Leonardo Times April 2016

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

1996

2016

JUICE

MISSION EUROPA

Scalar Drone A student-made drone Page 10 Year 20 | N°2 | April 2016

Ionic Propulsion Future of micro-propulsion Page 41

A320 NEO Aviation Department Page 44

KLM ROYAL DUTCH AIRLINES

Biofuel. You won’t notice the difference, but nature will KLM has proven that aviation can be more sustainable. As a pioneer we operated the world’s first commercial flight with biofuel. However, KLM will only use biofuels with no negative effects on food production and nature. Together with partners we stimulate the development of biofuel, only when used on a large scale biofuel will make the difference - klmtakescare.com

EDITORIAL

I have always felt that we, the people of science, struggle to communicate our fascination for engineering and technology to others. Even in technology, spirits drift apart about whose field is “the best”. Why do we love these boring numbers and formulae, why do we stare at diagrams for hours, why do we go through this ridiculously hard study?

Well, why do we?

Dear Reader, For you, this might be another edition of the Leonardo Times. For me, this is the first edition as the editor-in-chief. I will be building upon the work of Sushant Gupta, who, after three years of working on this magazine, has retired. Well, not exactly. I am happy to say that Sushant has not left us completely. He will be staying with us for a little while, as the final editor of the website (www.leonardotimes.com) and as an advisor. At this point I would like to express my sincerest appreciation for his work and vision which have brought this magazine further and have made it the paper which you now have in front of you.

I have spent quite some time thinking about how I should address you for the first time.

This might seem slightly ridiculous to you, and most of you will think: “Just say hello and let me read about some science.” But it’s not quite that easy. This spot, left for the editor-in-chief, gives me the opportunity to leave a message and some food for thought for when you go through the magazine.

There is no simple answer to this question, as most of you probably know. A simple answer like money, fame, fun or the greater good does not suffice. These might play a role, but I believe it’s something else, also seeing as neither of the aforementioned points are a given. For me personally, it is the inspiration that I get when I see what science and technology can do: when I see the images produced by the Hubble Space Telescope, when an aircraft manufacturer finds another way to save fuel or fly faster, or when a ground breaking invention reaches out to millions of people and makes their lives a little better.

And there we are. This is why I joined the Leonardo Times’ committee and why I am addressing you right now. I know a lot of people don’t even open the plastic in which this magazine is delivered, but if you happen to do it this time and find yourself reading these lines now, I hope you get inspired just like I did. This appeal goes out to everyone, whether you are an aerospace engineer or not- students, CEOs, alumni, parents, friends and everybody else.

This magazine has always inspired me and with Sushant’s position now in my hands, it is my time to inspire you.

I hope I will succeed.

In all honesty, I am in the dark regarding what I should say at this very moment, so I will just write about why I became a part of the Leonardo Times.

Victor Gutgesell

Letters from readers ...

LEONARDO TIMES

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

1996

Interview

Rick Tumlinson

2016

Stratos II+

One-fifth way to Space

Page 37

NASA’s

Asteroid Grand Challenge

Page 44

Page 64

Year 20 | N°1 | January 2016

Special Edition The Leonardo Times has always set a high standard for itself, but even compared to that, this recent Anniversary Edition is spectacularly good.

Wow, I was very impressed by the fascinating, well written articles in this modern format of the Leonardo Times.

Prof.dr.ir. Jacco Hoekstra

Over the past few years the Leonardo Times has achieved a giant improvement in the quality of their magazines.

Especially the overall layout of the magazine is better than ever before. With extensive usage of graphics the magazine has become very attractive to read. The Anniversary Edition really emphasised how professional the Leonardo Times actually is. I encourage you to maintain this standard and I look forward to reading upcoming publications. ir. Niels Singh

1957: Sputnik and the Space Race The article about the early space race was very fascinating. It filled up gaps in my knowledge about this early time of space engineering I had no idea existed. I appreciate the neutral tone about the different ideologies present during this time and that the main focus lies on the science and engineering. Looking forwards to read the rest of the series!

L.F.

If you have remarks or opinions on this issue, let us know by dropping an email at: LeoTimes-VSV@student.tudelft.nl

LEONARDO TIMES N°2 2016

03

FRONT FEATURES

14

PIAGGIO

CONTENTS

03 Editorial 07 Leonardo's Desk 08 In the News

RPAS In the recent years, RPAS (Remotely Piloted Aircraft Systems) have entered the aircraft market, being a new component of aviation systems based on cutting-edge development in aerospace technologies.

AERODYNAMICS 20 Development Cycle of Hand Launched UAVs 48 Fly Like an Insect

AVIATION DEPARTMENT 44 Certification of the Airbus A320 NEO

AEROSPACE STRUCTURES AND MATERIALS (ASM) 27 Airfoil Design for VAWTs 46 The Acoustics of Cracks

SPACE DEPARTMENT 17 10 Years of New Horizons

24 JUICE Mission The possibility of Europa sustaining life under its icy surface has long been speculated. Now, with the JUICE mission aiming to take in-situ samples of its vapor plumes, we are one step closer to the truth.

CONTROL & OPERATIONS (C&O) 14 Remotely Piloted Aircraft Systems

INTERNSHIP 34 One of a Kind

FLIGHT PERFORMANCE AND PROPULSION (FPP) 22 Modular Fuselage Design

TIME FLIES 38 Supersonic Commercial Travel

SPACE ENGINEERING 12 Docking with Large Space Debris 24 In-Situ Observations of Europa's Vapor Plumes 30 Gimbaling Onwards 32 Frozen debris about the Earth 36 Regenerative Cooling Using Methane 40 Ionic Liquid Ion Source Propulsion

STUDENT PROJECT 10 Scalar Drone VOLPATI

COLUMN 50 Engineering Peace

Supersonic Commercial Travel

ADVERTISMENTS 02 KLM

Supersonic commercial travel is a dream that once was. With the current additional research, it is a dream that could be once again.

06 ASML 31 Airbus Defence & Space 51 NLR 52 Fokker

38 04

N째2 2016 LEONARDO TIMES

Frozen Orbits

CNES

COLOPHON

32

A special type of orbit that is cleverly chosen such that the variation in the mean Kepler elements under the influence of Earth’s irregular gravity field is minimized.

Year 20, NUMBER 2, APRIL 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 four times a year with a circulation of around 5000 copies per issue.

EDITOR-IN-CHIEF: Victor Gutgesell FINAL EDITOR: Eleonoor van Beers EDITORIAL STAFF: 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.

FINAL WEB EDITOR: Sushant Gupta THE FOLLOWING PEOPLE CONTRIBUTED: Tom Schouten, Sushant Gupta, Sieglinde Goossenaerts, Raphael Klein, Jules Heldens, Bart Jacobson, Quentin van Keymeule, Daniel Hoppener, Jan Hoogland, Jannick Habets, Gerwin Lapoutre, Hans Huybrighs, Patrick Hanley, Sander van der Host, Diego Giuseppe, Thomas Mohren, Luka Denies.

DESIGN, LAYOUT: SmallDesign, Delft PRINT: Quantes Grafimedia, Rijswijk

Fly Like an Insect

KOHL

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

A robotic model of an insect wing gives insight into how embedded wing strain sensors can be used to detect inertial rotations.

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:

48

LeoTimes-VSV@student.tudelft.nl

LEONARDO TIMES N°2 2016

05

How do you make a lithography system that goes to the limit of what is physically possible?

At ASML we bring together the most creative minds in science and technology to develop lithography machines that are key to producing cheaper, faster, more energy-efficient microchips. Our machines need to image billions of structures in a few seconds with an accuracy of a few silicon atoms.

So if you’re a team player who enjoys the company of brilliant minds, who is passionate about solving complex technological problems, you’ll find working at ASML a highly rewarding experience. Per employee we’re one of Europe’s largest private investors in R&D, giving you the freedom to experiment and a culture that will let you get things done.

Join ASML’s expanding multidisciplinary teams and help us to continue pushing the boundaries of what’s possible.

www.asml.com/careers

/ASML

@ASMLcompany

LEONARDO'S DESK

GREAT ACHIEVEMENTS Dear reader,

eye for detail while creating this issue.

I would like to start this Leonardo Times’ preface with the momentous discovery of gravitational waves by the thousands of scientists of the LIGO project. For the first time ever, mankind was able to sense the motion of the universe in its most fundamental way. In the land of the blind, the one-eyed man is king and this brings us a step closer to answering the most essential questions as first postulated by the great Greek philosophers. The project is also a perfect illustration of how research and engineering can cooperate to achieve great milestones. The Laser Interferometer Gravitational-Wave Observatory is the most accurate instrument ever created by man and the extent of its precision is mind-blowing. These measurements are like assessing the water level rise due to a single drop of rain in the Ijsselmeer, or measuring the distance from the Earth to the Moon with the precision of a human hair, and thus powerful enough to measure the effect of a collision between two black holes over 1.3 billion light-years away with two four-kilometer long pipes.

The VSV ‘Leonardo da Vinci’ organizes a lot of activities throughout the year, however one of the largest managerial tasks lies in the organization of our annual Symposium.

Each year, we oscillate between an aviation and a space symposium, and for this year we have chosen the exciting topic of ‘New Space: Launching Entrepreneurship’. By the time that you read this preface, we can look back on keynotes from, amongst others, Harry van Hulten (test pilot for XCOR), Arnaud de Jong (CEO of Airbus DS The Netherlands) and Franco Ongaro (General Director of ESA ESTEC). I am convinced that we will look back upon a Symposium that was able to draw conclusions on the ways that the space industry is changing.

Johann-Diettrich Wörner (General Director of ESA) dubbed this movement Space 4.0 during his keynote at our faculty in January, and is a motion that has many components.

On one side, it is a farewell to the classic approach of thinking of concepts (composing music) and then creating products (playing the music). Status quo prefers what can be seen as a jazz ensemble: a continuous creative process of concept and production through dialogue. On the other hand, some elements of space have become more and more interesting to commercial parties. The results of, for example, Elon Musk’s SpaceX and Jeff Bezos’ Blue Origin, are followed with great interest. All these developments make

Back to reality. In your hands you hold the April edition of the Leonardo Times, and this edition is once again filled with the latest novelties in aviation and space, as well as the latest developments of our society. I would like to congratulate and thank the Leonardo Times editorial staff for their enthusiasm and

these exciting times to live in and, for our students, wonderful opportunities to start their careers.

Naturally, we also have a lot of students who will be starting their careers in aviation. For them, the VSV ‘Leonardo da Vinci’ organizes some great events too. On the 7th of January, all students had the opportunity to meet KLM CEO Pieter Elbers in a very relaxed and open atmosphere at our faculty, who answered questions on what it is like to run an airline.

Last thing that I would like to share with you is that we have organized a very special activity in May, one we were not able to have last year due to the hazardous weather conditions at Texel International Airport, which is the Flying Weekend. During this weekend, students can go back to the essence of aviation: flying. The ability for students to experience flight has always been a significant element of the faculty of Aerospace Engineering. This also endorses the principles of our namesake, who said: For once you have tasted flight, you will walk the Earth with your eyes turned skywards, for there you have been and there you will long to return.

With winged regards, Matys Voorn President of the 71st board of the VSV ‘Leonardo da Vinci’ LEONARDO TIMES N°2 2016

07

USAF

ALASKA AIRLINES

IN THE NEWS ...

New American bomber - the B-21

Alskan airline eclipse ORDNANCE SURVEY

Mapping Mars Discovery news

NASA

February 16, 2016, U.K. Great Britain’s national mapping agency, Ordnance Survey, recently mapped a portion of the surface of Mars using NASA’s open data. The map features some points of interest and, more importantly, a clear depiction and labelling of the main geographical features. It also contains detailed contouring of the landscape and critical information like terrain height. The scale of this map is said to be 1:4,000,000.

Unlike any other modern planetary maps, this map employs cartographic style to more effectively and plainly relay spatial information by combining technology, science & aesthetics. This involved using shades of colors to represent ground elevation or textures to show topographical features. One of the main aims behind creating this map was to assess its potential use when it comes to future Mars related missions. It’s probably best to ask Mark Watney about that. M.K.

The return of the X-planes NASA

February 18, 2016, NASA. The X-plane program is an ambitious undertaking by NASA to design, build and fly a variety of flight demonstration vehicles. It alludes to NASA’s century-old heritage in using experimental aircraft to test advanced technologies and revolutionary designs. The details of said plan are outlined in President Obama’s recently-released federal budget request for the fiscal year beginning in Oct. 2016.

Should it be approved, NASA Aeronautics will embark on a 10-year quest to drastically reduce fuel use, emissions, and noise by the way aircrafts are designed. Expected innovations include lightweight composite materials that are needed to create revolutionary aircraft structures, shape-changing wing flaps and even coatings to prevent bug residue build-up on wings. N.R. 08

N°2 2016 LEONARDO TIMES

Black holes in 5D? phys.org

Cosmic superlatives FIGUERAS

space.com

center of black holes, beyond the ‘event horizon’, where the gravitational “pull” becomes so strong that there is no escape. Hence, it cannot be observed from the outside. But a naked singularity would be visible from the outside and, theoretically, we would actually be able to witness the laws of physics break down. The ring-shaped black holes can only exist in a space with five or more dimensions.

Unfortunately, our current perception and understanding of the Universe limits our space-time within four familiar dimensions.

And general relativity lives to fight another day. M.K.

NASA

March 5, 2016, DJI, Manhattan, NewYork. DJI is a Chinese technology company who is globally known for their aerial imaging platforms and stabilizers. They allow for both armateurs and professionals to unleash their creativity and take cinematography to the skies. DJI’s newest release, the Phantom 4, takes matters to a new level through the implementation of cutting-edge software and sensors. The quad-copter is capable of actively following a subject, whilst avoiding any obstacles in its path. Dual compass modules and Inertial Measurement Units allow the Phantom 4 to constantly check the data it is receiving, ensuring the smoothest possible flight, regardless of the situation. This allows for anyone to produce breathtaking aerial

March 6, 2016 The 300-foot monstrosity was originally designed for the US Army’s Long Endurance Multi-intelligence Vehicle program. However due to budget cutbacks, the Army abandoned the project and the original designers at Hybrid Air Vehicles, bought it back for a fraction of the cost. The Airlander 10, having been altered for other purposes, is now only weeks from its maiden flight. N.R.

Magnificent cessation Space.com

ESA

DJI

The first glimpse of AI DJI

Airlander 10 The Verge

pictures and seamless video footage. With innovation taking out all the guesswork, perhaps artificial intelligence is just around the corner. N.R.

March 6, 2016 Symmetrical blue jets of gas ejected from the core of Hen 2-437, a bipolar nebula. The icy-blue lobes are formed due the material expelled by the dying star. M.K.

VSS Unity Virgin Galactic VIRGIN

February 18, 2016, University of Cambridge Researchers have successfully simulated the dynamics of ring-shaped black holes in a 5-D space, using supercomputers.

Black holes, already fascinating in 4-D space, could proceed to “break” the laws of physics (as we know them) in 5-D space. The simulation shows a ring-shaped black hole splitting into numerous small black holes, leading to a ‘naked singularity’ which would nullify general relativity.

A singularity is a point where gravity is so intense that space, time, and the laws of physics, break down. This point exists at the

March 3, 2016, Hubble Space Telescope The Hubble Space Telescope has once again astonished everyone with its capabilities. Recently so by measuring the distance to the most far-out galaxy ever recorded.

This galaxy, known as the GN-z11, is around 13.3 billion light-years away. This essentially means that we are looking at light coming from a galaxy that existed 400 million years after the Big-Bang, when the Universe was just about 3% of its current age. Not only is this a significant leap “back-in-time”, it is also a testament to the HST for exceeding its own expectations. M.K.

Go big AND go home!

Discovery News

March 2, 2016, Kazakhstan 11:27 PM EST (Kazakhstan time), the Soyuz TMA-18M spacecraft landed successfully back on Earth. Present on–board the spacecraft was NASA’s astronaut Scott Kelly along with Russian cosmonauts; Mikhail Kornienko & Sergey Volkov. Kelly, along with Kornienko, returned back to the Earth after nearly a year (340 days) in space. This, by far, was the longest stay in space by any astronaut and is seen as a vital opportunity to study the effects of prolonged spaceflight effects on humans… since we are aiming to head to Mars soon enough. M.K.

February 19, 2016, Mojave, CA Richard Branson recently unveiled his highly anticipated SpaceShipTwo at a ceremony in Mojave California. The new vehicle is the first vehicle to be manufactured by The Spaceship Company, Virgin Galactic’s wholly owned manufacturing arm, and is the second vehicle of its design ever constructed.

Stephan Hawking named the craft the “VSS Unity” in hope to bring people together in our conquest for space. N.R. LEONARDO TIMES N°2 2016

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STUDENT PROJECT

SCALAR Novel 3D printed Tri-Copter Concept Karel van Leeuwe and Daan Höppener, Master Students Mechanical Engineering and Aerospace Engineering, TU Delft Both fascinated by the emerging drone technologies, we started a project to develop a unique drone concept. We wanted to learn about the practical aspects of designing and producing an unmanned aerial system. Also, we took a look at what it would take to be a successful drone-related company. In this article we introduce our functional prototype and the steps we took to create it.

L

ast year we started a project in which we set out to build a unique tri-copter drone. We both had our reasons for this project.

Daniel had already planned on doing his MSc thesis at the faculty’s Micro Aerial Vehicle Laboratory (MAVLab), so he wanted to learn more about the hardware used in drones which lead to his decision to build one. Since product design is a hobby of his, the drone had to look esthetically pleasing.

today.

DESIGN PROCESS We went for a tri-copter configuration because it was more challenging and unique than designing a quad-copter. With a tri-copter, there are two clockwise, and one counter clockwise rotating propellers. This creates a

Karel was interested in how UAV systems are widely used in the USA for geomapping and crop surveillance. He wanted to know more about the technology of such systems, and a good way to do that was to start building a drone himself.

Together we set out to build a drone with a serious attitude in which the finished product would serve as a prototype for a drone-related business case. For us, the emphasis was on learning the practical aspects of designing and producing an unmanned aerial system including auto-pilot features and the ability to carry a GoPro camera. It needed to have comparable capabilities to that of a DJI Phantom III, the best selling consumer drone 10

N°2 2016 LEONARDO TIMES

Primary test flights.

moment imbalance due to propellor drag.

