−10

20

30 40 50 Reynolds number, Re [−]

Figure 1 - Development of cdw and error versus Reynolds number.

60 6 ×10

Secondly, a suitable meta-modeling method needs to be found. At Airbus an in-house collection of meta-modeling tools called GT-Approx is present. GT-Approx automatically determines which is the best fitting method based on several features of the input data (Yarotksy et. al, 2013). GT-Approx

show the difference between the MSES calculations and the GT-Approx calculations. It can be seen from that the errors for the two outer values are significantly higher than the error for the inner values. It is concluded that GT-Approx is good at interpolating, but not good at extrapolating.

In general, the fit for interpolating values is very good. For the inner values the error bars ROY VELDHUIZEN

tion yields that 2D method MSES is the program best suited for this purpose.

2D drag coefficient cd [−]

cd w 70 60 50 40 30 20 10 0 −10 −20

×10−4

0.4

0.5 0.6 0.7 Mach number, M [−]

0.8

be seen that the error increases progressively, and at higher Mach numbers is as large as the value of cdw itself.

The prediction accuracy is good, however for complex cases significant errors arise.

Especially for the higher Mach numbers the error is too large. In order to improve the accuracy, the influence of resolution increases is investigated. The goal of this procedure is to see how much the accuracy increases when more data points are added. As the error for M predictions is the largest, only increases in Mach-resolution are discussed here.

MACH RESOLUTION SENSITIVITY Substantial gains can be achieved by decreasing the step size ΔM. For example, Figure 3 shows that halving the value of ΔM reduces the average prediction error by 65%.

Upon decreasing ΔM to 0.0125 the improvement increases to 87%. Further decreasing the value of ΔM to 0.00625 does not result in significant gains. Figure 4 shows the value of cdw vs M for different resolutions (indicated by the black dots). It can be seen that the quality of the estimation has mostly improved in the region where the error was large, for the higher Mach numbers. This shows that adding more data points increased the capability of GT-Approx to fit more difficult surfaces.

FITTING CAPABILITIES OF COMBINED METHOD Now that both a suitable aerodynamic method and meta-modeling method are found, it is possible to evaluate the fitting capabilities of the meta-modeling method.

The difference between the two is used to judge how accurate the fit is. Research showed that the MSES data is accurately represented by GT-Approx as the error does not exceed 3.70∙10-3.

Predicting capabilities of combined method It is necessary to investigate if GT-Approx is also able to predict data. It is investigated how accurate GT-Approx can determine results for data-points that have not been previously calculated with MSES. To do this, the leave-one-out method is applied. This method uses all but one value to construct an estimate for this value. For example, data in the range M=0.4-0.7 is used to estimate the value for M=0.8.This was done for all variables, but only the most interesting variables are discussed here

PREDICTION OF WAVE DRAG AS A FUNCTION OF REYNOLDS NUMBER Figure 1 shows the result of the method explained above. The lines show the values of cdw calculated by MSES. The error bars

GT-Approx error, ∆cd [−]

selected the Splines with Tension method as the best meta-modeling method.

ROY VELDHUIZEN

Figure 2 - Development of cdw and error versus Mach number.

cd w 12

×10

−4

10 8 6 4 2 0 0.1

0.05 0.025 0.0125 0.00625 M -grid spacing interval, ∆M [−]

Figure 3 - GT-Approx cdw prediction error versus M-grid spacing. are hardly distinguishable. The average error for the inner values is 0.38 drag counts for cdw .

PREDICTION OF WAVE DRAG AS A FUNCTION OF MACH NUMBER The predicting capabilities of GT-Approx with respect to values of M are investigated.

The results can be seen in Figure 2. Here it can be seen that the approximation also shows extrapolation errors, as well as increases towards higher Mach numbers due to more complex data to be modeled. It can

3D MODEL EXTENSION To make this tool a suitable tool for preliminary aircraft design and evaluation, it is necessary to extend the method into the third dimension. The extension into the third dimension is done by applying a quasi 3D method. This method entails dividing the wing into a number of 2D sections. Using the simple sweep theory the local 3D conditions for these sections are then calculated. The simple sweep theory only gives reliable results when the flow is perpendicular to the local chord line. This is not always the case, as LEONARDO TIMES N°1 2016

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ROY VELDHUIZEN

wing and root effects, fuselage effects and engine installation effects result in a highly 3D flow for a large part of the wing. Investigation of 3D CFD data shows that the region of validity of the quasi 3D method is 0.6≤η≥1.03 (A value larger than 1 is possible because the calculation of η is done using an Airbus reference span). These local conditions are then used to estimate the 3D performance of the wing. To see how accurate the method is, it is compared with CFD data for two Airbus A320 wings: the original A320 wing, and a proposed modification called A320-PL7A. The modification features a span and chord extension, a wing retwist and a new airfoil selection.

Figure 5 shows the results of GT-Approx compared with data calculated directly

by MSES. The errors are small, averaging around 0.21 drag counts, thus showing that the meta-modeling method is capable of accurately reproducing the values generated

by MSES.

In general, it is concluded that the combination of an aerodynamic tool with a meta-model can be a successful one, greatly reducing computation times whilst maintaining accuracy, but this is highly dependent on the accuracy of the aerodynamic model.

References [1] D. Yarotsky, M. Belyaev, A. Krymova, E. Zaytsev, Y. Yanovich, and E. Burnaev, “GT-Approx Generic Tool for Approximation”, DATADVANCE, 1st ed., 2013

ROY VELDHUIZEN

Meta-model

0.6

0.7 0.8 0.9 Relative spanwise wing station, η [−]

1.0

Figure 5 - Comparison between MSES and GT-Approx approximation for A320-PL7A.

GT-Approx A320 CFD A320

GT-Approx A320-PL7A CFD A320-PL7A

A320

A320-PL7A

0.6 0.8 1.0 Relative spanwise station, η [−]

0.6 0.7 0.8 0.9 1.0 Relative spanwise station, η [−]

ROY VELDHUIZEN

CONCLUSION It is concluded that the aerodynamic tool MSES is an accurate 2D method and that the meta-modeling method GT-Approx is able to accurately reproduce complex data generated by MSES. It is possible to improve the accuracy of the meta-modeling method by adding more data points. Accuracies of 0.21 drag counts are achieved, whilst reducing the in-the-loop computation time from 112s to 1.03∙10-2s per iteration. Although the meta-modeling results accurately mimic the MSES results, the comparison with the CFD data shows that the combined model is not accurate. This can be attributed to the aerodynamic conversion of 2D to 3D data.

Direct

3D drag coefficient, CDw [−]

The difference in calculation times is large.

GT-Approx requires a lot of time to run multiple MSES calculations, and build a model from this data. However the most important parameter, the in-the-loop calculation time, is reduced by a factor of 10,000.

Figure 4 - GT-Approx prediction error versus M for different resolutions.

3D wave drag coefficient, CDw [−]

In Figure 6, values calculated by GT-Approx are compared with CFD data. Here it can be seen that the errors are quite large. The performance for the A320-PL7A is significantly better than that for the A320. Because of lack of more detailed CFD data no clear explanation was found for this phenomenon.

Figure 6 - Comparison between GT-Approx and CFD calculations for both test cases.

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N°1 2016 LEONARDO TIMES

FPP

DUTCH DESIGNS INTERNATIONALLY RECOGNIZED TU Delft Runner Up in two International Aircraft Design Competitions Dennis Berckmoes, BSc Student, Aerospace Engineering Christian Alba, BSc Student, Aerospace Engineering Dr. ir. Roelof Vos, Assistant Professor, TU Delft Since 2012, students from the faculty of Aerospace Engineering have been actively competing in International design competitions that are organized by the American Institute of Aeronautics and Astronautics (AIAA). This year, two teams, one undergraduate and the other graduate, each took a second place.

D

utch Designs can be typically characterized as minimalist, experimental and innovative. Not only do these traits apply to chairs and buildings designed by famous Dutch engineers, they also extend to aircraft designs created by students of the Aerospace faculty.

Every year AIAA organizes aircraft design

competitions in three different categories: undergraduate, undergraduate individual, and graduate. Students are asked to submit a proposal for a new aircraft design under a strict set of requirements that can vary widely between the categories. In 2014/2015, two teams competed, one in the undergraduate category and one in the graduate category. The undergraduate team was tasked to

Figure 1 - Members of the undergraduate design team (fltr): Waqas Hayat, Koen Kwakman, Richard Hoefsloot, Frank van Tilborg, Damian Milewski, Jan Fisher, Bas Zuurendonk, Dennis Berckmoes and Nick van Oene

design a military transport aircraft, while the graduate team had to come up with a new air-taxi concept for large urban areas.

UNDERGRADUATE TEAM The US armed forces is focusing on modernizing their current fleet by implementing new technologies to extend the lifetime and to advance the performance of their aircraft.

Even though this transformation has resulted in considerable improvements, it is expected that significant advancement will be achieved by introducing a new generation of aircraft. Therefore, AIAA issued a request for proposal (RFP) for a next-generation strategic-airlift military transport aircraft with an expected entry into service (EIS) in 2030. The aircraft to be designed is aimed to replace the military’s largest air transport aircraft, the C-5 Galaxy. The RFP asked for an aircraft that could carry a greater payload, both in terms of weight and volume, and at the same time have twice the range of the Galaxy. As part of the 2014 fall Design Synthesis Exercise, a group of nine aerospace students (Figure 1) responded to this RFP with a new design proposal.

For the first design stage, the team split up into three smaller groups, all tasked to bring forward their most promising concept. The first group investigated a canard blended wing body that has a pressurized central fuselage section and two unpressurized cargo bays embedded in the wing. The second proposal was an integrated wing body with a modular cargo compartment that can be LEONARDO TIMES N°1 2016

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Figure 2 - Isometric view of the WHALE. exchanged for different missions. The third concept, which the team regarded to be the most suitable, was an ultra-wide body aircraft, relying on the conventional tube and wing configuration.

