LT March 2013 by Anouk Scholtes

MARCH 2013

Leonardo Times Journal of the Society of Aerospace Engineering Students â&#x20AC;&#x2DC;Leonardo da Vinciâ&#x20AC;&#x2122;

page 24

Design Synthesis Exercise 2012

number 1

An overview of the Design Synthesis Exercise

Micro-Propulsion Research

Challenges towards future nano-satellite projects

The AHEAD Project

Advanced Hybrid Engines for Aircraft Development

Self-healing thermal barrier coatings Year 17

With application to gas turbine engines

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Global environmental concerns call for future innovative products. Currently, the aircraft industry is seriously considering to install Contra-Rotating-Open-Rotors (CROR) on mid-range 150-200 seater aircraft by the year 2020. Today, NLR (National Aerospace Laboratory) specialists work in close coรถperation with aircraft & engine manufactures to investigate noise, vibration and safety aspects of these novel aircraft concepts.

www.nlr.nl Advertentie_NLR.indd 1

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Contents

Editorial

From Leonardoâ&#x20AC;&#x2122;s desk

Current Affairs

Micro-Propulsion Reasearch

Design Synthesis Exercise 2012

An overview of the Design Synthesis Exercise

Internship Report - Engineering Excellence at Rolls-Royce

LVD - Military Flight Through Time

Modelling an Airline Operations

Cover articles

Table of contents

Micro-propulsion research

Control Centre 20

The AHEAD Project

Design Synthesis Exercise 2012

RVD - Pioneering the Red planet

Internship Report - Aircraft tooling and

Challenges towards future nano-satellite projects The Space Systems Engineering department is hard at work miniaturizing satellite subsystems to meet the growing demand for small satellites. One particular challenge is the field of propulsion for nano-satellites.

Student Project - Project Stratos

We vlogen met een zucht... Helicopter

automated equipment

The AHEAD Project

Industry - Early Beginnings to Now 44

Self-Healing Thermal Barrier Coatings

Advertisement index NLR

Faculty of Aerospace Engineering

Heerema

AkzoNobel

Dynaflow

Dutch Aviation Group

KLM

Fokker

The AHEAD project revolves around new engines to drive future aircraft development. This is essential, given the economic and environmental challenges that lie ahead in the field of aviation.

Advanced Hybrid Engines for Aircraft Development

Self-healing thermal barrier coatings

With application to gas turbine engines Thermal barrier coatings are widely used in turbines to increase energy efficiency through higher operating temperatures. These systems require regular replacing, illustrating both the need and opportunity for self-healing mechanisms.

MARCH 2013 Leonardo Times

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Editor’s letter Dear reader, The other day I was flipping through TV channels, when I was suddenly greeted by a moment of nostalgia. An animated sequence of a railway coach hurtling downhill, dramatic music playing in the background. I immediately recognised it: the intro to the animated series revolving around the character Kuifje. International readers will know this character as Tintin, so I will use the names and titles used in the English versions from here on out. As luck would have it, the episode in question was Explorers on the Moon. This episode follows Destination Moon in which Professor Calculus has developed a rocket in and for the fictional nation of Syldavia. The artist Hergé first published the comic book Destination Moon in 1950 and Explorers on the Moon followed in 1952, roughly a decade before any human ventured into space and two decades before Neil Armstrong set foot on the Moon.

surface. On the other hand, the rocket is a single-stage design, landing on the Moon in its entirety. The lunar rover it carries is more akin to a tank than the buggy-like rover used from Apollo 15 onwards. Then again, this might all be down to the novel propulsion system designed by Professor Calculus: it combines chemical propulsion for take-off with nuclear propulsion for highspeed travel and ‘artificial gravity’. It is a comic book after all, so some science fiction can be expected. Tintin also makes a startling discovery when he finds ice beneath the lunar surface. Recent evidence suggests that Hergé might have been well ahead of his time in that regard. Science fiction inspiring engineers and scientists alike is not new. In the end, that is what engineering is all about: turning science fiction into science fact. Take Jules Verne’s 1865 work From the Earth to the Moon, in which a space cannon is used to fire three astronauts to the Moon. In 1903, a Russian scientist dismissed the idea of cannon space travel, since the barrel would have to be impossibly long and an acceleration of 22,000g would be needed. However, he did admit that the story inspired him to study the possibility of space flight. The name of the scientist? Konstantin Tsiolkovksi. I hope you enjoy this issue of the Leonardo Times. You just might find some examples of science fiction becoming science fact. Benjamin Broekhuizen

HERGÉ

It would be a stretch to call the portrayal of space travel truly realistic, but Hergé did go out of his way to include several elements of realism. The rocket is clearly based on the German V-2 rocket, including its checkerboard pattern. The idea of weightlessness, complete with liquids forming spheres in microgravity, is prominently featured. Also, the reduced lunar gravity sees Tintin and friends merrily performing enormous jumps on the

Colophon Year seventeen, number 1, March 2013 The ‘Leonardo Times’ is issued by the Society for Aerospace Engineering Students, the VSV ‘Leonardo da Vinci’, of the Faculty of Aerospace Engineering at Delft University of Technology. The magazine is issued four times a year with a circulation of 5500 copies. EDITOR-IN-CHIEF: Benjamin Broekhuizen FINAL EDITOR: Pattareeya Srongpapa EDITORIAL STAFF: Céline Dohmen, Aryadad Fattahyani, Konark Goel, Sushant Gupta, Robert-Vincent de Koning, Benedict Krautheim, Jules L’Ortye, Alisa Nevinskaia, Stefan Scortescu, Lubi Spranger, Jeroen Wink, Nout van Zon THE FOLLOWING PEOPLE CONTRIBUTED: Soufiane Bourafa, Jasper Bouwmeester, Angelo Cervone, DSE groups, Jian Guo, Maarten Haneveer, Shahrzad Hosseini, Raoul de Jonge, Ivo van der Peijl, Sathiskumar Ponnusami, Arvind Rao, Jan Schneiders, Anouk Scholtes, Elisabeth van der Sman, Marijn Veraart, Feijia Yin, Barry Zandbergen DESIGN, LAY-OUT: dafdesign, Den Haag PRINT: DeltaHage B.V., Den Haag Articles sent for publishing become property of ‘Leonardo Times’. No part of this publication may be reproduced by any means without the 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, 2629 HS Delft Phone: 015 - 278 53 66 Email: VSV@tudelft.nl For more information the website can be visited at www.vsv.tudelft.nl At this website the ‘Leonardo Times’ can also be digitally viewed. Remarks, questions and/or suggestions can be emailed to the following address: LeoTimes-VSV@student.tudelft.nl

Leonardo Times MARCH 2013

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FROM LEONARDO’S DESK

Dear readers, Time has flown by incredibly fast since the release of the last Leonardo Times. The third educational period is already well on its way and slowly but surely spring is replacing winter. Unfortunately this means that most of you have probably already started preparing for your exams. Let’s take a look at the past activities and look forward to the activities in the near future.

ises a wintersports trip in the spring break in March. However, due to the new layout of the academic year, this holiday has been moved to the beginning of February. So, after 3 weeks of working very hard on the exams, 70 VSV-members travelled to Risoul in the French Alps to enjoy a week of snow and sun.

Immediately after the Christmas holidays the yearbook of the VSV was delivered to Leonardo’s Desk. A few years ago a new tradition was born at the VSV. The yearbook-committee hides the yearbook and the President of the VSV is sent on a quest to find the book and bring it back to the faculty. As the theme of the yearbook is ‘classified’, this resulted in me dressed in a tuxedo trying to find the yearbook. After going to Schiphol and working my way through Amsterdam I found the yearbook on the Dam Square and was the first VSV-member apart from the committee to read the yearbook in the train back to Delft and return just in time for the other members to receive their brand new yearbook. I want to thank the yearbook committee for organising a very nice registration of the 67th year filled with VSV activities.

After enjoying the slopes for one week we arrived back in Delft and it was time to focus on the VSV symposium. This year the symposium was organised by the Aviation Department in celebration of its twentieth anniversary and took place on the fifth of March in the Auditorium of the TU Delft. The symposium was themed: ‘SAFE: Safeguarding Aviation in the Future Effectively’ and focused on safety with regard to innovations in materials and maintenance, air traffic management and flight control. The committee has succeeded in gathering a large number of international speakers -experts in their respective fields- who answered questions regarding safeguarding aviation in the future. It is amazing to see what five students, whilst still following all their courses, can achieve in only 9 months with a lot of dedication. I would like to thank the Aviation Department for their hard work and congratulate them with the 4th lustrum.

The holidays were only separated from the exam period by one week, so after reading the yearbook most members started studying to earn those very important ECTS. Every year the VSV organ-

February also meant the busiest time of the year for Twan de Jong. In the VSV board he is responsible for the Career Affairs, which amongst others means organising ‘De Delftse Bedrijvendagen’, the big-

gest technical career fair in the Benelux. For the 18th time ’De Delftse Bedrijvendagen’ have proven themselves to be the best way for students to establish contact with companies that are of interest to them for possible internships, graduation projects and job applications. While the Aviation Department was preparing for the symposium, another committee was working very hard to organise the largest party of the VSV; AIRBASE. For only one day in the year the faculty will not be used for lectures but on the 22nd of March it will be transformed into a large party area and 1000 students will dance until early in the morning. Furthermore the Study Tour Committee is in full swing to select the companies they will visit during their stay in the United States and Canada in September. After the Study Tour returns to Delft, the VSV will still not be done travelling the globe. The faculty of Aerospace Engineering is known as one of the most international faculties of the entire TU Delft and therefore the VSV is planning to visit London, together with the study society of Applied Physics, for the Case Tour in October. As can be seen we will have no problems keeping ourselves busy in the coming months. On behalf of the 68th board, Raoul de Jonge President of the VSV ‘Leonardo da Vinci’ MARCH 2013 Leonardo Times

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Current Affairs

BOEING’S USE FOR POTATOES

21/12/12, Arizona, USA

JAMES AND THE GIANT PEACH

08/01/13, Leicester, UK

oeing is working on eliminating weak spots in in-flight wireless signals. Passenger seats on a decommissioned plane were loaded with sacks of potatoes for several days as signal strengths were checked. The company’s researchers say that potatoes “interact” with electronic signals in a similar way to humans. The technique also took advantage of the fact that potatoes - unlike humans - never get bored. A number of tests were performed to guarantee the best possible signal strength, while complying with safety regulations. Because passengers move around the cabin, wireless signals fluctuate randomly and their distribution becomes uneven. In a nod to the humor in using a tuber to solve a high-tech problem, researchers dubbed the project Synthetic Personnel Using Dialectic Substitution, or SPUDS. (S.S.) BBC

hysics is all about taking the world’s greatest mysteries and providing an explanation for them using physical laws. Not even mysteries in children’s books are left unsolved by physics nowadays. A group of physics students from Leicester University has subjected James and the Giant Peach, a classic tale by Roald Dahl, to physical modelling. In the story, orphaned James seeks protection with a bunch of anthropomorphized insects inside a huge stone fruit, which is then flown across the Atlantic Ocean by a flock of seagulls. Dahl said it would take only 501 birds to do the job. As James explains: ‘I shall simply go on hooking them up to the stem until we have enough to lift us. They’ll be bound to lift us in the end’. According to the student’s calculations however, a grand total of 2,425,907 seagulls would actually be needed to do the job. (J.L.) Alpha Galileo Foundation

GRAIL SATELLITES CRASH

17/12/12, Kennedy Space Center, USA

BALLOON SPACE TOURISM

27/11/12 Virgen de Camino, Spain

ot all space tourism is rocket science. Recent tests from Zero 2 Infinity have proven the feasibility of balloon space tourism. Human customers would enjoy stunning Earth views on their way up and a near weightless experience on their way down. The test balloon carried a humanoid robot to a height of nearly 32km, just a few kilometres shy of the altitude Felix Baumgartner reached during his skydive last October. Zero 2 Infinity eventually aims to offer hours of flight time to potential customers. Furthermore, all sorts of commodities have to be accounted for. ‘Some people will want to tweet or eat their favourite buffalo wings whilst they’re up there’ said Jose Mariano Lopez Urdiales, founder and CEO of Zero 2 Infinity. (J.L.)

he Gravity Recovery and Interior Laboratory (GRAIL) have crashed into a mountain on the Moon, ending a yearlong mission that clarified how the solar system formed. The two spacecraft had been flying around the moon, enabling scientists to assemble detailed gravity maps. The probes increased their velocity as they encountered stronger gravity and slowed down as they flew over less-dense areas. Out of fuel and edging closer to the lunar surface, the probes were commanded to crash close the moon’s North Pole, avoiding a chance encounter with any relics from previous expeditions. The discoveries will help scientists better understand how the moon formed and evolved, and what happened to Earth when it was showered with comets and asteroids early in its history. (S.S.)

TechNewsDaily

The Guardian

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Current Affairs

RASSOR

25/01/13, Kennedy Space Center, USA

uriosity and the Mars rover Opportunity are probably what comes to mind when thinking about NASA’s collection of robots. Although these ground-breaking robots are interesting, smaller machines can be just as exciting. Meet RASSOR, NASA’s newest mini-space explorer. The project is currently still in the prototype phase but NASA plans to send something similar to the Moon in the future. The job at hand: collecting resources. RASSOR will be tasked with digging up lunar soil and dumping it back into another machine. That second machine then separates water and ice from the remnants to make breathable air or rocket fuel. Usually a significant portion of a rocket’s mass is fuel. So if NASA can make fuel on-site with help from RASSOR, it will enable NASA to send a lot more cargo on a mission. NASA indicates that the same process could work on Mars as well. (J.L.) NASA

NEW SUPERSONIC GULFSTREAM

19/12/12, Washington DC, USA

n the release, Gulfstream revealed features of the supersonic business jet such as a telescoping nose, highly-sloped fuselage and variable-geometry wings. One executive said the company is “very close” to overcoming the noise problem that prevents commercial supersonic aircraft from operating overpopulated areas, using a so-called “relaxed isentropic inlet”. In the drawings, the telescoping nose is divided into six distinct sections at full extension. A side-view drawing reveals a highly sloped fuselage that peaks slightly aft of the leading edge of a highly-swept wing. The top-view drawing shows the mid-fuselage mounted wing also sweeps forward by as much as 30°. An experimental aircraft designation, X-54, has also been assigned to Gulfstream by the US Air Force for an undisclosed supersonic aircraft. (S.S.) Flightglobal

AIRCRAFT CATAPULT

15/11/13, London, UK

3D PRINTED MOON BUILDING 01/02/13, London, UK

n inflatable structure would be transported from Earth, and then covered with a shell built by 3D printers. To build the layered cover, the printers would use regolith, found on the Moon. The chosen building site is the Moon’s South Pole. It is designed to house four people and could be extended, said Foster and Partners. In 2010 a team of Washington State University researchers found that artificial regolith could be used by 3D printers to create solid objects. The plans are the result of a collaboration between a number of organisations including ESA. The consortium tested the practicalities of using a printer on the Moon by setting up a D-shape 3D printer, which are used to print very large house-sized structures, in a vacuum chamber with simulated lunar material. (S.S.) BBC

ccelerating a jet plane to take-off speed uses enormous amounts of fuel, with engines pushed to their maximum power to get a plane off the ground before the end of the runway. This not only uses lots of fuel, but those maxed-out engines make loads of noise, and can disturb populated areas. The proposed Airbus Eco-climb system includes a catapult system, a little different from steam catapults found on aircraft carriers. Airbus’ system would put the plane on a sled that travels along a track on the ground. The sled would be driven by electric induction motors, and could get the plane up to take-off speed in just 2/3 the distance of a regular takeoff. Once up to speed, the plane simply lifts up from the sled without turning a wheel, at which point the engines take over. (J.L.) Airbus