The solution is to enable thrust vectoring by tilting the aft propellor. To achieve this, a servo and a tilting mechanism are required.

With thrust vectoring, yaw control is more direct than compared to a quad-copter, as a quad-copter relies on differences in angular velocities of the clockwise and counter-clockwise propellors to generate a yawing moment.

To make the design as integrated as possible, we first selected the components which were required and built everything else aroud them.

THE DESIGN The tri-copter is built around the largest and heaviest component, the battery. A unibody structure forms the main part. The unibody is a hub of all of the electronics and components, and consists of an upper and lower part, which clamps three carbon-fiber tubes. Attached to these tubes are the motor mounts and the tilting mechanism. Inside the uni-body there are different levels. The bottom level houses all the “power electronics” such as the battery, power distribution and Electronic Speed Controllers (ESCs). All the “advanced electronics” are located on the top part of the uni-body structure. This includes the flight controller, GPS module, telemetry module and wireless video link. A white shell shields these electronics, and is removable from the unibody via a clicking mechanism. This enables easy and fast access to the advanced electronics. Another clicking mechanism was created on the bottom to remove the battery with ease.

A “payload bay” is present on the front of the tri-copter. It was designed to be able to hold a gimball with a GoPro camera attached. Other payloads can be attached as well. Hypothetically, it can also be used to hold a beer.

The most unique feature of the design is the tilting mechanism on the aft rotor, consisting of three parts. Two shells constrain the part where the brushless motor is attached to one degree of freedom. The shells also holds a servo which drives the tilting part.

As far as we know, this is the only tri-copter in the world which uses this mechanism, as conventional tilting mechanisms use a servo-rod mechanism, or their tilting rotation is not axial to the servo. Not only is our design very strong, it is also aesthetically pleasing, as it looks similar to the rigid motor-mounts.

Another unique feature is the automotive inspired head- and taillights. Other than orientation during flight, it serves little purpose besides aesthetics. It does, however, distin-

CAD render of the Tri-copter. guish our design from other tri-copter designs.

PRODUCTION AND TESTING Manufacturability was key to our design efforts, as we wanted to actually build the tri-copter. It was decided early on to use 3D printing as our main method of production.

Knowledge about this and other practical limitations such as tolerances and precision had to be carfully taken into account during our design process.

Our flight controller is based on the open source ArduCopter framework.

We were very methodical in conducting test flights to avoid accidents. The first test flights were very sucessfull. The tri-copter exhibited stable flying properties and was easy to control. Yaw performance proved to be exceptionally good.

THE FUTURE OF THE PROJECT/ REVIEW The drone itself was very well received amongst friends and internet fora. We were also following the drone market developments so we started thinking about ideas for launching our own drone-related startup company. For example, we saw huge poten-

tial in the development of UAV systems for crop surveillance in the European agricultural market. Both the technology and the market are already there; however, a big challenge is bringing the right actors together in order to set up a successful business. We have not pursued this idea yet, but we keep our eyes open for possible partnerships in the future.

We also learned that in the past year, many personal drones have been crowdfunded. Many of these projects exceeded their funding goal, and promise an array of very advanced features, such as flawless obstacle avoidance and follow-me flight modes.

Examples of such projects are the Lily, AirDog, Hexo+ and CyPhy drones. Although it is admirable that there are so many ambitious and devoted drone developers out there, we think that many of these projects over-estimate their own capabilities and the viability of their business cases. The consequence is that the products they deliver are likely to under-perform with respect to their advertised capabilities and create disappointed customers. Even worse, a heavy autonomous flying drone can impose serious safety risks, about which we feel too little attention is paid to.

CONCLUSION With this project we achieved our goal of designing and building a unique tri-copter.

The majority of this project’s time was devoted to integrating all the components into one coherent, sleek design. To us, it was an achievement that everything worked as we expected without major design iterations.

As a product of our efforts we want to make our design available for everyone, void of cost. Now we are working on an open source file-package. This includes CAD files of our drone, and recommendations for components to be used and an assembly manual. People all around the world can manufacture this design with a 3D printer, and use it for their own projects.

Interior view of the top part of the uni-body structure.

For more information, please contact: daanhoppener@gmail.com karelvanleeuwe@gmail.com LEONARDO TIMES N°2 2016

11

DELOO

SPACE ENGINEERING

DOCKING WITH LARGE SPACE DEBRIS Attitude Control Design Jannick Habets, MSc Aerospace Engineering, TU Delft

Space debris has become a major issue for the space industry over the last few years. The unexpected loss of contact with ENVISAT, the European Space Agency's (ESA) largest environmental spacecraft, increases the probability of future collisions. Therefore, ESA is investigating numerous removal options to retrieve this large piece of space debris.

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N째2 2016 LEONARDO TIMES

H

ow does one remove space debris?

Options range from solar sails to sling shots and from tentacles to tethers.

Some are more suited for small debris and some for large debris. One of the most prom-

ising techniques uses a chaser spacecraft that attaches itself to the debris by means of a robot arm. Subsequently, two sets of ‘tentacle’ arms will close around the target debris and four pushing rods will be deployed to keep the chaser firmly attached to the target. After de-tumbling the system and other in-orbit operations, a series of braking manoeuvres will take place to re-enter Earth’s atmosphere and eventually plunge into the South Pacific Ocean.

The proximity operations, or docking, require an accurate attitude control system and a detailed knowledge of the system. These operations have been divided into three phases: an unconnected phase in which the chaser spacecraft synchronises its motion with that of the (spinning) target debris, a semi-connected phase where the robot arm and tentacles form a flexible connection between the chaser and the target, and a connected phase where the chaser and the debris are assumed to be rigidly attached to each other (and form a stack). An important question is whether the system can remain stable and controllable in all of these three phases. This article focuses on how that is done.

EVOLVING SYSTEMS Because the system changes its configuration during its mission, it can be classified as an Evolving System; a system with (actively controlled) components that "mate" to form a single connected system [1]. In an Evolving System, the connection between the components becomes stronger during the evolution and can be represented by compliant forces and moments. Originally, Evolving Systems were envisioned to be applied to the assembly of large space structures, such as space stations or large aperture telescopes. Now, it can also be applied to the formation flying of satellites or autonomous rendezvous and docking. However, up till now, Evolving Systems have just been a theoretical framework; it has not yet been used in practice.

So let's try and apply Evolving Systems to the docking scenario. At first, the two satellites ENVISAT and the chaser - are unconnected, then as the robot arm attaches the tentacles close, and the pushing rods are deployed.

Therefore the system slowly becomes less and less flexible, and finally the system is assumed to be rigid. To simplify the complex behaviour of all these flexible parts, the connection between the chaser and ENVISAT can be modelled as a spring and a damper, which become more rigid as the system evolves.

Now, because attitude control is only concerned with rotational motion, the connection needs to be modelled as a three-dimensional torsional spring and damper. For the parameterisation of the spring, Euler's eigen axis was used as the instantaneous axis of rotation; a method that has not yet been found in literature.

With the system modelled, a simple linear

stability analysis can be performed to get an indication of the stability of the system.

Note that any nonlinear effects, such as gyroscopic coupling between the axes, disturbance torques, and nonlinear actuators, have not been taken into account. The analysis showed that the system remains stable during its evolution when the chaser is actively controlled. This is mostly because the motion of the chaser has little effect on the motion of ENVISAT due to the large size difference between the two spacecraft. ENVISAT has a mass of around 8,000kg, whereas the chaser weighs 1,500kg. But more importantly, the moments of inertia of ENVISAT are two orders of magnitude larger than those of the chaser. However, for a system with equally sized spacecraft, the linear stability analysis showed that instability could occur. Hence, future removal missions of smaller debris would require thorough stability analyses and even more advanced attitude control.

NONLINEAR ANALYSIS For a more accurate stability analysis, the nonlinear effects have to be considered as well. To this end, a representative simulator was built in MATLAB/Simulink. The simulator comprises two major parts; the attitude control algorithms and the control actuators. The latter consists of a Reaction Control System (RCS) and a control allocation algorithm. The attitude control algorithms that are investigated are a Linear Quadratic Regulator (LQR) and a Model Reference Adaptive Controller (MRAC).

The objective of the attitude control algorithm in phases 1 and 2 of the docking is to reduce the angular error between the chaser and the target debris to zero. In phase 3, the objective is to de-tumble the complete stack. The LQR is a very simple control method, which multiplies the state error between the chaser and the target by a pre-computed gain. This gain is derived based on the characteristics of the system and tries to minimise a certain objective function [2]. One can imagine that the gains for the unconnected system will be quite different from the connected system.

This means that the gains have to be scheduled between the various phases of the docking.

The Model Reference Adaptive Controller aims to minimise the difference between the output of the system (in our case the state error), and a reference model output [3]. The reference model can have any desired form, as long as it is within the limits of the actual system. It was decided to use the LQR in combination with a linear representation of the chaser model as the reference model, because it was already shown that the LQR can stabilise the system. However, once the two satellites are connected, the chaser reference model is not an accurate representation of the actual system; it is much heavier! So the adaptive controller will have trouble matching the outputs. Therefore, the connected (stack) model

was also used as a reference model. Now the system is disconnected, this is an overestimate of the actual model, and as a result the response of the system will be a lot slower.

The chaser is actuated by an RCS consisting of 24 thrusters placed in pods of three on the vertices of the chaser. After the control algorithm has computed a desired three-dimensional control moment, the thrusters have to try to deliver this moment. Therefore, the control moment has to be allocated to the correct thrusters. This problem can be translated into a Linear Programming optimisation problem, which can be solved with standard numerical tools. Furthermore, thrusters are discrete actuators and can only deliver full or zero thrust.

Thus, some type of modulation technique has to be implemented to translate the continuous desired thrust vector into a discrete thrust vector. A common technique is PulseWidth Pulse-Frequency (PWPF) modulation [4]. It is evident that with all these techniques, the actual delivered control moment will not be exactly the same as the desired control vector. But will this result in instability?

RESULTS Nonlinear simulations of the model revealed that using the chaser reference model will lead to instabilities. Therefore, only the stack reference model was used for further analyses. Furthermore, for the unconnected phase, both the LQR and adaptive controller are able to synchronise the motion of the chaser with ENVISAT. Second, the effect of the connection between ENVISAT and the chaser on the stability of the system is very small and both the controllers are able to control the system.

Third, the adaptive controller shows unacceptable performance during the control of the stack because of the large difference between the reference model for which the adaptive controller was tuned and the actual system. Using two different reference models for the unconnected and the connected phase could improve the performance of the adaptive controller.

Currently, further research is being performed to better investigate the use of a second reference model and to see what the effect of uncertainties in the model are on the stability of the controller.

References [1] Frost, S.A. and Balas, M., 2010, “Evolving Systems and Adaptive Key Component Control”. In: Aerospace Technologies Advancements. Ed. by T.T. Arif. Rijeka: InTech.

[2] Anderson, B.D.O. and Moore, J.B., 1989.

Optimal Control: Linear Quadratic Methods.

1st ed. Englewood Cliffs: Prentice-Hall.

[3] Kaufman, H., Barkana, I., and Sobel, K., 1998. Direct Adaptive Control Algorithms.

2nd ed. New York: Springer.

[4] Wie, B., 2008. Space Vehicle Dynamics and Control. 2nd ed. Reston, VA: American Institute of Aeronautics and Astronautics, Inc. LEONARDO TIMES N°2 2016

13

PIAGGIO AERO INDUSTRIES

C&O

REMOTELY PILOTED AIRCRAFT SYSTEMS The New Frontiers of Aviation Diego Giuseppe Romano, RT&D Engineer at Piaggo Aero Industries The founding principles of Remotely Piloted Aircraft Systems (RPAS) were introduced in the 1960s, but only in the last decades has a profound study of this type of aircraft been conducted. The USA and Israel hold the pre-eminence in this type of system, but the EU is actively trying to bridge the gap.

of 3 main components: 1. A Remotely Piloted Aircraft (RPA); 2. A Remote Pilot Station(s) (RPS), where the operator(s) command the RPA, fol-

EUROPEAN STRATEGY FOR RPAS Unmanned Aircraft Systems (UAS) are powered, aerial vehicles which do not carry any human operator on board and are able to fly autonomously or to be remotely piloted.

The request of such type of vehicles has increased in the past few decades mainly due to the geopolitical nature of conflicts in several parts of the globe. The absence of a pilot onboard has several advantages, some of which are that the duration of the mission is not linked to pilot’s skills and fatigue and in case the aircraft crashes or is shot down, there is no human loss.

According to ICAO (International Civil Aviation Organization) [1], there are three types of UAS, namely, RPAS, Model Aircraft and Autonomous Aircraft.

RPAS is a very complex system composed 14

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Figure 1 - European stakeholder and Regulatory System.

COMMERCIAL AND NON-COMMERCIAL OPERATIONS RPAS Operator Certificate Obligatory RPA MTOW

<150 kg

> 150 kg

Flight altitude

Very Low Level < 500ft

Above > 500ft AGL

Flight Density Population Unpopulated Lightly Populated Highly Populated

Teth

VLOS

E VLOS

B VLOS

VFR

Teth EVLOS

Type Certificate based on "Common Rules" but issued by Declaration signed by RPAS NAAs: Operator, RPAS Safety Assessment, • Language Pilot Approval by accredited • Proximity Qualified Entity (contracted by the • Fees Operator) Proportionate Rules

IFR BVLOS

RLOS

BRLOS

ICAO SCOPE International Flight Type Certificate Issued by EASA

JARUS (CS-LURS, 1309, ORG etc.)

Table 1 - Type of certifications for RPAS.

3.

lowing its flight and analyzing telemetry and all data useful for the completion of the mission; A Command And Control (C2) Link, which allows information exchange between RPA and RPS in both directions.

RPAS are classified on the basis of their ConOPS (Concept of Operations) and MTOW (Maximum Take-Off Weight). The above listed parameters, in fact, define the level of authorization necessary for the flight of RPAS. A synthetic scheme of current classification is reported in Table 1.

Actually, in the European scenario a fast developing RPAS activity is ongoing. The development activities are mainly focused in particular on VLL (Very Low Level) operations. These operations are normally characterized by RPAS for multiple applications with a maximum take-off weight below 150kg flying at an altitude below 500ft.

the terms of such authorization. Each contracting state undertakes to insure that the flight of such aircraft without a pilot in regions open to civil aircraft shall be so controlled as to obviate danger to civil aircraft.”

The European stakeholder and Regulatory System set-up for the definition of international rules governing RPAS is depicted in Figure 1.

Standard bodies provide MOPS (Minimum Operational Performance Standards) and MASPS (Minimum Aviation System Performance Standards).

EC (European Commission), through EU Funded Projects such as DeSIRE II [3] and SESAR [4], and in cooperation with EASA, define the Essential Requirements and the Safety Objectives.

Safety Objectives, MOPS and MASPS feed Technical Standards defined by EASA.

Among the several EASA (European Aviation and Space Administration) countries, sixteen have national rules for RPAS while eleven are still preparing them, but they are not harmonized.

Moreover, EASA RPAS Safety Objectives are used as input by JARUS (Joint Authorities for Rulemaking on Unmanned Systems) to define their standards for UAS.

Today, in EASA countries, it is possible to identify a large number of operators and manufacturers. In particular, about 2500 different operators and more than 110 RPAS manufacturers are present.

The information provided by JARUS, EC, EASA and Standard Bodies feed ICAO, which provides UAS SAPRS (Standard and Recommended Practices), which offer an international legal framework.

Presently, RPAS are the only type of UAS in the rulemaking process of ICAO for civil integration, being subject to article 8 ICAO of the Convention on International Civil Aviation passed at Chicago Convention of December, 7 1944 [2]. This article states that “No aircraft capable of being flown without a pilot shall be flown without a pilot over the territory of a contracting state without special authorization by that state and in accordance with

European Commission established the ERSG (European RPAS Steering Group) with the aim to develop a common European RPAS roadmap [5] for an initial RPAS integration by 2016 (see Figure 2).

TECHNOLOGIES FOR RPAS The basic approaches to implement unmanned flight (both autonomous and with a pilot-in-the-loop) have to compensate for the

absence of an onboard pilot. Therefore, they rely predominantly on: 1. Processor Technologies: RPAS, due to the high level of functionalities required (e.g. Automatic Take-Off and Landing - ATOL, Traffic and Ground Collision Avoidance etc.), need to use a VCMS (Vehicle Control Management System) instead of a common and “limited” FCC (Flight Control Computer). To enhance autonomous capability of RPAS, computer’s processors technology allowing faster computations, higher memory capacity, and safe responses (algorithms) are needed. Computers’ size, weight, reliability, integrity and dissimilarity for high level of safety are critical issues since most of the processing activities are onboard.

2. Communication Technologies: Airborne data link rates and processor speeds are in a race to enable future RPAS capabilities. In particular, data rates are limited by usable spectrum and by the requirement to minimize airborne system SWAP (Size, Weight, And Power). Another important challenge to be tackled is the congestion of communication bands (S, C and L), which today are very close to the theoretical maximum allowed (1.5bps/Hz with a theoretical maximum of 1.92bps/Hz). It seems mandatory to rely on commercial markets to drive link modulation methods technology, increasing the power of higher frequency (Ka-band), allowing a decrease of antennas size and weight.

3. DAA (Detect And Avoid): According to ICAO Circular 328 on Unmanned Aircraft Systems [5], DAA is “the capability to see, sense, or detect conflicting traffic or other hazards and take appropriate action to comply with the applicable rules of flight", therefore ensuring a safe integration of RPAS flight and enabling LEONARDO TIMES N°2 2016

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ERSG

Figure 2 - European roadmap for RPAS integration.

1.

•

•

•

• 16

full integration in all airspace classes limiting the risks of common hazards (e.g. conflicting traffic, terrain and obstacles, meteorological conditions, ground operations, wind shear and more). DAA capabilities are required for RPAS to limit risks of several different hazards which can impact RPAS. Among several hazards, the following have been enlisted: Conflicting traffic: RPAS can fly in areas where other flying objects are operating. Thus, it is mandatory to avoid the collision between RPAS and other flying objects, by using special sensors and command logics allowing the RPAS to detect the presence of other flying objects and to activate procedures to avoid the collision. In particular, airspace is generally divided into three spheres centered in the RPAS. If another flying object is detected in the most external sphere, a strategic conflict management is mandatory to allow a safe flight of both objects. If the object is detected in the inner sphere, a tactical process is carried out to keep the RPAS away from the hazard. Then the collision avoidance procedures must be used to avoid the imminent collision between the RPAS and the other flying object.