The ultra-wide body aircraft, mostly attributed to its shape, was conveniently named the WHALE (Wide Hull Airlift for Long Endurance), designed with a V-tail, truss braced wings and a lifting fuselage nose. The key design goals of this concept are decreasing the turn-around time, allowing more versatility in cargo transport and an increase in the aerodynamic efficiency.

The WHALE is capable of transporting any required piece of military hardware over trans-Atlantic distances without refueling whilst having an additional 72 seats available to carry personnel without compromising the cargo volume. Its versatility and efficiency expands the capabilities of the strategic airlift at a lower cost than the C-5 Galaxy.

system based on an innovative vehicle with VSTOL (Vertical and Short Take-Off and Landing) capabilities, allowing commuters to get in and out of a city at a faster pace and a moderate price, with low environmental impact. The required vehicle had to operate on both runways and helipads, carry a maximum of nine passengers, be part of a 30year service starting in 2020 (EIS) and break-even in the shortest time possible. Finally, some form of electrical propulsion had to be part of the design. The graduate team (see Figure 3) was tasked to bring design and engineering skills together with entrepreneurial and business skills for their final proposal.

"This is the fourth consecutive year that TU Delft has ranked in one or more categories"

The WHALE features a tapered fuselage, much like a glider, with a maximum width of almost twelve meters in the forward section and a total length of over seventy meters (see Figure 2). The dimensions were mainly driven by the necessity to carry 44 pallets. Opening up the forward cargo door would give access to four pallets simultaneously, effectively reducing the loading and unloading time. The fuselage was shaped such that the landing gear could be retracted into the fuselage, requiring no need for drag-intensive landing-gear pods on either side. Additionally, the use of struts to support the wings allowed for a slender wing design with a large span (eighty meters) without a high penalty in structural weight.

The most crucial aspect to the success of the WHALE is its propulsion system. In the context of an EIS in 2030, a new engine technology was selected: the Counter-Rotating PropFan (CRPF) engine. This new technology promises large reductions in fuel consumption and is currently being developed.

The CRPF system has however not yet been scaled up to provide a similar thrust output as the most powerful high-bypass-ratio turbofan engines. Even though this resulted in a total of six engines needed to propel the aircraft, the reduction in fuel consumption outweighed the added weight and drag.

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GRADUATE TEAM Considering the increasing amount of traffic congestions in large metropolitan areas, AIAA issued an RFP for designing an air taxi

The strategy the team adopted featured the creation of small departments, each one dealing with a different discipline, such as: performance, flight dynamics, structures, powertrain, noise, and network & operations.

Figure 3 - Graduate design team (left ro tight): Roelof Vos (supervisor), Clara Moreno, Christian Alba, Piotr Druzdzel, Reynard de Vries, Sofia Minano, Francesco Faggiano, Cristian Merino, and Adam Gabor Vermes.

power loss, represents an unmatched safety enhancement.

Given the unconventional configuration, a hybrid design procedure was necessary, resorting to numerous references from aircraft literature including sources on helicopter design procedures and autogyro design.

All relevant disciplines were integrated in an automated design tool built in the Matlab environment.

Figure 4 - Three candidate configurations for the air taxi design.

The first stage of the project included the proposal of the network and the evaluation of different designs proposed by three groups. The first explored the field of tilt-rotors, presenting a fixed-wing aircraft with three rotatable and electrically powered fans. The second proposed the adoption of a forward-swept tilting wing vehicle, carrying an electrically powered propeller on each semi-wing. The third proposal, which was eventually deemed by the team to be the most suitable for the project, was a Gyrodyne (Figure 5), featuring a helicopter-like main rotor, actively propelled during vertical takeoff and landing, and a fixed wing. During cruise and horizontal takeoff and landing, the main rotor would be disconnected from the

powertrain and put in autorotation, carrying a variable percentage of the total required lift.

Two wing-mounted propellers would provide the required thrust during cruise, and provide counter-torque in hovering.

The powertrain design was perhaps the most challenging task. After having concluded that a fully electrical power plant was not viable with today's technology, the team opted for a hybrid system with a constant-power gas turbine. A dual acting electric generator/ motor would direct the energy towards the main-rotor or thrusters depending on the flight leg while batteries absorbed or fed fluctuations. The redundancy of the powertrain design, and the capability of autorotation to land in a few meters, even in case of a total

As for the network and business plan, San Francisco Bay was deemed to be the best market for introducing this aircraft, where a fleet of 16 vehicles cruising at 160kts would serve a total of 10 operating sites covering an interwoven network of short-range routes.

With 750 daily flights, the system would reduce traveling time by up to 75% and costs by up to 58% when compared to normal taxi transportation.

TRADITION? It is not the first time that students from TU Delft have won prizes in the AIAA design competitions. This is the fourth consecutive year that TU Delft has been ranked in one or more categories. In 2015/2016 two teams will be competing as well. The question of their victory remains to be seen. At least they have good predecessors to aspire to.

ACKNOWLEDGEMENTS Dr. Sander Hartjes and Dr. Daan Pool for coaching the undergraduate team. In addition, Dr. Marilena Pavel is acknowledged for providing pivotal guidance for the Gyrodyne design.

Figure 5 - Isometric view of the Gyrodyne design.

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A TOPOLOGY OPTIMIZED PARAFOIL Membrane finite element solver applied to a kite Paul Thedens, MSc Graduate European Wind Energy Master (EWEM) Topology optimization has experienced vast growth in the past few decades, whilst moving towards industrial applications. A new finite element (FE) solver for membranes, developed at TU Delft, was combined to a topology optimization and was tested on a ram-air kite rib, since their fabrics have to provide maximum stiffness.

T

hin membranes have a broad range of applications in modern engineering, ranging from parachutes and kites to textiles used in civil engineering. Their advantages lie in the high area-to-weight ratio, which is also used in kite design. The load carrying structures in a kite are the ribs, connecting the lower and upper canopy and carry the loads to the bridle attachments.

This structure has to withstand all external loads and provide the stiffness such that the aerodynamic shape is not drastically altered during operation.

Ram-air kites have openings at the leading edge where the airflow enters the structure and inflates it from the inside. In order to avoid undesirable flight behavior resulting

from the deflation of single cells, the internal pressure needs to be constant throughout the whole kite. Therefore the ribs have holes, so called ‘cross-ports’, to allow the air to freely move between all cells and provide the required aerodynamic shape. The challenge lies in finding the optimum size and position of the cross-ports on a rib. If too large or placed at highly loaded regions, the rib would deform and reduce the kite’s aerodynamic efficiency, whereas small cross-ports add weight and might result in deflation of the structure. To find an initial layout of a rib structure for kites, a numerical structure optimization method called topology optimization in combination with a membrane finite element solver is applied.

Slack

Wrinkled

THEDENS

THEDENS

TRIA MESH

Taut

Figure 1 - Stress state of sheared membrane (left); and optimized topology of sheared membrane (right).

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TOPOLOGY OPTIMIZATION The structural layout for most part designs is crucial because the stiffness of a body is determined by both its material and geometrical properties. In topology optimization, the geometrical layout in a given domain with fixed boundary conditions, such as loads and supports, is iteratively optimized to increase the body’s stiffness (called compliance minimization). After applying a FE mesh over the domain, a fictitious density varying between zero and one is given to each individual element. This density has a direct influence on the element’s Young’s modulus and therefore simulates material for a high density, or void for a low density. The optimizer starts with a given set of densities and iteratively adds or subtracts them in regions where the strain energy is high or low, respectively. This is done until the stopping criterion is satisfied and the total stiffness is increased. To avoid intermediate densities the SIMP (Solid Isotropic Material with Penalization) method [1] is most commonly used, due to its simplicity to implement and solve.

THIN MEMBRANES Membranes are distinctive structures in engineering because they possess a negligible bending resistance, as they tend to wrinkle under the slightest compression. Wrinkling is an out-of-plane deformation and a purely local phenomenon, thus requiring a fine mesh to be resolved which drastically increases the computational effort for the FE solver.

In topology optimization, the FE solver has to compute the displacement field in each of the density iterations and therefore, the

Wrinkled

THEDENS

THEDENS Slack

Taut

Figure 2 - Stress state of rotated membrane (left); and optimized topology of rotated membrane (right).

neglected due to the low wind speed range kites fly at. The internal ram pressure caused by the stagnated airflow increases the structure’s stability and is superimposed on the aerodynamic pressure which results in a loading condition without compression. The optimization is done on two different flight conditions; 4° and 8° at airspeeds of 15m/s and 10m/s respectively. The final rib model consisted of both flight conditions, linearly combined, as a multi-objective optimization.

The resulting topologies are shown in Figure 3. In both load cases, the optimizer introduces holes between the four bridle supports.

The final model is the combination of the two load cases resulting from a Pareto optimiza-

THEDENS

THEDENS

use of a fine mesh should be avoided. Alternatively, wrinkles can be modeled as an inplane contraction in a purely stress positive field according to the tension field theory [2].

This method reduces the problem from three to two dimensions as out-of-plane deformations are disregarded, and hence solely the stress determines the membrane state. At TU Delft, this method was implemented into a membrane FE solver [3] and was tested in combination with topology optimization.

One of the challenges in topology optimization is to determine a suitable objective function and its sensitivity (first derivative w.r.t the density), thereby describing the structure’s topology. For geometrically non-linear structures, which take large displacements into account, a common objective function is the complementary energy expression. By minimizing this function, the total displacement can be reduced and thus a higher stiffness of the structure is obtained. The sensitivity can be determined analytically, resulting in a computationally efficient optimization method which a gradient-based optimizer is able to solve. However, numerical instabilities can still emerge in low-density regions inhibiting the membrane FE solver from converging, and therefore fine-tuning the load magnitude and mesh is required.