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MICRO-PROPULSION RESEARCH Challenges towards future nano-satellite projects The Space Systems Engineering department at the Faculty of Aerospace Engineering is hard at work miniaturizing satellite subsystems to accommodate the growing use of small satellites. One of the challenges the department has taken on is research into micro-propulsion. The limitations that come with small satellites make research in this field such a challenging adventure. An inside look at micro-propulsion research shows precisely which challenges are faced and which projects are underway. TEXT Angelo Cervone, Barry Zandbergen, Jasper Bouwmeester and Jian Guo, Space Systems Engineering TU Delft

he constant increase in number of small satellites launches during the last decade has led to a consequent increment of research activities on miniaturization of satellite subsystems. This is one of the reasons why “miniaturization” is among the 2012-2020 focus areas of TU Delft’s Faculty of Aerospace Engineering, together with “green aviation” and “planetary exploration”. However, due to limited cost and mass budgets, micro- and nano-satellites usually lack a propulsion capability, therefore limiting their lifetime and performance. The need for high-performance, highly miniaturized propulsion systems for small satellites is explicitly stated in the technology roadmaps prepared by the main space policy makers, including NASA1 and ESA2. To enhance their performance, the next generation of small satellites will require extremely miniaturized and highly integrated propulsion systems capable to meet stringent mass, power and volume constraints. In particular, for nano-satellite

applications, such propulsion systems shall be small, lightweight, and capable of delivering very low thrust levels (in the order of magnitude of μN up to a few mN) with a limited power consumption (possibly lower than 1W). In spite of these clear needs, there are still few ongoing activities in Europe on micro-propulsion, especially if compared to what can be seen in the United States and in Japan. In the Netherlands, TNO is active in the development of CubeSat propulsion systems based on a proprietary solid propellant cool gas generator technology. This research led to the development, in collaboration with TU Delft and the University of Twente, of the T3μPS micro-propulsion system3. The system will be demonstrated on board of Delfi-n3Xt, the nano-satellite presently under development at the Space Systems Engineering chair4, scheduled for launch in 2013. The T3μPS is however a cold-gas propulsion system, with a limited performance in terms of specific impulse. Heating the

propellant to a higher temperature will lead to significant improvements in terms of characteristic velocity, specific impulse and general propulsion performance. Improvements towards this direction are expected from the silicon-based MEMS resistojet design recently proposed by our group5. This enhanced propulsion system has been demonstrated to be more promising in terms of general performance than other options at higher specific impulse levels (such as ion and plasma thrusters), especially for missions requiring a total velocity change Δv lower than 200m/s. The micro-resistojet technology offers a series of exciting advantages, including: high thrust-to-power ratio, low system specific mass, an intrinsically uncharged plume and the possibility of using a wide variety of propellants. Further steps are however needed in order to investigate and eventually improve the actual feasibility of the system, presently demonstrated only at a prototype level.

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Figure 1. Cold gas propulsion board

THE DELFFI PROJECT The QB50 program is an international mission under the leadership of Von Karman Institute in Belgium, partly supported by the European Union. The mission is intended to establish a network of fifty nano-satellites developed by different institutions worldwide, with a range of mission objectives ranging from multi-point measurements in the lower thermosphere to re-entry research. The Space Systems Engineering chair will contribute to QB50 by means of two satellites, as space segment for the socalled DelFFi project6. The main objective of DelFFi is an autonomous formation flying demonstration between the two satellites, using innovative concepts for their navigation, guidance and control. This is a very challenging objective, since it has never been demonstrated so far with spacecrafts of such a small size. Two almost identical triple-unit CubeSats (Delta and Phi) will be used, with an in-orbit

demonstration payload constituted by a micro-propulsion system (for controlling the relative motion of the two satellites) and a radio-frequency navigation sensor (for relative ranging and inter-satellite communications). The formation flying experiment will allow the two satellites to fly at a controlled along-track separation of about 1000km, with a control window of 100km kept with an accuracy of 10km. The relative navigation accuracy required for this scenario is about 1km. The velocity change for maintaining the baseline distance between the satellites, in the low altitude orbit foreseen for QB50, is expected to be about 0.1m/s per day. Considering a thirty-days formation flying mission and accounting for maneuvers, contingencies and margins, a total velocity change of 6.3m/s per satellite is expected to be required. The mass budget allocated to the in-orbit demonstration payload is 420g per satellite, out of a total satellite mass of 3600g.

In particular, a mass of 330g is available for the propulsion system, with a maximum available volume of 3x10x10cm3. The power budget allocated to the inorbit demonstration payload is 290mW per satellite: 100mW are required by the radio-frequency navigation sensor, while an average of 190mW are allocated to the propulsion system. Taking into account the general project requirements, the torque disturbances and the possible misalignment and assembly errors, the thrust per satellite can be estimated to be 2mN as a maximum. On the other hand, duty cycle considerations lead to a minimum allowable thrust per satellite of about 0.14mN. Due to the presence of a deployable array the maximum allowed acceleration is relatively low, 2m/s2. DELFFI REQUIRES ADVANCED MICROPROPULSION The present candidate propulsion system for DelFFi is the T3ÎźPS. It consists of a

Table 1. Key requirements and constraints of DelFFi.

Along-track separation of satellites

1000km

Total satellite mass

3600g

Control window on separation

100km

Propulsion payload allocated mass

330g

Accuracy on control window

10km

Propulsion payload allocated volume

3x10x10cm3

Relative navigation accuracy

1km

Propulsion payload allocated power

190mW

Total mission Dv (baseline)

6.3m/s

Thrust range

0.14Ăˇ2mN

Total mission Dv (extended mission)

20m/s

Maximum allowed acceleration

2m/s2

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Figure 2. Resistojet prototype

Printed Circuit Board (PCB) and a plenum chamber in which the cool gas generators, the thruster and the thrust valve are mounted. The propellant is gaseous nitrogen, produced by the cool gas generators and then accelerated in the nozzle without any pre-heating. In 2010, a qualification model of the system has been successfully tested in vacuum at TU Delft. In this model, each cool gas generator was loaded with an amount of usable propellant equal to 0.125g, producing 0.1 normal liters of gaseous N2. A total of 8 cool gas generators were present in the model, for a total system mass of 140 g. The reported vacuum specific impulse was 68s. The following step in the flight qualification process will be a demonstration of the model on board of Delfi-n3Xt. A further development of the cool gas generator units, presently ongoing at TNO, will allow for scaling them up to a mass of 16.3g, of which 4.21g are usable propellant. This increased propellant-tomass ratio will lead, in turn, to a significant performance improvement. The MEMS resistojet system recently demonstrated by our team includes an inlet manifold, a heater section and a nozzle. Also in this case, the propellant is gaseous nitrogen. The gas is heated by an integrated thin-film heater made of aluminium, and elevated temperatures at the fluidic channel walls are ensured by using high

thermal conductivity silicon wafers. A single thruster unit has a dry mass as low as 162mg (excluding the propellant and the storage tank). The estimated vacuum specific impulse is 73s in the cold-gas mode, and can be increased up to 104s when the propellant is heated to 327°C. The nozzle throat width can be chosen among two values, 10μm and 5μm. A thrust of 0.38mN per thruster unit can be obtained with an available heating power of 190mW. In a paper recently presented at the IAC 2012 Conference in Naples, we have demonstrated how advantageous the MEMS resistojets technology can be if applied to the DelFFi satellites7. The total estimated mass of the satellite propulsion system, including propellant, is 271g if the T3μPS cold-gas system is used, but can become as low as 100g if this is replaced by a micro-resistojet. Thus, by using a resistojet system, a total of 171g are saved - almost half of the allocated payload mass! This saved mass can be used for additional payload or for upgrades of the other subsystems, thus increasing the general mission capabilities. In order to achieve this result, however, it is necessary to combine the beneficial aspects of the resistojet design with a high-density propellant storage system such as the TNO cool gas generator units. It is clear that DelFFi, as well as the other future flagship nano-satellite missions

planned by TU Delft, will require an advanced micro-propulsion concept. Our group at Space Systems Engineering is therefore planning to increase the research activities in this field in the upcoming years, and several challenging MSc thesis topics are expected to be offered to TU Delft students from 2013. WHAT CHALLENGES ARE WE FACING? In resistojets, when gaseous nitrogen is used as propellant and heated at a temperature in the order of 300°C, a specific impulse of about 100s can be reached. However, this value can be increased up to 600-1000 seconds by either increasing the heating temperature or changing the propellant (hydrogen, water). But what are the main scientific and technological challenges associated with the development and the qualification of this kind of propulsion device at a micro-scale? • With the typical nozzle size required to achieve thrust levels in the order of microNewtons, large viscous losses are present at the nozzle throat. This is caused by the low Reynolds numbers (typically less than 500) and the formation of a laminar boundary layer at a micro scale. Alternative geometries and materials need to be analysed to minimize the impact of this problem. • Traditional component interfacing techniques show functional limitations

Table 2. Comparison between the T3μPS cold-gas system and the MEMS resistojet equipped with cool gas generator units, when applied to one of the DelFFi satellites (total mission Δv = 6.3m/s).

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when used at small scale, and are therefore not suitable to micro-propulsion systems. Novel ways to join and interface miniaturized components shall be identified, based on new gluing/bonding techniques and advanced non-silicon materials. • Resistojets require a significant amount of power for heating the propellant: about 500mW per mN of thrust, for the prototypes tested so far at TU Delft. This is an important problem if we think of the strict power requirements of typical nano-satellites. Alternative heating technologies, based for instance on thinfilm heater chips, are required to minimize heat losses and achieve higher temperatures. • The maximum temperature at which the propellant is heated can be further increased by investigating innovative materials. A compromise needs to be found between temperature and mechanical strength. High thermal conductivity materials such as silicon are good candidates in terms of heat exchange properties, but cannot typically withstand high temperatures. Alumina has better thermal and chemical properties, but its machining at a small scale is very difficult. Low-temperature co-fired ceramic tapes, generally used for packaging electronic devices, have been recently proposed for micro-fluidic components; however, efforts are still needed to reduce the costs of their production and machining techniques. • Higher temperatures, when com-

bined with the small size of miniaturized components, lead to large pressure and temperature gradients and thus to high mechanical stresses and an increased risk of failures. A compromise needs to be found between performance and reliability. On top of these technical challenges there are also several critical aspects at a system level, for instance: design and validation of adequate facilities for testing micropropulsion systems, preparation of a complete verification & validation plan, integration of the system into the actual satellite, and final in-flight qualification. All the design activities shall of course take into account the lessons that we will learn from the in-orbit performance analysis of the T3μPS system on Delfi-n3Xt. CONCLUSIONS Our research team at Space Systems Engineering is continuously working to push the limits towards new frontiers of satellite miniaturization. Our future flagship nano-satellite projects, such as DelFFi, will require exciting research efforts for achieving the technological improvements needed to accomplish their ambitious goals. Motivated students are always welcome to join and share with us the emotions of this exciting adventure. If interested, contact us via the e-mail address A.Cervone@tudelft.nl or B.T.C.Zandbergen@ tudelft.nl.

References 1 Johnson, L., et al., NASA Technology Area Roadmap for In Space Propulsion Technologies, 2010 2 ESA, European Space Technology Master Plan , Issue 6, 2008 3 Moerel, J.L.P.A., et al., Development of Micro-Propulsion System Technologies for Minisatellites in the Netherlands, 5th International Space Propulsion Conference, Heraklion, Greece, 2008 4 Bouwmeester, J., et al., Design Status of the Delfi-Next Nanosatellite Project, 61st International Astronautical Congress, Prague, Czech Republic, 2010 5 Tittu Varghese, M., et al., A SiliconBased MEMS Resistojet for Propelling Cubesats, 62nd International Astronautical Congress, Cape Town, South Africa, 2011 6 Gill, E., et al., Formation Flying within a Constellation of Nano-Satellites: The QB50 Mission, Acta Astronautica, Elsevier Science Ltd., j.actaastro.2012.04.029, 2012 7 Cervone, A., et al., Application of an Advanced Micro-Propulsion System to the DelFFi Formation-Flying Demonstration Within the QB50 Mission, 63rd International Astronautical Congress, Naples, Italy, 2012

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Delft University of Technology The oldest and largest Dutch technical university, today it around 2,700 academic staff in eight faculties covering the complete spectrum of science and technology. Delft University of Technology belongs to the top 100 universities in the world, holds a position 77 on the Times Higher Education 2012.

Wanted: Aerospace Engineering Scientist Vacancies: Post-docs/Assistant professors/ PhD students Join the Aerospace Engineering Faculty Environmentally friendly aircraft, insect-sized unmanned aircraft and nano-satellites, new composites or self-healing materials, personal air transport, discovery of extra-terrestrial life forms or new planets where we could live in the future. These are examples of the research at Europeâ&#x20AC;&#x2122;s number one Aerospace Engineering Faculty. Be part of our community. The Aerospace Engineering Faculty has around 2,700 BSc and MSc students, 241 PhD students and 27 professors supported by

In addition there are many smaller facilities like computation clusters, micro-aerial vehicles workshop, an avionics lab and much more. Facilities Unique for our faculty are the high quality facilities we have for both our education and research: for (wind energy) up to Mach 12 (for re-entry)

departments. Research Our research for the coming years focuses on:

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Apply Can you inspire our students with high quality education? And are you daring enough to stray from well-trodden paths? Then take a look at www.jobsindelft.nl to discover how you can apply for one of the vacancies for the Faculty of Aerospace Engineering, TU Delft.

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Internship Report

ENGINEERING EXCELLENCE AT ROLLS-ROYCE A taste of English culture

Rolls-Royce is one of the most well-known brands in the world and synonymous with the highest engineering quality. Amongst Aerospace Engineers, Rolls-Royce is directly associated with the Trent turbofan aircraft engines. The engines power the world’s newest passenger aircraft, including the Boeing 787 Dreamliner and the large Airbus A380. A Rolls-Royce powered aircraft takes off or lands every 2.5 seconds. TEXT Jan Schneiders, MSc Student Aerospace Engineering

hen I proudly tell friends about my internship at Rolls-Royce, often I get asked what an Aerospace Engineer would do at a car manufacturer. Or the comment that all those cars must have BMW engines by now. As a reader of the Leonardo Times you probably smile hearing this and I don’t have to tell you that the Rolls-Royce I did my internship at does not manufacture cars or engines for the automotive industry anymore, since back in 1973 the automotive division was separated from the company. At the time the Aerospace division was struggling as it had heavily invested in the RB211 engine, which was the first three spool engine and turned Rolls-Royce from a small player in the airline industry into a global competitor. Currently, Rolls-Royce is one of the largest manufacturers of large civil aero engines; engines that power the newest aircraft including the Boeing 787 Dreamliner, the Airbus A380 and soon also the Airbus A350 XWB. But did you know that’s not the only thing Rolls-Royce does together with its more

than 40,000 highly skilled employees? During my internship I worked within the Civil Aerospace division as a Development Engineer, but next to Civil Aerospace, Rolls-Royce has three other divisions; Defence Aerospace, Energy and Marine. The company is a world leader for power in the onshore and offshore oil and gas industry and does not only design turbine engines for use in air, but also on land. Next to this, Civil Nuclear is becoming a larger part of the energy division. This is not the first time the company is working with reactors though: Rolls-Royce provides the nuclear propulsion for the Royal Navy’s submarine flotilla. To illustrate the size of this business, over 1,000 engineers play key roles in the design and support of the nuclear submarine propulsion plant. Rolls-Royce marine does not include only advanced propulsion systems, but is also encompassing vessel design. Indeed, a wealth of experience in ship, propulsion and power systems design has seen RollsRoyce design more than 700 ships over

the last thirty years, many of them built for working in the world’s harshest areas. SPREAD YOUR WINGS Since the beginning of my Aerospace Engineering studies, Rolls-Royce has been the company I wanted to work for. Working as a Development Engineer may however not seem the first choice for someone like me, specialising in Aerodynamics. The Development department’s responsibility is to validate the engines to ensure their compliance with the engine and aircraft certification requirements. This proved to be an eye-opening experience. Working closely together with all specialist areas required combining all knowledge gained during my bachelors of Aerospace Engineering and proved to be a very challenging multitasking experience where every day was different. It was certainly not a desk job and often I found myself down the shop floor discussing parts to gain a better understanding of their functioning – and to gain an

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Figure 1. It was impossible to miss the Olympic Games last summer in England. The torch being carried through Derby was one of the highlights.

appreciation for the many very large and very small components that make up a modern aero engine. DERBY, UK Rolls-Royce has many different sites around the world. I was based in Derby in the United Kingdom. “Derby, ehmm, where?” was my first thought. Derby, the city in which Rolls-Royce opened a factory as early as in 1907. I had to look it up on a map. Derby is centrally located in England and is only one and a half hours by train from the London St. Pancras train station. It’s also only a short drive to the beautiful Peak District. A short drive along which you are continuously reminded that the English absolutely love very narrow roads, corners and roundabouts. And of course, that they drive on the wrong side of the road. After a few phone calls to local letting agents, I had arranged some viewings in different apartments around the city. On my second day in the city, I found a beautiful apartment right in front of the city centre’s cathedral. Already after the first night in the flat I had made my first friend in the city – the cathedral has been greeting me for the past six months with a cheerful chime every fifteen minutes.