Terrain and obstacles: RPAS must identify the topography of the surrounding environment in order to avoid collision with the terrain such as mountains, hills and all other possible obstacles in its path.

Hazardous meteorological conditions: Similar to manned aircraft, weather conditions can have significant impacts on the flight of RPAS, since hail, lightings, storms etc. can require a modification of RPAS trajectory.

Ground operations: RPAS must also N°2 2016 LEONARDO TIMES

•

safely operate on ground, to avoid any collision with other objects.

Airborne hazards such as wake turbulence, wind shear etc., which affect not only manned aircraft but also RPAS.

Other technologies to be developed to improve future RPAS can be inserted into the following two main groups: 1. Platform Technologies: in order to extend mission capability of RPAS, it is mandatory to reduce airframe structural weight, and increase reliability and electrical power availability. Thus, key enabling technologies to extend RPAS endurance are composites materials, high reliability EMA (Electro-Mechanical Actuators), high voltage electrical power generation and modular distribution and high-efficiency propulsion systems for long-endurance, high-altitude RPAS. 2. Payload Technologies: RPAS’s usual payload is composed of electro-optical sensors, surveillance radar, electronic surveillance sensors and hyper-spectral sensors. Therefore, it is prudent to improve performance and reliability of the abovementioned devices, reducing their size and weight.

CONCLUSIONS UAS have already been introduced in the 1960s, but only in the last few decades have they been deeply studied, and now they represent the future of aviation, in both the military and civilian domains.

Particularly, among the several types of UAS; RPAS represent the new frontier of aviation, based on radical development in aerospace technologies.

The integration of RPAS into non-segregated airspace is a long-term activity, requiring ad-

vanced technology for DAA, C2 BRLOS (Beyond Radio Line of Sight) as well as robust regulatory framework.

Moreover, the EU is trying to fill the gap gathered up to now with respect to leading countries such as U.S.A. and Israel, encouraging European industries towards the study of UAS through EU funded Research Projects.

A Regulatory Regulatory System has been set-up to define rules for UAS. Piaggio Aero Industries is contributing to a truly European flagship technology initiative on Air Traffic Insertion (ATI) of RPAS by participating in EU funded Research Projects as well as developing their own unmanned aircraft.

References [1] Doc 10019 AN/507, "Manual on Remotely Piloted Aircraft Systems (RPAS)", First Edition 2015, International Civil Aviation Organization.

[2] http://www.icao.int/publications/Documents/7300_orig.pdf [3] https://www.eda.europa.eu/info-hub/ press-centre/latest-news/2015/05/18/edaand-esa-launch-desire-ii-demonstrationproject [4] http://www.sesarju.eu/ [5] "Roadmap for the integration of civil Remotely-Piloted Aircraft Systems into the European Aviation System, Final report from the European RPAS Steering Group, ANNEX 2 A: Strategic R&D Plan for the integration of civil RPAS into the European Aviation System", June 2013, Ref. Ares(2015)2206466 - 27/05/2015.

[6] Cir 328, AN/190, "Unmanned Aircraft System", 2011, International Civil Aviation Organization.

NASA

SPACE DEPARTMENT

10 YEARS OF NEW HORIZONS What a journey Sieglinde Goossenaerts, Student Aerospace Engineering, President Space Department, TU Delft

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NASA

Figure 1 - Pluto and Charon, as composed from images from New Horizons.

It has already been ten years since the launch of New Horizons, and it has been quite a journey. NASA has called 2015 ‘the year of Pluto’, with extremely high-quality images making the world news. This article presents an overview of New Horizons’ accomplishments and remaining secrets.

T

he first spacecraft to ever do so, New Horizons’ mission was to fly by Pluto and its moons, then go on and explore the Kuiper Belt which has never been explored before. The mission was initiated as a result of curiosity that lingered about the planets on the outer edge of our solar system and whatever lies beyond. As such, New Horizons is equipped to provide information about the composition and structure of the dwarf planet and its moons. Launched on January 19 2006, this exciting mission is now ten years old and just under 32 astronomical units away from Earth [1]. Scientists that participate on the mission from all over the world are eager to study and explain the data sent home by the New Horizon and decipher what it could mean for our understanding of space and our own solar system.

So, why Pluto? Completing our knowledge 18

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of the solar system, for one, has been a highly important point on the International Space Mission's agenda. Barely anything is known about it, and scientists are excited to fill this information gap. And they have quite a lot of study to be excited about – according to NASA, “Pluto offers an extensive nitrogen atmosphere, complex seasons, strangely distinct surface markings, an ice-rock interior that may harbor an ocean, and at least five moons for study. Among Pluto’s five moons, its largest one, Charon, may itself sport an atmosphere or an interior ocean, or both, and possibly even evidence of recent surface activity (younger than 100 million years). The smaller moons (named Nix, Hydra, Styx and Kerberos) are scientifically valuable bonuses, since New Horizons officially began in 2001 as a mission to just Pluto and Charon, years before the four smaller moons were even discovered.” [2]

GETTING THERE The data on all these factors are acquired by some impressive on-board technology that could be finally put to test during the Pluto flyby, which lasted two weeks during July 2015. These instruments measure a whole set of data, specifically that of the surface of Pluto and Charon, but possibly also on interesting objects that are orbiting in the Kuiper Belt. The instruments can do the following tasks: measure the composition and structure of Pluto’s atmosphere, its surface composition, temperature and geology and its atmospheric temperature and pressure.

Other instruments provide high-resolution encounter images, study solar winds and atmospheric escape, or energy particles and plasma in Pluto’s atmosphere, and lastly measure the concentration of dust particles [3]. A highly advanced line-up for a first-time mission to space, but a necessity, considering Pluto is the furthest reconnaissance mission target ever explored.

The instruments survived their trip to the edge of our solar system without a hitch. The

NASA

Part of: New Frontiers program (NASA) Lenght of preparation phase: 5 years and 10 days Launch date: January 19 2006 Cape Canaveral Launcher: Atlas V Flyby: Jupiter Closest approach of pluto: July 14,2015 at 12,500 km Cost: $720 million Stabilization: spin-stabilized Fuel: Hydrazine Size: 0.7 x 2.1 x 2.7m Antenna size: 2.1m (smaller backup antennae present) Weight: 478kg Power: 202W Internal temperature: approx. 20°C Thrust: 4x 4.4 N 12 x 0.9 N

The New Horizons spacecraft, artist impression.

world was in awe with the high-resolution images that New Horizons sent back home, the scientists are ecstatic about all the new conclusions to be drawn from the data about the mysterious planet situated far away from the earth. Maneuvring New Horizons to the exact position for this was an extremely high-precision job and required on-board data updates and the ever-improving images of the planet to alter its position. The mission only had one shot at succeeding, since a maneuver to orbit Pluto would require an extraordinary amount of fuel that could simply not be fitted onboard the spacecraft.

PLUTO’S SECRETS Luckily, we will be able to enjoy the discoveries from this flyby for a long time. In the few days of encounter of New Horizons and Pluto, a huge amount of data was measured and stored. So much in fact, that while some crucial data have already been sent over, more information on Pluto’s secrets will continue to be sent to Earth over the next 16 months following the flyby. In short, a complex astronomical puzzle about Pluto, Charon and their surroundings that is laid out piece-bypiece, an unseen treasure of knowledge just waiting to be unfolded.

So, what long-awaited information has New Horizons already sent home? For starters, Pluto offers an extreme diversity in terrain.

Ice volcanoes, spewing a mixture of water ice, nitrogen, ammonia or methane particles; wide, crater-free plains that stretch on for kilometers; islands and ice-water mountains in pools of frozen nitrogen are among Pluto’s unfolded geological features. A picture of Pluto and Charon can be seen in Figure 2.

The many different features and presumably ‘young’ smooth planes suggest that Pluto’s geology is still very much active.

On enhanced color images, the ice water present on Pluto appears very red. Other regions seem bluer, while certain areas look almost yellow. The source of this is still

unknown, but might be sought in organic compounds on the surface. Its atmosphere is blue, like the one of the Earth, and is thought to be mainly composed of nitrogen and methane. On the long mountain ranges on Pluto, even methane snow is thought to be present. Only recently, a picture of Pluto came through showing what seemed to be a cloud. Its atmospheric pressure is 10 microbars lower than expected and stretches out about 150 km into space. [4][5][6][7]

OTHER SATELLITES Some interesting data about Pluto’s moons has become available too, as well as the confidence that between the planet and its outermost moon Hydra, no other moons have been formed. Charon has no detectable atmosphere and its surface is highly different from the one on Pluto with some puzzling dark-colored terrain on its north pole and no ice. Its moons Nix and Hydra have a reflective surface, possibly indicating the presence of water-ice. These moons are also thought to possibly be the only regular moons (permanently near the host planet) of Pluto and Charon and are spinning in a very fast manner with a complex pattern. This could possibly be explained by the binary planet system that Pluto and Charon form together. The scientists responsible for the preliminary names of regions on Pluto and Charon's surfaces sure were not shy of using their imagination either: names includeMordor Macula and the Spock, Leia and Skywalker Craters. [4][5][6] A lot of questions, however, remain unanswered, and there is only a hope of starting to put the pieces together once all of New Horizons’ flyby data arrives on Earth next September. So far, we have some large question marks within the data, including the following: Is the atmospheric pressure lower than expected due to recent external or internal effects, and what would these effects be?

Why are some of Pluto’s mountains formed in curious tree bark-like rippling shapes?

How is Pluto, a dwarf planet, still geologically active after 4.5 billion years? How did Pluto’s system of binary planets and various small moons come into existence? And what else are we going to find in the Kuiper Belt? [4][5] [6] Let’s keep exploring this fascinating area of space, because it still holds many secrets and curiosities just waiting to be discovered.

References [1] New Horizons: The First Mission to the Pluto System and the Kuiper Belt, https:// www.nasa.gov/ , Tricia Talbert, NASA, 2015 [2] New Horizons Pluto Flyby press kit, http:// pluto.jhuapl.edu/ , NASA, 2015 [3] Spacecraft Payload, http://pluto.jhuapl. edu/ , The Johns Hopkins University Applied Physics Laboratory LLC., 2016 [4] The Pluto system: Initial results from its exploration by New Horizons, http://science.sciencemag.org/ , S. A. Stern a.o., Science, 2015 [5] Pluto is an active world of 'spectacular' color: Nasa reveals first scientific results from New Horizons' historic flyby of dwarf planet, http://www.dailymail.co.uk/ , Ellie Zolfagharifard, 2015 [6] Pluto Is Beautiful, Complex and Thoroughly Puzzling for Scientists, http://www. space.com , Mike Wall, Space.com, 2015 [7] New Horizons’ latest, https://www.nasa. gov/feature/methane-snow-on-pluto-speaks , Tricia Talbert, 2016 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.

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HANLEY

AERODYNAMICS

DEVELOPMENT CYCLE OF HAND LAUNCHED UAVS

Scientific method used throughout the conceptual design and prototyping of small hand launched UAV

Patrick Hanley, Aerospace Engineer, Owner of Hanley Innovations, Ocala, Florida Area

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This article summarizes the method of optimization of design parameters to meet the design objectives of small hand held UAVs, using modern tools for aerodynamic conceptual design and analysis.

S

mall hand-launched unmanned aerial vehicles (UAVs) are indispensable during emergencies due to their ability of providing visual coverage at the location of interest. Small electrically propelled UAVs are portable, lightweight and silent during flight. They are easily stored in backpacks or carrying tubes and are readily deployable even in the absence of takeoff and landing bases.

Engineering parameters that define the usability of small UAVs are weight, endurance, size (wing area) and range. Trade-offs need to be made taking them into consideration.

A UAV will gain weight due to increased wing area, payload weight (surveillance equipment, battery, servos and assembly for control, etc) and size (the capacity to carry the equipment). However, the weight gained adversely affects the range and endurance. An increased wing area will augment the lifting capacity of the UAV at the cost of increased weight and drag. The successful design and development of small UAVs require a technically efficient and cost effective method for design, testing and prototyping.

elevator setting is required to set the correct lift coefficient at launch. Extreme elevator deflections in upward direction can result in early pitch-up and stall while the deflections that are too little result in a dive into the terrain.

Other design considerations are materials and propulsion system (motor, propeller and battery), all of which can affect the weight and endurance of the aircraft.

AERODYNAMICS CONCEPTUAL DESIGN AND ANALYSIS PROCESS Two software packages that facilitate the design process and provide access for both small and larger UAV developments are NASAâ&#x20AC;&#x2122;s OpenVSP for conceptual design and Stallion 3D version 4.0 (an aerodynamics analysis tool) by Hanley innovations (developed by the current author).

OpenVSP is a conceptual design package that allows the rapid and accurate design of airfoils, wings, fuselage and control surfaces.

The software exports files in the STL format (amongst others) that can be read into computer-aided engineering (CAE) packages for engineering analysis.

DESIGN CONSIDERATIONS

To reduce weight and complexity, a simple rudder and elevator system provides control of the small hand-launched UAV. The rudder produces side-slip that in turn causes the aircraft to bank due to the coupling between the sideslip and roll moment. This combination controls turning by banking the aircraft in the desired direction.

A successful and cost effective design methodology requires that the center of gravity location, the stability derivatives and launch behavior are determined even before the first prototype is tested. In addition, the launch position of the rudder and elevator must be determined for a successful handlaunch. The aircraft needs to be trimmed using the vertical stabilizers in order to oppose the torque of the motor during launch. The

Stallion 3D performs detailed aerodynamic analysis on 3D STL files generated by a variety of CAD packages (including OpenVSP).

Stallion 3D compiles easily on designers' and engineers' laptops or PC workstations, and provides just in time (SameDayCFD) to drive the conception, design and implementation of a successful UAV. The UAV design process starts by using OpenVSP to design a simple wing-body concept that will be able to support three pounds (structural weight, propulsion and payload) during flight. The idea is to keep the structure as small as possible for easyHANLEY

One of the main considerations that facilitate a successful design of a modern UAV is the wing, which must have a simple structure in order to reduce excess weight. At the same time, the aerodynamic characteristics must be efficient in order to provide the required lift and endurance for the intended mission. A high-lift wing (high-lift airfoil shape) facilitates hand launch capabilities, but it also increases the drag, due to their typical high pitching moments that require a larger horizontal stabilizer. This combination increases the drag whilst also marginally reducing the lift.

portability . For the conceptual aerodynamic analysis, the initial design is exported as an STL file and directly imported into Stallion 3D. The software rapidly computes the aerodynamic parameters based on the shape and flight conditions such as angle of attack, sideslip angle and quasi-steady rates of rotation. The initial analysis (see second image in the visual) showed that the UAV concept will not perform well during flight. The computations suggested that the lift to drag ratio obtained using the current wing and fuselage combination would not provide the desired range and endurance.

A re-design with a higher aspect ratio wing was performed using the OpenVSP software in a matter of hours (see third image in the visual). The results of the revised analysis (see fourth image in the visual) confirmed that the design would satisfy the range and endurance specifications for the target overall weight of the UAV. With a satisfactory wing design in hand, the next design iteration was the tail and rudder concept necessary to provide stability and maximize the flight endurance (see fifth image in the visual). The horizontal tail size and angle were optimized to maximize the endurance during loiter. The sixth image in the visual is an example of the calculation performed with Stallion 3D to implement the desired tail volume and rudder for the design.

Finally, a series of computations were performed to determine the power required as a function of flight velocity for the design (Figure 1).These calculations provide the parameters necessary to select a battery, electric motor and propeller to provide the desired range and endurance for the UAV.

CONCLUSION Startups and small businesses interested in entering the UAV market require a fast and cost-effective method to take their concept from the idea (requirements) phase to a working prototype. A proven path is the use of computer aided design and engineering tools that can be used to test the design before building a prototype. NASA OpenVSP and Stallion 3D from Hanley Innovations are two packages that work well together for this purpose. The duration of the design and simulation process was two days using Stallion 3D version 4.0 running on a four core laptop PC. More information about OpenVSP is available from OpenVSP.org. More information about Stallion 3D is available from hanleyinnovations.com.

Figure 1 - Performance of the final design for a 3 pounds (aircraft weight and payload).

References [1] Stallion 3D, http://www.hanleyinnovations.com/stallion3d.html LEONARDO TIMES N°2 2016

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VAN KEYMEULEN

FPP

MODULAR FUSELAGE DESIGN Coping with seasonal variations in passenger demand Quentin Van Keymeulen, MSc Aerospace Engineering, TU Delft The subject of this research is a new concept of modular aircraft, designed to cope with the seasonal variation in passenger demand by opening the fuselage and increasing its length with extra bits of fuselage. The goal is to find out if this new aircraft concept is more profitable than the current alternatives.

T

new product strategy aims to develop future programs in incremental steps, rather than the more risky alternative: "moon-shots" [4].

According to Boeing’s ex-CEO Jim McNerney, the focus of the aircraft manufacturers should be on replicating systems and technologies which are already proven and paid for. The vision is sensibly the same at Airbus.

As a result, the more attractive options are to re-engineer familiar platforms and harvest new technology to deliver programs like the A320 NEO and the 737MAX. The consequence of this conservative approach is that there are less new programs launched by aircraft manufacturers. The first new program scheduled is by 2030, to replace the A320 NEO and the 737MAX, and even those programs are going to be conservative [5].

he long standing 5% growth rate per year in air traffic passenger demand (measured in Revenue Passenger Kilometers (RPK)) is expected to continue for the next 20 years [1]. Limiting the environmental impact of aviation is clearly going to be a challenge for the aircraft manufacturers and airlines. To be profitable, airlines require a high intensity of operation. This is why the important seasonal variation in passenger traffic is a crucial problem. The effect is well documented in Figure 1 which shows two years of international traffic starting in July 2012, according to IATA’s monthly report. As it can be seen, there is an important variation between the quietest month, February, and the busiest months of July and August. The seasonal variation can be computed between the quietest month (252 •10^9RPKs, February 2013) and the busiest month (360 •10^9RPKs, August 2013) compared to the average of the year 2013: 304•10^9RPKs. So the lowest month has 17% less traffic than the average and the highest month has 18% more. This results in a maximum variation of 35%.

and the need to decrease emissions, there is also an emphasis in the aerospace industry to move from the initial "higher, faster, farther" era to the "better, faster, cheaper" era. This means that the goal is to decrease the total life-cycle cost of aircraft while keeping good performance. This in turn translates to aircraft manufacturers being more conservative in taking risks, and privileging incremental innovations instead of radical ones.