VERIFICATION OF NUMERICAL RESULTS The developed objective function was tested on several simple problems to verify its validity. The first problem consists of a rectangular membrane, clamped at the bottom and sheared to the right hand side at the top edge. This problem introduces an interesting stress distribution because both left top and bottom right corners are in a slack state, whereas most of the rest is wrinkled (Figure 1). The taut state at the supports is introduced due to the Poisson effect. From an engineering perspective, a slack membrane does not contribute to the structure’s stiffness because it carries zero stress. The optimizer reduces the density in those areas immediately due to the low occurring strain energy, thus cutting off both corners (Figure

THEDENS

MEMBRANE TOPOLOGY OPTIMIZATION

Figure 3 - Optimized topology of rib for /alpha = 4deg and V=15m/s (top); optimised topology of rib for /alpha = 8deg and V=10m/s (middle); and optimized topology for combined load cases (bottom).

1). The black elements correspond to material (density is one), whereas white are void.

At the interface of the material parts, some grey elements can still be found which ultimately disappear when a projection filter is used. The application of projection filters also caused numerical instabilities for the FE solver and is therefore not used on all problems.

The second problem is an annular membrane with a rectangular cutout in the center. The edges of the cutout are clamped and the whole membrane is rotated counterclockwise. As expected, the introduced torque causes severe wrinkling in the membrane but no slack state occurs (Figure 2).

The optimized topology can be found in Figure 2 and it can be seen that the initially wrinkled regions become void as they solely carry loads in one direction and have a lower strain energy compared to the taut elements.

RIB OPTIMIZATION Optimization of the rib structure of a ram-air kite requires the loads acting on a rib to be determined. A simple 2D panel code is sufficient to obtain the pressure distribution over a cell. Viscid and compressible effects are

tion where both load cases have the same weight factor. Compared to a rib used in ram-air kites, the optimized rib shows a good initial design. The shape of the holes still has to be improved to avoid stress concentrations, which is the next pasteprt of the part design. However, this is beyond the scope of the research. In summary, the developed optimization method can be applied to various membrane problems thus reducing the slack and wrinkled regions, as well as to rib structures where an initial design can be obtained. The drawbacks are the numerical instabilities, which lower the robustness of the method and require fine-tuning of load magnitude.

References [1] Bendsøe, M. “Optimal shape design as a material distribution problem” Structural optimization, 1 (4), 193-202, 1989.

[2]Wagner, H. “Ebene Blechwandtraeger mit sehr duennen Stegblechen” Z. Flugtechnik u. Motorluftschiffahrt 20, 1929.

[3] de Rooij, R. & Abdalla, M. M. “A finite element interior-point implementation of tension field theory” Computers & Structures, 151 (0), 30 – 41, 2015.

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F N O I T A M trim R

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f o t c e f f e e Th

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Ir. Evert Windels, Graduate Aerospace Engineering, Flight Performance and Propulsion A flock of birds flies in formation when travelling long distances, due to an energy saving advantage. Research on this phenomenon has been conducted throughout the beginning of the twentieth century, and it focused on how much can be gained using formation flight, where unfavorable effects have only been a topic of research for the last few decades.

BACKGROUND The phenomena of birds in formation has been researched since 1914 by Wieselberger (Wieselberger, 1914), who initially identified a benefit. This benefit was defined in aerodynamic theory by Lissaman et al. in 1970 (Lissaman, 1970).

Behind a finite lifting surface, a region of upwash and downwash is created. Both regions are separated by the tip vortex, present due to the finiteness of the lifting surface. A graphical representation can be seen in Figure 1a, showing the tip vortex and regions of up- and downwash behind a C-17 aircraft. Within the regions of up- and downwash, the local effective angle of attack will change. The upwash velocity component will increase the

local effective angle of attack whereas the downwash velocity component will lower the effective angle of attack. An increase in the effective angle of attack will locally tilt the lift vector forward, reducing the lift induced drag component. This specific drag component is increased in the region of downwash. The effect of upwash on lift and drag is shown schematically in Figure 1b. The benefit of the formation flight lies within this reduction of lift induced drag, determined to be a 52.6% reduction when compared to a solo flight condition using a Vortex Lattice Method (VLM) ‘AVL’ (Fransen, 2012).

This benefit has been proven by multiple research studies throughout the past few decades, most notably by NASA through the Surfing Aircraft Vortices for Energy project (SAVE).

The VLM showed a region of 10% around the vortex core, where the results deviate from what is expected. The black dotted lined box within the subsequent result figures indicates this. Results within this region should be discarded. The position for optimal induced drag reduction, the 52.6% reduction compared to solo flight condition, was chosen at -0.15 y/b lateral separation and 0.1 z/b vertical separation. Figure 2a shows a graphical representation of the trail aircraft with relation to the lead aircraft for this position, -0.15 y/b and 0.1 z/b.

AERODYNAMICS The formation flight condition implies that a ‘trail’ aircraft flies within the flow field of a ‘lead’ aircraft, as shown in Figure 1, effectively immersing part of the wing in the region of upwash and/or downwash. Due to the localized effect of the upwash and downwash behind the lead aircraft, the trail aircraft’s wing loading will be affected, and the wing loading becomes asymmetric. Figure 2b shows an example of the wing loading when the trail aircraft is positioned at a fixed location with relation to the lead aircraft.

The location of the trail aircraft within the wake field of the lead aircraft determines the degree of asymmetry, which decreases with distance with respect to the wake field. This is expected, as the upwash effect also diminishes, as can be seen at the far right end of Figure 1a.

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BIENIAWSKI

Figure 1 - (a) Forces acting on an airfoil when positioned in an upwash flow field; (b) Flow region behind a C-170 transport aircraft, identifying the regions of upwash and downwash separated by the tip vortices.

The asymmetric wing loading will affect the force balance of the trail aircraft, creating a pitching and rolling moment. The pitching moment changes due to the increase in lift, accompanied by the decrease in induced drag. This local increase in lift will also induce a rolling moment. A coupled yawing moment is also created, where pitch and roll are more pronounced. The degrees of ‘interference’ moments are strongly related to the location in the wake field, making the aircraft statically unstable. A disturbance will make the aircraft change position, where each position induces moments that push the aircraft again to another position, not necessarily the original position. The change in rolling moment throughout a segment of the wake field is shown in Figure 3.

Each position requires a specific control deflection setting for steady straight flight, which needs to be adjusted when the position changes (active control required).

These control deflections will affect the induced drag benefit. The goal of this research was to analytically quantify the reduction in benefit due to control deflections using a

simulation model, positioning the aircraft at multiple positions within the wake field. Interactions by changing position, regarding stability, were not yet investigated although the simulation model does offer options to study the positional changes.

SIMULATION MODEL To perform an analysis on the impact of control deflections upon the induced drag benefit during a formation flight, an analytical simulation model was used. The model has a modular built up and was created by Mark Voskuijl and others (Pfeiffer et al., 2011) (Voskuijl et al., 2012). The model was able to analyze and run simulations with aircraft geometries, when the aerodynamic data was provided. The model was extended and adjusted to perform the formation flight analysis. The positional analysis of the trimmed trail aircraft in the formation flight condition, at multiple positions in the wake field, showed a reduction in benefit of 5% at the optimal position, -0.15 y/b and 0.1 z/b. The difference further increases when moving away from this position. Figure 4 shows both the induced drag reduction in untrimmed condition as

trimmed condition for a segment of the wake field, accompanied by a graphical representation at the position of optimal induced drag reduction. Flight at the optimal position also revealed a potential fuel flow reduction of 18%, due to the reduction of induced drag.

Although this is an estimate, it proves that much can be gained by flying in formation.

The initial quantification of the impact of trim upon the formation flight together with the fuel flow benefit highlights the importance of further research.

The simulation model was also used to briefly perform a dynamic analysis, by solving the state space representation of the trail aircraft in formation flight. An unstable condition was highlighted by positive real eigenvalue solutions, where other eigenvalues showed stable behavior. As was highlighted before, further research into the dynamic and static stability behavior is required.

Van der Kleij did a study upon the stability topic by analyzing and designing a controller for the formation flight of a Boeing 747 (Van der Kleij, 2012). The inability to retain

Figure 2 - (a) Graphical representation of trail aircraft with relation to lead aircraft at position for optimal induced drag reduction, -0.15 y/b and 0.1 z/b; (b) Wing loading of trail aircraft rectangular wing with NACA0012 wing profile, flying at standard atmospheric conditions (0 meters) 0.55 Mach with a lift coefficient of 0.55, of a homogeneous formation where both wings are separated by eight wingspans.

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Figure 3 - Rolling moment distribution for a segment of the wake field of a homogeneous two A330-300 aircrafts echelon formation flying at 0.6 Mach at 11,000 meters altitude, alongside an explanatory graphical representations of the wake field axis definition and a situational geometry sketch (black star indicates vortex location). one position within the wake field without requiring active control was highlighted, although the study showed that no dangerous situation was created by the formation flight condition. At the optimal location, the aircraft would have been experienced a volatile pitch down and a left hand roll, behind the lead aircraft.

CURRENT RESEARCH Research on the topic of formation is ongoing, the NASA Surfing Aircraft Vortices for Energy (SAVE) project being the most notable one. Recently presented studies show the development models and tools to further analyze the effects of formation flight (Halaas et al., 2014) (Slotnick et al., 2014). Next to the theoretical approach, test flights are performed using a C-17 aircraft to quantify the (dis-)advantages (Bieniawski, 2014). The test flights have already shown a potential fuel flow reduction ranging between 7-9%, only half compared to the results of the simulation model. The simulation model, how-

ever, neglected viscous and compressibility effects.