I got used to the English manners soon after my arrival. Indeed it was nice to see people queuing up for a bus instead of crawling around its entrance. Also the healthy English breakfast quickly became a standard and delicious Saturday treat. One habit I could not get used to was drinking tea with milk. The English drink a lot of tea and the office’s fridge was completely packed with pints of milk. When I got a pack of milk at the canteen to drink straight from the pack, people would offer me tea – questioning why I was drinking just milk. INTERNATIONAL SOCIETY I knew no one in the city of Derby upon my arrival. This quickly changed after the intern induction day – my first day at the company. Almost all interns start on the same day in summer, making it very easy to meet new people and network around. As the main and almost sole reason for coming to Derby is to work for one of the big companies in the city – next to RollsRoyce also Bombardier has a site in Derby for example – none of my fellow interns already knew their way around the city. Quickly the first pub crawls were planned and soon everyone felt at home in the city. To facilitate networking even more and to provide an excuse for some more social activities, there is an International

Society. Many members of this more serious society are working at Rolls-Royce permanently for already quite some time, which allows for quite some interesting discussions during the socials. SUMMER INTERNSHIPS One thing that caught my eye during my stay in England was the vast amount of work experience many students in England have at renowned companies. Some students I met had already worked at a few of the world’s top companies over several summer internships – work experience they gained already during their bachelors. The summer internships are a very interesting opportunity to gain work experience, while at the same time meeting many new friends abroad. Many companies offer these relatively short ten week programmes during the summer holidays. If you want to gain some work experience during your bachelors, taking a look at the different summer internships is certainly a great idea. A quick web search will give you an idea of the vast amount of possibilities. Indeed, Rolls-Royce also provides the possibility to do a challenging summer internship. Keep in mind that applications for summer internships usually open late summer and close by Christmas, so you will need to plan in advance. MARCH 2013 Leonardo Times

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LVD

20th lustrum Dutch Military Aviation

HD-ACHTERGRONDEN.BLOGSPOT.NL

MILITARY FLIGHT THROUGH TIME

This year marks the 100th anniversary of Dutch military aviation. Quite a number of aircraft have made their entry and served the Netherlands throughout the past couple of years. The 20th Aviation Department of the VSV â&#x20AC;&#x2DC;Leonardo da Vinciâ&#x20AC;&#x2122; takes special interest in this lustrum celebration and therefore presents you some unforgettable milestones from the past decades. TEXT Shahrzad Hosseini and Anouk Scholtes, Students Aerospace Engineering, President and MDE Affairs of the 20th Aviation department

THE EARLY DAYS What once started out with four pilots and a rented aircraft, soon turned out to become an organization with a large collection of aircraft flying in Dutch airspace and beyond. Starting 100 years ago with a single serving trainer aircraft, De Brik, innovation delivered the era of the jet aircraft commencing with the Gloster Meteor from Britain. Modernization of aircraft kept increasing throughout the years and brought us, amongst other, the F16 in the 1970s, and the Chinook in the 90s which are both still serving today. TAKING OFF WITH DE BRIK When the Dutch Military Aviation Department took off in the year 1913 a singleseater aircraft was rented from the designer, Marinus van Meel. A rent of eleven euros per day allowed the Department to fly De Brik, with First Lieutenant F.A. van Heyst as pilot. Later, the plane became property of the Department for 1,600 euros and served to train the very first Dutch pilot candidates.

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This wooden trainer aircraft flew on gasoline and was powered by a 7-cylinder Gnome rotary engine. The wing surface was 46.5m2 and it had a length, span and maximum weight of 11m, 16m and 500kg respectively. Soon new aircraft made their entrance in the Department, but the legendary De Brik will always be remembered as the aircraft with which the Dutch Military took off. GLOSTER METEOR INITIATES JET FIGHTER ERA With the introduction of new combat aircraft at the end of the Second World War a new era began, the era of jet fighters. The British and German Air Force had already introduced the first jet combat aircraft when in 1948 the British Gloster Meteor was introduced in the Dutch Military Aviation Department. With the arrival of this new jet fighter, the propeller combat aircraft were not replaced immediately. The old Spitfire was

still in use up and until 1954. However, the Gloster Meteor left its mark on the period of 1948 through 1959 in which 266 aircraft of this type were acquired. When in 1949 the first eight Meteors arrived in Leeuwarden, this became the first operational jet base in the Netherlands. The first test flights of this fighter, manufactured by Gloster Aircraft Company, took place in 1944. The full-metal plane had low-mounted straight wings and a wing span of 11.32m. It had a highmounted tailplane and was equipped with a tricycle landing gear. The Meteor was powered by two Rolls-Royce Derwent turbojet engines. With these engines, the aircraft could reach a maximum speed of 965km/h. Since these Derwent engines used up almost 18,000L of kerosene per hour, the range of the aircraft was only 965km. Therefore, the Meteors were mostly used for interception purposes only. Besides being the first jet fighter of the department, the Meteor also gave a boost to the Dutch aircraft industry. In 1949 an

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KONINKLIJKE LUCHTMACHT

Figure 1. De Brik in 1913 with First Lieutenant F.A. van Heyst

improved version of the Meteor was produced in the Netherlands. This caused a fast recovery of the Dutch aircraft industry between 1949 and 1954. On the 6th of April in 1954, the last Meteors were assigned to the Air Force. The Meteor had served the Air Force very well, yet the aircraft industry was modernizing quickly: the production of new jet fighters breaking the sound barrier had already started. GOING SUPERSONIC WITH THE F-16 ‘FIGHTING FALCON’ Since the establishment of the Dutch Military Aviation Department in 1913, the aircraft industry went through a lot of developments and improvements. Many marvelous aircraft had already served the Air Force when in June 1979 the F-16 ‘Fighting Falcon’ was introduced in the Netherlands. This aircraft still serves the Dutch Military Aviation today. Halfway through the 90’s the F-16 went through an overhaul. This new version of the F-16, the F-16 ‘Fighting Falcon MLU (Mid Life Update)’ was needed to optimize the functioning of the aircraft in the upcoming years. Studies have proven that the F-16 was technically able to have a longer life time than the estimated 20 years which was used as a guideline. However, the operational equipment had to be modernized and therefore the MLUprogram was set up. This MLU-program assured that F-16’s were able to function optimally during night and bad weather conditions. With a span of ten meters, including its missiles, the F-16 has a smaller width than the first jet fighter, the Meteor. The F-16 ‘Fighting Falcon MLU’ has an empty weight of about 11,000kg and a maximum weight of 16,000kg. The aircraft, produced by Lockheed Martin (former

General Dynamics), is powered by one Pratt & Whitney 100-PW-200E turbojet. With the power of this engine, a maximum speed of 2,000km/h can be reached. The range of the F-16 is much higher compared to the range of the first jet fighter. In contrary to the 975km that the Meteor was able to fly without refueling, the F-16 is able to fly 2,700km. Since 1979, the Air Force has purchased a total of 213 of these aircraft, of which 177 were single-seated and 36 were doubleseated. Of this total of 213 aircraft, 87 are still used today. The expectation is that from 2015 onwards, the F-16 will be replaced by a new aircraft. BOEING CH 147 CHINOOK AS SERVING HELICOPTER Jet aircraft were not the only vehicles which improved throughout the years. Helicopters have played a major role in the Air Force to provide transportation for militaries, weapons and equipment. In 1993 seven Chinook helicopters were delivered in the Netherlands and soon these were equipped with new modernized systems. The maximum weight of the Chinook is 24,494kg and fast (un)loading is facilitated through a large entrance in the back of the vehicle. Larger cargoes are transported underneath the helicopter, using three cargo-hooks. These front- and back hooks and the central hook can carry a weight of 9,072kg and 12,700kg respectively. As for the transportation of military personnel, the Chinook can carry 33 people. Another 24 people can be seated on the floor in an operational condition. The Chinook is mainly recognizable by its triple-blade rotor blades located on the front and aft of the vehicle. Power is generated by a set of two Honeywell turbo-

shaft engines with each a maximum continuous power of 3,069kW. The maximum velocity reaches 315km/h and a range of 250km is the minimum constraint for this vehicle. TIME KEEPS AMAZING With these amazing 100 years to look back to, developments of aircraft in the Dutch Military Aviation have been impressive. Innovation keeps amazing the world of aviation and continues delivering new high tech systems. On the memorable day in 1913 on which the national Military Aviation took off, a supersonic jet was still a dream. Today’s high tech systems, aerodynamic qualities, engine capacities and the increasing rate of innovation were futuristic concepts at the time. Considering the development of technology today, we may wonder: what will the next century bring? CONTACT LVD-VSV@student.tudelft.nl References http://www.defensie.nl/luchtmacht http://www.mvc-atlantis.nl http://historywarsweapons.com

Aviation Department The Aviation Department (LVD) of the Society of Aerospace Engineering Students ‘Leonardo da Vinci’ fulfills the needs of aviation enthousiasts by organising activities, like lectures and excursions in the Netherlands and abroad.

MARCH 2013 Leonardo Times

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MODELLING AIRLINE OPERATIONS CONTROL

TEXT Soufiane Bourafa, PhD student Aerospace Engineering, Operations chair

CHALLENGES AIRLINES FACE Each day of operation, an airline is often faced with challenges that may translate into large deviations of its fleet from original plans. These challenges arise from disruptive events, also known as irregularities, which can range from severe weather conditions, airport congestion, up to an aircraft mechanical failure. Such events impact all aspects of the airline’s operation, but are most detrimental to the schedules for basic resources such as aircraft and flight crews (Clarke 1998). The fact that a single flight does not depart on time, may result into passengers missing their next flight connection, or pilots not being able to continue flying due to work-rule regulations. Since a single flight leg is a component of different types of schedules, a perturbation in one leg may have significant downstream effects. According to (Ball et al. 2007), such fragility is exacerbated by the growing complexity of the air transportation system and the tight coupling of its various elements. THE AOCC – THE AIRLINE’S NERVE CENTRE In order to deal with disruptive events

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and reduce their impacts, major airlines have established Airline Operations Control Centres (AOCCs), as seen in Figure 1. These centres gather an extensive array of operational information and data, with the purpose of maintaining the safety of operations, and efficiently manage aircraft, crew, and passenger operations. A typical AOCC is comprised of different teams coordinating together during the aftermath of irregularities. These teams include operations controllers, crew planners, customer service coordinators, dispatchers, ATC coordinators, complemented by station operations control units at airports (Ball et al. 2007). When disruptions occur, these teams adjust in real-time the flight operations by delaying departures, cancelling flights, rerouting aircraft, re-assigning crews, and accommodating disrupted passengers. The AOCC is therefore a highly complex, dynamic, and fast paced environment in which decisions made by its operators facilitate disruption recovery. Clearly then, decision-making in this environment is critical, so even small improvements to the decision-making process could translate into significant revenues.

DECISION-MAKING AT THE AOCC The importance of decision-making has been recognised in aviation with the focus predominantly on pilots and air traffic controllers in relation to safety aspects. However, only limited research appears to have been conducted in the AOCC. Yet, this decision-making environment is extremely intense and the outcomes of decisions made are critical to achieve desired operational outcomes. Operators at the AOCC are faced with different trade-offs every day. These trade-offs are created by the complexities inherent to the processes managed and the finite resources of operational systems. Potentially, there are conflicting goals leading to dilemmas and bottlenecks that must be dealt with. Examples include minimizing the fuel costs, maximizing on-time performance and customer satisfaction, complying with local regulations, minimizing the cost of reserve aircraft and crew, and rapid recovery from disruptions. The widely established system engineering approach has not been developed to capture the ‘socio’ part of a socio-technical system. Then it should not come as a surprise when this creates un-

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INTER VISUAL SYSTEMS

NASA

Figure 1. A look inside KLMâ&#x20AC;&#x2122;s AOCC

Figure 2. Performance assessment feedback

foreseen behaviour that goes unnoticed during the implementation of a complex socio-technical system. Instead, such system behaviour should be identified early on in the development phase. This requires an approach to identify the emerging behaviour of a socio-technical system early in the development of changes in air transportation operations. SOCIO-TECHNICAL PERSPECTIVE The focus of this research is on human operators working at the AOCC environment and the impact this environment has on their work. The main objective is to develop a model that can capture both the physical and social reality of the AOCC, their interactions with one another, and the external dynamic environment. This is because a successful model of a sociotechnical system is one that is able to deal with different configurations of both the social and physical network, enabling it to identify a suitable technology mix (van Dam 2009). In the Airline Operations Control (AOC) context, a suitable technology mix would be one that minimizes the impact and cost of disruptions, and improves safety. The model parameters are thus the humans, elements of the work

environment and how they are connected and influence each other. Hence, the question this research aims to answer is: how can we model a socio-technical system like the AOC, in a way that will enable changing both social and physical system components, in order to evaluate AOC decision-making performance? Our approach is to embrace Agent-Based Modelling and Simulation (ABMS) because it has been extensively used to: a) analyse complex socio-technical systems; and b) address cases where agents need to collaborate and solve problems in a distributed fashion. ABMS provides a platform to integrate multiple heterogeneous components at different levels. Models of actors, technological systems, and the operating environment as well as the interactions between them can be naturally covered. In the context of air transportation, in particular where different actors, hardware, and software are interacting elements of a complex sociotechnical system, we consider agents as autonomous entities that are able to perceive their environment and act upon this environment. The agent-based model can be used to assess the impact of choices made during irregularities on

multiple performance criteria, such as safety and economy. Scenarios involving new procedures and technologies can also be assessed. One example that the aviation community has been interested in recently is the Single Pilot Operations (SPO) concept. In this concept, the copilot may be on the ground, and may be looking after more than one aircraft at the same time. This is because advanced technologies, particularly communication and navigation capabilities, have already relieved the cockpit of a number of jobs. Direct communication means pilots could offload high workload tasks such as re-routing to an AOC system. The assessment of such advanced concept would serve as feedback for the operation design, through highlighting which activities automation should support, which model of decision-making automation should support, and how the role and responsibilities of the human agents can be best allocated towards safe and efficient air traffic operations. This process is visualised in Figure 2.