The load factor airlines have managed to reach in 2013 is 79.5% [3]. It is a historical record but there is still room for improvement.

One way of improving the load factor is by using modular aircraft, which is the subject of this article.

Figure 1 - International Passenger Market - July 2012 to July 2014 [2].

Next to the forecast growth of the market

Table 1 - Mass penalty.

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VAN KEYMEULEN

Rather than betting the company with revolutionary technology, aerospace firms are increasingly changing their approach. The

For this research, two main tools have been developed. The first one is a family aircraft design tool used to generate a reference basis. This MATLAB optimization tool is designed to assign the optimal aircraft to the optimal routes using operations research and a mixed integer programming approach.

The second design tool is based on the Faculty's aircraft preliminary design tool called “The Initiator”, modified to design and analyze the modular aircraft. The inputs are the number of seats and the range of the aircraft.

The output is a concept aircraft defined by aircraft geometry, operational performances, weight estimation and aerodynamics.

Figure 2 - Mass penalty and plugs locations. out that a large wing with a small tail is the best concept and that the plugs should be located near the end of the fuselage, where the stresses, constraints and fuselage structure complexity are the lowest, as displayed in Figure 2.

The mass penalty of the connection mechanism is approximated by sizing an idealized bolt connection for nine load cases (steady flight and hard landing) with a safe life philosophy. The failure criteria used for the stresses are the resulting yield after 50,000 cycles using a safety factor of eight. The resulting mass penalty for the short and long version is given in Table 1.

Next, the profitability is studied. The revenues are calculated by assuming standard yield of 0.1 and 0.3 $/pax/nm for economy and first class respectively. From those revenues, the total operating costs, interests and taxes are subtracted to give the profits. As expected, the modular aircraft is less profitable than VAN KEYMEULEN

Both tools were used in the two study cases: the aircraft (carrying 100 and 150 passengers in the short and long configuration respectively) and a fleet of aircraft. The goal of the first study case is to analyze the impact of the mass penalty of the connection mechanism on the profitability of the aircraft. Since the aim is to change as little parts as possible between the long and short versions of the aircraft, it was assumed that the wing and tail would stay constant and that the engines and landing gears would be changed between both aircraft configurations. It turns

VAN KEYMEULEN

A modular aircraft, as investigated in this research, has a fuselage that can be opened to allow the addition of sections in order to increase its passenger capacity. Varying the size of the fuselage would take place twice a year to follow the seasons, or maybe a few times over the course of the aircraft’s life to adapt to the market. The concept of having a modular fuselage is in line with this reduction in risk-taking strategy. In addition, it offers more flexibility to the airlines that have to make long-term investments in aircraft without knowing the traffic demand and competition state in the future.

the optimal aircraft. It turns out that the mass penalty has a small impact on the profitability of the aircraft compared to the impact of the wing design. Indeed, the large aircraft's wing is used on the short version. This leads to a sub-optimal wing loading negatively affecting the aircraft's performance and profitability.

At the fleet level, the better fit between the passenger demand and offer allows for less spill. However, this advantage does not compensate for the sub-optimal design.

To conclude, the goal of this research was to find out if a modular concept is a good solution for a more cost-effective aircraft. This was studied by analyzing the impact of the mass penalty and the aircraft's performance on its profitability. The results show three things: that the biggest impact is caused by the non-optimal wing, that the mass penalty has little impact on profitability and that in order to make the modular design competitive with the optimal aircraft, the load factor should be increased from 80% to 86%.

Therefore, the next step would be to find out if such a concept could improve the load factor enough to be competitive.

References [1] Boeing. Long-term Market outlook 2013-2032.http://www.boeing.com/boeing/ commercial/cmo/ [2] IATA. “Air passenger market analysis”.

(July 2014). http://www.iata.org/whatwedo/ Documents/economics/passenger-analysis-jul-2014.pdf.

[3] IATA. “Air passenger market analysis”.

(December 2014). http://www.iata.org/ whatwedo/Documents/economics/passenger-analysis-dec-2014.pdf.

[4] Doug Cameron. “Boeing CEO Wants Incremental Innovation, Not "Moon-Shots”.

In: The Wall Street Journal (May 2014).

[5] Stanley Caravalho. “Boeing plans to develop new airplane to replace 737 MAX by 2030”. In: Reuters (Nov. 2014).

Software optimization tool used for sizing and location of landing gears and engines.

LEONARDO TIMES N°2 2016

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NASA/ESA/KORNMESSER

SPACE ENGINEERING

IN-SITU OBSERVATIONS OF EUROPA'S PLUMES

A feasibility study for the JUICE mission

Hans Huybrighs, MSc Aerospace Engineering, TU Delft,PHD student at the Max Planck Institute for Solar System Research/Swedish Institute of Space Physics/Technical University of Braunschweig

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The discovery of water vapor plumes on Europa, one of Jupiter's moons, indicates that material may be released from the subsurface ocean. Recent research shows that it could be feasible with the ESA JUICE (JUpiter ICy moon Explorer) mission to take in-situ samples of these plumes, and thereby study the contents of Europa's ocean, without having to penetrate through the icy surface.

Figure 1 illustrates why Europa's ocean is thought to be interesting as a potential habitat. Four basic criteria can be identified for (Earth-like) life: liquid water, a stable environment (this means that liquid water is present for an extensive period of time), essential elements (the basic elements needed for life: S, P, O, N, C and H) and chemical energy (some source of energy). When these criteria are evaluated for several habitats in the solar system, it can be seen that Europa (and Earth) really stands out. The evidence pointing to the presence of liquid water on Europa has already been outlined previously. Furthermore, it is thought that this ocean has been liquid for a large part of this moon's history. The basic elements have been observed at the Galilean moons or are thought to be present from modeling of the formation of the moons. Photosynthesis is not a likely source of energy in Europa's ocean, due to the lack of sunlight in the ocean. However,

Figure 1 - Hydrogen and oxygen emissions in the Europa aurora. The plume, a surplus of oxygen and hydrogen is visible at the south pole. some form of chemosynthetic metabolism is more probable. Unlike the other Galilean moons, Europa's ocean is thought to have a direct interface with the rocky crust beneath.

This implies that geothermal vents at the bottom of the ocean could release reducing substances into the ocean that could fuel chemosynthetic metabolism (comparable to the black smokers on Earth's ocean floor).

Oxidizing substances that are formed at the surface of Europa (created by the charged particle bombardment) and transported back into the ocean could also be of importance for chemosynthetic metabolism.

EUROPA'S WATER VAPOR PLUMES In December 2012, a large water vapor plume was observed at Europa with the Hubble Space Telescope (Roth et al., 2014a).

The scientists conducting these observations were studying Europa's aurora. Europa is known to have a tenuous atmosphere, or exosphere. Particles in this exosphere are bombarded by high-energy electrons from

SURFACE HABITATS SHALLOW WATER Earth

Mars

Jupiter's magnetosphere that cause auroral emissions. These auroral emissions are studied in the ultraviolet spectrum, but not in the visible spectrum, because they are too weak compared to other visible light sources in the environment. During the observations made in December 2012, a large surplus in H and O emissions indicative of H2O, was observed (see Figure 2). It is suggested that this is caused by the presence of two water vapor plumes, which are approximately ~200km high and persisted for seven hours (the Hubble observation window). To reach such altitudes, supersonic velocities of 700m/s are needed (still lower than the escape velocity of approximately 2000km/s).

From the observations, an enormous mass flux of 7000kg/s is estimated. No plume signatures have been observed in repetitions of the original observation in January and February of 2014 (Roth et al., 2014b), when Europa was at a similar orbital position. Saturn's moon Enceladus has regular plume activity that is linked to the position of Enceladus in

DEEP HABITATS TRAPPED OCEANS Ganymede

Callisto

ESA ESA

HABITABILITY OF EUROPA'S OCEAN

NASA/ROTH

EUROPA'S OCEAN Though no mission has ever penetrated Europa's ice layer or even landed on the surface, Europa is thought to have a liquid ocean because of several reasons. Firstly, the presence of certain surface features on Europa can be explained by, or require the presence of a liquid layer. Secondly, measurements of Europa's gravity field indicate that a liquid layer could be present. However, the strongest argument is the presence of Europa's induced magnetic field. While moving through Jupiter's strong magnetic field, a magnetic field is induced in Europa.

This requires the presence of a conductive layer inside of Europa - the most likely candidate being a salty ocean. Estimates of the thickness of the ice-ocean layer range from 80-150km, of which the outer 7-15km could be ice.

TOP OCEANS Titan

Europa

Enceladus

Liquid water Stable environment Essential elements Chemical energy Table 1 - Present state of the existing and past habitable worlds in the solar system. For each object the status of the four pre-requisites for a habitable environment is ranked from red (not possible), to yellow (likely but not yet demonstrated) and to green (demonstrated or very likely).

LEONARDO TIMES N째2 2016

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its eccentric orbit about Saturn. The failed repetitions of observations indicate that at Europa the mechanism is more complex and/or the sources of water are limited (only few cracks penetrate to the ocean, or a reservoir needs to be refilled over time).

IN-SITU OBSERVATIONS OF THE PLUMES DURING THE JUICE MISSION

HUYBRIGHS

By taking samples of the plumes, the composition of Europa's ocean could be investigated, without having to penetrate the ice or even land on the surface. The first mission that could do this is the European Space Agency's JUICE mission. JUICE will study Jupiter and its giant icy moons: Europa, Ganymede and Callisto. The instrument on

During the Master's thesis project of Hans Huybrighs- conducted at IRF and supervised by Dr. Yoshifumi Futaana, Professor Stas Barabash and Professor Bert Vermeersen, the feasibility of in-situ observations of Europa's water vapor plumes was investigated. This was done by modeling the trajectories of plume particles, and simulating how PEP will observe these particles during the two flybys of Europa that JUICE will make.

The project was focused on the modeling of small plumes with a mass flux less than one kg/s, which is significantly smaller than what had been inferred from the observations.

The argument is that if large plumes are present, smaller ones are likely to be present as well, and possibly more often. By simulating the trajectories of millions of water particles

Europa is embedded in Jupiter's magnetosphere. At Europa's orbit in this magnetosphere, a strong flux of high-energy electrons is present. These electrons will collide with some of the plume particles and ionize them. The trajectories of ionized particles will not be dominated by gravity but by electric and magnetic fields present in the magnetospheric environment. The particles will essentially be picked up by plasma that is rotating about Jupiter at Europa's orbit. The ionized plume particles will start moving along with this plasma flow and will be transported far from Europa. The trajectories of those particles were also simulated to obtain the distribution of plume ions. By simulating the instrument observations by one of the ion instruments onboard of PEP (JDC, Jovian plasma Dynamics and Composition analyzer), it was shown these plume ions can also be detected.

EUROPA MULTIPLE-FLYBY MISSION More opportunities to observe the plumes might be possible during NASA’s Multiple-Flyby Mission that will make 45 flybys of Europa, formerly known as the Europa Clipper Mission. Recently, nine instruments have been selected for this mission. In June the mission concept was also approved. The spacecraft will carry instruments that could study the plumes in-situ: one instrument to study charged particles (Plasma Instrument for Magnetic Sounding, PIMS) and one to study neutral particles (MAss SPectrometer for Planetary Exploration/Europa, MASPEX).

A dust instrument will also fly onboard Europa Clipper (SUrface Dust Mass Analyzer, SUDA). If launched with the SLS, the NASA mission could make it to Europa even before JUICE.

CONCLUSION

Figure 2 - Cartoon illustrating the main aspects of the model. The vertical background figure shows the density distribution of water resulting from a plume at the south pole of Europa. The horizontal plane shows the density of ionized plume particles, moving away from their source, along with the plasma flowing at Europa’s orbit. board of JUICE that will perform the in-situ measurements is the Particle Environment Package (PEP). PEP is a six-sensor instrument suite that is tasked to study the particle environment at Jupiter. These sensors characterize properties of electrically charged and electrically neutral particles such as mass, velocity and direction. The development of PEP is led by the Swedish Institute of Space Physics (IRF), located in the very north of Sweden. The principal investigator of the instrument is Professor Stas Barabash. JUICE will be launched in 2022 and make two flybys of Europa in 2031.

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of the plume, the neutral particle distribution around Europa was obtained. A cartoon summarizing the capabilities of the plume model is shown in Figure 2. The mass- and thus composition- of neutral particles can be determined by one of the sensors in PEP (NIM, Neutral and Ion Mass Spectrometer) with high precision. The observation of neutral plume particles with NIM was simulated and this showed that if a small plume is present at the time of the flyby, the particles will be observable by NIM, even if it is a considerable distance away from the closest approach of the spacecraft to the surface.

During the next two decades, both the JUICE and Multiple-Flyby missions could allow us, for the first time, to study Europa's mysterious and possibly habitable subsurface environment, by taking in-situ samples of the Europa plumes. It has been shown that this is feasible with instruments on-board JUICE, even for plumes that have significantly lower mass flux than what has been observed. More, and possibly earlier, opportunities could occur during the Europa Multiple-Flyby mission.

References [1] L. Roth, K. D. Retherford, J. Saur, D. F. Strobel, P. D. Feldman, M. A. McGrath, and F. Nimmo. “Orbital apocenter is not a sufficient condition for HST/STIS detection of Europas water vapour aurora”. In: Proceedings of the National Academy of Sciences (Nov. 2014), p. 201416671. issn:1091-6490. doi: 10.1073/pnas.1416671111.

[2] L. Roth, J. Saur, K. D. Retherford, D. F. Strobel, P. D. Feldman, M. A. McGrath, and F. Nimmo. “Transient Water Vapor at Europa’s South Pole”. In: Science 343.6167 (Jan. 2014), pp. 171–174.

VAN DER HORST

WIND ENERGY

AIRFOIL DESIGN FOR VAWTS Including correct simulation of flow curvature Ir. Sander van der Horst, MSc Graduate Aerospace Engineering, TU Delft With the depletion of fossil fuels, increasing emissions, and the inevitability of global warming, the interest in renewable energy grows. Conventional solutions, like horizontal axis wind turbines, are reaching the limits of their capabilities. Therefore, there is renewed interest in other models, such as the Vertical Axis Wind Turbine (VAWT).

The VAWT , however, has some downsides as well. The blades pass through their own wake, it has a difficulty self-starting, and no stall mechanism so far has been invented that is safe enough. The aerodynamics asso MIGLIORE

W

hile there are multiple variations on the VAWT, the most viable one is the Darrieus turbine, patented in 1932 (Darrieus, 1931). This turbine operates on the principle of aerodynamic forces acting on vertically placed blades, spinning around an offset center. When enough torque is generated, power is produced. The advantages of this configuration are that it is easily scalable, will not suffer from gravitational loads and has a low center of gravity, as heavy parts like the generator are placed near the surface (Eriksson, 2008). Especially the latter characteristic make it a good contender to its horizontal axis counterpart, as a VAWT can easily be placed on floaters and anchored in the deep sea (Akimoto, 2011). For the HAWT (Horizontal Axis Wind Turbine) this is far more problematic and costly, as placing an offshore HAWT can be even more expensive than the turbine itself (MonĂŠ, 2014).

Figure 1 - Virtual airfoil transformation.

LEONARDO TIMES N°2 2016

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U2DIVA

-0.6

C l = 0.306

XFOIL

C l = 0.316

Pressure coefficient C p [-]

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VAN DER HORST

-0.8

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0

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Figure 2 - Pressure solution of the modified XFOIL compared to the benchmark. ciated with them are so complex that it currently remains difficult to understand or model these phenomena. However, it is thought that some of these problems can be mitigated through custom airfoil design (Migliore, 1980). Accurate modeling of VAWT aerodynamics will result in improved airfoils and has the possibility to enhance the turbine output.

Therefore, this makes for an interesting and cutting-edge research field.

A specific aerodynamic phenomenon was highlighted in this research, namely flow curvature. This phenomenon arises as a VAWT airfoil not only has a translational motion, but also a rotational motion. As a result, the angle of attack varies over the chord. Namely, the rotational velocity at each point on the chord is normal to its local radius. This variation of angle of attack has large repercussions on the performance of the airfoil, and therefore also the blades. In essence, an airfoil orbiting the VAWT center will act as having added camber and added angle of incidence to the flow (Zervos, 1988). Specifically, the added rotational motion alters the surface velocity of the airfoil. The pressure distribution, in turn, is then changed and eventually this alters the aerodynamic forces and their azimuthal distribution. In the end, a change in power output and efficiency of the turbine is experienced. Previous research has shown that this will almost always result in negative outcomes.

Now if these flow curvature effects can be estimated and accounted for, advantages can be made in the turbine design and its performance. This was the objective of this research. Below, a concise summary of its outcomes is presented. It shows how researchers in the past have dealt with flow curvature, and presents a novel method to 28

N°2 2016 LEONARDO TIMES

do so. It will be shown that this new simulation model has merit for future VAWT design.

The impacts of flow curvature have been investigated as early as 1975, and are thoroughly described by Migliore, 1980. Similar to several other authors, their method to implement flow curvature was by modifying the actual airfoil of the turbine to a virtual one, incorporating an approximation to the flow curvature. In Figure 1, one can see such an approximation, where in order to “bend the curved streamlines of the VAWT airfoil straight, the virtual airfoil is bent as well”.

The latter airfoil will obtain a camber and an incidence angle according to the original situation, but now operates in straight flow.

This means that it can be investigated using conventional methods.

to compute the airfoil characteristics, such as pressure distribution and aerodynamic forces. With a small modification, the option to also include the additional surface velocities of a rotating VAWT airfoil was added. This alteration has been verified to produce the correct result, and could therefore be used to compare the transformed airfoils to. Finally, it has been observed that all the methods perform equally well when regular design parameters of current turbines are applied.

Please note that these outcomes only concern inviscid, so “theoretical” results. For real-life situations, viscous calculations are necessary. A proven method of designing airfoils for such cases is the XFOIL panel code. This software, developed in the eighties at MIT (Drela, 1989), allows the user to easily apply an inviscid potential flow solver coupled with viscous boundary layer calculations. In essence, it can make calculations for airfoils in real-life situations.