To conclude, formation flight remains a popular research topic, where the reduction in induced drag effectively can result in a significant reduction in fuel consumption. The power lies within the operational aspect, where the current aircrafts can be used to fly within a formation. However, attention must be paid however into the fatigue life of the control surfaces as well as the aero-servo-elastic interactions, which was beyond the scope of this research. This may pave possibilities for further master thesis topics and interesting studies.

References [1] Carl Wieselsberger. Beitrag zur erklärung des winkelfluges einiger zugvögel. Z. Flugtechnik u. Motorluftschiffahrt, 5:225– 229, 1914.

[2] PBS Lissaman and Carl A Shollenberger.

Formation flight of birds. Science, 168(3934):

1003–1005, 1970.

[3] Dietrich Hummel. Aerodynamic aspects of formation flight in birds. Journal of theoretical biology, 104(3):321–347, 1983.

[4] T Pfeiffer, B Nagel, D Böhnke, A Rizzi, and M Voskuijl. Implementation of a heterogeneous, variable-fidelity framework for flight mechanics analysis in preliminary aircraft design. In German Aeronautics and Space Congress, DLRK, 2011, Bremen, Germany, 2011.

[5] Mark Voskuijl, Jan de Klerk, and Daan van Ginneken. Flight mechanics modeling of the prandtl-plane for conceptual and preliminary design. In Variational Analysis and Aerospace Engineering: Mathematical Challenges for Aerospace Design, pages 435–462.

Springer, 2012.

[6] Bert Fransen. Formation flight: Theoretical investigation regarding applicability of wind tunnel tests for the validation of theoretical formation flight benefits for long range transport aircraft. Master’s thesis, Delft University of Technology, March 2012.

[7] C.A. van der Kleij. Close formation flight control with applications in commercial aviation. Master’s thesis, Delft University of Technology, September 2012.

[8] S.R. Bieniawski, R.W. Clark, S.E. Rosenzweig, and W.B. Blake. Summary of flight testing and results for the formation flight for the aerodynamic benefit program. In AIAA 52nd Aerospace Sciences Meeting, number AIAA 2014-1457, 2014.

[9] D.J. Halaas, S.R. Bieniawski, D.T. Whitehead, T. Flanzer, and W.B. Blake. Formation flight for aerodynamic benefit simulation development and validation. In AIAA 52nd Aerospace Sciences Meeting, number AIAA 2014-1459, 2014.

[10] J.P. Slotnick, R.W. Clark, D.M. Friedman, Y. Yadlin, D.T. Yeh, J.E. Carr, M.J. Czech, and S.R. Bieniawski. Computational aerodynamic analysis of formation flight for aerodynamic benefit program. In AIAA 52nd Aerospace Sciences Meeting, number AIAA 20141458, 2014.

Figure 4 - Comparison of induced drag reduction of the trail aircraft in formation flight, compared to the solo flight condition, in untrimmed and trimmed condition accompanied by a graphical representation of the optimal induced drag position (-0.15 y/b and 0.1 z/b).

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SPACE ENGINEERING

NASA’S ASTEROID

The narrative around asteroids has been largely one of ‘Impact-Threat Science’. The concept that asteroids are a threat has lead to a push for reconfiguring Astronomy as ‘interventionist science’, ultimately suggesting militaristic endings. Many other asteroid scientists suggest contrasting innovative solutions. We caught up with Jason Kessler, Program Executive of NASA’s Asteroid Grand Challenge at the Border Sessions Festival in The Hague, where he was one of the speakers.

NEOO, ARM AND AGC In 1998, NASA initiated Near Earth Objects (NEO) Observations programs with the aim to discover 90% of the NEOs larger than one kilometer in diameter and in 2005, Congress extended that goal to include 90% of the NEOs larger than 140 meters. The programs have been remarkably successful at achieving their goals.

In 2013, NASA announced Asteroid Initiative. The initiative includes Asteroid Redirect Mission (ARM) and Asteroid Grand Challenge (AGC). In ARM, NASA is developing a first-ever robotic spacecraft to visit a large near-Earth asteroid, whose mission is to collect a multi-tonne boulder from its surface and redirect it into a stable orbit around the moon. Once there, astronauts will explore it and return with samples in the 2020s. Asteroid Grand Challenge is designed to accelerate NASA’s efforts to locate potentially hazardous asteroids through non-traditional 64

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collaborations and partnerships with other government agencies, international partners, industry, academia, and citizen scientists to detect, track, characterize, and create mitigation strategies. The challenge could also help identify viable candidates for ARM.

THE INTERVIEW The Leonardo Times sat down with Jason Kessler to shed some light on how innovation works a broader scale, the changes in which new ideas are streaming into NASA and how budding Aerospace Engineers could contribute to the Asteroid Grand Challenge.

Considering the detection quotient of Asteroid Grand Challenge, back in 2013 there was Chelyabinsk meteor over Russia, and if something like that would happen now you would give us an update?

If we knew about it, yes. It was so wild about that day, because you may not remember

JASON KESSLER Asteroid Grand Challenge Program Executive at NASA

M. AHMETVALEEV

GRAND CHALLENGE Eleonoor van Beers, Victor Gutgesell, Editors Leonardo Times, Sushant Gupta, Editor-in-Chief, Leonardo Times

Meteor streaking through the sky above Chelyabinsk, Russia, on Feb. 15, 2013. The small asteroid was about 56 to 66 feet (17 to 20 meters) wide.

Jason Kessler started his career at NASA in 1994 and served in various positions in the following six years culminating with Deputy Chief of Staff to NASA administrator. Thereafter, he went on to get an MBA on full scholarship and successfully started his own business in New York. Combining his experience in public and private sectors, Mr. Kessler returned to NASA as Deputy Project Director at SERVIR, which focused on earth observation data and developing decision tools and training to help developing regions with climate change adaptation. In recent years, he has served as the NASA Lead for LAUNCH, an open innovation platform founded by NASA, NIKE and USAID. LAUNCH aims to move beyond incremental change and make an impact at a system-wide level. Currently serving as the Program Executive for Asteroid Grand Challenge, his project focuses on finding all potential asteroid threats to human populations and knowing how to handle them.

Estimates suggest less than 10% of objects smaller than 300 meters in diameter and less than 1% of objects smaller than 100 meters in diameter have been discovered. It will take a global effort with innovative solutions to accelerate the completion of the survey of potentially hazardous asteroids.

but 2012 DA14 was the asteroid that everyone was paying attention to because it was going to come within the Geo-belt. And then all of a sudden outside of Chelyabinsk, a 17m Asteroid disintegrates up in the atmosphere. And their dashcams captured this so beautifully which made the event go ‘viral’ around the world so beautifully.

We are not that good to be able to respond to it with the program currently. But we should not forget that the Near Earth Objects Observations program is in place since 1998. They have found 98% of all asteroids till today. The founding that they have done for the survey scopes this aspect. They’ve been working hard at this problem for a long time. Asteroid Grand Challenge was just a way of engaging more broadly and figuring out: Can we bring in fresh ideas to solve this problem? So there is this whole team at NASA and throughout the world who are funded to do the detection and classification and some mitigation.

It’s studies at this point. There are new ideas like Bong Wie, a professor at Iowa State is funded to do kinetic impact studies. The challenge is that in order for anything to be out of a model and a real test it has to be outside of the Earth’s gravity.

There’s a paper about mounting a giant laser

aboard the ISS to deorbit space debris, and use that same laser, a bit upscaled maybe, to deorbit asteroids.

Laser ablation is one idea that I’ve heard, not talked about consistently, but the idea is fine if you were able to impart some delta-V change because you’ve got ablation happening on the surface. You’ve even got white paint.

That’s because they’re icy rocks. And the sun melts the ice…but that’s only some asteroids.

And that is why, characterization is so important. The white paint one is a very wild idea, so you paint half of the asteroid white, and the sun does the rest. But how do you actually get the white paint on it!

Are you also building up hardware for Asteroid Grand Challenge?

On the mitigation aspect we haven’t really spent much time because we really need to know where the things are first, so the focus has really been on detection and the mitigation is really only been theoretical at this point. But here’s an exciting one. In 2012, NASA held International Space Apps Hackathon and the winner was Open Space Agency (OSA). James Parr, the founder of LEONARDO TIMES N°1 2016

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In this concept image, the robotic vehicle descends to the surface of a large asteroid to collect a boulder that it can redirect to a distant retrograde lunar orbit.

OSA based in London, took the idea of an Ultrascope and ran with it. They’ve built a $300 telescope- 3D printed and laser cut it’s an automated robotic observatory. They built one and took it to a township in South Africa, imaged the Jovian moons while he was at the wired conference, controlling the telescope in New York, through the clouds to South Africa. The goal is to eventually have an 18inch mirror that can actually do asteroid follow-on, and actually have a series of these particularly in the southern Hemisphere, and in southern Africa where the sky is very dark and we don’t have a lot of resources to do follow-up work. This won’t be detecting asteroids but they can help with characterization- spin rates and potentially shapes.

NASA

Could you provide us with some insights into the mission and how students can apply their minds to solutions for the Asteroid ‘problem’?

I think now the big challenge we see- and

it is relevant to your classmates as you are the future generation- is that Engineers are trained to solve problems. You are educated that ‘under these conditions, I need this valve to work’, and open innovation requires that the engineers do not try to solve the problem, rather the engineers are required to decompose, describe and communicate the problem so that there’s a way of engaging a broader audience to actually solve the problem. So there’s this shift from engineers being problem solvers to problem definers and Grand Challenge for me, is an experiment in engaging broadly to solve problems. So it’s a culture change because if you’ve been trained your whole career to be the one that solves the problem it’s difficult to shift into decomposing the problem for others to solve.

I think, if your generation would be able to think about it that way, it would enable future missions to be designed in such a way that the fresh ideas are more easily integrated.