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NASA

THE AHEAD PROJECT Advanced Hybrid Engines for Aircraft Development

Aviation is an ever-increasing market and more passengers and cargo are carried each year. The world is becoming ever more connected. However, this does come at a price: aviation has a marked influence on the environment. If aviation is to thrive in the future, breakthroughs in aircraft design and propulsion systems are needed. The AHEAD project is an attempt at achieving such a breakthrough. TEXT Arvind G. Rao and Feijia Yin, Flight Performance and Propulsion TU Delft

CHALLENGES FACED BY AVIATION Commercial aviation has made substantial progress since its inception and is now the backbone of a modern society. In the past ten years, passenger numbers have grown by 45% and freight traffic has increased by more than 80% on a tonne-kilometre basis [1]. Moreover, aircraft emissions have reduced significantly over the last forty years, for example, noise has reduced by 20 decibels, fuel consumption by 70%, carbon monoxide emissions by 50% and unburned hydrocarbon and smoke by 90% [1]. Despite all these positive developments, some serious challenges toward the environment, the community and the availability of fuel resources are encountered by aviation. The total emissions from the aviation sector are still increasing rapidly and now the sector is an active contributor to global warming. Therefore, the Advisory Committee for

Rao.indd 20

Research in Aeronautics (ACARE) has targeted the reduction on various fronts of noise, air pollution and fuel consumption. The ACARE goal is shown in Figure 1. It aims to reduce CO2 emissions by 75%, NOx emissions by 90% and the perceived noise levels by half in the year 2050, compared to the baseline year 2000 [2]. To achieve this objective, a combined improvement in the aircraft, power plant and the air traffic management system is required.

that aviation will see a significant use of alternative fuels, starting with synthetic fuels such as Gas To Liquid (GTL), Coal To Liquid (CTL) and biofuels. In a few decades, hydrogen or hydrogen-rich fuels, such as Liquid Natural Gas (LNG) can probably be used to reduce the carbon footprint of aviation for long range aircraft. By the end of this century, we might have the technologies in place for powering an aircraft electrically.

As is known, the reduction of NOx emission mostly depends on the evolution of combustion technology. However, CO2 emission is the product of chemical reactions between the carbon content of the fuel and air: as long as conventional fuel is in use, the ACARE goal to reduce CO2 emission remains difficult. To achieve this target, alternative fuels have been put forward. A scenario of future aviation fuels are indicated in Figure 2. It is anticipated

Due to its much higher energy density than kerosene, hydrogen can reduce the amount of fuel which needs to be carried onboard. Moreover, as a type of non-carbon fuel, burning hydrogen will be able to reduce the CO2 emission significantly, which makes it very attractive. Some efforts have been made to prove the feasibility of implementing the hydrogen in aviation. The â&#x20AC;&#x153;Cryoplaneâ&#x20AC;? concept under the 5th Framework Program of the Euro-

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NASA

Figure 1. ACARE vision for Europe

Figure 2. Primary energy source for long range aircraft

Figure 3. LH2 tank storage scheme of “Cryoplane” project

pean Commission is one of the examples. Conventionally, fuel is stored in the wings of an aircraft. However, the liquid hydrogen (LH2) has to be stored in pressurized cryogenic cylindrical tanks, which do not fit in the wings. Therefore, the fuselage was considered to accommodate the fuel tanks in the “Cryoplane”, as indicated in Figure 3 [3]. Although the fuel tanks are accommodated, this configuration is not so suitable from a passenger comfort, safety and aerodynamics point of view. THE MULTI-FUEL BLENDED WING BODY AIRCRAFT To summarize, according to the current research efforts based on current technologies, there seems to be a very little chance to meet the ACARE goals and therefore breakthrough technology is needed. During the past years, an innovative Blended Wing Body (BWB) configuration has been studied by many researchers around the world, including the “CleanEra” group from TU Delft, and it seems to be a promising candidate to replace the existing aircrafts. Instead of a separate fuselage with wings, an integration of body and wing is used for the BWB [4]. This results in a larger amount of space available within the aircraft, thus making it possible to carry cylindrical fuel tanks to store the

Figure 4. A futuristic BWB aircraft layout with LH2 and biofuel tanks

cryogenic fuel. A novel way to overcome the storage problems of hydrogen is a multi-fuel BWB aircraft presented in Figure 4. The wings of a BWB have sufficient room for storing LH2 tanks, without interfering with the passenger section. Further away from the central line, where wing thickness is reduced, liquid biofuel can be stored. Thus, a multi-fuel BWB concept with a combination of biofuel and cryogenic fuel is proposed and investigated by the “AHEAD” project sponsored under the 7th Framework of EU. THE HYBRID ENGINE To power the multi-fuel BWB aircraft, a new type of propulsion system—called the hybrid engine—has been conceived, which is able to meet the requirements of the multi-fuel BWB aircraft. The novel features of this engine and its schematic are shown in Figure 5. The novel engine proposed is quite different than a conventional turbofan and includes many breakthrough technologies. The various novel technologies involved in the proposed engine configuration are described as follows. Boundary Layer Ingestion (BLI): this is

a method of increasing the propulsive efficiency of the engine by embedding the engine within the airframe such that the engine can ingest the low velocity boundary layer flow of the aircraft, reducing the engine ram drag. Also, the jet of the engine contributes to aircraft “wake filling”, thus reducing the overall dissipation. Counter-Rotating Fans (CRF): The aircraft-engine integration of future BWB aircraft presents unique challenges due to BLI. Such configurations also require that engines be smaller in diameter to reduce the nacelle-wetted area. Thus, it can be seen that the current trend of increasing bypass ratio and diameter of engines will not be able to meet the requirements of future BWB class of aircraft. The proposed hybrid engine with counter-rotating fans has a smaller diameter and higher propulsive efficiency for the same bypass ratio. Furthermore, since each stage of the fan is less loaded than a single stage fan, a CRF engine can sustain more non-uniformities in the flow generated due to BLI compared to a conventional architecture. Bleed Cooling: With increasing pressure ratio, the temperature of bleed air (the air that is used for cooling the hot section components like the turbine blades and MARCH 2013 Leonardo Times

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vanes) increases, leading to the increase of the amount of bleed air required for the hot components cooling. This increase has an adverse effect on the thermodynamics of the gas turbine engine, reducing the efficiency of the cycle. The cryogenic fuel used in the proposed hybrid engine is an excellent heat sink, which can be used for cooling the bleed air, thus reducing the amount of bleed air required. Meanwhile, the temperature of the cryogenic fuels is increased, which reduces the use of combustion heat to increase its temperature, resulting in less fuel consumption for a given temperature within the combustion chamber. The Hybrid Dual Combustion System: The proposed innovative hybrid engine uses two combustion chambers as shown in Figure 5. The main combustor operates on LH2/LNG while the second combustor (between the high pressure turbine and the low pressure turbine) uses biofuel in the flameless combustion mode. Such a novel combustion system has never been used before for aero-engines. There are several advantages of this unique layout. Firstly, since the flammability limits of hydrogen/methane are wider than kerosene, the combustion can take place at lean conditions, thus reducing NOx emissions significantly compared to a conventional kerosene combustor. Secondly, the LH2 used for the first combustor can be used for cooling the bleed air, as mentioned in the previous section. Moreover, using LH2 in the first combustion chamber will increase the concentration of water vapor and reduce the concentration of O2 in the second combustion chamber, thus creating a vitiated environment in which flameless combustion can be sustained. The implementation of the flameless combustion can minimize the emission of CO, NOx, UHC and soot. Additionally, the reduced emission of soot and unburned hydrocarbon also reduces the amount of nucleation centers available for condensation of water vapor in the plume, thus reducing contrail formation. RESULTS AND CONCLUSIONS The “AHEAD” BWB aircraft is an environmentally friendly aircraft burning cryogenic fuels (like LNG/LH2) and biofuels. It is preliminarily designed for carrying around 300 passengers over a 14,000km range. The comparison of the layout of the BWB to the Boeing 777-200ER is provided in Figure 6. The shorter and wider body of the aircraft makes it more aerodynamical-

Rao.indd 22

Figure 5. Schematic of the Hybrid Engine

Figure 6. Comparison of the BWB with a Boeing 777-200ER

ly efficient than a conventional cylindrical body aircraft. Combined with the advanced hybrid engine, the multi-fuel BWB is able to reduce CO2 emission by around 65% compared to a conventional Boeing 777-200ER aircraft. To conclude, if civil aviation is to maintain its growth, radical changes in the aircraft and propulsion systems are required. The proposed multi-fuel BWB aircraft utilizing a hybrid turbofan engine has the potential to reduce CO2, NOx and noise emissions substantially. The authors would like to thank the European Commission for funding this project (FP7-AAT-2011-RTD-284636) and the DSE group on “Design of Multi-Fuel BWB aircraft” from Aerospace Engineering Design Synthesis Exercise 2012.

References 1. Air transport action group (ATAG), “The economic & social benefits of air transport”, 2005. 2. Advisory Council for Aeronautics Research in Europe(ACARE), “Flight path 2050 Europe’s vision for aviation”, Report of the High Level Group on Aviation Research, Publication Office of European Union, 2011, ISBN 9789279197246. 3 . Klug, H.G., and Reinhard, F., “CRYOPLANE: hydrogen fuelled aircraft — status and challenges”, Air & Space Europe, Vol. 3, No.3-4, May-August 2001, Pages 252-254 4 . Liebeck R.H., “Design of the Blended Wing Body Subsonic Transport”, Journal of Aircraft, Vol. 41, No. 1, January-February 2004.

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DESIGN

SYNTHESIS EXERCISE

2012

TEXT Ir. J.A. Melkert - Coordinator Design Synthesis Exercise

he design synthesis exercise forms the closing piece of the third year of the Bachelor degree curriculum of the Faculty of Aerospace Engineering at TU Delft. In this exercise the students learn to apply their acquired knowledge from all aerospace disciplines in one complete design. The object of this exercise is to improve the students’ design skills while working in teams with their fellow students. In the exercise Systems Engineering plays an important role. In the design/synthesis exercise, students work in groups of ten, for a period of approximately ten weeks full time on the design of a (part of an) aircraft or spacecraft. Despite the fact that the final designs result from a design process executed by small groups of students with limited experience, it may be concluded that the designs are of good quality. Not only the

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scientific staff of the Faculty of Aerospace Engineering, but also the external experts and industry which have supported the design projects, have expressed their appreciation of the results. In the fall exercise of this year eleven groups worked on a range of topics. They ranged from designs in the field of aeronautics and space to earth observation and wind energy. The students presented their results in the design symposium held on January 31. During the symposium their presentations were judged by a jury consisting out of eight experts from academia and industry.

tificate proving this, eternal fame and a group dinner sponsored by the company ADSE. This design focused on the development of a large short range aircraft primarily aimed at the Asian market. The exercise is coached by multidisciplinary teams of experienced staff members. Each team has one principal tutor and two additional coaches. These guide the student through the exercise and grade them at the end. Next to that, a team of six staff members coordinates the whole of the exercise. This in all makes it the largest educational activity of the faculty.

At the end of the symposium the jury awarded the “Fedde Holwerda Design Challenge Trophy” to the team that worked on the design called “Design of a Jumbo City Flyer”. In addition to the trophy, all team members received a cer-

Leonardo Times MARCH 2013

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TAKING THE NEXT STEP TOWARDS ZERO EMISSION GENERAL AVIATION

Innovation, sustainability and safety are not the most commonly used words when discussing about General Aviation. A declining reputation and a decrease in demand are not sketching the most flourishing future for this industry. By changing the mentality of engineers, authorities and even pilots however, this form of transport could be revitalized. Within ten weeks, guided by experts, this DSE group has been able to redesign Burt Rutanâ&#x20AC;&#x2122;s Long EZ by optimizing its aerodynamics, structure and most importantly developing a fuel cell based propulsion system with zero emission contributing to an extremely low nuisance factor. TEXT DSE group 1

he original Rutan Long EZ is a homebuilt aircraft with a canard configuration, designed by Rutan Aircraft Factory in the late seventies. In the previous decades, it has served as a General Aviation aircraft bringing pleasure to those who fly it and their accompanying passengers. In this period, several derivative aircrafts are built, based on the Long EZ. It can be seen as a commonly used, innovative small aircraft typically used for medium range flights with a maximum range up to 3,000km. So why would somebody try to redesign something that is working perfectly fine? The answer is simple: To prove that zero emission General Aviation is no longer science fiction and can be accomplished with currently available technology. With this reasoning, this DSE project regarding the Zero EZE has been initiated. Within a timeframe of ten weeks, numerous adjustments have been made to the original Long EZ, which can be summarized by splitting them into three main topics: Propulsion, Aerodynamics and Materials & Structures.

PROPULSION While aiming at sustainable flight, the propulsion system is the most important part

of the aircraft that has to be redesigned. Several options are currently available: Batteries, such as Lithium-ion, LithiumZinc and different types of Air batteries, all promise sustainability. The problem withbatteries, however, is the high weight penalty, the availability of materials and the End of Life disposal issues. Using an alternative fuel such as biodiesel leads to a more sustainable way of flying, but this DSE group had something completely different and more innovative in mind. In cooperation with the Process and Energy department of the University, several options about implementing a Hydrogen based fuel cell have been discussed. When asked if we were joking about putting two human beings into this aircraft, we knew we were onto something new and exciting. With an in-house developed program called Cycle-Tempo, two fuel cells have been designed, capable of delivering 70kW each with an efficiency of 49% and a combined weight of just 90kg. The water produced will be used to cool the fuel cell system, while the excess heat will be used to control the temperature in the cabin. To perform a flight of around 1200km with a cruise speed of 155kts, 15kg of Hydrogen will be stored in specially designed 700bar pressure tanks.

AERODYNAMICS To increase the performance of the aircraft, a low drag body has been designed to store the fuel cell system, the pressure tanks, the electrical motor, the retractable landing gear and all other subsystems, while leaving enough room to provide the pilot and passenger with a comfortable, spacious cockpit. The wings and canard are designed in order to generate more lift to cope with the added weight of the storage tanks and have higher stability during the entire flight envelope. MATERIALS & STRUCTURES Applying an Advanced Grid Stiffened structure for the fuselage and a sandwich structure for the wings optimizes the Zero EZE. These methods are validated using a Finite Element Model computer program. The material used for both the wings and fuselage is Carbon Reinforced Fibre Polymer, CRFP, resulting in a weight loss of 20% for the structural part alone. CONCLUSION The newly designed Zero EZE is an ambitious, innovative project indicating that theoretically it is possible to perform medium range flights with small aircraft, all the while producing zero emissions!

