Stories of Aerospace Engineering

Read the stories of researchers and students at the Faculty of Aerospace Engineering, and discover the scientific questions they are working on and the solutions they come up with.

TU Delft expanding in space

The Delfi space program is preparing to launch its third satellite, and TU Delft satellite technology may even go beyond the far side of the moon.

A precision mirror positioning system for compact earth observation space telescopes

Sean Pepper has won the Heinz Stoewer award for his thesis work on a nanometre-scale positioning system for mirrors used in a Deployable Space Telescope.

TU Delft’s team Silverwing reaches the finals of the GoFly Prize

By Heather Montague As one of five finalists in the Boeing sponsored GoFly Prize, TU Delft’s own team Silverwing aims to win with its S1 design, a personal flying motorcycle. Although it might seem like something out of a science fiction movie, human flight may soon become a reality. By founding the GoFly Prize, CEO Gwen Lighter set out to stimulate innovation in the development of personal flying devices. The three-phase global competition, announced in November 2017, aims to foster the development of safe, quiet, ultra-compact, near-VTOL (vertical take-off and landing) personal flying devices capable of flying twenty miles while carrying a single person. Making people fly TU Delft’s Silverwing came into being when two aerospace students put together a small team to submit a concept for the first phase of GoFly. When their idea was selected as one of the top ten out of hundreds of entries, Technical Manager Victor Sonneveld, a master’s student, and Team Manager James Murdza (BSc 2018) quickly pulled together a larger multi-disciplinary team. It has since grown to 34 students representing ten nationalities and nearly every faculty at TU Delft. In March, team Silverwing learned they had been chosen as one of the top five designs by GoFly. During this second phase of the competition, teams had to present a more detailed design and built various test set-ups, including a half-scale prototype. The S1, a tailsitter aircraft, rotates 90 degrees to take off and land on its tail, requiring no runway and less space than a car. “It’s basically a flying motorcycle, but what makes it special is that it takes off and lands vertically,” said Ruben Forkink, an aerospace graduate and Silverwing Chief of Partnerships & Business Development. “At the desired altitude you transition from vertical to horizontal flight and then you basically ride it like a motorcycle and transport yourself from A to B. Then you transition back from horizontal flight to land vertically on your tail.” Going beyond the call Although it was not a requirement of the competition, the S1 is battery powered, fully electric and able to fly autonomously. “We’re one of the few teams that opted to go completely electric,” said Nisarg Thakrar, an aerospace master’s student and member of the Silverwing structures team. “From our point of view, to be successful, it has to achieve the modern requirements, being electric and autonomous.” And although the limitations of battery technology make it challenging to carry the required amount of weight, making it autonomous means that the S1 could be used to transport packages, not just people. Students bring a lot to the table As competitions go, the GoFly Prize is unique in that it is open to anybody from anywhere in the world. “What’s really great and what makes us stand out is that we are the only undergrad team in the finals,” said Forkink. The other finalist teams include PhDs, researchers and companies with industry experience. “We have a lot of bachelor’s students on our team so it’s a challenge, but that’s what we really like,” noted Forkink. “We are able to combine the knowledge from all of these faculties and that makes us a real multidisciplinary team.” Putting hands-on education to work The aerospace faculty has played an integral role in Silverwing’s design and development process. According to Forkink, the team has members from all of the different tracks at aerospace, and knowledge gained in the classroom has been useful. “We have students that go to their lecture and 30 minutes later they come here and start working on what they just learned.” And Thakrar believes the master’s programme structures track has been a huge asset in the design of the S1. “We do most of our own work, but we do have limitations and at that point we can consult with professors as well as external parties that help us,” he said. “In my opinion, one of the best ways to be a good engineer is through application, not only through books and this project has been a great way to support that idea.” The final stage Team Silverwing is currently finalising the S1 design to prepare for manufacturing and they hope to have a test flight by the end of this year. In early 2020, they will participate in a final fly-off in the United States. During this last stage of the competition, the aircraft must take off vertically, cover an eleven-kilometre course and then land again vertically. Points will be awarded for low noise levels, size (the smaller the better) and speed. The winning team will receive a US$ 1 million grand prize. "GoFly is excited to see Team Silverwing-- a young team made up of many undergraduates-- competing with established companies and veterans of the industry, and holding their own,” said Lighter. “Team Silverwing brings novel innovation and out-of-the-box thinking to their personal flyer. We look forward to seeing Team Silverwing at the GoFly Final Fly Off next year, and we can’t wait to see them change the world." On April 30, 2019 Silverwing will unveil their award-winning design for the S1 to the general public. Want to see it? Click here .