There is a lot of work that needs to be done in breaking the problem down. For ARM, that’s

A close-up view of Eros, an asteroid with an orbit that takes it somewhat close to Earth.

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a technique used to solve otherwise tedious problems in creative new ways. Say we have a certain amount of money we can award on contract to the individual that solves the problem, and we’re looking for new solutions that think outside of the box.

In which areas can students specifically contribute?

We find innovation happens at that edge of perspective and idea. And that’s the area that I spend most of my time in. I think for engineering students, the challenge is likely the design and manufacturing of the hardware.

A colleague of mine is looking into understanding where crowdsourcing can work for hardware. At AGC, we haven’t done that much in terms of hardware design and that’s an edge that could be a real interesting place to explore for students. We recognize that to open certain problems to the ‘crowd’ is not going to be useful, and is potentially a waste of time. It is not realistic to think that somebody who has no background or experience in that area is going to bring a solution to. However, there is some trade space and while innovation is the current buzzword and open innovation is also the current thing to do, it would be nice to know where it works well and where it doesn’t work well. We found that when you don’t necessarily know what you want, it works wonderfully well. For example. with a T-shirt design contest. You’ll get as many solutions as the number of people that give in designs. If you don’t know what you want, it’s great because now you have all these ideas to choose from and you just go ‘Ah, I like this one’. Or you can go really specific and say this is the technical problem I need to solve, I need this valve to work under these conditions, find somebody to come up with that solution. So for young engineering students, it might be an interesting thing to look at – where is crowdsourcing useful? In our experience, I’d say $55,000 prize money is a much cheaper outcome than that an engineer would take more than a year. Students that are looking to get employed in an aerospace company, or any other company for that matter, and had experience in this and were able to come in and say ‘I know how to help solve problems by engaging a crowd’, this is something to look into. It would be an attractive offer or skill that one could bring to a future employer.

Is crowdsourcing a sustainable way to keep innovating the industry?

I would say that crowdsourcing is going to be a tool within the innovation tool kit- it’s a way of potentially breaking through to fresh, radical ideas, the one example that I like to give is mapping dark matter. We ran a challenge on an incentive platform that primarily scientists and engineers use. The challenge was to map dark matter, and the winner turned out to be glaciologist. He used his knowledge on detecting changes at the edge of glaciers, and it turned out that that

Catalina Sky Survey 60-inch telescope is dedicated to discovery of near earth asteroids problems, they’re working on them, and the best of that are going to be known through the competition. For companies, it can be a way of finding their future talent so hackathons are an example of hiring people.

den, and there was a guy that spent 6 weeks at the Space Centre, and he’s got a business that he’s built with a water cleaning idea from his time there. So there are ways.

Is it also accessible for Europeans to participate in these projects?

The difficulty for NASA is that we’re funded by the US taxpayers, so for them, they’re not interested in their money going to fund a graduate student from the Netherlands that potentially could have been taken by an American one! However, there are exchange programs that make it possible for students to spend a short fellowship or some time working in a NASA Centre. I was in Swe-

[1] What is the Asteroid Grand Challenge? https://www.nasa.gov/feature/what-is-theasteroid-grand-challenge [2] Border Sessions, The Hague , http://www. bordersessions.org/about-border-sessions/ [3] Asteroid 2012 DA14 – Earth Flyby Reality Check, http://www.nasa.gov/topics/solarsystem/features/asteroidflyby.html [4] Ultrascope – OSA , http://www.openspaceagency.com/ultrascope/

References

ESA

Can we say that crowdsourcing is a way to get around funding barriers?

To some degree. We’re still funding through prize money associated with it. For innovation, I’d say it’s a way of going around constraints in thought. We are tapping into an incredible new resource of human caliber that particularly sees and thinks differently than we do, and so the ability for more glaciologist-types to see our problem and say ‘ Aha! I see another way’. So I see it less as a way around funding, I think funding is an aspect, but more as having platforms available for fresh breakthrough ideas to be sourced. The other thing that we found in crowdsourcing and citizen science activities is it’s a great talent search. You may be familiar with ‘fold it’- it’s a 3D-drug design competition and the winner turned out to be a schoolgirl from the UK. Her mind was able to see in three dimensions where the proteins folded in such a way that you could have application. When you run these kinds of challenges, it can be a way of finding talent. 7% of the participants are superstars, so it’s a way of sourcing new talent because you’re giving them real world

CATALINA SKY SURVEY

was the breakthrough needed with dark matter. So the astrophysicists had been at it for a while but weren’t getting anywhere, yet when many different scientists came in the breakthrough came from a completely different field. Is that always how we want to innovate? No, but in order to see a problem differently, it’s a different history, it’s a different experience, its a different background that enables me to see the Rubik’s cube differently than you do. And if all those ingredients are right you can get a breakthrough. However I wouldn’t say it’s the only future, it’s a future.

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G.B. SPIRLET

FPP

CAMBER AND TWIST MORPHING CONTROL SURFACES Designing a morphing wing for an unmanned demonstrator G.B. Spirlet, MSc. Graduate Aerospace Engineering Morphing structures are as old as aviation itself. Yet despite continuous research on the topic over the past century they have never been widely used on production aircraft. Morphing has long been expected to bring better fuel economy by improving aircraft performance over a wider band of flight conditions, and the search for a practical form of this elusive technology continues to this day.

therefore rarely used to tweak performance during flight. Some fighter aircraft and sailplanes form an exception to this mindset, as these use leading and trailing edge flaps to continually optimize the aircraft angle of attack during manoeuvres.

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G.B. SPIRLET

WHAT IS MORPHING Wings of aircraft are typically designed for a narrow band of cruise conditions where optimum performance is achieved. Even if all design decisions take into account the penalties inflicted on other flight conditions, these penalties are weighted according to the aircraft’s expected flight profiles during service. This results in specialized aircraft which do not perform optimally when used in off design flight conditions. A common example of compromise in conflicting requirements is the wing planform area: a larger wing improves short field performance, and a small wing improves cruise performance.

Conventional high lift devices can be used to satisfy the field performance requirements at the expense of increased weight at little added drag in the cruise design condition.

The operational use of these discrete aerodynamic surfaces is further discretized by regarding their deployment as a departure from the ‘clean configuration’, and these are

Figure 1 - The wing configuration showing the areas dedicated to span morphing (orange) and twist/camber morphing (blue). The rigid wingbox is shown in red.

Trivial components such as landing gear satisfy only two of the three properties. If the designer deems the added complexity and weight of retractable landing gear to outweigh the drag penalty of a fixed undercarriage then the former will be fitted. Operating procedures during takeoff and landing ensures that the gear is not deployed when it is not needed, e.g. it is retracted as soon as a certain climb rate is reached. However, typically the landing gear only has two positions, up and down, and partially deploying landing gear to improve flight characteristics is only incidentally applied in emergencies (in 1964 a B-52 bomber lost most of its tail surface due to an extreme gust load, the pilots lowered the rear landing gear in flight so that the added drag behind the center of gravity would help stabilize the aircraft).

Figure 2 - Twist and camber morphing deformations of the leading edge skin. A combination of inputs will result in a combination of camber and twist deformation. design is found in the Grumman F14, where the optimum wing sweep angle is automatically adjusted for the Mach number and pressure altitude for optimum manoeuvre performance whilst limiting the root bending moment.

A concept as drastic as a variable sweep wing is the result of almost diametrically opposed design requirements involving a capability in both high supersonic speeds and extended subsonic range. Commercial aviation tends to have more subtle variations in flight conditions, thus more subtle geometry changes are sufficient to optimize for these.

A study by Embraer indicates that a morphing system may result in L/D improvements of 10% to 25% throughout a typical transport aircraft cruise mission [Catalano, 2002]. The morphing concept evaluated in the study consists of a rigid central wingbox section with articulated leading and trailing edges.

The AFTI mission adaptive wing flying testbed has shown L/D improvements up to 15% in the transonic range by using adaptive flexible leading and trailing edge flaps.

Improvements up to 100% have been measured in low speed flight [Boeing, 1988]. The same testbed in an active gust alleviation configuration has shown 20% reductions in

root bending moment [Thornton, 1993].

Though a large volume of research can be found on the topic of morphing the technique is rarely applied to production aircraft.

Some notable examples are the Grob elastic flap system used on the G104, and the variable camber Krueger flaps on the Boeing 747. Except for some recent commercial projects by the Flexsys company the interest in this field seems to have peaked in the 1980's, but the recent rise of unmanned aviation has provided a low cost platform on which to test morphing technologies and many universities have since conducted small scale adaptive wing research.

THE CHANGE PROJECT This history of enthusiastic research continues to inspire today’s academics to come up with a morphing related projects of their own, unfazed by the lack of applications for all previous inventions made in the field. Thus the European Commission funded CHANGE project [change.tekever.com] was set up to study and develop a novel morphing system which integrates different morphing mechanisms into in a single wing. The resulting design will be flight tested on an unmanned aircraft which integrates three dif G.B. SPIRLET

A common example of a rigid actuated structure which can be considered as a morphing system is the variable sweep wing. This technology was developed in the 1960's to meet the requirement of aircraft which could combine long range high altitude cruise and low level supersonic flight. An example of the morphing approach used on a swing-wing

G.B. SPIRLET

Morphing can be described as a set of technologies that increase a vehicle's performance by manipulating certain characteristics to better match the vehicle state to the environment and the task at hand [Barbarino, 2011]. Conventional slats, flaps and even ailerons could therefore be considered as morphing systems by this definition. A common, though false [Bowman, 2007], sentimental connotation of morphing is that the geometry of the wing is changed seamlessly with no gaps or discontinuities, though this would imply that true morphing falls under the category of science fiction fantasies which cannot be achieved using currently available technology. A definition may be found in that morphing aircraft are designed specifically to incorporate adaptive geometry features which can continually be modified to achieve optimal performance in flight, and that systems are installed to monitor flight conditions and make adjustments accordingly. This defines morphing not as a group of technologies or mechanisms, but rather as how these technologies are used both during the design stage and in flight.