XFOIL’s inviscid solver revolves around the principle of the stream-function. This is a potential flow solution for a singularity or a distribution of these. As the original source code assumes straight flow, some modifications were necessary to include a rotating VAWT airfoil. This airfoil can be simulated by an airfoil continuously rotating about an arbitrary axis within the airfoil itself. Namely, the motion of the original VAWT airfoil only differs from such a simulated airfoil by its translational motion due to the VAWT arm. By removing this arm, both airfoils rotate about the mounting location of the airfoil. Obviously, the kinematic equations will change, and a derivation of this similarity can be made to be a very significant result. This says that varying the normalized rotational velocity of the air-

Several authors present methods to perform such a virtual airfoil transformation, while only six of these describe their work detailed enough to be reproduced. An important parameter in all these methods is the chord-to-radius ratio of the turbine. One can imagine that if this ratio increases, the variation of angle of attack over the chord will increase, resulting in enhanced flow curvature effects. Their transformations have been applied to investigate any performance differences. A visual inspection and a calculation of their pressure distribution showed that for common chord-to-radius ratios below 0.2 (Kirke, 1998), no distinguishable differences or advantages of any method could be found.

The virtual airfoil transformation solutions have been computed by the use of the U2DIVA panel code (Simão Ferreira, 2009).

This inviscid potential flow solver uses singularity solutions placed on the airfoil surface

The Darrieus wind turbine is a type of Vertical Axis Wind Turbine patented by Georges Jean Marie Darrieus, a French aeronautical engineer in 1931.

The stream-function formulation of the potential flow solver has been modified to include new boundary conditions of an airfoil with arbitrary rotational velocity and center of rotation. As now, the reference frame is rotating, a change in the computation of pressure coefficient has to be made. The method of computing the surface velocities of the airfoil is also modified, as the original code was incompatible with the new modifications. A result is shown in Figure 2, where the pressure distribution of a NACA0015 airfoil computed by XFOIL is compared to the U2DIVA benchmark, for a chord-to-radius ratio of 0.2 and a mounting location at half the chord.

The inviscid solution showed that no cumulative differences between the computed pressure distribution and the benchmark larger than 10% have been found (i.e. between the lift coefficients). It is assumed that with the modified potential flow solver, the viscous calculations can be left untouched and should perform as before. As there are no viscous benchmark solutions for rotating airfoils, this cannot be verified.

A final investigation into airfoil optimization and turbine performance was performed with the newly modified version of XFOIL. Using optimized software based on a genetic algorithm, numerous different airfoils were generated and analyzed for their aerodynamic and structural properties. The optimizer scores each airfoil on two objectives, one to optimize the power output of the turbine and the other to maximize the area moment of inertia of the airfoil so as to obtain a blade which is as stiff as possible (Simão Ferreira,

VAN DER HORST

foil can simulate the chord-to-radius ratio, on which flow curvature effects depend. This provides for an excellent opportunity to implement in XFOIL.

Figure 3 - Power coefficient for optimized airfoils under varying operating conditions.

2015). The result is a whole range of optimized airfoils, varying from very aerodynamic and not so stiff, to structurally optimal and aerodynamically infeasible. Only the former are used in further investigations.

Under the same circumstances, airfoils optimized for straight flow were compared to ones optimized while rotating. In this manner, one would be able to see if a power improvement could be obtained. Using software, the turbine power output over a range of operating conditions was simulated. Figure 3 shows the power coefficient calculated for three airfoils- the first is an airfoil optimized for straight flow, but simulated while rotating around its quarter chord. The latter two are airfoils optimized for rotating flows, one turning about the quarter chord and the other about the half chord location. As can be seen, up to a tip speed ratio of five, which is the region typical for a VAWT, at least one the airfoils optimized with the inclusion of flow curvature performs better. Even though the difference is small, the potential for power enhancement can be recognized.

Although the above simulations lack some verification and surely need to be extended and improved, there are clear signs that the presented method can lead to improved tailored airfoil designs for vertical axis wind turbines. Including such a virtual modification of the rotating airfoil is currently not applied in the design process, but shows that increased turbine power output and efficiency can be obtained. This will not only aid in the proliferation of VAWTs, but of wind energy in general, hopefully solving our global energy crisis in the future.

The H-rotor arrangement of the vertical axis wind turbine.

References [1] J. Moccia, “European Wind Energy As-

sociation: Wind energy scenarios for 2020”, 2014.

[2] G.J.M. Darrieus, Turbine Having Its Rotating Shaft Transverse to the Flow of the Current”, 1931.

[3] S. Eriksson, H. Bernhoff, and M. Leijon, “Evaluation of different turbine concepts for wind power”, Renewable and Sustainable Energy Reviews, vol. 12, no. 5, pp. 1419– 1434, 2008.

[4] H. Akimoto, K. Tanaka, and K. Uzawa, “Floating axis wind turbines for offshore power generation - a conceptual study”, Environmental Research Letters, vol. 044017, no. 6, p. 6, 2011.

[5] C. Moné, T. Stehly, B. Maples, and E. Settle, “2014 Cost of Wind Energy Review”, National Renewable Energy Laboratory, Tech. rep., 2014.

[6] P. G. Migliore, W. P. Wolfe, and J. B. Fanucci, “Flow Curvature Effects on Darrieus Turbine Blade Aerodynamics”, Journal of Energy, vol. 4, no. 2, pp. 49–55, 1980.

[7] A. Zervos, “Aerodynamic Evaluation of Blade Profiles for Vertical Axis Wind Turbines”, in European Community Wind Energy Conference, Herning, Denmark, 1988, pp.

611–616.

[8] B. K. Kirke, “Evaluation of Self-Starting Vertical Axis Wind Turbines for Stand-Alone Applications”, Ph.D. dissertation, Griffith University Gold Coast Campus, 1998.

[9] C. J. Simão Ferreira, “The near wake of the VAWT 2D and 3D views of the VAWT aerodynamics”, Ph.D. dissertation, Delft University of Technology, 2009.

[10] M. Drela, “XFOIL: An Analysis and Design System for Low Reynolds Number Airfoils”, Lecture Notes in Engineering, vol. 54, pp. 1–12, 1989.

[11] C. Simão Ferreira and B. Geurts, “Aerofoil optimization for vertical-axis wind turbines,” Wind Energy, vol. 18, pp. 1371–1385, 2015.

LEONARDO TIMES N°2 2016

29

DJI

SPACE ENGINEERING

GIMBALING ONWARDS

Engineering cinematography

Nicolas Ruitenbeek, BSc Student Aerospace Engineering, TU Delft, Editor Leonardo Times What initially started as an extravagant way to ink one’s fountain pen has become an extremely intriguing piece of technology used across multiple industries. Gimbal-based stabilization is predominantly found in spacecraft propulsion; however, it is also being used to revolutionize other market fixations such as filmmaking, photography, and marine navigation.

P

hilo of Byzantium (280-220 BCE), also known as Philo Mechanicus, was a Greek engineer, inventor, and writer on mechanics. His extensive work and research on mathematics, military engineering and general mechanics make him one of the founding fathers of modern-day engineering. In one of his publications he describes an eight-sided inkpot with an opening on each side. The pot can be tossed and turned such that any face is on top, and a pen can be dipped and inked through the opening. Yet the ink never runs out through the holes on the other sides. This was achieved through suspension of the inkwell at the centre. The latter was mounted on a series of concentric metal rings so that it remained stationary and upright regardless of the inclination of the pot.

The basis for gimbal stabilization had henceforth been discovered.

The applications of the gimbal varied throughout the antiquity period. It became widely used for military situations, notably when siege-crafts prepared to attack coastal towns. Ancient author Athenaeus Mechanicus (30 BCE–14 CE) described the gimbal being used to keep the siege machines upright, while the military engineers yoked the merchant ships together, preparing to assault settlements. In China, inventor Ding Huan from the Han Dynasty (202 BCE–220 CE), created a gimbal incense burner. During the 9th century, French inventor Villard de Honnecourt, saw a pacifist alternative, and used 30

N°2 2016 LEONARDO TIMES

Cardan suspension to improve the accuracy of compasses.

Although the gimbal was already being used in a wide variety of applications, it was not until it was picked up by the aerospace industry that it started to gain recognition. In spacecraft propulsion, rocket engines are mounted on a pair of gimbals, allowing a single engine to vector thrust about both the pitch and yaw axis, enabling an increase in maneuverability.

Gimbaled thrust thereby became a vital component in maintaining the stability and control of a rocket throughout its flight path. It is also being used for guidance systems of modern missiles. SpaceX’s reusable rocket prototype dubbed the “Grasshopper” uses a three-axis gimbal system to hover, translate, and maneuver in any possible direction. However, gimbal-based thrust vectoring systems do not end there. With its vast use in space and rocketry applications, gimbals are also used in military aircraft. The ability to change the thrust angle allows for a drastic increase in agility. Aircraft such as the Lockheed Martin F-22 Raptor used thrust vectoring about its pitch axis. Though whilst being regularly used in aerospace applications for thrust and stabilization systems, gimbals have surfaced in the filmmaking and cinematography industries as well, with startling results.

Capturing smooth video footage is a nightmare for any filmmaker. Take out your smartphone and try to film your immediate sur-

roundings going from left to right in the shape of an arc. The footage will come out shaky no matter how long you hold your breath. This is due to our human nervous system and micro muscle movements. Hundreds of thousands of dollars can be spent on equipment such as glide-cams, rail-cams, and cranes, which help remove these human imperfections.

Such devices are often cumbersome and difficult to operate. Additionally, this is often not enough as some parts of the machinery may trigger vibrations, hence post-processing and stabilizing algorithms will have to be used.

The potential for gimbal-based stabilization for cameras was discovered and spread like wildfire. Using high-torque brushless motors, a video camera could be stabilized about all the three axes. A single operator carrying such system is now able to produce flawlessly stable footage. With a second operator, the camera can be controlled and operated remotely, effectively reducing the manpower from an entire team to just two individuals. Companies like DJI and Freefly attached these systems onto aerial platforms to give filmmakers a different perspective.

Such systems have also become extremely affordable, reliable, and user-friendly over the past four years, allowing anyone to produce perfectly stabilized video footage, essentially changing cinematography forever.

Gimbal-based systems, which were primarily used in the aerospace industry, have had tremendous success and have greatly assisted flight stabilization and control. However it is important to remember that breakthroughs and advances in one industry, just might completely transform another.

Our mission one hundred percent www.airbusDS.nl

NASA/JPL

SPACE ENGINEERING

FROZEN ORBITS ABOUT THE EARTH Counteracting orbital perturbations in the long run Jan Hoogland, MSc Aerospace Engineering, TU Delft There are six intuitive orbital components that are often used to describe the shape and orientation of a satellite orbit. These elements are varying constantly due to perturbations, but for a cleverly chosen orbit - the frozen orbit - the long-term effects of at least some of these perturbations can be cancelled.

The paper on the orbit design of Seasat, (Cutting et al, 1978) demonstrated the existence of a family of near-circular polar orbits that suffered from minimal secular variations in the mean argument of pericenter (ω) and the mean eccentricity (e). Normally, these two orbital elements suffer from variations caused by the flattening of the Earth at the poles (the equatorial bulge, or J2-effect). It is possible to ensure static behavior of the argument of pericenter and the eccentricity by placing the satellite in an orbit at the critical inclination (63.4 degrees), but global coverage is not possible at this inclination.

For Seasat, a minimal variation in both the mean argument of pericenter and mean eccentricity was a necessity, as this would guarantee a constant altitude profile above Earth’s surface as a function of latitude only.

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THE ANALYTICAL WAY

Despite Seasat’s early failure after just 105 days in orbit, it gathered more oceanographic altimetry data than all other surface-based efforts before it. The newly applied frozen orbit concept proved to be successful and

One of the pillars of orbital perturbation theory is a set of six equations governing the rate of change of all six orbital elements – the so-called Lagrange planetary equations.

These equations are expressed in terms of disturbing potential, which is a location-de-

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HOOGLAND

Theoretically, this would eliminate the need for corrective maneuvers.

1.18E-03 Mean eccentricity [-]

I

n 1978, a key Earth observation satellite was launched from Vandenberg AFB in the United States. This satellite, carrying the name Seasat, was to monitor Earth’s oceanographic phenomena. To carry out this mission, the satellite was equipped with an array of Earth observation instruments, such as the first space-borne Synthetic Aperture Radar (SAR) and a radar altimeter. To maximize the quality of the data from these instruments, the orbit had to be carefully selected in order to minimize the influence of orbital perturbations. As such, Seasat was the first mission to make use of a so-called ‘frozen orbit’.

has been applied to numerous missions since. Well-known Earth observation missions such as Envisat, ERS-1 and ERS-2 all fly in Sun-synchronous, repeating ground track frozen orbits.

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Figure 1 - Evolution of the actual mean argument of pericenter and mean eccentricity of ERS-2 in 2003. Green and red marks the start and end of the year, respectively, and each dot marks the averaged mean orbital elements for a day.

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89

89.5 90 90.5 91 Mean argument of periapsis [deg]

91.5

92

Figure 2 - Evolution of the simulated mean argument of pericenter and mean eccentricity for a frozen orbit under the influence of several non-zonal perturbations. Time between marks is one week. pendent correction of the simple spherical symmetric point-mass gravitational potential.

The disturbing potential is often formulated in terms latitude-dependent (zonal) terms, longitude-dependent (sectorial) terms, and terms depending on both latitude and longitude (tesseral). If only the first two zonal terms of the gravity field expansion (the J2-effect and the J3-effect) are taken into account, it is possible to derive a simple set of conditions linking the mean eccentricity and mean argument of pericenter together:

where e, a, i and ω denote the mean eccentricity, semi-major axis, inclination and argument of pericenter, respectively. RE is Earth’s equatorial radius, and J2 and J3 are the coefficients for the zonal expansion of the gravity field. As simple as the equation for the frozen eccentricity may be, its derivation is rather complicated. Additionally, it is emphasized that only taking into account the first two zonal terms of the gravity field does not make for a very realistic representation. However, the complicated derivation can be repeated for more realistic zonal gravity field models, and though the resulting expressions are nowhere near elegant, they can be solved numerically. This way, it can be shown that the inclusion of higher degree zonal terms (all the way up to J25, for example) has a significant effect on the final frozen eccentricity.

Many more research efforts have been put into further refining the required conditions for a frozen orbit, most of them venturing deep into the field of higher order astrodynamics. However, most of these methods rely on formulating the perturbing accelerations as a disturbing potential, and this

limitation may be overcome when using a purely numerical method to find frozen orbit conditions.

MEAN VS. OSCULATING ELEMENTS The prediction of a satellite trajectory is made easy nowadays by numerically integrating the equation of motion, to which models for various orbital perturbations can be added.

Aerodynamic drag, solar radiation pressure, third-body gravity and of course, Earth’s irregular gravity field; all of these can be taken into account. However, numerically integrated orbits result in state predictions in terms of osculating orbital elements, whose behavior is governed by short-periodic, long-periodic, secular and continuous variations, caused by orbital perturbations. It is possible to remove these effects and thus to transform from osculating to mean elements by making use of the so-called Eckstein-Ustinov theory (Spiridonova et al, 2014) and numerical averaging. However, especially for near-circular orbits, it is not possible to transform from osculating to mean elements by averaging only.

With such a tool, it is possible to take a closer look at the behavior of the mean eccentricity and mean argument of pericenter for a satellite actually flying in a frozen orbit. In Figure 1, the evolution of these elements has been plotted for ERS-2 throughout 2003, showing nearly static behavior close to the original design values. This serves as verification for reconstruction methods.

OPTIMIZATION TO FIND FROZEN CONDITIONS With the mean elements available, and with the goal to minimize variations in two of these components, it is possible to ap-

proach this goal as an optimization problem.

This can be done by numerically integrating the trajectories resulting from a variety of injection positions and velocities, and evaluating the variations in the mean argument of pericenter and the mean eccentricity for these predicted trajectories. The resulting approach can be verified for the case of using simple zonal gravity field models, as for these models the numerical method can be compared to analytical solutions. The found frozen mean eccentricities are a match to within 0.1%.

When looking for the frozen eccentricity in realistic force models, e.g. taking into account drag, radiation pressure, third-body gravity and a gravity field model complete up to the 25th degree, it follows that the frozen conditions do not significantly change when compared to the case of a simple zonal model complete up to degree 10 (J10).

Therefore, the analytical solution ‘does the job’ just as well.

The influence of non-zonal perturbations can be determined by numerically integrating the found frozen orbit by including various perturbations, as shown in Figure 2.

From this figure, it becomes apparent that radiation pressure is the most influential perturbation, next to the inclusion of tesseral and sectorial gravity field terms. ERS-2 is not affected by radiation pressure as much (Figure 1), as it is placed in a Sun-synchronous orbit.

LOOKING BACK & LOOKING AHEAD The combination of numerical integration, optimization, and transformation from osculating to mean elements has led to an alternative design method for frozen orbits. Whilst being quite computationally expensive and performing just as well as simpler analytical models, there is potential in the chosen approach. The objective function used to minimize variations in the mean argument of pericenter and mean eccentricity can be adapted to minimize variations in other orbital elements, or optimize for a certain variation, for example a Sun-synchronous orbit.

If you have further ideas or want to contribute to this research as a graduate student, contact the author for further information by email at: jhoogland1@gmail.com References [1] E. Cutting, J.C. Frautnick, and G.H. Born.

Orbit analysis for Seasat-A. Journal of the Astronautical Sciences, 26:315–342, 1978.

[2] S. Spiridonova, M. Kirschner, and U. Hugentobler. Precise mean orbital elements determination for LEO monitoring and maintenance. ISSFD, 2014.

[3] V.A. Chobotov. Orbital Mechanics 3rd Edition. AIAA Education, 2002.

[4] M. Capderou. Satellites – Orbits and missions. Springer-Verlag, 2003.

[5] K.F. Wakker. Astrodynamics-II Lecture Notes. Delft University of Technology, 2011.

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LOFTHOUSE

INTERNSHIP

ONE OF A KIND Discovering and improving the BAC Mono Tom Schouten, Student Aerospace Engineering, TU Delft In October 2015 I started my six month internship at Briggs Automotive Company (BAC) in Liverpool. BAC was founded in 2009 by the brothers Neil and Ian Briggs and is the manufacturer of the BAC Mono, a single seater road legal sports car, inspired to bring the Formula 1 experience to the road.