MARCH 2013 Leonardo Times

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CUBESAT

The advent of Cubesats causes a paradigm shift in space exploration and Earth observation, removing the limits posed by prohibitive costs and high complexity. The exponential advances in commercial-off-the-shelf (COTS) technology over the last decade have only made this transition easier, with universities and research organisations alike developing CubeSats and placing them into orbit. Moreover, large companies like Boeing and NASA have also shown interest in this promising, but yet unexplored territory.

n recent years, the growing interest of the space industry in nano-satellite technology has brought about new and exciting possibilities with respect to Earth observation. The idea of forming nanosatellite constellations has made costeffective solutions with high temporal resolutions possible. The goal of this DSE assignment is to design a CubeSat constellation that can provide competitive near real-time imagery in the visual, near infrared and far infrared spectral bands. This is to be achieved using cameras that have been specifically developed for CubeSat use in previous DSE assignments. The first of these cameras is the ARCTIC, which excels at high sensitivity thermal infrared imagery. The other cameras are ANT-2 TMA and RCC designs, which are improved versions of the original ANT camera. These are used to provide imagery in the visual and near infrared spectrum. The outcome of this DSE assignment is a constellation named the Competitive CubeSat Constellation for Earth Observation (C3EO). Market surveys on the rel-

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evance and requirements of a CubeSat constellation have led to the conclusion that both high spatial and temporal resolution are important. To achieve these goals, a three-segment constellation is designed, comprising of 24 ANT-2 RCC satellites at an altitude of 288km and 27 ANT-2 TMA satellites at 500km in sun-synchronous orbits, in addition to 37 ARCTIC satellites at 443km in a polar orbit. The satellitesâ&#x20AC;&#x2122; technical parameters are very similar to each other, with exception of power systems and propellant mass. The constant lighting of sun-synchronous orbits permits the use of lower efficiency thin film cells in the ANT-2 platforms, while the frequent eclipses of a polar orbit constrain the use of solar cells in the ARCTIC satellites to high efficiency triple junction cells. All three satellite types possess electrospray thrusters for orbital manoeuvres, such as phasing and drag compensation, as well as an active attitude control. Furthermore, all subsystems are employed in a 2-by-2U CubeSat structure such that the cameras and antennas can point nadir simultaneously. Finally, data downlink is an important driver in the constellation design, given the high data volumes that are generated by the ANT-2 RCC satellites. All

TEXT DSE group 3

imagery is downlinked by S-band transmitters to a total of eight ground stations, which are distributed around the Earth. Together, these segments deliver full Earth coverage in thermal infrared and near full coverage in the visual and near infrared spectrum. Additionally, a temporal resolution of one day with the ANT-2 TMA and ARCTIC platforms is provided, alongside a weekly resolution with the ANT-2 RCC platform. Such a constellation has a wide range of uses, from disaster monitoring to scientific research and environmental protection. Both the TMA and RCC variants are powerful tools in oceanography, with the ability to monitor corals and phytoplankton, as well as forestry and agriculture. The ARCTIC camera, in combination with its polar orbit, allows the constellation to map surface temperatures across the Earth as well as the ice extent. The cost analysis has shown that the average image price could be as low as 0.1 â&#x201A;Ź/ km2, almost an order of magnitude lower than competitors like Rapid Eye. The possibility of selling 2% of all the imagery collected at this price shows the economic potential of the C3EO constellation is truly exceptional.

Leonardo Times MARCH 2013

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DRAGONFLY

The beautiful island of Curaรงao is a holiday destination for thousands of people. The Caribbean island with its colourful houses, its characteristic marine life and the gentle inhabitants are facing a problem: they are located in a region notorious for its drug trafficking routes, the so-called Caribbean Corridor. Currently, the Dutch Caribbean Coastguard is monitoring the region, using boats, helicopters and airplanes. TEXT DSE group 4

THE MISSION

22m/s cruise speed.

The Dutch Caribbean Coastguard needs a solution to be able to monitor the territorial waters, up to 22 km from the coast.

The Dragonfly is not only a good performing airplane, it is also a boat. The hull is designed in such a way that it will generate hydro-static lift during its take-off run, reducing the drag and shortening the takeoff run.

The Dutch Caribbean Coastguard currently has a fleet of several boats, airplanes and helicopters to monitor this area. The UAV to be designed has to be able to carry out missions autonomously, while being solar powered and able to land and take off from water. It also has to be able to send real time photo and video imaging back to the ground station.

THE SOLUTION The solution to this problem is the Dragonfly. Now that the first steps have been taken towards solar powered flight, it is time to take it to the next level. The Dragonfly is a unique combination of solar powered and amphibious flight. The Dragonfly is a tandem wing, twin-engine aircraft. The tandem wing configuration provides a large surface area for the solar panels and excellent performance at the

The entire topside of the UAV is covered with solar cells, giving it the ability to fly for 3.5 hours during daytime. On battery power, the endurance is 1 hour of cruising. The wingspan and length are 2.5m. Since it is made from glass and carbon fibre composites, it only weighs 10kg and the wings can be detached to accommodate transport and handling.

one infra-red camera. In the nose there is a built-in pan-tilt camera, which is able to classify, identify and track boats as small as a Yola drug boat. The infra-red option means that even during the night, the Dragonfly can still perform its mission on a battery load. The Dragonfly will be able to monitor the territorial waters of Curaรงao for a lower price, while still providing more up to date information. In fact, a fleet of 200 Dragonflies is able to monitor 20 000km2 per day!

The Dragonfly is able to operate fully autonomously for an extended period of time and is able to return to base when maintenance is needed. During the time at sea, the Dragonfly will get its power from the bright Caribbean sun. When the Dragonfly detects a potentially interesting object, it will transmit live footage to the ground station, where they can decide what to do. The sensors to perform all this consist of one electro-optical and

MARCH 2013 Leonardo Times

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THE JUMBO CITY FLYER

A growing aviation market, increasing pressure to be environmentally friendly, and rising fuel costs create business opportunities for those able to overcome these challenges. To this end, an aircraft was envisioned that can carry around 500 passengers over a distance of 2,500km, while being cheaper to operate and with a lower environmental impact than a Boeing 747-400 on the same mission. To stand a chance in the highly competitive market, this aircraft needs to have its maiden flight by 2025.

viation is a major player in the world economy and it is growing steadily. It is expected to grow by 5 percent annually in the coming decades and a major part of this increase can be attributed to routes shorter than 2500km. Add to this the rising fuel costs and the growing global pressure on the aviation industry to reduce its environmental impact and it becomes obvious there will be a huge market for short range, economically efficient, low emission aircraft.

TEXT DSE group 6

passenger compartment, able to seat 514 passengers, and a lower deck cargo compartment able to fit 32 LD1 containers. The aircraft is powered by liquefied natural gas (LNG) and its structure is composed mainly of composite materials.

to that, LNG as fuel reduces the amount of CO2 emitted by the aircraft and the cost of LNG is lower than that of conventional jet fuels. This compensates the disadvantages and makes LNG a better option than conventional jet fuels.

At this moment, the short high-capacity flights are performed by large aircraft, such as the Boeing 747 or the Airbus A380. These are designed for an entirely different mission and an aircraft optimised for a short range high-capacity mission does not exist at this moment. An optimised design such as the Jumbo City Flyer promises lower operating costs and lower emissions.

The fact that the Jumbo City Flyer flies slower than current jet aircraft is because this decreases the drag and the lower flight speed means there is no need for swept wings. A lower flight speed also increases the flight time, but only marginally so, since the Jumbo City Flyer will operate on short routes. An advantage of the straight wing is that it provides more lift and has a lower structural weight compared to a swept wing. The lower flight speed also means turboprops are better suited to the aircraft than jet engines, as turboprops operate more efficiently at Mach 0.62.

All these improvements combined lead to a reduction in fuel consumption and CO2 emissions. The CO2 emitted per passenger by the Jumbo City Flyer on a flight between Beijing and Hong Kong is 40% lower than that by a Boeing 747-400. The Jumbo City Flyer is expected to have a cost of $170 million, whereas a Boeing 747-400 sells for $350 million. In addition, the Jumbo City Flyer is expected to lower fuel costs by 50% compared to a Boeing 747-400, which can reduce operating costs for an airliner by almost 16%.

The Jumbo City Flyer has four turboprop engines mounted under its straight, lowmounted wings. The straight wings are a consequence of the fact that it flies at Mach 0.62. On the inside, it consists of a two-deck

The use of LNG as a fuel means a special fuel system is required, as LNG is stored at around -160째C. The specific energy and energy density of LNG lead to a higher fuel volume, but a lower fuel mass, when compared to conventional jet fuel. Next

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Leonardo Times MARCH 2013

2/27/13 10:38

STRATOBLIMP

On October 14, 2012, Felix Baumgartner made his record-breaking free fall for the Red Bull Stratos project. This mission inspired a DSE team of 10 students to design a comparable record-breaking mission of their own: StratoBlimp. The StratoBlimp is a next generation high altitude weather balloon system, featuring a UAV that is capable of autonomous soft precision landings, whilst carrying onboard an HD camera and meteorological sensors. During the DSE, the StratoBlimp team has designed and constructed a record attempting glider to perform this unique mission mid-2013. TEXT DSE group 7

or high altitude atmospheric observations, meteorological institutes such as the Dutch KNMI still rely on daily measurements taken by weather balloons. These balloons ascend to altitudes of up to 35km and may drift as far as 150km from the launch site before bursting. The sensor unit hanging under the balloon then descends with the help of a parachute. Because the effort and cost involved in finding these units is considerable, only the expensive units are retrieved. The cheaper models are not actively collected and only a fraction is returned by honest finders. Although the meteorological institutes are aware of the impact that the heavy metals contained in the sensor units have on the environment, up until now no sustainable alternative was available. The StratoBlimp is an autonomous UAV, equipped with an HD camera and meteorological sensors, that ascends hanging below a large balloon. As it films its entire mission, including the blackness of space, it falls to the earth at speeds exceeding 400km/h. After four kilometers of free fall it obtains enough velocity to glide back to the initial launch spot or to a different location selected prior to or during the mission. Contact will be maintained with

a station on the ground to send measurement data and its GPS coordinates. In return, the ground station may alter the mission target, autopilot settings or landing location of the return vehicle. Alternative landing sites can range from roads to rooftops. The tripod-mounted selfdirecting antenna makes the ground station easily transportable, which allows all components required for a full mission to fit into the back of any ordinary-sized car. Deployment takes place in minutes and with a mission time of about three hours, multiple launches a day are possible at any location the size of a soccer field. UAVs today are mainly used in earth observation and espionage, but like previous MAVlab projects, such as Delfly and Atmos, the StratoBlimp project pushes the use of MAVs to new boundaries. The vehicle will come across a density more than fifty times lower than that experienced at sea level. Temperatures will drop below -65Â°C, potentially freezing the electronics and causing ice to form on the wing and control surfaces. Furthermore, jet-stream conditions with wind speeds of over 150km/h will have to be overcome. To comply with local regulations, the mass of the vehicle

should not exceed one kilogram. A safety parachute is ready to be deployed at any time during descent in case of malfunction. With a prototype cost of â&#x201A;Ź2,500, StratoBlimp can carry an expensive payload to high altitudes whilst sparing the environment and reducing operating costs. At the Symposium in January, the progress on the prototypes of the return vehicle and ground station was displayed. Although the designs were completed and the prototypes have been constructed, a lot of time and effort will still be required before the StratoBlimp can soar through the stratosphere. Due to the enthusiasm of the group and thanks to the support of the tutors, the project will be continued throughout 2013. The prototype will be further optimized and extensively tested before demonstrating its record-attempting flight at the 2013 Cansat competition.

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ANCILE PROBES

For some decades, scientists have rigorously investigated the planet Mars. A history of satellites and landers gave mankind more insight into the origin of the ‘Red Planet’. One question that is still unresolved is the possible existence of plate tectonics on Mars. The Ancile mission aims to provide a definitive answer to this question by placing multiple probes on the Martian surface. The probes will track their own positions over a period of five years and any relative movement between these probes will prove the existence of plate tectonics.

he Ancile mission’s objective is to prove or disprove the existence of plate tectonics on Mars. Plate tectonics is a global phenomenon by which crustal plates slowly move with respect to each other due to a planet’s internal convection streams. The most characteristic results of this process on Earth are the formation of mountains and deep sea trenches when these plates collide. Unfortunately, on Mars these features are less pronounced. The focus of the research is the area known as Valles Marineris (VM), a straight canyon roughly 200km wide and 3,000km long and easily visible from space. It is suspected to be the result of two plates sliding along each other, known as a transform fault. To make sure the mission can prove VM is due to plate tectonics, the movement of both sides of the canyon will be tracked. Knowing plate tectonics on Earth displace the surface by several millimetres each year, the accuracy of Ancile needs to be in the order of one millimetre per year. A technology suitable for the mission is called Very Long Baseline Interferometry (VLBI). The technique uses radio signals from a single source at a great distance, which can be transmitted from the Deep Space Network on Earth. Then, the delay in the arrival of the signals in between

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ground stations makes it possible to track the absolute distance between these stations. To map a 3D image of the ground of VM, one seismometer is placed on each station, making sure its origin is determined. Now, we only need to place these ‘stations’ on Mars. All probes will be transported to Mars housed in a transfer module, consisting of two rings of eight probes placed above each other. The module will spin up and release the probes in two stages before they arrive to Mars, to make sure all of VM is covered by the probes. Although the transfer module will crash on the surface, the individual probes de-spin and deploy inflatable heat shields before entering the atmosphere at a velocity of 5.5km/s. The probe decelerates to a speed of less than Mach 2 before deploying a parachute to further slow the probes down and align them vertically for penetrating the surface. The heat shield is reshaped to be stable in the subsonic region after falling through the sound barrier by deflating specific sections of the shield. At 90 m/s the probe penetrates the ground and embeds its pin into the soil.

TEXT DSE group 8

ic energy. The penetrating pin is released from the probe during impact, driving itself 60cm deep into the ground to place a seismometer out of reach from wind noise. The probes deploy flexible solar panels by inflating two tubes, rolling-out a solar panel of 2.7 by 0.3m on the ground. A communication link is established using a phased-array antenna on top of the box. From the point of deployment, the probes need to be operational for five years. During this time, their data will be relayed through the Mars Reconnaissance Orbiter and be analysed on Earth. Our DSE group is confident the gathered data will conclusively determine whether or not Mars is shaped by mechanics similar to the ones we see on Earth. This mission is named after the shield of the Roman god Mars, Ancile. The myth goes that Mars sent it down from the heavens to the second king of Rome, King Numa Pompilius, as a symbol of luck.

The bottom of the housing is covered by a crushable honeycomb structure to reduce peak shocks and absorb 85% of the kinet-

Leonardo Times MARCH 2013

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STRATOMAV

Looking at the expected growth in global air traffic, it is urgent that the climate effects of contrails are investigated. With this knowledge, effective environmental policies can be developed. Continuous local measurements on contrails are required to compare data from satellites, in-situ measurements and lab experiments. The ever increasing capabilities of UAVs, their low cost, fast development times and flexible application possibilities make them an ideal platform to perform such scientific research. TEXT DSE group 11

DESIGN PURPOSE The purpose of this project is to develop a Micro Aerial Vehicle (MAV) that is able to perform stratospheric research on the regional influence of contrails on the ground surface temperature. By remaining continuously airborne in the stratosphere for at least a year (which extends the current operating time of UAVs), StratoMAV is able to take regular measurements on contrails. The collected data is downlinked in near real-time. StratoMAV is constrained to have a total mass of at most five kilograms, a life time of at least five years and a maximum unit price of â&#x201A;Ź50,000. WING DESIGN The result is a high efficiency, low weight UAV with a 7m wide, high aspect ratio wing, which enables a low cruise speed of 18m/s, and a twin boom inverted V-tail. A high camber, thin airfoil has been chosen to generate sufficient lift, as the air density is low in the stratosphere. The airframe mass is only 16% of the total aircraft mass. A D-box is placed in the front of the wing. It contains a single spar and is made out of composites to provide high stiffness, re-

sulting in low deflection. The aft section of the wing is composed of balsa wood ribs and the wing is covered in lightweight transparent foil. PROPULSION AND POWER SUBSYSTEMS DESIGN A single high efficiency custom tractor propeller (low rpm, fixed pitch) was chosen to operate in the low density conditions. It has a diameter of 0.87m, is located mid-wing and is foldable to allow the UAV to glide down during descent. A custom two-stage gearbox with aluminium spur gears enables the low rpm. Power is supplied by thin film solar cells and state-ofthe-art lithium ion batteries with a high specific density. Instead of sizing the batteries for the worst case scenario, the flight route was optimized by flying at different latitudes. As a result, the batteries take up 44% of the total mass.