Figure 3 - The full range of deformations which can be achieved by the system. The mechanism and actuators are contained inside the airfoil shape.

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The work for the thesis involved coming up with concepts for the twist and camber morphing systems and developing these into a workshop ready design. This followed a fairly standard iterative design approach where the most promising concept is selected for further development. This process started out with coming up with very basic concepts, even the idea of using inflatable structures was considered at this stage.

The most promising concept however was that of a rigid glass fibre skin constrained in such a way that both twist and camber can be achieved using just two mechanical actuators per surface. This is achieved by clamping the top of the skin along the entire span of the system, and allowing translation and rotation in the plane tangent to the skin surface on the bottom skin. With these constraints the deformation mechanism is such that an asymmetric input at the lower corners causes an asymmetric twist deformation, while a symmetric input causes a symmetric camber deformation. This principle is shown in figure 2 (concept.png).

The input force and displacement required to meet the target wing deformations were calculated with an ABAQUS simulation.

Aerodynamic loads were obtained from a CFD simulation of the wing in several target configurations, this analysis was performed by one of the project partners. The resulting aerodynamic and elastic loads were used to select the actuators and to size the mechanism which constrains the skin and transfers the loads to the wingbox. The skin is supported at the interface with the wingbox by aluminium ribs. The top edge of the skin is clamped by fastening it to the ribs with countersunk fasteners. The bottom skin of the leading edge is held in place by ball linkages which constrain the movement to a constant distance from the top skin, thus allowing only in-plane motion. At the trailing edge this is achieved with two guide plates at either side of the lower skin. This allows it to slide forwards and aft as well as sideways.

The actuation is done using commercial electric servos which actuate the edges of the lower surface via control rods. The in70

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VOLARAVELA

ferent morphing techniques: span extension, camber morphing and twist morphing. This is expected to result in an aircraft which can optimize its wing performance over a wide range of angles of attack and airspeeds, allowing efficient cruise as well as loitering capabilities within one aircraft type. A total of nine partners are involved in this consortium, which includes both universities and industry. As one of the project partners, TU Delft is to provide a design proposal for the camber and twist morphing system. The layout of the wing as determined during the course of the design is shown in figure 1 (wing.png). The light blue areas were reserved for the camber/twist morphing system. Another university (UBI) has been tasked with developing a span extension mechanism.

A Grob G104 with its unique elastic flaperon sytem. put system uses over center mechanisms to reduce the loads on the actuators at the extreme positions. The total deformation envelope of the final design is shown in figure 3 (deform.png).

Building mockups has greatly helped in understanding how structures deform, and were instrumental in determining the method to be used for actuation. They make for great mental aides when figuring out what boundary conditions to place on FEM models. As a hobby side project, an RC model aircraft using this principle for all the wing control surfaces was built, which somehow flies quite nicely (search youtube for ‘BWESA’ for a video). In the spirit of modern system engineering practices the invention has to be given a fancy acronym, in this case this led to the coining of the terms Bend Warp Edge Servo Actuated (BWESA) flap and BWESA slat for the trailing and leading edge surfaces respectively.

The limitations of the concept as applied in this particular application are that some sections of the wing are not equipped with adaptive surfaces, and therefore remain at a constant camber and twist angle. A wing with full span leading and trailing edge surfaces can be made using this modular design, though it cannot be combined with a full chord span extension system. Suggestions for future research on the topic would include a more in depth optimization of the skin thickness to reduce weight and elastic actuation loads. This can be combined with an aerodynamic study to improve the aerodynamic properties of the deformed shape via a topological optimization. The current limitation to only linear twist distributions can

be partly mitigated by placing many short modules along the span, which would enable the wing to assume a wider variety of lift distributions.

This technology may also find future applications in wind turbine rotor design. Current variable pitch rotors have a fixed twist distribution and rotate the entire blade to optimize for varying wind speeds. This technology has the potential to achieve an optimal angle of attack over the entire blade span while also offering a better actuation response for active gust alleviation.

References [1] Silvestro Barbarino, Onur Bilgen, Rafic M. Ajaj, Michael I. Friswell, and Daniel J. Inman.

“A review of morphing aircraft. Journal of Intelligent Material Systems and Structures”, 22(9):823–877, 2011.

[2] Jason Bowman, Brian Sanders, Bryan Cannon, Jayanth Kudva, Shiv Joshi, and Terrence Weisshaar. “Development of Next Generation Morphing Aircraft Structures”.

In 48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2007.

[3] F.M. Catalano, P.C. Greco Jr, and A.L. Martins. “Viscous and Wave Drag Optimization for a Transport Aircraft Mission Adaptive Wing”. In Proceedings of the ICAS 2002 congress, 2002.

[4] Boeing Advanced Systems Co. “AFTI/F1ll Mission Adaptive Wing Briefing to Industry”. Technical report, Boeing, 1988.

[5] Stephen V. Thornton. “Reduction of Structural Loads Using Maneuver Load Control on the Advanced Fighter Technology Integration AFTI/F-111 Mission Adaptive Wing”.

Technical report, NASA, 1993.

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VAN BEURDEN

ASM

CONTINUOUS ULTRASONIC WELDING Upscaling a promising bonding technique to demonstrator size Martijn van Beurden, MSc Graduate, ASM, Faculty of Aerospace Engineering, TU Delft

M

echanical fastenings, mostly rivets, have been omnipresent in joints of aircraft since the dawn of aircraft engineering. This is for good reasons: they are easy to inspect and replace, can be disassembled, show well-defined behaviour and are therefore easy to design with. However, there are a few drawbacks, such as introducing stress concentrations. This is not as much a problem in metal structures, as they show plasticity to alleviate stress concentrations, but this is not possible in composite structures, more specifically the fiber reinforced plastics that currently see increasing usage in primary aircraft structures.

For fiber reinforced plastic composites that are based on a thermoset matrix material, adhesive bonding is the only alternative currently in use. Nevertheless, it has seen limited applications as adhesive bonds cause difficulties in certifying an airplane or part.

However, when the composite uses a ther72

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moplastic matrix material, which is also more and more commonplace, welding is a viable possibility. There are various kinds of welding processes for thermoplastic composites, most very different from the well-known metal welding processes. In the research discussed here, the welding process used is VAN BEURDEN

Recently the drive for weight reduction has lead to the incorporation of composite materials in load bearing aircraft parts. However, joining is still mostly done with mechanical fasteners, which is not the best solution. For thermoplastic composite materials, another way of joining is available, namely welding. The master thesis research discussed here was on continuous ultrasonic welding of thermoplastic composites.

Figure 1 - A photograph of a welded lap shear specimen. The two carbon-fiber reinforced PPS parts are joined by the yellow PPS energy director that has partly flown out of the joint area.

In ultrasonic welding, two thermoplastic composite parts with a so-called energy director in between them are pressed together, ultrasonic vibration is applied, the energy director and the matrix surfaces of the composite melt, interdiffuse and form a bond. An example of a resulting specimen can be seen in Figure 1. The energy director is usually the same material as the composite matrix. This ultrasonic vibration is produced by first generating high frequency electric power and applying that to a piezoelectric device called a generator. The amplitude of this vibration is increased by the use of a booster and a sonotrode. Frequencies between 20kHz and 70kHz can be used for the vibration, but 20kHz is preferred, as a lower frequency means the machine can supply more power, due to the fact that no high-power, high frequency units are available.

CONTINUOUS ULTRASONIC WELDING As said before, ultrasonic welding is one of several welding processes available. The main advantages over other welding processes is its processing speed (which is of the order of one second) and not needing any special material to form a bond (the bondline is usually the same plastic as the composite matrix). However, the maximum size of the welded area is limited to about 8cm by 30cm. This restriction can be increased by using specific tool configuration for the application (Herrmann, 2003), but this is an expensive option. To find a more general solution, the research discussed here has developed the tools necessary for further research in making the ultrasonic welding process a continuous one.

This master thesis consisted roughly of two parts: designing, building and validating a machine capable of continuous ultrasonic welding and developing a procedure to make continuous welds with it.

MACHINE DESIGN Designing the machine started with making a set of design goals. The machine has to be able to weld a fairly large demonstrator panel, so it should have two degrees of freedom (one horizontal and one vertical) with a stroke of about 50cm horizontally and 10cm vertically. The speed of that movement should be able to keep up with the welding process, which means its horizontal speed should be about 12cm/s. Furthermore, it should be stiff enough to make an even weld (i.e. keeping the welding head level) and the welding power, welding force and head position should be measured often enough to be able to discern small details in the welding process, which gives a sampling frequency of 1000Hz. Finally, the machine should be easy and safe to work with.

This resulted in the (mechanical) design

VAN BEURDEN

the ultrasonic welding.

Figure 2 - The design of the mechanical part of the machine. A press unit holding the ultrasonic device is mounted on two rails and driven by a stepper motor. shown in Figure 2. A press unit from the company that already supplied the ultrasonic converter takes care of the vertical degree of freedom, while a custom-made frame supplies the horizontal one. Other components include an ultrasonic power supply, a motor controller, a PLC (Arduino Mega) and a PC. The user of the machine to input welding parameters and read out feedback data uses the PC. The PLC controls the welding process and makes sure that the process stops if a set welding time, energy or travel is reached. The motor controller and ultrasonic power supply take care of supplying power to the motor and the generator respectively.

MACHINE VALIDATION After the construction of the machine was completed, it had to be tested. To do this, a set of lap shear samples was welded on the machine and on a reference ultrasonic welding machine. These validation samples were for plain, non-continuous samples, as there is no reference for continuous welding yet.

As the stiffness of the machine, which needed to produce good welds. was one of the unanswered questions during the design phase, different frame configurations of increasing stiffness were compared as well.