Can ancient algae help replace chromium-6 in coatings?

Timelapse: corrosion protection of the letters ‘TUDelft’ What seemed like a wild idea in 2014, using the external skeletons of algae to prevent corrosion, has now been shown to provide long term protection of aluminium used in airplanes. In a few years’ time, it may provide a safe and environmentally-friendly replacement for the use of chromium-6. “Because of its toxicity, the European Commission has forbidden the use of chromium-6,” says Paul Denissen, PhD researcher in the Novel Aerospace Materials group at the faculty of Aerospace Engineering. “Use of chromium-6 is only still tolerated in situations where good alternatives are lacking, for example to protect airplanes against corrosion.” He explains that the aluminium alloy most used in aviation is especially susceptible to corrosion because of the copper that has been added to increase material strength. Typically, multiple boundary layers are applied to protect this aluminium against weathering. One of these layers is a primer coating loaded with chromium-6. “Our research focusses on using the external skeletons of a sort of algae to develop an environmentally friendly alternative for the use of chromium-6 in this layer.” Challenging chromium-6 Chromium-6 is a so-called active corrosion-inhibitor. When a treated surface is damaged, for example by scratching, the chromium-6 atoms will be released from the primer layer. They will create a thin layer of chromium oxide on the exposed metal surface, preventing further corrosion. After their release, chromium-6 atoms can continually redistribute themselves, providing continuous protection of the damaged area. “There are a number of alternative corrosion-inhibitors that are also very good at creating a protective barrier,” Denissen explains. “Unlike chromium-6, however, they can oxidize only once, and the protective layer they create is not permanent. Long-term protection therefore requires the continuous release of these inhibitors. More importantly, these alternative inhibitors may already chemically react with the primer coating at the time of its fabrication or application, thereby weakening their anti-corrosive power.” Quite some challenges to overcome, with a possible solution coming from the world of algae. Various shapes of the external skeleton of diatom algae Source : https://paleonerdish.files.wordpress.com/2013/06/diatoms.jpg Pill-box protection Diatoms are a group of microalgae that have been roaming the earth for more than 100 million years. These single cell organisms come in various sizes, ranging from one to a few tens of micrometres. They have a hard, inorganic shell to protect them from the environment. This cell wall is made out of silica, the same material as glass, and contains many nanometre-sized pores. Inspired by the pill-box shape of these shells ( see figure ), it was Santiago Garcia, associate professor in the same group and the supervisor of Denissen, who came up with the idea to use them for active corrosion protection in coatings. Garcia explains that “my idea was to fill these shells with alternative corrosion-inhibitors, and then add these loaded shells to the primer coating. I envisioned the pill-box structure to prevent the unwanted chemical reaction between inhibitors and coating.” He also imagined the pores to allow the immediate and sustained release of these inhibitors when the protective layers are damaged, and the metal surface is exposed. “And these algae shells are easily available at low-cost,” Denissen adds. Rapid development Denissen explains that his 2015 master’s thesis was merely a feasibility study, to see if this approach could be successful. “Now, we are three years into my PhD and despite limited resources we have just shown corrosion protection potentially equalling that of chromium-6. We still use our first pick of algae shells, but we have substantially increased their filling with inhibitors as well as their release efficiency, leading to a much-improved protection.” 30-day protection by algae coating with corrosion-inhibitors Testing in Paris After intensive work in Delft to proof the concept, the researchers travelled to Paris for a challenging experiment. “We were curious as to the long-term protective power of our coating for large damages, as required by several companies,” Denissen says. Together with their collaborators from the group of Polina Volovich at Chimie ParisTech, they applied a 1 mm wide scratch to samples of aluminium used for airplanes, covered in a variety of their test ‘algae-coatings’. These samples were subsequently immersed in large volumes of a highly corrosive environment. The researchers got what they bargained for ( see figure ). “We were astounded,” continues Denissen, “what we saw was full protection against corrosion, even after thirty days of immersion. Only a couple of alternative solutions come this close to the results obtained with chromium-6. It’s an amazing result after only such a short period of development.” Visualising corrosion protection Denissen and Garcia have also developed a novel method to study the onset and development of corrosion. It allowed them to gain a detailed understanding of the results they obtain with their algae shells, guiding further optimisation. “It is relatively simple technology, using a basic optical camera,” Garcia explains. “Optical techniques have traditionally been used to obtain qualitative information or to make beautiful pictures. What we have shown is that optics can be used to monitor and quantify local corrosion processes at a very high resolution, in real time. It is mature technology, allowing us to analyse any coating, commercially available or still in development.” Optimal protection “We use our experimental findings to build a computer model for further optimization of our coatings,” Denissen says. This can prove very beneficial as these algae shells come in more than 100.000 sizes and shapes. And there are more variables to tune, such as the type of corrosion-inhibitor used, whether or not to add an outside layer to the algae shell to even better regulate inhibitor release, or the optimal concentration of shells in the coating. “We may for example want to use disc-shaped shells to reduce our protective layer to the thickness currently used by the industry,” Denissen explains. “We are also looking into using combinations of inhibitors and shells in our coatings, further improving corrosion protection.” A small revolution It is not an easy task to replace chromium-6. “There are many barriers, resulting in a lack of good alternatives,” Denissen says. “For example, the Dutch Ministry of Defence wants proof that alternatives will provide twenty-year protection of their military equipment. But there are no good methods to accelerate this evaluation, to validate it in only a limited time-span.” More importantly, he explains, many of the tests used to validate the efficiency of new coating materials are designed specifically for chromium-6. “It is not a level playing field. It means that you have to prove your alternative coating to behave similar to chromium-6, rather than prove that it provides adequate protection.” Nevertheless, a small revolution has recently taken place. Rather than waiting for coating manufacturers to replace chromium-6, airplane manufacturers are now actively developing their own solutions as well. “At the moment, we are already talking to both.” Future perspective Despite very promising results, Denissen stresses that “we need a few more years to develop and demonstrate our algae-based coating before it can be used on planes, bridges or any metal surface that needs protection against corrosion. Does our coating protect sufficiently against scraping and scratching? Can it withstand frequent variations in outside temperature? Will it bond well with the other protective layers?” Garcia adds that “our main commitment is to find solutions to societal problems. We are currently talking to several industry partners about collaboration. Together we can speed up the development and launch of our technology and we expect to be ready for operational experiments by 2022, on an airplane.” Until completion of those experiments and passing the required certifications, the airplane industry may require the European Commission to again extend its leniency, tolerating the use of chromium-6 for the time being. You can find scientific publications, related to this research, here in Corrosion Science and in Electrochimica Acta .