The carried payload consists of four spectrometers, one thermal camera and a processor. Contrail detection is achieved by a pattern recognition algorithm on the thermal data. If a contrail has been detected, StratoMAV determines in which direction the contrail is moving and then flies along it, making sure that the spectrometers are aligned with the border of the contrail. The radiation flux of contrails is then determined by measuring the solar and terrestrial radiation. At the end of a contrail, StratoMAV turns around and follows the contrail again in the opposite direction. Normally, the StratoMAV will continue taking measurements on the contrail until the contrail has faded to such an extent that it is no longer detected by the contrail detection algorithm.

PAYLOAD AND SCIENCE MISSION A Paparazzi autopilot system was chosen, together with a modem and a 900MHz patch antenna. A combination of active and passive thermal control is applied.

MARCH 2013 Leonardo Times

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NASA

RVD

PIONEERING THE RED PLANET

Adventures on Martian soil

Mars has always obsessed humankind - the Red planet, the ‘New Earth’. And with the recent successful landing of NASA’s Curiosity rover, Mars is closer than ever. Ever since 1960, we have actively been sending probes and rovers to observe the planet, but not without defeat. The road to the red planet is long, and the landing is rough. And since we do not have the technology yet to bring pieces of Mars to our laboratories, we’ll have to bring the laboratories to Mars. TEXT Ivo van der Peijl and Marijn Veraart, Students Aerospace Engineering, President and Treasurer of the 27th Space Department.

THE EARLY DAYS Between October 10, 1960 and 1967, six Mars missions were undertaken, five by the USSR and one by USA. This was maybe too ambitious for the early days, because two failed to reach earth orbit, two failed to leave it and two had problems en route. It was December 20, 1967 when the Mariner 4, an American Mars flyby probe, flew by the surface, and sent back 22 close-up photos. Man’s first successful flight to Mars was a fact. Reaching it was now possible. Landing was the next logical step. PIONEERING THE SURFACE The USSR had the first landing success. Their 1,210kg Mars 2 lander crashed on the surface of Mars, but was the first manmade machine to actually touch the planet. Only five days later, the Mars 3 lander made a successful landing, but operated for only fifteen seconds, just enough time to take one picture of the horizon. The exact reason for the lost communication was unknown. Researchers suspected a dust storm was responsible for both the destruction of the communication system, and the bad quality of the picture. Fur-

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ther attempts, the Mars 4 through 7, were all partially successful. They all gathered some data, but none of them were able to either enter the intended orbit, or make a successful landing. It was NASA who had the next success. The Viking 1 landed on the Martian surface July 20, 1976, shortly followed by the Viking 2. These identical orbiters and landers were sent to the planet to take photographs, collect scientific data and perform some biology experiments in search of extra-terrestrial life. Unexpectedly, chemical activity was found in the soil, but no evidence of microorganisms. Scientists believe Mars sterilizes itself. They think the combination of extreme dryness, the oxidizing nature of the soil and the solar ultraviolet radiation prevents the formation of living organisms. The Mars Pathfinder was the next step in Mars exploration. It was the first successful lander that carried a rover, the Sojourner. After the successful landing in 1997, the landing site was renamed the Carl Sagan Memorial Station, in honor of the astronomer. Sojourner was a small rover. With its 10.5kg, the 30cm tall rover travelled at a

velocity of 1cm/s. The main task of the rover was to examine rocks nearby the landing site. Equipped with an Alpha Particle X-ray Spectrometer (APXS), the composition of rocks could be determined. The oldest Mars-related spacecraft that is still in use today is the 2001 Mars Odyssey. This spacecraft is orbiting Mars at an altitude of approximately 3,800km. The Odyssey has multiple objectives. It uses its three main instruments for studying the radiation environment, determining the distribution of minerals and determining the presence of twenty chemical elements. A second task is to support other Mars missions. The orbiter provides a communications relay for the rovers Spirit, Opportunity and Curiosity. At this very moment, 95% of all the data collected by the Curiosity is sent through the Mars Odyssey. The record for the longest operating rovers is held by the Mars Exploration Rovers, named Spirit and Opportunity. Or specifically, in the hands of the Opportunity, which is three weeks younger than the Spirit. Communication was lost with Spirit in 2010, after 2,208 Martian days, a stun-

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CURIOSITY In the evening of August 5, 2012 the Curiosity rover, the most technologically advanced rover ever built, landed in Mars’ Gale Crater. The Curiosity’s main mission, also known as the Mars Science Laboratory, is to determine whether Mars ever was, or is, habitable to microbial life. To do this the rover is equipped with seventeen different cameras and a robotic arm containing advanced laboratory-like instruments and tools. One of the most interesting parts of the mission was the unique landing (Fig. 1). This specialized landing sequence, which included a giant parachute, a jet-controlled descent vehicle and a bungee-system called the ‘sky-crane’, was required because the landing techniques for previous rover missions could not accommodate the larger and heavier rover. The Curiosity actually has the size of a small MiniCooper and at $2.5 billion; it is the most expensive mission to the Red Planet yet. The hope for the question of life on Mars peaked at the end of November last year, when mission chief scientist John Grotzinger came with the news: “This data is going to be one for the history books. It’s looking really good”. Of course, a lot of excitement raged in the newspapers and on the Internet. NASA later clarified that Grotzinger’s (it is in the name) news referred to the mission itself and not to specific results. Indeed later, they came with the statement that the rover had indeed found something in the dirt, but there was no big news from the first soil test. So far, there is no definitive sign of chemical ingredient necessary to support life. Now the question can be asked, what did Curiosity find in the soil? Water, sulphur and perchlorate, an oxidizing salt, also detected during a previous Mars mission, and the remnants of an ancient streambed. As said by mission scientist Ralf Gellert: “This is typical, ordinary Martian soil.” Some interesting hints of a simple carbon compound have been found in the soil, it only needs to be determined if it is native to the Red Planet, or hitchhiked from Earth or came from space. It is believed by scientists that the best chance of finding life supporting carbon is at Mount Sharp, a five kilometers high mountain in the center of the Gale Crater.

NASA

ning 2,118 days more than planned. Both rovers landed in January 2004. Their main goal was to find information about water on Mars. Therefore, their landing sites were specifically chosen. Spirit landed in Gusev Crater, a possible former lake. Opportunity landed in Meridiani Planum, where minerals could contain clues. The Mars Exploration Rovers have survived a complete change of seasons. They withstood changes in temperature, radiation and dust storms. In doing this, they collected vital information that can and will be used in future Mars missions.

Figure 1. A figure showing the different stages of the Curiosity descent.

Therefore, after the last half year of driving, snapping pictures, scooping up dirt and zapping at rocks, Curiosity has started its trek to Mount Sharp – a trek that will take up 9 months. This road trip brings great expectations, as it is the main reason that the rover was targeted to land in the Gale Crater. Expectations are high as Curiosity’s job is to figure out if the landing site had the correct environmental conditions to support basic forms of life. It could also have been a six-month journey when driving nonstop, but scientists will want to command the rover to rest and study the rocks along the way. It now will be a ninemonth odyssey… THE FUTURE OF MARS EXPLORATION Recently, a surprising announcement from NASA came with respect to near future Mars exploration. It will send another rover to Mars in 2020. Mixed reactions followed, as to why NASA keeps focusing on Mars while there are ice-covered moons like Saturn’s Titan, which remain relatively unexplored. On the other hand it simply makes a lot of sense to conduct this new mission, as it will be built from Curiosity’s spare parts, can make use of the same landing technique and has prevailing positive conditions (until now the Curiosity is a big success). Of course, new instruments will be present in the $1.5 billion-budgeted Curiosity II. NASA has been hinting that it is interested in a “sample catch” that will collect and store Martian soil samples. These samples would be collected by a future (manned?) mission to Mars, and returned to Earth for further analysis. As said by NASA administrator Charles Bolden: “The Obama administration is committed to a robust Mars exploration program. With this next mission, we’re ensuring America remains the world leader in exploration of the Red Planet, while taking another significant step toward sending humans there in the 2030s.”

REFERENCES Chronology of Mars exploration: http://history.nasa.gov/marschro.htm Viking mission: http://photojournal.jpl.nasa.gov/catalog/PIA09703 Pathfinder mission: http://mars.jpl.nasa.gov/MPF/index1. html NASA Mars Rover Overview http://marsrovers.nasa.gov/overview/ NASA Curiosity Overview http://www.jpl.nasa.gov/missions/ details.php?id=5918 NASA Curiosity article http://www.boston.com/news/science/2012/12/03/mars-rover-curiosity-surprise-soil-test/IoYQVJlRSJXTzjJq3QW8NO/story.html http://articles.timesofindia. indiatimes.com/2012-12-31/science/36079075_1_mars-rover-curiosity-mount-sharp-gale-crater Future of Mars exploration http://www.extremetech.com/ extreme/142414-nasa-will-senda-second-curiosity-rover-to-marsin-2020 SPACE DEPARTMENT The Space Department promotes astronautics among the students and employees of the faculty of Aerospace Engineering at Delft University of Technology by organizing lectures and excursions.

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Internship report

AIRCRAFT TOOLING AND AUTOMATED EQUIPMENT Internship at Electroimpact, Seattle USA

If we consider the enormous amount of parts that are necessary to build a commercial aircraft, it becomes clear that assembling all parts with great accuracy is a challenge. The development of new tooling solutions and automated equipment for the manufacturing of commercial and military aircraft is therefore of great importance. The increasing use of robots results in faster, safer, less expensive and more precise manufacturing processes. TEXT Elisabeth van der Sman, BSc. Student Aerospace Engineering

have always had a passion for aviation and robotics. It fascinated me that huge machines could be controlled to perform extremely precise jobs. In my second year of aerospace engineering I realized that I wanted to learn more about robotics and manufacturing. I started looking for a job to gain hands-on work experience. Close friends of my family in Seattle advised me to approach Electroimpact. Not being familiar with the company, I opened their website and my eye fell on a number of pictures showing a great variety of machines for aircraft manufacturing. While reading I noticed another interesting aspect; engineers are responsible for building and testing their products. Being able to follow a project from the initial planning to the final product was something I found quite unique. With much enthusiasm I sent my resume and cover letter and shortly afterwards a Skype interview followed. When they let me know that they were happy to have me as an intern it seemed too good to be true. However, a lot of paperwork still had to be filled in order to get a Visa. Electroimpact was very helpful and the application process was soon completed. As the last exam period was about to finish I packed my bags and

prepared for the flight to Seattle. ELECTROIMPACT Electroimpact is a highly experienced provider of factory automation and tooling solutions. The company started its life primarily as a supplier of machine tools to Boeing. But over the years Electroimpact has gradually expanded its business overseas to act as a supplier for other major aerospace companies such as Airbus, Spirit Aerosystems, the Japanese heavy industries companies MHI, KHI, FHI, as well as Bombardier and Embraer. The company is situated in Mukilteo near Seattle and close to the Boeing Everett factory. The campus includes two very large high-bay construction and buyoff facilities featuring cranes with up to 32 metric ton lifting capacity, as well as several smaller buildings. As mentioned before, a unique characteristic is that engineers are responsible for both design and development, following projects from the initial planning to the final product. The engineer that designs the tool or machine is also responsible for detailed drawings, coordinating manufacturing, assembly, and any tooling setting or machine align-

ment. This minimizes the disconnection that happens at a typical company between an engineer, drafter, manufacturer and assembler. MY EXPERIENCE AT EI Each summer Electroimpact hires around 30 young interns. The interns are divided into groups according to their study program namely mechanical, electrical and IT engineering. As an intern I had a great time working at the company. I was pleasantly surprised to meet so many young students of my own age. The other interns were all American students, mainly from Washington State. They were very keen on showing me the American traditions and every lunch break was a great opportunity to exchange ideas while eating hamburgers and donuts. The location of the company provided the opportunity for trips to the seaside and kart races. Also the senior engineers were very willing to share their knowledge and experience. As all engineers like problem solving, they would always explain how to achieve an even better result. My internship lasted two months from the beginning of July to the end of August,

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and my assignment was related to the metrology field. In the first week I learned how to use laser trackers to measure a control network. Once the data from the laser tracker had been collected, I learned how to bundle the data using Spatial Analyzer. Next I investigated ambient and laser light sensors and DC motors for prototypes of new products. For this task I focused on improving my CAD skills before starting the design of my own parts using Solidworks. To check the mechanical functions I made assemblies and animations. As soon as I completed the Solidworks design, it was time to evaluate the actual product. The parts I had created were produced with 3D printing. It was amazing to see the real parts on my desk a few days after the CAD model had been completed. I mounted the light sensors on the parts to test the complete prototype. To analyze data from the light sensor a control network had to be set up. The network consisted of a CPU, a circuit board to amplify the signal and a computer to see the results. It was a lot of fun to solder wires and calculate the maximum voltage that the sensors could handle. Various power sources had to be attached and trimmed to the right voltage using multimeters. When the computer screen started showing the results it felt like the calculations and the manufacturing work had all been definitely worth it. This internship gave me the opportunity to learn about the different aspects of being an engineer. I received a broad and varied assignment that contained a good mix of research, design, manufacturing and testing. The American easy going style of jeans and t-shirts and the cooper-

ation between the engineers contributed to a very pleasant working environment. SEATTLE (CULTURAL AND FREE TIME ACTIVITIES) For aviation enthusiasts Seattle is the perfect place to be. The city is surrounded by many large and small airfields. Any type of flying is therefore possible. I had the opportunity to fly at the Evergreen Soaring Club in Arlington in a Grob G103. The view from above was absolutely astonishing. On the ground below, the lakes and forests form a beautiful pattern while the snow- covered mountains span the horizon. Furthermore, I had the chance to try formation flying in an aerobatics aircraft. An engineer from Electroimpact built his own RV-8 and offered to show me his skills in making loopings, barrel rolls and chasing the tail maneuvers. Every summer Seattle offers an incredible air show called Seafair. The C-130 aircraft from the Blue Angels team begins each demonstration showing the maximum performance of the plane. Shortly afterwards the jets appear in their diamond formation. They show the most difficult maneuvers reaching a minimum distance of approximately 45cm apart. If you want to closely inspect the Blue Angels F/A-18 Hornet, the Museum of Flight is something you do not want to miss. The museum has an amazing collection of old, new, civil and military aircraft. The Blackbird and the Blue Angels aircraft were two of my favorite ones. I was a guest at my family’s friends’ house in the Capitol Hill area close to the center of town. They really made me feel at home and encouraged me to discover Seattle’s social and cultural life.