It turned out that by following the original design, the machine was not able to produce consistent welds. However, with a few elements added to the frame to stiffen it up, the machine produced samples that were consistent, of reasonable strength and with fracture surfaces that looked similar to the reference. Therefore, it can be concluded that the machine is functioning correctly, but the frame has to be stiffened up a bit.

MULTIPLE PASS WELDING One of the major problems that surfaced during previous research on the topic of continuous ultrasonic welding is the limited weld compaction (Agricola, 2014). During welding, the energy director is melted, and pressed 'outward' to force it to flow. This flow induces wetting, which is crucial for creating

a good bond. However, in continuous welding, not all the energy director material melts at once. The un-molten material cannot be compressed, so the molten material can only be pushed out slightly, which results in too little flow to make a good bond possible.

In order to solve this problem, the idea of welding in multiple passes came about: welding one continuous seam with as much flow of the energy director as possible, and weld the same seam again until the desired flow is achieved. However, as welding a spot that has already been welded (partly) has not been mentioned in literature yet, this research started by proving that it is possible to weld spots in multiple 'steps'.

It turns out that a lap shear samples, of which the weld was made in two steps of equal weld compaction (twice 0.09mm), are comparable to those with one weld of the full weld compaction (0.17mm) in fracture strength, fracture surface and cross-section.

Therefore, it can be concluded that multiple pass welding is probably a good strategy for continuous ultrasonic welding.

CONCLUSIONS While this research only paves the way for research into continuous ultrasonic welding, the prospects are promising. Combining this technology with thermoset-thermoplastic (hybrid) welding that is currently being developed at the TU Delft as well, could result in weight and cost savings in aircraft construction by eliminating the need for mechanical fastening.

References [1] T. Herrmann, Ultrasonic twin converter technology for welding large plastic parts or packages, in ANTEC 2003 Conference Proceedings (2003).

[2] F. Agricola, Up-scaling of the Ultrasonic Welding Process for Joining Carbon Fibre PEEK Composites - A Clean Sky Eco-Design Specific Case, Master’s thesis, TU Delft (2014).

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ASM

DAMAGE TOLERANCE OF STIFFENED STRUCTURES A simplified residual strength prediction method Emiel van Hummel, MSc. Graduate Aerospace Engineering

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he desire to reduce the structural weight and increase the crack resistance of aircraft structures has resulted in the development of Fiber Metal Laminates (FMLs) at the Delft University of Technology. The introduction of this stacked layer material consisting of both fiber reinforced composites and metals has resulted in an increase in structural performance compared to that of their metal constituent. Initially, aramid and aluminum were combined (ARALL), followed by the development of GLARE. This material is characterized by stacking several thin aluminum sheets (0.2-0.5mm) with glass fiber reinforced composites oriented at different angles and has superior production capabilities to that of aramid fibers.

One of the benefits of fiber metal laminates is that they can be assessed using existing knowledge developed for metal structures. For example, the residual strength of flat plates can analytically be determined modifying the material resistance found for aluminum alloys (De Vries, 2001) or determining the critical crack tip opening (Rodi, 2012). Therefore, the increased complex74

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ity compared to that of a monolithic metal structure should be accounted for, meaning the incorporation of the fiber contribution on the crack growth behavior. Investigation revealed that both the amount of fibers in loading direction and fiber material properties have an additional influence on the material resistance to cracking compared to their metal constituent.

However, in practice fuselage structures consist of a skin, stringers and frames. Therefore, in this thesis the residual strength of structures consisting of both skin and stiffeners are analyzed, as it is expected that the stiffener presence will affect the crack growth characteristics. Currently no reliable prediction method is available to determine the residual strength of bonded stiffened structures. The analysis of these local reinforcements are currently performed using Finite Element Method (FEM) models and large panel tests, which are both undesired due to their high cost and time consumption; instead a more simple and versatile method is desired with the ability to describe the crack growth characteristics of stiffened structures. Therefore, the objective of this stiffener

VAN HUMMEL

The recent application of Glass Laminate Aluminium Reinforced Epoxy (GLARE) in the Airbus A380 has proven to be a suitable candidate to replace metal structures. The reduction in weight and increased performance results in a reduction in both costs and emissions. Current analytical analyses performed at the Delft University of Technology have been focused on flat panels.

In this thesis, the transition has been made from these panels towards stiffened structures.

stiffener

Figure 1 - Schematic illustration of the load transfer from the skin to the stiffener in front of the crack.

VAN HUMMEL

thesis was to develop an analytical method able to determine the residual strength of stiffened structures. Put simply, this would enable the user to make crack growth predictions, which are especially advantageous in early design phases.

STIFFENER INFLUENCE The addition of local reinforcement features, like stringers and frames, has revealed interesting residual strength characteristics.

During large residual strength tests it was observed that these structures may possess the ability to arrest unstable crack growth when damaged, which is of great interest for the analysis of damage tolerance aircraft structures. As a result, it is expected that the local presence of the stiffener will influence the load distribution. Locally when the cracktip reaches the stiffener, load will be transferred from the skin to the stiffener reducing the local stress severity in front of the cracktip (Figure 1). Ultimately it may be possible to tailor the local reinforcements, enabling an increase in residual strength and/or arrest unstable crack growth, resulting in a possible reduction of structural weight.

Figure 2 - Residual strength experiment in process with crack reaching the stiffener. fortunately, no damage arrest and accurate data for stiffened structures was available supporting the primary goal of this project.

Therefore, additional test samples were developed and tested enabling the identification of the damage arrest features of stiffened structures.

PREDICTION METHOD To be able to develop a method predicting the residual strength of stiffened structures in a simplified manner, the Linear Elastic Fracture Mechanics developed for metal structures have been modified. Both the stiffener influence and the introduction of FMLs have been incorporated by modifying existing parameters. First, the stiffener influence has been accounted for in the description of the stress intensity factor (Rans et al., 2013), followed by the influence of the FML in the material resistance (de Vries, 2001). These are then combined to be able to determine the crack growth characteristics of the stiffened structures, subsequently resulting in the residual strength (failure) prediction of stiffened structures.

LARGE PANEL TESTS

FUTURE PROSPECTS

In pursuit of the identification of the crack arrest capabilities of stiffened structures additional test samples have been developed and tested. Therefore, four test samples are analyzed, consisting of a skin with an initial crack length and two stiffeners in front of the crack-tip, on both sides (Figure 2.) and stiffener side. Using the 1000kN MTS test bench the residual strength tests were performed, and the crack length was measured during every load increase.

The possibility of tailoring local reinforcements may increase the residual strength and/or crack arrest capabilities as well as the allowable fatigue stress levels in fuselage structures. Therefore, the processes accompanied with this phenomenon are being attempted to be captured in one simple prediction method. Although the developed method is able to predict reasonably accurate results for the stiffened panels tested, additional modification to the method are required to enhance the predictions. In the process of developing a simplified method, some of the effects intentionally neglected induce a larger influence on the residual strength prediction as initially expected.

Therefore, some modifications to the method are proposed, including a correction for the elastic-plastic behavior of the stiffener.

Nevertheless, residual strength predictions are made within 7.5% of the actual test results, capturing the process quite accurately in a generally undiscovered field of research.

As a result, the different stages of the crack growth process were captured. Comparing the experimental results with the model predictions, a comparable residual strength could be predicted. However some mismatches were observed, which can be appointed to the stiffener influence. Currently a linear elastic stiffener is assumed until failure, while in practice the stiffener will act VAN HUMMEL

This prediction method is then implemented in a Matlab code and verified using data available for both metal and FML skin and stiffeners, at the Delft University of Technology. Based on the data, a good correlation was obtained, for both flat and stiffened panels made of either aluminum or GLARE. Un-

in an elastic-plastic manner resulting in a mismatch between the model prediction and experimental results. The added deformation constraint set by the stiffener is also not adequately assessed, inducing differences in the predicted crack length, when the crack reaches the stiffener.

2a

References [1] T.J. De Vries. Blunt and sharp notch behaviour of Glare laminates. PhD thesis, TU Delft, April 2001.

[2] C. Rans, R. Rodi, and R. C. Alderliesten.

Analytical prediction of Mode I stress intensity factors for cracked panels containing bonded stiffeners. Engineering Fracture Mechanics, 97(0):12–29, 2013.

[3] R. Rodi. The Residual Strength Failure Sequence in Fibre Metal Laminates. PhD thesis, TU Delft, March 2012.

Schematic illustration of the panel design used during the experimental tests.

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PROPELLER WITH BOUNDARY LAYER INFLOW A Design and Analysis Study of an Installed Pusher Propeller Nando van Arnhem, MSc Graduate, Flight Performance and Propulsion Integrated propulsion systems with the goal of reducing the fuel consumption of aircraft have gained increased attention. One of these propulsion concepts is to position a propeller inside the boundary layer of the aircraft's fuselage rather than in the free stream flow, which results in 'Boundary Layer Ingestion' (BLI).

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everal aircraft propeller configurations exist, such as pusher and tractor configurations in which the propellers are either wing or fuselage mounted. A number of studies from as early as the 1920s (Fage and Collins, 1920), indicate a benefit of positioning a propeller in the boundary layer or wake of the aircraft. These studies include analytical, numerical and experimental analysis on this concept. Most of the analyses were performed with idealized propellers or propellers designed for uniform inflow.

Very limited attention was paid to the consequence of non-uniform flow in the propeller design. As the fuselage boundary layer is highly non-uniform in the radial direction, a pusher propeller operating at the aft of the fuselage as depicted in Figure 1 requires a dedicated design.

The objective of this MSc thesis done in the Flight Performance and Propulsion group is to obtain a better understanding of the power benefit of a fuselage mounted pusher propeller by developing a numerical method to design the aerodynamic shape of the propeller and validate the results.