Pablo is a Spanish TU Delft master student in the Spaceflight track and we were working at BAC simultaneously. The small company and limited number of people in engineering meant the focus was mostly on incremental upgrades of the Mono instead of research

SCHOUTEN

T

he Mono is lightweight, under 600kg, due to the tubular space frame chassis and carbon composite body panels.

The sequential Hewland gearbox, directly derived from Formula 3, is a structural component, bearing all rear suspension loads.

The 2,5L four cylinder Mountune engine delivers over 300bhp, making the Mono both quick (0-60mph in 2,8s) and fast (top speed of 170mph). This all combined with the central seating location and low center of gravity makes for a unique experience. This experience is further brought to the customers by delivering fully bespoke liveries and a seat and steering wheel molded to the driver’s posture, ensuring each Mono is ‘one of a kind’.

and development: evolution versus revolution. Being part of a small engineering team meant my responsibilities went beyond the technical aspect of things. I was expected to design prototypes, contact suppliers and test my proposed solutions. Personally I enjoyed this side of my work as much as the technical design for Mono. It was very satisfying to be involved in and responsible for a project from conceptual design to implementation.

ENGINEERING INTERN My role at BAC was as a junior design engineer. The description stated in my contract was very open: to be involved in future model year options meaning my work at BAC was varied. This was one of the main reasons to choose BAC as an internship location. The size of the company was another reason from the start of my internship I was treated as an integral member of the team of 25 people.

Of these 25, only four were working fulltime in engineering, including Pablo and myself.

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Mono assembly in progress at BAC headquarters, Liverpool.

SCHOUTEN

Detail of Liverpool Maritime Mercantile City, UNESCO world heritage.

DISCOVERING MONO BAC upgraded the Mono to include a 2.5L engine shortly before my internship commenced. The change from 2.3L to 2.5L involved more than a simple engine swap as multiple subsystems had to be revised as well. Most of the revisions had been implemented, however, there were still some unfinished projects. In my first week I worked on a return spring system for the throttle cable.

The 2.5L featured a drive-by-wire system instead of the mechanical system used on 2.3L Mono. The result was an unsatisfactory throttle pedal feedback due to the absence of mechanical friction, which was resolved by designing the spring back system. This small assignment made me familiar with the CAD software used at BAC and the process of design and implementation mentioned before.

During the subsequent weeks I was mostly occupied with updating the 'Bills-of-Materials' (BOM) for the 2.5L Mono. This list includes every single part on the Mono, from bodywork panels to single bolts and nuts.

Updating this list to reflect the current builds provided me with in-depth knowledge of the composition and assembly of the car, which proved to be very useful during the remainder of the internship. The BOM updates familiarized me with automotive terminology and the interaction of components on a high-end sports car. The end result, an actual list of parts for Mono, is not only used by engineering but is also used by purchasing and manufacturing and will aid the company in transitioning to an online product lifecycle management system. This system is intended to be implemented this year and will allow BAC to continue growing as a sustainable business.

IMPROVING MONO During the second half of the internship, my focus was on the support of the 2017 mod-

el Mono, planned to be presented in July 2016. The main update for the 2017 model is a modified chassis which provides more space for the driver. Updating the chassis is not as straight-forward as it seems, as most systems present on the car are directly connected or related to the chassis geometry in one way or another. The wide chassis was the main engineering development project during my time at BAC and it showed me the impact such a project has on all levels of a business. It also showed me what a small company can achieve when the employees are motivated, capable and willing to go the extra mile.

Parallel to the work on the BOM and product design for the 2017 model, was the support for manufacturing of the Mono at BAC. The Mono is a low volume sports car with a total of fifty complete builds as of February 2016.

The low volume production combined with the customizability of Mono meant that every car faces its own issues from time to time. During my time in Liverpool I have experienced inconsistency in quality from suppliers, unavailability of off-the-shelf components and unreleased part revisions. Each of these issues required the input from engineering in one way or another.

An example was related to the BAC bespoke exhaust system. The exhaust manifold was touching a chassis tube for a newly manufactured exhaust set. In order to keep up with the manufacturing schedule I visited the supplier to discuss possible solutions to prevent future production inconsistencies. In the end I designed a steel jig for the supplier to ensure the clearance between chassis and exhaust. Other issues arose from the availability of off-the-shelf components. As the Mono was designed several years ago, some components will be harder to come by as time progresses. Replacement parts are not always identical in dimension or quality

and thus require engineering to assess replacement solutions. Contacting suppliers for information, investigating and proposing solutions and then implementing these solutions was a nice change of pace compared to some of my larger assignments and it taught me to be concise, clear and correct in my way of working.

LIFE IN THE UK The city of Liverpool surprised me in a positive way. Admittedly, apart from the history in music and the professional football teams, I was unfamiliar with the city beforehand. Liverpool and its residents were as welcoming and the Liverpool city center is always alive and vibrant. During daytime the people like to enjoy themselves in one of many pubs, usually accompanied by live football and music. At night the public shifts to clubs and outdoor bars (yes, even in winter) to party until the sun rises. The area where Pablo and I lived, next to Penny Lane, was populated with plenty of takeaway restaurants and pubs, making it a lively area to be. Going out for food or having an indoor karting session with the BAC team were nice breaks from the workweek that encouraged and motivated me to give my best.

In conclusion, I am very satisfied with my internship experience in Liverpool at BAC. The company is welcoming and the small team means you are immediately seen as a full member of the team. My responsibilities and assignments were varied which made for a satisfying work experience. The approachability of colleagues and their enthusiasm regarding everything on wheels was also a pleasant introduction to the automotive industry. Discovering Liverpool with friends, family and colleagues left me with some great memories. I am definitely planning on revisiting this wonderful city in the future again.

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DENIES

SPACE ENGINEERING

REGENERATIVE COOLING USING METHANE Analysis of oxygen/methane rocket engines Ir. Luka Denies, MSc Graduate Aerospace Engineering, TU Delft Methane is a promising propellant for future launch vehicles. In the cooling channels of a regenerative cooled engine, it would be close to its critical point.

This results in drastic changes in the fluid properties, which makes cooling analysis a challenge.

M

ost liquid rocket engines that have flown until recently burnt a hypergolic propellant combination of oxygen/kerosene or oxygen/hydrogen. Over the past years, several groups have initiated development programs to demonstrate the capabilities of methane-fueled engines. Additionally, both Blue Origin and SpaceX have announced that they are developing large oxygen/methane first-stage engines for orbital launch vehicles.

Methane has properties in-between kerosene and hydrogen. Oxygen/methane engines can achieve slightly higher specific impulse values than oxygen/kerosene, though still substantially below oxygen/hydrogen.

While operating, rocket engines become very hot. The most commonly used cooling method in large liquid rocket engines is regenerative cooling. Here, one of the propellants used in the rocket engine (usually the fuel) is pumped through channels around the combustion chamber (see the diagram in Figure 1). As the fuel absorbs heat, its enthalpy increases, which improves the DENIES

The use of hypergolic propellants for launcher engines is usually eschewed in the West

because of their toxicity, which imposes handling constraints. Using liquid hydrogen leads to similar restrictions because of its low boiling temperature, but oxygen/hydrogen engines can reach very high specific impulse. Oxygen/kerosene, on the other hand, leads to lower specific impulse but is easier to handle.

Methane's boiling temperature of 111K is higher than hydrogen, but still remains cryogenic. This temperature is similar to the boiling temperature of oxygen, which reduces the need for insulation between the tanks. In addition, it can offer benefits over kerosene for reusable engines because it does not result in soot depositions. This has the potential to reduce refurbishment costs.

Figure 1 - Diagram of a regeneratively cooled rocket engine. Propellant is used to cool the chamber wall before being injected into the combustion chamber.

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DENIES

turbulence models were investigated during the validation. It was found that the choice of turbulence model had a limited influence on the results. The successful validation of OpenFOAM with the custom library for varying properties means it can be applied for rocket engine design.

ENGINE CHAMBER MATERIALS Traditionally, the launcher industry uses copper alloys to construct regenerative cooled combustion chambers. They offer a high allowable temperature and high thermal conductivity, but are also heavy and expensive.

Recently, several companies have used aluminum combustion chambers. Aluminum alloys have weight and cost advantages, but have lower allowable temperature and thermal conductivity.

Figure 2 - Phase diagram of methane, showing the vapor curve (continuous line) and the critical pressure (dotted line). performance of the engine. Since the heat transferred to the coolant is recovered, this technique is called regenerative cooling. To design methane-fueled rocket engines, it is important to analyze the cooling properties of methane.

SUPERCRITICAL FLUIDS Figure 2 shows the phase diagram of methane. At low pressure, there is a clear distinction between the liquid and gaseous phases, at the vapor line. Fluids at supercritical pressures (above the dashed line) are characterized by the absence of a vapor curve; there no longer exists a phase change between liquid and gas. Instead, the fluid gradually changes from fluid-like at low temperatures to gas-like at high temperatures. This results in strong variations of the fluid properties near the critical point, necessitating the use of highly detailed property models if one wants to analyze supercritical fluids.

The critical point of methane occurs at a temperature of 191K and a pressure of 46bar. In rocket engines with a low to moderate combustion chamber pressure, the methane coolant would be close to the critical pressure. Inside the cooling channels, it would also cross the critical temperature.

This means that the fluid property variations are important to take into account, making the regenerative cooling analysis of oxygen/ methane rocket engines challenging.

COMPUTATIONAL FLUID DYNAMICS Because of the complex behavior of methane around the critical pressure, empirical relations to calculate the heat transfer are inaccurate. Therefore, computation fluid dynamics (CFD) was used to analyze the cooling effect of methane inside the rocket engine's cooling channels. The open-source CFD package OpenFOAM was chosen because it is freely available and can be easily

adapted (provided one is willing to dive into the code).

To analyze supercritical methane, it was required to model the drastic property variations. A custom OpenFOAM library was written that reads two-dimensional property tables and interpolates them at runtime. The property tables were generated using a Python script that calculated density, enthalpy, viscosity and thermal conductivity for a set of pressure and temperature points. This custom solution allows for the fast calculation of fluid properties (through interpolation), while still providing high accuracy results.

VALIDATION The use of OpenFOAM with the developed library was then validated by comparison to the experimental data obtained by the Italian Aerospace Research Center (CIRA). CIRA is interested in developing an oxygen/methane rocket engine. To validate their own CFD tools, they conducted an experimental campaign [1]. They performed tests pumping supercritical methane through a rectangular channel.

The test article consisted of a copper block with electrical heaters at the bottom. At the top of the block, there was a single rectangular channel, representing a cooling channel. Inside the copper block, thermocouples were embedded while the mass flow; pressure and temperature of the methane coolant were measured at the inlet and outlet.

This way, the cooling properties of supercritical methane could be measured.

Through cooperation with CIRA, the experimental data obtained was used to validate OpenFOAMâ&#x20AC;&#x2122;s results for the supercritical methane analysis. An accuracy of 15K for the wall temperature prediction was demonstrated. The pressure drop inside the channel was predicted to be within 10%. Different

The developed tool for cooling analysis was therefore employed to compare aluminum and copper for a generic 10kN combustion chamber. It was discovered that a thermal barrier coating must be employed to protect the hot gas side of an aluminum combustion chamber; otherwise regenerative cooling is not feasible. A thermal barrier coating could consist of for example, a layer of aluminum oxide, which is obtained through anodizing the chamber. Even with such a coating, the pressure drop required to cool the coated aluminum chamber is three times higher than that of a copper chamber.

A difference in pressure drop has effects on the vehicle level. A larger pressure drop in the cooling channel of a rocket engine necessitates a higher feed pressure. For a pressure-fed engine, this means the tank must be stronger and heavier. It is found that even at modest fuel mass, the increase in tank mass is eight times as large as the decrease in engine mass offered by aluminum. This shows that using aluminum for the chamber wall is not advantageous with respect to copper for a pressure-fed, regenerative-cooled, oxygen/methane rocket engine.

In summary, the research has shown that it is possible to model supercritical methane using open-source CFD software. The developed library to cope with strongly varying fluid properties was validated using experimental data obtained by CIRA. Regenerative cooling analysis of a 10kN oxygen/methane rocket engine then showed that using aluminum instead of copper as wall material would lead to excessive pressure drops, causing a mass increase on the vehicle level.

References [1] R. Votta, F. Battista, A. Gianvito, A. Smoraldi, V. Salvatore, M. Pizzarelli, G. Leccese, F. Nasuti, S. Shark, R. Feddema, and S. Meyer, Experimental Investigation of Methane in Transcritical Conditions, 50th AIAA/ ASME/SAE/ASEE Joint Propulsion Conference (Cleveland, 2014), AIAA 2014-4005, doi:10.2514/6.2014-4005.

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TIME FLIES

SUPERSONIC COMMERCIAL TRAVEL The past, the present and the future Raphael Klein, Editor Leonardo Times, Aerospace Engineer Graduate.

The Concorde is a widely recognized plane, perhaps even more than the Boeing 747. To this day, it remains the only supersonic plane that operated commercial flights, despite a disastrous attempt from Tupolev to imitate the Anglo-French plane. Since its last flight in 2003, no commercial passenger has flown past the speed of sound. This could all be changing in the coming years as more and more private companies are investing in supersonic private jets, along with NASA’s recent announcement. years later, in 1975, it completed the entirety of the trials it was designed for. By then, the Aerospatiale and the British Aerospace Cor-

The engineers that designed the Concorde had to deal with a lot of challenges, the most prominent being the drag and the temperature. These challenges, specifically the drag issue, had been in the minds of ULLRICH

G

one are the days where any passenger could travel from Paris or London to New York in a little over three hours. These days, any traveler will have to take anywhere between five and a half and over nine hours. Whether you blame it on FAA noise regulations or the economy, the final outcome remains that no non-military aircraft has gone past the sound barrier since the Concorde’s last trans-Atlantic flight on October 24, 2003, which landed in London Heathrow.

poration (BAC), had already started producing the airliners that would take passengers across the Atlantic daily, to hundreds of other destinations around the world. The first commercial flight was in 1976.

CONCORDE: SUPERSONIC LEGEND It is five years after an agreement between the British and French governments that F-WTSS, the first pre-production Concorde, was finally rolled out of its factory. Two years after its rollout, the aircraft performed its first flight. Six months later, it flew for the first time past the speed of sound and another four 38

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Concorde and its Russian counterpart, the TU-144, at Sinsheim museum in Germany.

NASA

However, regardless of all the technologies the Concorde packed, it was never enough.

The Concorde’s main technical problem always remained its efficiency in air and noise pollution. Although the air pollution could have ultimately been solved by upgrades to

NASA

engineers since the 1950s. It was solved in part by Dietrich Küchemann, with the use of a slender delta wing. Furthermore, because the Concorde was to fly above Mach 2.0, the temperature the aircraft would experience would reach almost 130C, forbidding the use of common aluminum on the sharp leading edge of the aircraft or the nose. Certification requirements also lead to a compromise in design for the nose of the aircraft. As the pilot had to see the runway upon landing and take-off and since the aircraft was performing both of these tasks at high angles of attack, the nose was designed such that it could drop down. In this way, the pilot could take off and land the Concorde similar to any another aircraft. The third main problem was the engine and its inlet. The latter had to be designed such that the engines would be able to perform both at low subsonic and supersonic speeds in a reliable fashion. The engines selected for the aircraft were the now famous Rolls-Royce Olympus engines. For the inlet, a marvel of engineering was used with a design , which controls the location of the shock waves by the use of ramps, to appropriately slow down the flow at supersonic speeds and accelerate the flow at subsonic speeds.

QuietSpike boom test on a F-15. the engine, the problem of noise pollution was never solved and is the main reason why it is still not possible for commercial passengers to fly at supersonic speeds around the world today.

THE SONIC BOOM AND FAA RULES When an aircraft flies above the speed of sound, it will create a so-called sonic boom.

The merging of several different shock waves around the aircraft creates the latter.

The further one is from the sonic boom, the lower the sound becomes. However, even though the sound attenuates, on the ground two main disturbances often remain forming the characteristic N-wave boom signature.

This sonic boom is highly disruptive for local inhabitants - who has not heard about sonic boom created by fighters scrambled to intercept some Russian patrol mission above the North Sea? It can also lead to damages when the aircraft is flying too low. One of the examples is the Brazilian air force inaugurating the Brazilian supreme court with a low fly-over, shattering all the windows of the newly built court. Considering that low flying supersonic aircraft are rare, it is due to the noise that the FAA banned any supersonic flight over the continental United States. This was best demonstrated by the Concorde flight linking Paris to Caracas. On the way to Venezuela, the Concorde had to reduce its speed below Mach 1.0 as it flew over Florida LEONARDO TIMES N°2 2016

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AERION

before accelerating back to normal supersonic cruise speed above the Gulf of Mexico and the Caribbean.

The FAA ruling was a major hit for the Concorde’s economic prospects and potential clients. It was also seen as a windfall for the Europeans’ main opponent: Boeing, which had failed to develop a similar aircraft. Most American airlines would have wanted to connect the east coast to the west coast at supersonic speeds. This was not possible anymore. Moreover, a lot of countries followed by default the FAA ruling for their sovereign airspace. This meant that the Concorde was not allowed to fly over many parts of the world, effectively reducing its flight possibilities to trans-Atlantic flights. This was the main failure of the Concorde program.

Aerion supersonic private jet concept.

Another path can be taken to finance the construction of a supersonic plane: via the rich and wealthy of this world. Over the past decade, small private companies have emerged as the only players willing to look at supersonic flights. Their aim: To provide millionaires and billionaires with a private jet that can fly past the speed of sound. Several projects are meant to deliver this promise: the Aerion and the Spike S-512 are the two most famous. The Aerion is shaped following the area rule with a slender fuselage ending abruptly where the wing and the engine are mounted before leaving space for an elongated T-tail.

NASA AND COMMERCIAL AIRLINERS NASA never really gave up on supersonic commercial airliners. In the past, it has been funding different projects to try to deal with the sonic boom. It funded the modification and testing of an F-5, configured specifically to reduce the sonic boom. It also tested the QuietSpikeTM. This device is a spike that extends at the front of an aircraft to displace 40

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Boeing supersonic airliner concept.