This is a lovely area with nice restaurants, fancy shops and parks. I really loved watching baseball games with them. The Seattle baseball stadium is home to the Mariners. They play nearly every day of the week and during home matches the stadium completely fills up with fans. I was surprised by the interest and passion for sports in Seattle. In addition to baseball, Seattle has a football team and an American football team with good players that keep the reputation of the city high. The most common shop around town is definitely Starbucks, as Seattle is the city where the company was founded. Small local beer breweries also provide a nice place to relax after a day’s work offering a diverse range of flavors and types. I discovered that the Dutch are not the only ones who love special types of beer since a visit to the brewery after work was common among engineers. After work I would join the other interns for a trip to Mukilteo’s beach or for an evening canoeing on Washington Lake. For a 21st birthday party I had the chance to go to an American fraternity from the University of Washington as some of the interns were members there. Finally, there are also beautiful things outside of Seattle. With my family friends I travelled to Oregon for a weekend visiting the cities of Portland and Ashland. This is a trip worth making as every summer in Ashland there is a high quality Shakespeare festival where they perform old and modern plays that attract a huge crowd. In retrospect, I can say that this internship was an amazing opportunity and a unique experience. MARCH 2013 Leonardo Times

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Student project

PROJECT STRATOS Reaching space with a student-built rocket

In the spring of 2009 a team of 15 TU Delft students travelled to Kiruna, Sweden with only one goal: to launch the rocket Stratos I they had been working on for 2 years to an altitude of over 12km, thereby claiming the European Amateur Rocket Altitude record. These students were part of Delft Aerospace Rocket Engineering (DARE), a Dream Team of the TU Delft involved in research, development, manufacturing and launching of rockets. However, this record-breaking launch was not a single project; it was the first part of a larger endeavour of which the primary goal was to become the first student team in the world to reach space with a student-built rocket. TEXT Maarten Haneveer, BSc Student Aerospace Engineering

PROJECT STRATOS Stratos I that flew in Kiruna, Sweden in 2009 was the first rocket designed and produced by DARE capable of reaching the stratosphere. Stratos I flew on an inhouse developed solid rocket fuel combination of KNO3 and industrial sugar. According to radar and telemetry data, the rocket reached a height of 12.3km, whilst also collecting scientific data using electronics situated in the nose cone. This meant that Stratos I broke the European Amateur Rocket Altitude record [1]. Remnants of the flight capsule are still being displayed in the hall of the Electrical Engineering, Mathematics and Computer Sci-

ence (EWI) faculty at TU Delft. After the successful launch, the team was in a euphoric state. Straight after the flight capsule was retrieved and returned to Delft, the team started discussing a follow-up project. The team members knew that they had the capability to design, manufacture and launch rockets to extreme heights (on an international level), and this gave them such a confidence that DARE came up with a new and even bigger challenge: becoming the first student team ever to reach space. A preliminary study concluded that with a higher specific impulse and an increased performance of the propulsion system, it was possible

to reach the Kármán line – the boundary of space – at 100km altitude. Additional calculations showed that the solid rocket fuel used in Stratos I (Isp=120s) needed to make way for a type of fuel with a specific impulse of above 180s. Thus developing a new propulsion system and a new type of rocket fuel was essential. It became clear that redeveloping a propulsion system and reaching an altitude of 100km was more feasible if done stepwise. The team decided that the most reliable way to reach space was to first develop a new propulsion system and fly this system on a rocket half-way to space

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The vastness of Project Stratos calls for a large team: technical teams working on electronics, propulsion, simulations, telecommunications, aerodynamics and recovery, but also non-technical teams operational on payload acquisition, sponsoring, public relations, logistics and launch site communications. More than forty DARE members, from multiple faculties, each with their own strengths, are currently actively partaking in one of Project Stratos’s many sub teams. Each different sub team is led by a team leader, and together with two project managers they have to ensure the entire project and all its members are on the same wavelength, whilst also keeping up the pace in developing their respective subsystem. This combination of member’s contribution to (non-)technical aspects and management functions results in a dynamic yet effective cooperation between the teams. As mentioned, Stratos II needed a far better performing engine to guarantee reaching the 50km altitude. In the middle of 2012 two propulsion teams could provide propulsion systems meeting all requirements. These teams were the Solid Six (solid rocket fuel) and Dawn (hybrid rocket fuel). Obviously, each team wanted their system to propel Stratos II, however due to safety, cost and reliability considerations, only one propulsive system would be chosen. Trade-off tables were made, weights were given to criteria and long nightly meetings with the team leaders were held to ensure the right propulsion system would be chosen. The result of weeks of revising all aspects and argumentations of both teams led to the decision that Dawn, the hybrid team, would provide Stratos II with its propulsion system. HYBRID PROPULSION A solid rocket motor makes use of a solid fuel and oxidizer combined into a single

Figure 1. Thrust Curve of Dawn Hybrid Engine

DARE

STRATOS II Since Stratos II will reach the lower end of the mesosphere – one of the most poorly understood parts of the atmosphere – its secondary mission is to be a research rocket. Space agencies such as NASA use research (or sounding) rockets [2] to conduct measurements and carry out scientific experiments during its suborbital flight. Stratos II will provide 12 payload slots and advanced electronics, thereby striving towards the professionalism of corporate sounding rockets.

DARE

(50km) and after that continue on to the ultimate goal of 100km. The initiative of two different rockets, Stratos II (50km) and Stratos III (100km), was born. This endeavour towards the altitude of 100km, consisting of the research, development and manufacturing of the three Stratos rockets, was named Project Stratos.

Figure 2. Dawn Engine Test Fire 12-sept-2012

grain. This makes these types of rockets relatively simple but also less efficient in the amount of thrust they produce for every unit of propellant compared to, for example, liquid engines. Liquid rocket engines, using liquid fuel and oxidizer, are far more complex but offer better performance than solid motors. A hybrid engine, like the one developed by Dawn, combines properties of both solid and liquid engines. Hence it is more efficient than a solid engine but less complex than a liquid one. The development of the hybrid engine gained a lot of momentum during the DARE minor of 2011, in which a complete working test bench was created and valuable data was acquired (Figure 1). The knowledge gained during the minor and the corresponding fire tests (Figure 2) resulted in the first hybrid engine concept. (Figure 3) is a schematic representation of the hybrid engine. The numbers represent the different subsystems. The largest volume in the engine is for the oxidizer tank (1). This will be an aluminium tank in which N2O will be stored under pressure. N2O is also known as nitrous oxide or laughing gas. Below the tank is the feed system (2), which connects the tank

to the engine. It contains a special valve that can be opened (and shut) remotely using an electronic system. When the valve is opened, oxidizer will flow through the pipes of the feed system towards the combustion chamber. The N2O first passes the feed system to the injector (3). The injector is placed in the combustion chamber (5) where it vaporizes the incoming nitrous oxide, making the oxidizer react more easily with the solid fuel grain. Subsequently the igniter (4) is set off by an electrical current, igniting and heating up the combustion chamber and fuel inside it. When the N2O enters the combustion chamber, it will be hot enough to start the reaction with the fuel. The fuel and oxidizer will start to burn, and form gasses and build up pressure inside the combustion chamber. These gasses are then expelled through the nozzle (6), which, due to its shape, will accelerate the gasses immensely and thus propel the rocket. In June 2012 the Morning Star rocket was launched successfully near Leipzig, Germany. The Morning Star used the concept engine described previously, and was the first rocket launched by DARE to contain a fully working hybrid engine (Figure 4).

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DARE

Figure 3. Schematic Overview Dawn Engine

Figure 4. Dawn Team with Hybrid-powered Rocket (Morning Star) in Leipzig

Another great benefit of the hybrid engine is the choice of fuel and oxidizer. Separated, nitrous oxide and Sorbitol are inert and therefore a lot safer to handle. Furthermore, travelling abroad to a yet to be determined launch location will be easier as less certifications are needed for the logistics of the hybrid engine. Currently, the Dawn team is making a full scale hybrid engine. This engine will be used for full scale engine testing at TNO in April, from which the final characteristics can be calculated. Once these tests are done, the hybrid engine is ready to be used in Stratos II. The hybrid engine largely defines the characteristics and dimensions of the rocket. According to the current design and choice of engine, Stratos II will be a single staged, hybrid (N2O and Sorbitol + additives) engine driven rocket with a maximum velocity of around 1000 m/s and a maximum acceleration of 5G for the duration of 18 seconds. The capsule will be 160mm in diameter and by means of a coupler connected to a 200mm engine section. The total height of the rocket is designed to be 5.5m, containing 99.6 kg of fuel and oxidizer within. Further characteristics of the Stratos II are a specific impulse of 190 and a total thrust of 10,000N. In (Figure 5) a detailed flight plan is illustrated. Once the rocket is launched, it will accelerate to its maximum velocity and after 18 seconds engine burn-out will occur. From there on Stratos II will decouple its engine section and continue coasting to

its apogee of 50km, whilst sending down in-flight data. Once the capsule starts returning to Earth, the flight computer will initiate the recovery system which will bring the capsule containing the scientific payloads safely to the ground, from where it will be retrieved and brought back to the team. The launch described cannot be possible without the use of sophisticated flight electronics and a durable capsule. These two components ensure a safe environment for the launch crew, the rocket and for the safe return of the payloads and are therefore of significant importance for the success of the project. Letâ&#x20AC;&#x2122;s elaborate a little bit more on them. ELECTRONICS AND CAPSULE The electronics segment include the flight computer and a ground station, built on experiences gained from Stratos I and developments within DARE over the last 2 years. The flight computer works in twofold: execute the rocket flight plan and provide power and communication for the payloads. Consisting of various sub systems such as a transmitter, a measurement board, a storage board and others, connected by a backbone and controlled by a master control unit (MCU), the flight computer monitors and controls the flight and is capable of routing the data received from the measurement board and the payloads to the storage board and the transmitter, which in turn sends the data back to the ground station. These electronics are situated in the top

of the capsule. Another function of the electronics is the ignition of the hybrid engine and the activation of the recovery system. The recovery system consists of a dual parachute system. A small drogue parachute will deploy first to decelerate the capsule after apogee and the main parachute will then be deployed to ensure a safe landing. This system reduces the shocks on the capsule whilst simultaneously reducing the footprint of the capsule. The electronics, payloads (Figure 6) and recovery system are all situated inside the capsule which, in the top part, is made of glass fibre to ensure radio transparency for the telecommunications. With an acceleration to 5g in 18 seconds and top speed of 1000m/s, one can imagine that high compressive loads and temperatures (up to 450Â°C) are exerted on the capsule. Therefore, a strong yet light skeleton and deployment system have been designed for the internal structure of the capsule. On the tip of the nosecone heat-resistant materials are being added to cope with the high temperatures and preventing the cone from melting mid-flight. PAYLOAD AND SPONSORING Combining all the technical aspects results in a rocket reliable of reaching and delivering payloads to a 50km altitude. The payload section consists of 12 slots with Standard PC/1-4 (Pumpkin) CubeSat PCB dimensions, each with a nominal power supply of 1W, SPI compliant communication protocol and availability of 2kB/s storage data rate. Slots can be bought up by private, educational or industrial entities

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DARE

for use of experiments of their choosing. Suggested scientific research and technological experiments that can be executed during flight are magnetic field and upper atmosphere radiation measurements, testing of navigation, positioning and attitude determination systems and of electronic systems/sensors designed for space and astronautical operations. At the moment of writing, (international) interest has been shown in this project and contacts regarding potential payloads have been initiated. Even though Project Stratos is a student team and therefore has no labour costs, the materials, logistics, tests and PR still have to be accounted for. Luckily there are many companies and organizations interested and willing to invest in Project Stratos. The main sponsor, Dutch Space, largely sustains the continuity of the project whilst also exchanging their knowledge and experience, proving themselves to be of vital importance to the project. Other companies, such as TNO and TU Delft, respectively provide test sites and workshops. The help of these companies and organizations helps continue the dream for the 100km, and simultaneously results in a professional involvement with the industry.

Figure 5. Stratos II Flight Plan

on these organizational aspects of the project. DARE is certain that the hard work of all the teams of the past years and the upcoming months will result in a successful launch of the Stratos II rocket at the end of 2013. From thereon DARE will be one step closer to attain the title of being the

first student team in the world reaching space. For more information on joining Project Stratos, sponsorship and payload opportunities, as well as news or updates about the project, please visit ProjectStratos.nl or send an email to info@projectstratos.nl.

DARE

LOOKING AHEAD Many technological challenges have been solved by the hard-working DARE rocketry enthusiasts since the start of the project. Full scale motor tests are scheduled in April and a launch is scheduled at the end of 2013. However, preparations for the launch side, logistics, payloads, sponsoring and PR have to be made in order to continue the project smoothly once Stratos II is rolled out. In the upcoming months (social) events are planned to get Project Stratos out to the public, calls for payloads will be intensified and potential partnerships are being sought to increase the financial security of the project. Furthermore, a concrete launch site will be acquired along with the corresponding certificates and logistics will be dealt with. Project Stratos is currently recruiting new team members excited in collaborating

References [1] http://www.hobbyspace.com/Rocketry/Advanced/records.html [2] http://sites.wff.nasa.gov/code810/ Figure 6. Payload Section Design

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“We vlogen met een zucht...”

HELICOPTER INDUSTRY- EARLY BEGINNINGS TO NOW An outlook on the helicopter market and its major players in the rotorcraft industry

The helicopter is probably the most flexible aircraft that we know today. Although its history dates back to around 1500, the first practical helicopter wasn’t manufactured until the 1940s, roughly three decades after the Wright brothers’ first powered human flight. Today, helicopters fulfil a wide range of tasks both in the civil and in the military sectors. Rescue missions requiring high precision, surveillance or quick transport are all possible due to this wonder of vertical flight. TEXT Lubi Spranger, BSc Student

he first helicopter-like machine was envisioned by the revolutionary inventor Leonardo da Vinci in the mid 1500s in the form of the sketch of an aerial screw. Based on the principle of compressing air through its rotational motion to generate lift, it was supposed to undergo vertical flight according to the same principle as today’s modern helicopters. Before practical helicopters as we know them were actually able to lift off and sustain flight for a remarkable period of time, more than three centuries had to pass by until the final breakthrough at the end of the 19th century with the invention of the internal combustion engine, providing the required power for full-scale models. Intensive experimenting throughout the 20th century lead to the major problems presented to vertical flight being resolved. One of the main issues lay in the torque created by the rotor blades on the fuselage, leading to an unwanted spin of the main body opposite to the direction of the rotor. This problem was resolved by either including a vertical tail rotor able

to counterwork this undesired motion or by using two oppositely spinning blades on the main rotor shaft. Another difficulty that was faced by early helicopter engineers was the dissymmetry of lift. As the rotor blades turned in a fixed direction, the rotor blades would alternately spin in the direction of the airflow and against the airflow, leading to an unequal generation of lift due to the difference in speeds. Again, a solution was quickly found in the form of the swashplate, which allowed for equal lift on each side of the central rotor shaft by alternating the rotor blade angles. Cycling controls were introduced to control the helicopter’s roll and pitch, making sure the pilot didn’t unexpectedly face the horizon upside-down. Through the work of different pioneers from Europe and the USA the first practical helicopter came to life in 1936, the Focke-Wulf Fw 61, designed by the German professor Henrich Focke. The Ukrainian-American inventor Igor Sikorsky had designed the successful VS-300 model by 1940 which managed controlled flight for-

wards, backward, up, down and sideways. Sikorsky’s design laid the foundation for modern single-rotor helicopter designs. Other pioneers in the field included the American Stanley Hiller, Jr. who invented the first helicopter to have all metal rotor blades that were very stiff and made it possible to fly at much higher speeds. Another American inventor in the field, Arthur Young of the Bell Company, made significant contributions to the design of the world’s first commercial helicopter, the Bell Model 47. Today, helicopters find a wide range of application with great variety in individual design, both for civil and military uses: be it in the public sector for police operations, rescue missions with air ambulance or for industrial purposes such as shuttle services between an oil platform and the mainland. The world moves more and faster than ever before and desires more flexibility. The demand for rotorcraft increases as better utility helicopters allow for the access of more remote drilling locations in the oil industry. The market