SIMPLIFIED ANALYSIS OF UNI76

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FORM INFLOW When transverse kinetic energy losses (or

uniform inflow

V∞

non-uniform inflow

the swirling motion) and profile drag losses are neglected, it can be easily shown with simple momentum theory that for a constant thrust, the required power reduces with a reduction in the axial velocity encountered by the propeller disk. However, the propulsive efficiency (the ratio of the power produced to power required) also reduces due to the

Tshaft Disolated

V∞ Disolated ∆Dskin + ∆Dpressure Tshaft

Figure 1 - Definition of the uniform inflow configuration (top) and the installed non-uniform inflow configuration (bottom). The indicated forces are for the equilibrium condition of fuselage-propeller combination.

relatively high induced axial velocities at low airspeeds. Therefore, for a constant thrust, the power versus velocity and efficiency versus velocity curves seem to be contradicting. This simplified analysis indicates that it may be favorable to position a propeller in a locally reduced velocity field, such as the boundary layer of the fuselage, while the fuselage maintains a given flight speed. However, the complexity of the problem requires that a three-dimensional propeller should be considered instead of simplified momentum theory to quantify the power benefit.

parison purposes a Uniform Inflow (UI) and a Non-Uniform Inflow (NUI) propeller are designed for the equilibrium condition. To estimate the interference drag, a non-uniform Actuator Disk (AD) model is used at the predefined location of the propeller. It is configured with a pressure jump equal to the defect in total pressure upstream of the AD, based on findings from a previous research (Lv, 2014). An 11% increase of drag is found which is primarily due to the increased pressure drag.

A design procedure is developed, in which the propeller shape is optimized using shape functions to describe a smooth pitch and chord distribution. A NACA four series airfoil is used to limit the number of design variables for a gradient based optimization algorithm. Input quantities for the design routine include an inflow field from the CFD analysis of the isolated fuselage, the design advance ratio V/nD, and a thrust requirement. The radius is set to 99% of the total gage pressure of the undisturbed air. The design objective of all optimizations is minimum power.

The optimization results show that the NUI propeller requires a significant 6.93% less power compared to the UI propeller even though the thrust is 11% higher. In the low axial velocity region towards the root, the NUI propeller shows a significant increase in thrust and a moderate increase in torque.

This is also the case for the bound circulation distribution, which shows that the root sections benefit from the favorable low axial velocity in the inner radii, shown in Figure 2.

To achieve moderate angles of attack, the blade pitch distribution is relatively constant for the NUI propeller. Additionally, a wide chord in the root is observed to obtain the high circulation. The low axial velocity results in relatively low Mach numbers in the root sections. This leads to lower compressibility effects and a lower thrust coefficient versus advance ratio curve. The outflow angles of the NUI design, which dictate the direction of trailing vortices, show a relatively larger contribution of vorticity in the plane of rotation (which induces axial velocity) when compared with the vorticity in axial direction (which induces a swirl velocity).

Upstream of the propeller, the reduced pressure acts on the fuselage surface as pressure drag, and the increased velocity results in higher skin friction, as shown in Figure 1.

These interaction effects are assumed to be determined a-priori from the CFD simulations. The tapered fuselage induces a radial flow and pressure field, which are both neglected. For the reference design case, an axisymmetric body from ESDU is subject to steady RANS CFD simulations. For com-

Optimal UI propellers have a constant efficiency distribution (Durand, 1935). The optimized propeller shows that the distribution of local efficiency over the blade is no longer constant when the axial velocity is changing along the radius. This may also be found analytically and is analogous to the momentum analysis for a uniform inflow, which shows a reduced efficiency at lower axial velocities.

Several authors have found a similar trend (van Manen, 1951). A useful quantity to

OPTIMIZED DESIGN FOR NONUNIFORM INFLOW A propeller analysis tool for both uniform and radially non-uniform inflow, named N-XROTOR, is developed. It uses the lifting line code XROTOR (Drela, 2014) for the propeller performance quantities and XFOIL (Drela, 1989) for the airfoil properties. The propeller analysis code shows good agreement with the experimental results of two reference uniform inflow propellers.

tip

compare the UI and NUI propeller is the ratio between thrust and power, which can also be plotted along the blade. This quantity may be considered as the effectiveness with which a particular propeller or propeller section can produce a certain thrust. For a UI propeller, this constant value along the blade increases with a reduction in flight speed. The NUI propeller shows a significantly increased dT/dP value towards the root, as shown in Figure 2, and directly shows the benefit of such configuration. Although it seems that this ratio may be useful in propeller design and the comparison of configurations, it has not been used in other propeller research in the knowledge of this author.

CFD ANALYSIS Both steady and unsteady RANS CFD simulations were performed on the reference N250 propeller. The transient simulation represents the vorticity distribution in the propeller slipstream better than the steady method.

This results in deviations in thrust and power of about 1% between these methods. The steady method is chosen for the installed pusher propeller because of the computational benefits. The N-XROTOR shows that the values of the predicted N250 propeller’s thrust and power are higher than the actual ones by 5.25% and 3.67% respectively.

At the same time, the thrust and power of the installed pusher propeller are overestimated by N-XROTOR by 4.15% and 4.71% respectively. The lower thrust and torque distributions are expected to be the result of a decambering effect. A fully turbulent boundary layer was compared with a partially laminar boundary layer, which is present in the N-XROTOR simulation. Furthermore, the radial flows, which are expected to affect the boundary layer and to reduce chord wise flow, are not captured in N-XROTOR. This radial flow on the propeller blade is found to be quite significant and varies along the blade.

The distribution of bound circulation and the resulting trailing vorticity shows good agreement with the radial flow on the propeller blade, visualized using wall shear streamlines, shown in Figure 3. In addition,

NXROTOR NXROTOR (uniform inflow) CFD

1.5 0.025

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root non−uniform inflow design 0.0 uniform inflow design 0.2

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Figure 2 - Comparison of the optimised uniform and non-uniform inflow propellers: geometry (left), bound circulation (center) and thrust-to-power ratio (right) which includes CFD results for the installed non-uniform inflow propeller.

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Figure 3 - Effect of trailing vorticity (shown as isosurface of a transient simulation on the N250 propeller on the left with colors indicating axial vorticity) on the radial flow visualised by wall shear streamlines (center) and a schematic of bound circulation with trailing vorticity induced radial flow. the finite chord modeled as lifting line results direction at the plane of the propeller. This FUTURE WORK in a variation of circulation in the chord wise leads to an additional thrust and torque on For future research it is suggested that the direction, which implies a generally lower the propeller, which, however, are shown to interference effects are integrated in the effective angle of attack in the CFD simulabe negligible. design procedure of both the aft fuselage tion. However, the CFD simulations show a shape and the propeller. In addition, the efgenerally good agreement with N-XROTOR. The pressure distribution on the fuselage fects of circumferential variations of the flow Installation Effects There are mutual intershows that the AD approximates the uporiginating from a fuselage under an angle of ference effects between the propeller and stream effect fairly well. However, simulation attack should be well understood. The perthe fuselage. The CFD simulation shows a downstream of the full blade shows that the formed analysis and identified power benquite significant overestimation in the values pressure is rapidly decreased to a low finite efit are currently only for a propeller, which of the thrust in the root region. The propelvalue at the aft end of the spinner. It has been propels a fuselage in equilibrium condition.

However, the benefits of this configuration (only root vortex from Γhub visualised) vorticity behind spinner for a complete aircraft should be identified as well. For MSc research opportunities related to BLI, the reader is kindly requested to conmagnitude Γb tact Dr. A. Gangoli Rao. Prof. L.L.M. Veldhuis is the contact person for research on propellers and propeller integration.

For any questions regarding this article, please contact: nandovanarnhem@gmail.com References

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Figure 4 - Schematic of a trailing vortex resulting from finite bound circulation at the root and the corresponding 'vortex drag' (left). On the right the vorticity distribution at a plane behind the spinner in the CFD simulation. ler-spinner junction results in a high velocity and pressure gradient, and consequently in a separated flow, which reattaches downstream of the airfoil. In this region, a local low pressure is observed and thereby an additional thrust force. Also, the tapered spinner constrains the root region to induce an axial velocity, resulting in a higher angle of attack in the CFD simulation. The fuselage-induced stream wise pressure gradient varies in radial 78

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found that this is the result of a strong hub vortex originating from the finite circulation at the propeller hub, schematically shown in Figure 4. Each blade releases such vortex, which rolls up into strong vorticity in axial direction. This vortex results in a tangential velocity leading to a low pressure acting on the spinner as pressure drag. This increases the fuselage drag by almost 2%.

[1] A. Fage and H.E. Collins. An Investigation of the Mutual Interference of Airscrews and Bodies of the Pusher Type. Technical report, Advisory Committee for Aeronautics, 1920.

[2] XROTOR User Guide., August 2014.

[3] M. Drela. XFOIL: An Analysis and Design System for Low Reynolds Number Airfoils.

Conference on Low Reynolds Number Airfoil Aerodynamics, Jun. 1989.

[4] P. Lv. Research progress on Boundary Layer Ingestion. Presentation (unpublished), 2014.

[5] W.F. Durand. Aerodynamic Theory Vol. IV. Julius Springer, 1935.

[6] J.D. van Manen. Invloed van de ongelijkmatigheid van het snelheidsveld op het ontwerp van scheepsschroeven. Ph.D. Thesis, Delft University of Technology, The Netherlands, 1951.

Global environmental concerns call for future innovative products. Currently, the aircraft industry is seriously considering to install Contra-Rotating-Open-Rotors (CROR) on mid-range 150-200 seater aircraft by the year 2020. Today, NLR (National Aerospace Laboratory) specialists work in close coรถperation with aircraft & engine manufactures to investigate noise, vibration and safety aspects of these novel aircraft concepts.

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