LOCKHEED

The supersonic dream never faded in anyone’s mind. It is still the vision of most frequent flyers to be able to travel from London to Auckland in under six hours. This vision has become recurrent over the years. In 2011, at the start of the Salon du Bourget, Airbus Group (EADS at the time) introduced the Zero Emission Hypersonic Transportation (ZEHST), which was hailed as the successor of the Concorde. It was penned as the Concorde’s replacement. It would fly faster - Mach 4, higher - 100,000 feet - and with a lower ecological footprint. It was to fly from London to Tokyo in under two hours. The ZEHST was to be powered successively by turbofans, rocket engines and scramjet technologies. This is analogous to the Skylon project where all these three engines are combined in one. Since being unveiled in 2011, ZEHST has not been mentioned again and the Airbus Group seems to have turned to electrical planes instead.

BOEING

THE FUTURE

Lockheed Martin N+2 supersonic concept. and reduce the intensity of the shock wave.

It was designed by Gulfstream and tested on a modified F-15. So far, these attempts have been fruitless and nothing has come from them.

In more recent news, NASA has revealed the design of a new supersonic commercial aircraft that is meant to take the air in the late 2020s and transport about 100 passengers.

NASA has awarded a $20 million contract to Lockheed Martin to build and test the demonstrator aircraft. It would have its sonic boom reduced from the whooping 105dB of the Concorde to a more reasonable 75dB at cruise altitude. This would potentially allow the fly-over of continental inhabited areas.

The demonstration is initially meant to be for only a single pilot. It would fly at a speed of Mach-1.4 by 2020 when the flight tests are meant to begin.

CONCLUSION The supersonic dream is still alive and will continue to be as long as people fly. With the Concorde in mind, a lot of companies and governmental agencies are now starting to invest heavily in research and testing around the problem of sonic boom. Sooner or later, researchers will crack this sonic boom problem.

This should once more revolutionize the air transportation industry and could help bring us back to the golden days of aviation.

References Conway, Erik. High-Speed Dreams: NASA and the Technopolitics of Supersonic Transportation, 1945–1999. JHU Press, 2005. nasa.gov/ lockheedmartin.com aerionsupersonic.com/ faa.gov/ cnn.com/ guardian.co.uk/

EPFL/HELDENS

SPACE ENGINEERING

IONIC LIQUID ION SOURCE PROPULSION High potential micro propulsion technology or an endless research line?

Jules Heldens, MSc Graduate Aerospace Engineering, TU Delft There is a need for miniaturized space propulsion technology to increase the capabilities of nanosatellites, for example to enable formation flying. Ionic Liquid Ion Source (ILIS) based micro-propulsion is one of the technologies developed for this purpose. However, none of these technologies have yet found widespread application. This article presents the workings, current state of development and future outlook of ILIS based propulsion.

Micro-propulsion technology has been a topic of investigation from the advent of small satellite technology. However, the first flight proven system fit for nanosatellites was only demonstrated in 2014 by the formation flying CANX4&5 mission (UTIAS-SFL, 20014). As such, the development of micro-propulsion is somewhat behind. This is due- at least in part- to the complicated nature of the technologies considered.

Important requirements for such micro-propulsion systems are low mass, small form factor, and low power consumption. Although thrust and specific impulse (Isp)

requirements are wholly dependent on mission specifications, higher Isp is always desirable as it reduces the required amount of propellant needed.

IONIC LIQUID ION SOURCES AND PROPULSION An Ionic Liquid Ion Sources (ILIS) is a MicroElectroMechanical Systems (MEMS) device that is able to produce a high velocity ion beam from an ionic liquid, by means of electrospray ionization. Ionic liquids consist

Thrusters based on ILIS technology are characterized by a mass on the order of 100g, size on the order of tenths of a CubeSat unit, a power requirement on the order of 1W depending on its configuration, thrust levels on the order of nano- to micro-Newtons and an Isp in the range of 1000-3000s (Courtney, 2011)(Vitug, 2014).

Ions are extracted from the ionic liquid by a process called ‘electrospray ionization’, HELDENS

ABOUT MICRO-PROPULSION Over the past one and a half decades, the general trend of the miniaturization of satellite subsystems has led to many flight proven and commercially available parts and subsystems for application in nanosatellites.

Such systems include onboard data handling, power control units, guidance, navigation and control etc.

almost exclusively of positive and negative ions. Due to equal presence of positive and negative ions the liquids are neutral on a macroscopic scale. The ion beam emanating from an ILIS device exerts a tiny force on the device which, in space, can be used for propulsion.

Figure 1 - Schematic representation of Taylor cone formation and electrospray ionization.

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as visualized schematically in Figure 1. An electric potential, in the order of kilovolts, is applied to the structure containing the ionic liquid. A separate emitter electrode, placed above it is grounded as seen in Figure 1a and 1b. The electric traction exerted by the electric field on the ions in the liquid deforms the liquid meniscus into a conical shape called a Taylor cone, Figure 1c. Depending on the balance between the liquid’s internal pressure, the surface tension, and the electric force, either droplets (Figure 1d) or pure ions (Figure 1e) can be liberated from the ionic liquid meniscus. These operational regimes are termed the ‘droplet regime’ and the ‘Pure Ionic Regime’ (PIR). In practice, there is no sharp boundary between these regimes. In fact, both droplets and free ions can occur simultaneously in a so-called ‘mixed regime’.

The liberated charged droplets and/or pure ions can subsequently be accelerated by the same field that freed them from the liquid.

The accelerated particles leave the thruster via an opening in the emitter electrode.

By virtue of their relatively large charge to mass fraction, single ions can attain higher exit velocities than droplets, resulting in high Isp in the PIR. However, the PIR is difficult to achieve and in reality, it is a situation in which only a very low percentage of droplets are present in the emission. As the droplet content has a relatively large impact on the Isp that can be achieved, this has been an important topic of research.

particles (e.g. droplet or different ion species), here indicated by blocks of different colors. The particles pass through an Einzel lens, which focuses the inherently divergent beams of charged particles. Finally, an electrostatic gate is passed before the particles enter the flight tube- the space between the gate and the sensor. The latter is placed at the right side of the vacuum chamber. Inside the flight tube there are no electromagnetic fields that change the particle’s velocities.

After emission is established, the gate is closed and a timer is started. In this way, the arrival time of the particles in the flight tube, just behind the gate at the time of closure, can be measured. With this time and the known length of the flight tube, the speed of the particles can be calculated. Since each particle species has a speed corresponding to its particular charge to mass ratio, the particle species can be identified. With the knowledge of the species’ mass and speed, their impulse can be inferred. In turn, the ILIS device’s thrust and Isp can be calculated. In other fields, such as biology, this technology is used primarily for species identification. A particular advantage of ILIS devices in mass spectrometry is that ionic liquids themselves are useful solvents. Moreover, since ILIS devices operate in vacuum, there is less signal loss compared to non-vacuum ion sources since there is no need for vacuum stages in which a part of the ion beam is lost.

STATE OF DEVELOPMENT The trend of satellite system miniaturization, motivated by high launch costs, re-sparked

Compared to ion engines, electrospray propulsion systems perform better at low power levels. This is relevant as power, in e.g. CubeSats, is usually restricted to about 10W in total. At this time, research into colloid (droplet) and field emission (pure ions) regained momentum (Lozan, 2003). Since then, researchers at amongst others MIT and Yale in the U.S. as well as EPFL in corporation with ESA in Europe have demonstrated working thrusters in laboratory environments.

Although the governing conditions for PIR operation are known, the exact physics behind this mode are still not completely understood. It has been shown that PIR operation can be achieved under conditions of high liquid conductivity and surface tension (Garoz, 2007). Furthermore, high field concentration is needed in order to reach sufficiently high electric traction forces at manageable potentials over the electrodes. It was only shown last year that the internal liquid pressure, controlled by capillary back-pressure, can have a controlling influence on the operational regime (Courtney, 2015). Still, there are many questions to be answered. For example it is currently unknown if Taylor cones are formed and remain stable, or whether EPFL/HELDENS

Capillary forces are used to transport the ionic liquid from a reservoir to the emission site using roughened metal needles or porous emitter structures. These structures are designed in cone or slit configurations, such that concentrations of the electric field occur at the tips of the cones or slits. Emission will occur at locations where the field is strong enough, so that in the case of droplet emission, the surface tension will be broken, or in the case of pure ions, the strength will overcome the energy barrier associated to ion evaporation. This is done to control the location at which the emission occurs to some degree.

interest into electrospray propulsion in the 1990s. This technology was initially developed in the 1960s by, amongst others V.E. Krohn, but abandoned in favor of ion thrusters which then could deliver the desired performance but were less complex (Lozano, 2003).

An exploded view of an ILIS device based on porous materials is shown in Figure 2, featuring the porous reservoir and emitter disks, the emitter electrode, as well as a plastic jig and guard ring used to fix the assembly. The visual shows an assembled ILIS device.

Aside from propulsion, Ionic Liquid Ion Sources also find application in the field of mass spectrometry. Conversely (Time-ofFlight) mass spectrometry is an important diagnostic tool for ILIS research, as it can provide data on the type and amount of the particles that are emitted, as well as their speed. Figure 3 schematically shows an ILIS device serving as ion source in a Timeof-Flight mass spectrometry setup. On the left, the ILIS device is seen emitting different 42

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Figure 2 - Exploded view of an EPFL ILIS device.

LOZANO

Figure 3 - A schematic representation of a Time-of-Flight mass spectrometry setup. Adapted from (Lozano, 2003). they appear and disappear in a fluctuating fashion. Moreover, it is unknown when emission in the PIR exactly occurs- does it occur only after the Taylor cone is fully formed or somewhere during formation. Due to such unknown it is currently very difficult to make reliable predictions and simulations with respect to the performance of a thruster design.

Another subject of research is the circumstances that lead to electrochemical decomposition in ILIS based thrusters. As particles of one polarity are emitted, the particles of opposing polarity accumulate. Chiu et al.

(Chiu, 2007) have demonstrated that this can lead to large thrust decrease over time.

Although an effective mitigation method has been established, emission potential alternation (Lozano, 2004), the physical effects occurring during the thrust decrease in the thruster are not yet understood. The author’s master’s thesis project, conducted at EPFL in Switzerland, investigated the effect of propellant contamination, caused by electrochemical decay, on the ion beam emitted by an ILIS thruster.

Despite the many unknowns, effective ILIS thrusters are being designed and tested. In mid-2015, MIT’s Space Propulsion Laboratory, together with Aerospace Cooperation, launched the ILIS-propelled AeroCube 8, with which this technology saw its first deployment in space. Unfortunately, at this time, no information on the success of the mission is known to the author.

FUTURE OUTLOOK The question that remains is whether ILIS propulsion is the pacing propulsion technology that will become key to many missions in the future, or whether it is merely an endless research line. Considering the advanced state of development that this technology is currently in, as well as the continued efforts shown by U.S. institutes (MIT, NASA) and corporations (Accion, Busek), it seems likely that this technology could reach maturity.

However, it should be considered that other miniaturized propulsion concepts are being developed as well, e.g. the Cubesat Ambipolar Thruster (Sheehan, 2014), cold gas systems [Bodin, 2013] and resistojets (Busek, 2016) etc.

Ionic liquid Ion Source based micro-propulsion has taken large steps in the last few years. Although it will always remain uncertain, the future surely looks interesting in the field of space propulsion.

References [1] “CanX-4&5 Formation Flying Mission Accomplished”, http://utias-sfl.net, University of Toronto Institute for Aerospace Studies – Space Flight Laboratory, 2014 [2] Courtney, D.G., Lozano, P., “Ionic Liquid Ion Source Emitter Arrays Fabricated on Bulk Porous Substrates for Spacecraft Propulsion” PhD thesis, Massachusetts Institute of Technology, June 2011 [3]Vitug, E., ‘‘MIT SPL delivers the Scalable ion Electrospray Propulsion System (S-iEPS) for CubeSats to NASA’’,http://www.nasa.gov,

NASA, 2015 [4]Lozano, P., Martínez-Sánchez, M., “Studies on the Ion-Droplet Mixed Regime in Colloid Thrusters” PhD thesis, Massachusetts Institute of Technology, February 2003 [5]Garoz, D. et al., ‘‘Taylor cones of ionic liquids from capillary tubes as sources of pure ions: The role of surface tension and electrical conductivity’’, Journal of Applied Physics, 102, 2007 [6] Courtney, D.G., Shea, H., ‘‘Influences of porous reservoir Laplace pressure on emissions from passively fed ionic liquid electrospray sources’’, Applied Physics Letters, 107, 2015 [7] Chiu, Y.H., et al., ‘‘Vacuum electrospray ionization study of the ionic liquid, [Emim] [Im]’’, International Journal of Mass Spectrometry, 265, pp. 146-158, 2007 [8] Lozano, P., Martínez-Sánchez, M., “Ionic liquid ion sources: suppression of electrochemical reactions using voltage alternation”, Journal of Colloid and Interface Science, 280, pp.149-154, 2004 [9]Sheehan, J.P., et al., ‘‘New Low-Power Plasma Thruster for Nanosatellites’’, Joint Propulsion Conference, AIAA 2014-3914, Cleveland, July 2014 [10]Bodin, G., et al., ‘‘THE CANX-4&5 MISSION: ACHIEVING PRECISE FORMATION FLIGHT AT THE NANOSATELLITE SCALE’’, 64th International Astronautical Congress, Beijing, IAC-13-B4.7B.5, 2013.

[11] ‘‘Propulsion for CubeSats and NanoSats’’, http://www.busek.com/, Busek, 2016

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AIRBUS

AVIATION DEPARTMENT

CERTIFICATION OF THE AIRBUS A320 NEO An insight into the certification of the new generation of Airbus aircraft.

Bart Jacobson, Student Aerospace Engineering, President of the 23rd Aviation Department Airbus has reached a new milestone with the realisation of the new A320 NEO. After completing its 14-month flight test program, the A320 NEO, equipped with Pratt & Whitney’s Pure Power PW1100G-JM engines, was approved by both the European Aviation Safety Agency (EASA) and the U.S. Federal Aviation Administration (FAA). [1]

baggage and modern ambient LED interior lighting. The added bonus is that the new cabin also brings a reduction in weight. [3]

THE ORIGIN OF THE A320 NEO

Before a newly developed aircraft model may enter into operation, it must obtain a type certificate from the responsible aviation regulatory authority. To receive this type certificate, it is necessary to prove that the aircraft meets all the rules and requirements that are set by the aviation regulatory authority, for instance that it is safe enough and that it

emissions during take-off. The procedures to decrease noise levels during flight, such as navigation performance and continuous descent approaches, are also optimised.

Furthermore, the passenger cabin configuration will be improved, providing more shoulder-level room for passengers, ten percent greater stowage volume for overhead

AIRBUS

Airbus A320’s introduction in 1988 was quite some time ago, which is why Airbus started looking into a replacement for its bestselling airliner. To reduce costs, a decision was made to upgrade the current airframe instead of designing a whole new aircraft. In 2006, Airbus started its A320 Enhanced program after choosing to upgrade the A320 family. The A320 Enhanced program led to the A320 NEO (New Engine Option) program which was initiated in 2010. [2]

CHANGES IN THE AIRFRAME The A320 NEO program consists of some major changes to the airframe of the A320 CEO (Current Engine Option). The A320 NEO will receive two new, more fuel efficient engine choices, the CFM International’s LEAP-1A and the PurePower PW1100G-JM from Pratt & Whitney. Next to the new engine configuration, the A320 NEO will also feature new 2.4m high, 200kg Sharklet wingtips, which will increase lift and decrease drag.

This means that the aircraft can take off using less thrust from the engines, which in turn leads to reduced noise and environmental 44

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AIRCRAFT CERTIFICATION PROCESS

Figure 1 - Airbus A320 NEO bins.

AIRBUS

United Arab Emirates, one A320 NEO flighttest aircraft suffered minor damage which led to grounding of the aircraft for a few weeks. Earlier, a manufacturing defect was found in a 10-inch-diameter retaining ring in the power plant's combustor section. This resulted in a three months pause of flying that aircraft. [5]

THE FUTURE

Figure 2 - Pratt & Whitney PurePower PW1100G-JM. meets all of the environmental requirements.

In the European Union (and most of the rest of the Europe) this regulatory authority is the European Aviation Safety Agency (EASA). In the United States, this authority is the Federal Aviation Administration (FAA). The aircraft certification process is not just a sort of test at the end to see whether the final aircraft is air worthy; it is a very long process which starts at the beginning of the design stage and continues while the plane is in active service.

The certification processes of EASA and the FAA are not exactly the same, but they are quite similar. The process of EASA consists of four main steps and they will be explained herein [4]: Step 1, Technical Familiarisation and Certification Basis: After starting the design process, the aircraft manufacturer presents the project to EASA when it is considered to have reached a sufficient degree of maturity. EASA’s certification team and the set of rules that will apply for the certification of this specific aircraft type are being established (Certification Basis).

This is a first check to see what type of aircraft will be designed and thus which set of requirements it must meet throughout the design process.

Step 2, Establishment of the Certification Program: EASA and the manufacturer need to define and agree on the means to demonstrate compliance of the aircraft type with each requirement of the Certification Basis. Here, EASA and the manufacturer basically agree on the methods of testing and the types of experiments that will be held to prove that the aircraft will meet the final requirements, once finished. This goes hand in hand with the identification of EASA’s “level of involvement” during the certification process.

Step 3, Compliance demonstration: The aircraft manufacturer must demonstrate

compliance of their product with regulatory requirements: the structure, engines, control systems, electrical systems and flight performance are analyzed against the Certification Basis. So it is a check to see whether the aircraft meets the requirements that were agreed upon in Step 1. This compliance demonstration is not only done by analysis during the ground testing (such as tests on the structure to withstand bird strikes, fatigue tests and tests in simulators), but also by means of flight tests. EASA experts perform a detailed examination of this compliance demonstration, by means of document reviews and by attending some of these compliance demonstrations (test witnessing).

This is the longest phase of the type-certification process. In the case of large aircraft, the period to complete the compliance demonstration is set to five years and may be extended if necessary. In the case of the modifications made on the A320 to make the A320 NEO, this step took 14 months of flight tests alone [1].