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WWW.IMAP.COM

WALLPOPER.COM

research company Lucintel predicts a steady growth in the helicopter market due to increased military demand from emerging economies and the recovering global economy. It places an estimate of the rotorcraft industry value at $24.7bn by 2017. Dividing the global helicopter manufacturing industry into the four different sectors [North America, Europe, Asia Pacific (APAC) and Rest of World (ROW)], APAC is predicted to be the dominating sector by 2017 which is explained with the expected rising military expenditures in the report by Lucintel. Their forecast of the 2012-2017 Global Helicopter Industry also predicts the following challenges that the helicopter industry will have to face in the coming years: high import tax for aircraft, budget cuts in the defence industry, great availability of second hand helicopters and on top of that unfavourable terms of financing. Hence, it becomes clear that there are a number of difficulties manufacturers will have to deal with. Nonetheless, the report also indicates important industry growth drivers such as global economic growth, new technological developments, rising demand for multipurpose helicopters and freshly emerging markets. These new market sectors will lead to an increased demand of helicopter use both for industrial and civil purposes. In particular, the military market is expected to expand faster than other market segments. Rolls-Royce also predicts a ‘strong long term demand for vertical lift’ in their Helicopter Market Forecast 2011-2020 driven by technology advancements (such as digital cockpits, autonomous cargo delivery and re-supply for military types) and changing global market requirements. Their turbine rotorcraft deliveries are estimated at a value of $140bn with the turbine engine market amounting to a predicted value of > $12bn. The number of rotorcraft to be produced as predicted by Rolls-Royce is placed at 16970+. An analysis of the trends in the civil market indicate that although singles and light twin helicopters lead the market by units, intermediates and light twins lead the market by value. Market drivers as identified by Rolls-Royce are emerging markets such as in India, Brazil and China as well as the existing fleet demographics. Currently, about 43% percent of the global fleet is aged 25 years or above, according to the statistics presented by Rolls-Royce. This presents new opportunities to helicopter manufacturers, since with the replace-

Figure 1. The global helicopter market in 2009, broken up by manufacturer

ment of the old models latest technologies can be incorporated into various new designs. Figure 1 indicates the major players in the global helicopter market in 2009. In the civil sector the largest manufacturers are Eurocopter, AugustaWestland (AGW), Bell and Sikorsky and in the military sector Sikorsky, Eurocopter, Russian Helicopters, Boeing, Bell and AGW. The civil helicopter market is dominated by European companies, whilst American companies are prominent in the military helicopter market. Eurocopter is the leading helicopter manufacturer worldwide by revenue and units of turbine helicopter deliveries in the civil sector. A subsidiary owned 100% by EADS, Eurocopter was formed in 1992 from the French company Aérospatiale and Daimler-Chrysler Aerospace AG from Germany with its current headquarters located in Marignane, France. AugustaWestland is an Anglo-Italian helicopter company which was formed as a 50:50 joint venture company from the British company GKN and the Italian industrial group Finmeccanica. Bell Helicopter was formed as early as 1935 and specialised in the manufacture of fighter craft in its early days and holds its headquarters in Forth Worth, Texas. Based in Stratford, Connecticut, the Sikorsky Aircraft Corporation was founded in 1925 and is a leading defence contractor. With a history that dates a long way back to the early work of pioneer Igor Sikorsky, the company remains one of the main manufacturers in the USA, including the manufacture of the presidential helicopter, currently the models VH-3 and VH-60. Research carried out by Frost & Sullivan

forecasts an expenditure of the helicopter market until 2015. The company predicts that over one fifth of the helicopters produced worldwide will be sold to customers outside the US and Europe, namely to the Middle East, Africa and Asia Pacific. The helicopter industry remains a fascinating sector of the aviation industry with many new technologies to be looked forward to in the coming years. Future helicopter models are designed to be faster, more fuel-efficient and safer whilst noise and particle emission levels are reduced and capacity is increased. The helicopter has become one of human’s most flexible tools and a life without flexibility has become almost unimaginable for most of us. References http://www.flightglobal.com/Features/ helicopters-special/census/ http://inventors.about.com/od/ hstartinventions/a/helicopter.htm http://www.helis.com/introduction/ prin.php http://www.prweb.com/releases/2013/1/prweb10296613.htm http://www.rolls-royce.com/Images/2011_Helicopter_Market_Forecast_tcm92-27154.pdf http://www.flightglobal.com/Features/ helicopters-special/census/ http://www.eurocopter.com/site/en/ref/ Eurocopter-Today_325.html http://www.imap.com/imap/media/resources/Aerospace_8_1FED752787A1E. pdf http://bellhelicopter.com/Company/ AboutBell/History/History.html http://www.agustawestland.com/ http://www.sikorsky.com/Index http://en.wikipedia.org

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FOURSTUARTS

SELF-HEALING THERMAL BARRIER COATINGS With application to gas turbine engines

Thermal Barrier Coating (TBC) systems have been applied in turbine engines for aerospace and power plants since the beginning of the 1980s to increase the energy efficiency of the engine, by allowing for higher operation temperatures. TBC systems on average need to be replaced about four times during the lifetime of an aircraft. Hence, life extension of such systems are always desirable in order to minimise costintensive maintenance operations. This research focuses on developing self-healing TBC systems to enhance their lifetime. TEXT Sathiskumar A. Ponnusami, PhD Researcher, Aerospace Structures

BACKGROUND Gas turbine engines generate thrust by expanding the hot gases (coming out of the combustion chamber) in the turbine. With the fact that thermodynamic efficiency of any heat engine depends on the maximum operating temperature, efforts are continuously made in order to increase the temperature of the hot gases coming out of the combustion chamber in gas turbine engines. However, the maximum attainable temperature is limited by the material resistance to higher temperatures. To withstand higher temperatures, turbine blades are made of nickel-based superalloys which possess high strength even at elevated temperatures. In order to further increase the turbine inlet temperature without damaging the blades, a coating of ceramic material is deposited onto the blades, which is commonly called a thermal barrier coating (TBC). The blades and vanes in the hot section of turbine engines and the walls of the combustion chambers are coated to increase the energy efficiency of the engine, by allowing for higher operation temperatures, and to enhance the structural integ-

rity of the blades, by protecting the core from the aggressive environment during service [Nichols, 2003]. THERMAL BARRIER COATINGS A modern high-temperature coating system comprises a thermal barrier coating (TBC) layer on top of a bond coating (BC) layer. A thin thermally-grown oxide (TGO) layer is formed during operation between the TBC and BC layers as a result of oxidation of metallic constituents of the bond coat. The structure of a typical TBC system is shown in Figure 1. The TBC is made of yttria-partially stabilised zirconia (YPSZ) to allow higher operation temperatures [Levi, 2004]. The BC is usually composed of a MCrAlY alloy (where M denotes nickel and/or cobalt), which protects the underlying substrate material. TBC systems experience thermal cycles due to starts and stops of a gas turbine engine, as shown in Figure 2. Especially during cooling from the operation temperature to room temperature, high stresses develop due to a mismatch between the coefficients of thermal expansion of the substrate and the different layers in the

coating system [Hille et al., 2009]. These stresses result in the development of crack patterns in the TBC that coalesce and ultimately lead to failure. Cracks that run through the TBC perpendicular to its surface are not detrimental per se, but in conjunction with cracks that develop parallel to the interface lead to spallation, i.e., fragmentation of the TBC. NEED FOR SELF-HEALING The lifetime of TBC systems currently lies between 2000 and 4000 thermal cycles (or flights) [Stolle, 2009]. Correspondingly, TBC systems on average need to be replaced about four times during the lifetime of an aircraft and these are costintensive maintenance operations. Hence, life extension of such systems is always desirable in order to reduce maintenance costs. Several efforts were made in gas turbine industry to enhance the life time of the TBC system, for example, by varying the deposition method, coating composition, etc. One of the innovative ideas to improve the lifetime is to incorporate a self-healing mechanism into the system. This, in turn, means that the cracks formed

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during operation should heal by itself. In other words, the system automatically regains its strength and toughness even after the formation of microcracks. MECHANISM OF SELF-HEALING: The principle of the self-healing mechanism is demonstrated in Figure 3. A self-healing agent is encapsulated and embedded within the TBC topcoat layer during the coating process. When the crack reaches the microcapsule, the capsule breaks and the self-healing agent diffuses into the crack, where it can oxidise and heal the crack. In an explorative research [Sloof, 2007], it was demonstrated that the addition of Mo-Si based particles leads to the filling of cracks in the TBC layer. As shown in Figure 4, it was successfully demonstrated that (i) Mo-Si (molybdenum alloyed with silicon) based healing particles can be deposited together with the yttria-partially-stabilised zirconia (YPSZ) using plasma spraying to produce the thermal barrier coating, and (ii) cracks developing in the TBC layer are healed by oxidation of the Mo-Si based particles. The principle of the crack healing with particles containing Mo-Si is based on the formation of SiO2 by oxidation when such a particle is exposed to the ambient gas at high temperatures through a crack in the TBC. The Mo forms a volatile oxide (MoO3) and will leave the coating via the crack path, thereby compensating for the volume increase upon oxidation. The SiO2 fills the crack and closes it, thus postponing failure of the TBC system. Nonetheless, this self-healing mechanism is not fully understood and therefore needs to be thoroughly analysed in order to significantly improve its efficiency. Hence, the research is aimed at optimizing the self-healing capacity of thermal barrier coatings with Mo-Si based dispersed particles for application in gas

Figure 1. Structure of TBC system

turbine engines. This will be achieved through a combined experimental-modelling analysis of a modified self-healing approach that relies on the encapsulation of the healing particles. The purpose of the encapsulation is to prevent premature oxidation of the healing agent. A shell of alumina (Al2O3) will be created around the healing particles by selective oxidation of a limited amount of Al that is added to the particles. With this new approach, the healing mechanism will become active only when required, i.e., when a crack breaks up the alumina shell. RESEARCH PLANS The project is divided into two concurrent parts that will be executed at Delft University of Technology. The first part will be carried out by Zeynep Derelioglu and supervised by Dr Wim Sloof at the Department of Materials Science and Engineering (Faculty 3mE). It comprises the experimental understanding of the mechanisms of damage development and crack healing in a self-healing TBC upon thermal cycling and the practical realization of such a system. The second part will be conducted by Sathiskumar A. Ponnusami and supervised by Dr Sergio Turteltaub at the Aerospace Structures and Computational Mechanics group of the Faculty of Aerospace Engineering. This part concerns the modelling of damage and healing processes and the development of design strategies for self-healing TBCs. The extent of the self-healing effect of the modified TBC can be determined experimentally in a thermal cycling test and theoretically from numerical simulations. In the experiments, the evolution of damage (cracking and delamination) is monitored quantitatively as a function of the number of thermal cycles with acoustic emission and microscopic techniques. In addition, detailed microstructure analyses

will reveal the transformation of the healing particles into crack-filling oxides. The modelling approach allows for the explicit simulation of complex damage patterns, generation of healing oxides and subsequent repair processes. Virtual prototyping through parametric studies is meant to guide the design process of new selfhealing coatings and thus improve the efficiency during development. The manufacturing of the self-healing TBC system will be done by KLM and Sulzer and the testing of the system under thermal cycling conditions will be carried out by the National Aerospace Laboratory (NLR). This research project is part of the IOP SelfHealing Materials Program chaired by Prof Sybrand van der Zwaag of the Faculty of Aerospace Engineering and is funded by the Dutch government. CHALLENGES INVOLVED Many challenges are involved in the development of self-healing TBC systems. First of all, the manufacturing of encapsulated healing particles itself is a big challenge. Then, when the crack emanates during operation, triggering of the mechanism that repairs cracks is crucial. First, the crack must run into the healing particles and not be deflected. Next, the crack must break-up the alumina shell encapsulating the particles. Then, high temperature oxidation must result in the formation of SiO2 to fill the cracks. Optimal size and distribution of the healing capsules should be determined with guidance from the modelling and design process. Healing efficiency has to be studied in order to ensure proper healing has occurred in order to regain the toughness. These challenges will be addressed in this combined experimental-modelling research project in order to arrive at an optimal self-healing TBC system. RESULTS The research will focus on developing a novel ceramic thermal barrier with self-healing capability. Therefore, understanding of the mechanisms of damage development and crack healing is essential. Modelling of these mechanisms will enable optimization and design of new TBC systems. Routes will be devised for controlled manufacturing of both the healing particles and the modified TBCs. If successful, this project will lead to a new generation of affordable TBCs with improved lifetime in gas turbine engines. Consequently, a significant economic benefit can be obtained by reducing the number of TBC replacements in critical turbine engine components. QUALITY AND INNOVATION Self-healing TBCs with extended lifetime do not exist for commercial applications yet. The development and practical imMARCH 2013 Leonardo Times

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duced engine downtime. Both users and manufacturers of the self-healing TBC system within the Dutch industry participate in this project to define requirements for successful application. SUSTAINABILITY A TBC system itself already contributes considerably to sustainable technology, because it enhances the engine efficiency by allowing higher operation temperatures, which saves fuel and thus reduces CO2 emissions. Furthermore, it protects the high-tech structural components (made of single-crystal superalloys) against severe high temperature corrosion, thereby contributing to durable use of resources. The materials and their amounts used to produce the TBC system are abundant and not environmentally hazardous. Figure 2. Typical thermal cycle of a gas turbine engine

plementation of a novel self-healing TBC is very attractive, since the maintenance frequency of jet and gas turbines critically depends on the lifetime of the TBC. The proposed research involves (i) the development of the TBC material, (ii) the advancement of coating manufacturing technology and (iii) the implementation of self-healing coatings into industrial applications (jet and gas turbine engines). In this project, the scientific research groups will collaborate with industry which ensures knowledge transfer from academia to industry and users, and vice versa.

ECONOMIC PERSPECTIVE If a TBC system with sufficient self-healing capacity can be realised, then the economic benefits will be significant. First, the manufacturer of such a coating system can offer a unique product and thereby acquire a stronger position in the market. Secondly, the users of a TBC system with self-healing capacity, e.g. airline companies and producers of electricity, will benefit from the longer lifetime of the coating system itself and hence the critical components of the gas turbine, which brings about less engine revisions and thus a re-

CONCLUSION It has already been demonstrated that a TBC with a healing agent can be manufactured with existing technology (i.e., plasma spraying) used in industry [Sloof, 2007]). Thus, once an optimal design is realised and effective healing particles are developed, it is anticipated that there are no obstacles for introduction of selfhealing TBCs into industrial practice. The involvement of industrial participants (i.e., KLM and Sulzer) in this research project, and in particular with the manufacturing of the self-healing TBC system, ensures a successful transition into applications. References 1. J.R. Nichols, Advances in coating design for high-performance gas turbines, MRS Bull 28 (2003) 659-670. 2. T.S. Hille, T.J. Nijdam, A.S.J. Suiker, S. Turteltaub, W.G. Sloof, Damage growth triggered by interface irregularities in thermal barrier coatings, Acta Materialia, 57 (2009) 2624-2630.

Figure 3. Schematic of crack-healing mechanism in a TBC system with encapsulated Mo-Si based particles.

3. C. Levi, Emerging Materials and processes for thermal barrier systems, Current opinion in solid state and materials science, 8 (2004) 77. 4. R. Stolle, Conventional and advanced coatings for turbine airfoils. Available from: http://www.mtu.de/ en/technologies/engineering_news/, retrieved in January 2009. MTU Aero Engines, 80995 MĂźnchen, Germany.

Figure 4. Crack healing in a thermal barrier coating (TBC) system by Mo-Si based healing particles. (a) TBC layer composed of yttria-partially-stabilised zirconia and Mo-Si particles co-deposited by plasma spraying on a MCrAlY bond coating (BC). (b) Micrograph of self-healed TBC by SiO2 (dark gray) formed due to high-temperature oxidation of Mo-Si particles (arrows indicate remnants of Mo-Si particles). (c) Si distribution map of a selected area showing that the crack is filled with SiO2.

5. W.G. Sloof, Self Healing in Coatings at High Temperatures in: Self Healing Materials â&#x20AC;&#x201C; an Alternative Approach to 20 Centuries of Materials Science, S. van der Zwaag Editor, Springer, Dordrecht, The Netherlands, 2007, pp. 309-321.

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