Step 4, Technical closure and issue of approval: If EASA is technically satisfied with the compliance demonstration by the manufacturer, EASA closes the investigation and issues the certificate. Once this is done, the aircraft is allowed to fly in European airspace. EASA works closely together with foreign agencies by delivering the primary certification for European aircraft models which are also being validated in parallel by foreign authorities for operation in their airspaces, e.g. the FAA for the US or TCCA for Canada. Conversely, EASA will validate the FAA certification of US aircraft models (or TCCA certification of Canadian models) according to applicable Bilateral Aviation Safety Agreements between the EU and the concerned third country.

In the end, the certification went very smoothly and a rigorous program that tested its airframe and systems well beyond their design limits, ensured that the aircraft has successfully met all the airworthiness criteria. Starting September 2014, a total of three flight test aircraft, with the PW1100GJM engines accumulated more than 1,070 flight hours aloft, of which 300 hours were completed in an airline-like environment to ensure operational maturity at the time of entry into service.

The first NEO variant’s airworthiness approval will be followed by certification of the LEAP-1A-powered A320 NEO in the coming months, and then subsequently the A321neo and A319 NEO versions for each engine type.

With the certification of the A320 NEO, Airbus has made a large step towards the delivery of the A320 NEO. The A320 NEO has received firm orders from over 75 customers for more than 4,300 aircraft comprising versions with both engine types, a total which represents a 60 percent market share for the NEO Family. [1] References [1] http://www.airbus.com/newsevents/ news-events-single/detail/on-schedule-airbus-a320neo-with-pratt-whitney-enginesreceives-type-certification/ [2] http://www.airbus.com/aircraftfamilies/ passengeraircraft/a320family/ [3] http://www.airbus.com/aircraftfamilies/ passengeraircraft/a320family/spotlight-ona320neo/ [4] https://easa.europa.eu/easa-and-you/ aircraft-products/aircraft-certification [5] https://www.ainonline.com/aviation-news/air-transport/2015-10-01/ airbus-pratt-analyzing-latest-a320neo-engine-snag 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.

OBSTACLES IN THE CERTIFICATION PROCESS A320 NEO During the hot weather trials in Al Ain in the LEONARDO TIMES N°2 2016

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WVTF

ASM

THE ACOUSTICS OF CRACKS Continuous Damage Monitoring in Offshore Wind Turbine Towers Gerwin Lapoutre, MSc Student Aerospace Engineering, TU Delft The field of offshore wind energy is rapidly growing, yet the costs are high. In order to minimize dependence on subsidies, Structural Health Monitoring can be a powerful tool for maintenance decision making. This can be used to reduce operational and maintenance expenses, estimate the remaining lifetime, and improve future wind turbine designs.

In order to produce electricity, the structure should be in good condition. During the lifetime of a wind turbine, it can experience severe loading conditions. Loading comes from the wind, gusts, waves and rotation of the turbine, and the uncertainties are significant. The loading may lead to fatigue in several components, while the uncertainties often result in overly conservative designs.

Near the end of the design lifetime, one could gain a few years of electricity produc46

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tion, if the structure is still healthy. On the other hand, if the structure shows no signs of fatigue when it is dismantled, it might have been too heavy and thus expensive.

Common offshore wind turbines need to be

EWEA

T

he Dutch government envisions having 16% of energy production from renewable sources by 2023. Furthermore by 2050, they aim to become fully reliant on sustainable energy. Currently, the share of renewable energy is only 5%.

Achieving these ambitions requires a drastic change in energy production, in which wind turbines will play a pivotal role. In order to realize this, the cost of offshore wind energy has to be reduced by 40%. This cost reduction has to come from savings of the initial cost, as well as from savings in operations and maintenance.

attached to the seabed. Different foundation types are available to make this possible.

Most well-known are ‘Monopiles’ and ‘Jackets’ which are shown in Figure 1. Currently, monopile foundations are used in 74% of offshore wind turbines, while the jacket foundations are used only in 5% of the installations.

Both have their advantages and disadvantages. While the monopile type is easier to install, it is limited to water depths of up to 30 meters. The jacket foundation is generally lighter than the monopile, but is also more

Figure 1 - Two types of wind turbine tower foundation. The monopile type on the left, the jacket type on the right.

complex. The future expectation is that as wind turbines are placed in ever-deeper waters, the need for jacket foundations will increase their market share.

When a tree is breaking, a loud cracking sound can be heard. On a smaller scale, something similar happens in metals. As fatigue crack growth occurs, elastic energy is released. This elastic energy can travel through a structure in the form of an elastic wave. The velocity at which the elastic wave travels depends on the thickness of the plate, the frequency, and the wave mode.

The frequency of this elastic wave is typically in the ultrasonic domain (more than 20kHz) and ultrasonic sensors are used for its detection. Such sensors typically consist of a piezo-electric crystal that, when pressure is applied, creates a potential difference over the crystal. The potential difference (voltage) can be measured and recorded. These sensors are capable of detecting high frequency vibrations accurately. They always ‘listen’, but only record the received signal when it crosses a pre-determined threshold. An example of such a signal is shown in Figure 2.

Because the fatigue crack emits this Acoustic Emission (AE), its growth can be detected at an earlier stage compared to more conventional techniques.

As the signal travels through the structure, its strength, i.e. the amplitude measured by the sensor, decays. To determine the maximum distance at which a sensor could pick up a fatigue crack growth signal, modeling is performed. Aspects that affect this distance are the sensitivity of the sensor, the strength of the signal at the source, noise and geometry of the structure. This maximum distance is required to determine the coverage of a single node of sensors, and can therefore be used to determine the optimum sensor layout on an actual wind turbine.

Figure 2 - An example of a recorded signal.

From the data that is recorded by the sensors, the source location is determined. This is done using the Quasi Beamforming (QBF) method. This method requires four sensors which are located in close proximity at a distance of several tens of centimeters. The source location is calculated using the difference in arrival times, and the corresponding wave speed of the signal. The advantage of this method is that it is not affected by different wave speeds, and the source location is consequently calculated more accurately.

The system is being tested in the laboratory and the testing focuses on detection and localization. This is done at the Structural Dynamics lab of TNO in Delft. The sample that is being tested is a T-joint, similar to what is used in jacket foundations, of which the brace is loaded in tension. This loading results in fatigue crack formation in the joint.

Using an artificial source representing the fatigue crack sound, the localization capabilities were tested, as shown in Figure 3.

During these tests, an accuracy of 5% was obtained. The error here is defined as the distance between the estimated location and

the actual location, divided by the distance between the actual location and the center of the node. These tests show that AE monitoring can successfully locate fatigue crack growth.

APPLICATIONS Wind turbines are not the only field of application for AE monitoring. The technique has also been used in fatigue testing of aircraft, as well as in pressurized vessels and pipes.

Currently, a similar system is in operation on the ‘Van Brienenoordbrug’ (Pahlavan et Al., 2014). AE monitoring systems have the most benefits in situations where visual inspection is not possible or too expensive. It can also detect fatigue crack growth at an earlier stage than visual inspection.

CONCLUSION AE monitoring can be used to accurately detect and localize fatigue crack growth. This is important to precisely and accurately estimate the remaining lifetime of support structures in offshore energy production and to improve future designs. Once installed, this technique can provide continuous fatigue development monitoring with minimal effort, even at hard-to-reach locations. Although it requires some initial costs, no visual inspections or site visits are required to check for fatigue cracking. The most beneficial application of this technique is the monitoring of remote structures subject to severe cyclic loading, such as offshore wind turbines.

This MSc thesis project is under supervision of Dr. Kassapoglou (TU Delft) and Dr. Pahlavan (TNO). For further details on this project or when interested to work on this or similar subjects, please contact: c.kassapoglou@tudelft.nl or pooria.l.pahlavan@tno.nl References

Figure 3 - Result from localization plotted onto structure, with red rectangle showing actual source location.

[1] Pooria L. Pahlavan, Joep Paulissen, Richard Pijpers, Henk Hakkesteegt, Rob Jansen, “Acoustic Emission Health Monitoring of Steel Bridges”, Proceedings of the 7th European Workshop on Structural Health Monitoring, pp. 1163-1170, 2014 LEONARDO TIMES N°2 2016

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HINTERWORTH

AERODYNAMICS

FLY LIKE AN INSECT Bio-inspired inertial sensing by flapping wings Thomas Mohren, MSc Aerospace Engineering, TU Delft Insects have incredible flying capabilities, which exceed by far anything manmade in terms of economy, size, maneuverability and sensory capacity. Recent findings have shown that the insect wing serves a sensory function in controlling flight (Dickerson, 2014). A robotic model of a simplified insect wing shows that inertial rotations can indeed be detected with wing mounted strain gauges, encoding a wing twist uniquely present during body rotations.

INERTIAL SENSING IN INSECTS There are over 1 million species of flying insects, compared to roughly ten thousand species of birds and bats. Given their astounding flight capabilities, their abundance and the impact they have on humans (pollination, carrying disease, etc.), we know remarkably little about how insects fly.

with information from the visual system. Flying insects have enormous eyes and a large part of their brain is devoted to interpreting visual information. However, vision is inherently slow (Land, 1974), too slow to explain the rapid flight corrections observed in free flight.

Insects of the order of true flies (Diptera) have developed specialized hammer-like organs

However, many questions regarding insect flight remain unanswered. Insect flight is inherently unstable, and the thorax is equipped with steering muscles that change the wing kinematics constantly. The longstanding belief was that flight corrections were made 48

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Evolution suggests that if the halteres derived from wings also serve a sensory function, the antecedent wing must have had a sensory function as well. Wings and halteres are covered with biological strain gauges with remarkably similar properties and high HINTERWORTH

A major breakthrough in understanding insect flight was the discovery of the leading edge vortex (Ellington, 1996), which allowed insects to achieve lift coefficients much higher than what was deemed possible at the time. Since then, experiments on robotic wings combined with Particle Imaging Velocimetry (PIV) have unveiled numerous aerodynamic mechanisms involved in flapping flight at low Reynolds numbers. It turns out that depending on scale, aerodynamic forces can be much smaller than the inertial-elastic forces arising from flapping wings (Combes, 2003).

to detect Coriolis forces resulting from inertial rotations (Dickinson, 1999). These halteres (Figure 1) beat at wing-beat frequency and are evolutionarily derived from wings. Halteres have been shown crucial for flight, and the question arises how other flying insects such as moths gather information about their inertial rotations.

Figure 1 - The haltere of a fly.

timing precision. In experiments, moths exhibit stabilizing abdomen reflexes to mechanical wing perturbations during flapping flight (Dickerson, 2014), providing the first behavioral evidence of the wing as both an actuator and an inertial sensor. Early experimental and computational work proposed wing twist as the mechanism for detecting inertial rotations (Eberle, 2015).

METHOD The thesis work focused on understanding the mechanism involved in detecting gyroscopic forces. This was done by experimentally and computationally modeling a flat plate with a size and flexural stiffness similar

The flapping wing mechanism and the data acquisition systems were controlled by two micro Arduinos, both driven by small batteries. Two strain gauges at the wing were sampled at ~1 kHz and the measurements were logged on an SD card. This device was then mounted in a rigid frame and driven to rotate at 6π radians per second.

As these gauges were positioned symmetrically about the longitudinal axis, they capture exactly the same strain in case of a symmetric wing bending. If a difference in strain was measured between the gauges, this would indicate the presence of a torsional deformation mode resulting in a wing twist about the longitudinal axis. By analyzing the difference between the two strain gauges in the frequency domain, the effect of inertial rotations on the periodic wing deformation was determined. .

RESULTS In the simulation results a torsional mode was observed in case of inertial rotations where the magnitude of strain due to wing twist depended linearly on the rotation rate.

This wing torsion resulted in exceedingly small wing strain (less than 1%) compared to the bending. Constant inertial rotations resulted in wing twist at the flapping frequency and at the first harmonic.

Wing twist turned out to be very difficult to detect in the experimental set-up. Similar to the computational simulations, the strain resulting from wing twist was less than 1% of the strain due to wing bending. By averaging multiple measurements, small but significant strain differences between the left and the right side of the wing base were found. Although certainly not as distinct as the results from simulation, the experiments confirmed the presence of wing twist resulting from inertial rotations.

to that of a hawk moth wing. The mechanical flapping flat plate was equipped with strain gauges at the left and at the right side of the wing base to capture the wing deformation.

Similarly, a structural finite element simulation had strain probes at both sides of the wing base. The flat plate was flapped with a fifteen degree amplitude at ten hertz frequency, whilst undergoing rotations about an axis orthogonal to the flapping axis. This resulted in a Coriolis force which consequently excited an additional wing deformation.

The experimental set-up (Figure 2) was constructed to allow for constant inertial rotations of the flapping wing device. This ensured that the measurements were not influenced by the initial accelerations and it allowed for a longer time sample for analysis.

CONCLUSIONS & DISCUSSION By using computational and experimental models, wing twist was confirmed as a potential mechanism for detecting inertial rotations in flapping wings. Flat plates of sizes EBERLE

Figure 2 - The experimental set-up; Two strain gauges are mounted on a flapping wing, whilst being rotated at a constant angular velocity.

Figure 3 - Wing twist after main bending signal is subtracted.

comparable to a hawk moth wing showed a torsional mode that was detectable by a pair of strain gauges at the base of the wing.

The strain due to wing twist turned out to be less than one percent of the wing strain from bending, making it exceedingly hard to detect.

Although the wing shape of insects such as moths is much more complicated and since twist is present in all phases of the wing stroke, the fact that only two strain gauges proved sufficient for detecting wing twist in these models is remarkable. The fact that the effects of inertial rotations are exceedingly hard to detect can explain why insects have so many sensors on their wings. Moths have over two hundred strain gauges on either wing, a number very similar to the amount of strain gauges found at the base of the haltere. This is a large number, especially considering the evolutionary cost of maintaining such an extensive sensory network. A hypothesis that can explain the large amount of sensors would provide the potential for such an array to increase accuracy and to reject noise. Learning more on how strain information is encoded and compressed in the nervous system will be crucial in our understanding of insect flight.

Last year I had the good fortune to spend a year in the Daniel lab at the University of Washington in Seattle to do my thesis research. This work was made possible by the Fulbright program and AFOSR. For more information: Thomas Mohren, tlmohren@gmail.com References [1] Combes, S. A., & Daniel, T. L. (2003). Into thin air: contributions of aerodynamic and inertial-elastic forces to wing bending in the hawkmoth Manduca sexta. Journal of Experimental Biology, 206(17), 2999-3006.

[2] Dickerson, B. H., Aldworth, Z. N., & Daniel, T. L. (2014). Control of moth flight posture is mediated by wing mechanosensory feedback. The Journal of experimental biology, 217(13), 2301-2308.

[3] Dickinson, M. H. (1999). Haltere–mediated equilibrium reflexes of the fruit fly, drosophila melanogaster. Philosophical Transactions of the Royal Society of London B: Biological Sciences, 354(1385), 903-916.

[4] Eberle, A. L., Dickerson, B. H., Reinhall, P. G., & Daniel, T. L. (2015). A new twist on gyroscopic sensing: body rotations lead to torsion in flapping, flexing insect wings. Journal of The Royal Society Interface, 12(104), 20141088.

[5] Ellington, C. P., Van Den Berg, C., Willmott, A. P., & Thomas, A. L. (1996). Leading-edge vortices in insect flight.

[6] Land, M. F., & Collett, T. S. (1974). Chasing behaviour of houseflies (Fannia canicularis).

Journal of comparative physiology, 89(4), 331-357.

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STACK'S BOWERS GALLERIES

COLUMN

ENGINEERING PEACE Pax Technologica Sushant Gupta, Final Editor, www.leonardotimes.com Aerospace Engineering is unlike any other discipline of engineering or science; it is of utmost strategic importance. As an aerospace engineer and an enthusiastic flag bearer of scientific progress working towards technical advancements, what should one’s view be on the subject of technology used for “mala fide” objectives like war?

I

recently paid a visit to the Vredespaleis, or the Peace Palace, in The Hague. The Peace Palace houses the United Nations affiliated International Court of Justice amongst other institutions including a well-stocked library. While browsing through the books, Andrew Carnegie’s writings caught my eye.

Carnegie, an American steel magnate born in 1835, turned philanthropist later in his life and was a major sponsor of the building. In his writings, as an unabashed capitalist and a philanthropist, he advocated that science, education and peace are the most important conditions for progress. Persisting with this thought, one of the tangents could be whether the science and peace binary is true, false or non-existent.

well-meaning intent of the scientific community, the harsh reality is that war continues to take place in the modern world.

As the quote goes, “Those who cannot remember the past are condemned to repeat it”, a little indulgence in the historical perspective around war will do no harm in shaping the understanding of the issue. Since antiquity, outcomes of war have shaped civilizations. Armies have come a long way from the days of bows and arrows. As one moves from the ancient to the modern age, it is increasingly the balance of technology that has determined the victor. Despite the best efforts of the civil society and largely

Then what does an engineer think about when he/she embarks on development of a technology that may be ultimately used on the battlefield? For the sake of academic discussion, let me state two extreme positions one could possibly take: carry out one’s scientific work knowing fully well about the potential future “misuse” of technology, or simply abandon work on any strategic technology. Having said that, should the engineer even take a call on this issue? Is this not a political call? I would argue that the answer

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Science and Engineering have been sucked into becoming willing or unwilling partners in the conduct and conclusion of wars. The “ulterior” use of any pioneering technology is inevitable if one looks back at the history.

Prominent examples include drones, fly-bywire technology, stealth aircraft, missiles, weaponization of space and the dreaded nuclear warheads to be mounted upon airborne vehicles. Each of the technologies mentioned, much like other scientific and engineering milestones, can and have been used in warfare.

to this lies in a political/ethical mix and only the individual must be left to decide this.

Having stated the above, I believe that it is technology itself that is the answer to this dilemma. Progressively, innovative technologies will lead to a point, that the act of physical war itself would become meaningless for humanity to even consider waging war and incurring loss of life. How that plays out will remain to be seen but this has happened in the recent past in Europe. In the times of Cold War, there was no large scale escalation of troops in Europe due to a credible deterrence in the form of nuclear weapons technology combined with the understanding amongst politicians and people that Europe had seen two devastating wars fought one after the other. From the arithmetical point of view, for every misuse of technology, there are several beneficial uses. The engineer and the scientist should, with increased fervor, carry on with their pursuit of novel technologies. The society will eventually come to an understanding that the misuse will be impractical.

I rest my case by concluding that due to developments in science and engineering, human society would evolve into a peaceful era of Pax Technologica.

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