Gas turbines: essential for the transition to renewable energy sources

Gas turbines are best known as the jet engines that power aircrafts. But they also are the work horses of large power plants generating electricity for our industry and homes.

Teacher of the Year 2018: Calvin Rans

I encourage my students to dig deeper into topics themselves He likes to give his students a glimpse of understanding so that they will dig deeper into the topic themselves. Calvin Rans, Assistant Professor in the Aerospace Structures and Materials Department, enjoys the art of engaging people in very complex ideas and concepts. And so successfully that he was elected both Teacher of the Year 2017-2018 at the Faculty of Aerospace Engineering, Delft University of Technology and Best Lecturer of TU Delft 2018. ‘Students won’t learn from what you say in the classroom. Just like kids, they have to make the mistakes themselves. This means that you have to find a way to help them navigate through their own learning process.’ On behalf of the LR Faculty, Calvin received a little art deco style metallic aircraft ‘flying’ over half the globe. ‘Ironically, I have an exact duplicate of the statuette at home. My wife bought it a few months ago, completely by chance!’ The prize from the entire university includes a certificate and a sum of money. The awards are a recognition for Calvin’s excellent work at TU Delft. ‘I like my students to apply the knowledge they’ve acquired from courses in some way that’s useful and focus on that rather than on their grades. Of course, students have to pass exams. But I stimulate them to be more satisfied with the understanding they gain than with a grade.’ p>Calvin Rans studied Aerospace Engineering at Carleton University, and then held a post-doc position at TU Delft. His research background and all of his professional activities have been involved the fatigue and damage tolerance of aircraft structures, in particular: damage-tolerant design and additive layer manufacturing (3D printing). At the bachelor’s level, Calvin teaches ‘Mechanics of Materials’ (1st year) and ‘Structural Analysis and Design’ (2nd year); at the master’s level, he teaches two courses: Joining Methods and Forensic Engineering. Online, he teaches ‘Air Safety’ and is involved in the ‘MOOC Introduction to Aerospace Structures and Materials’. Online teaching Calvin is a big proponent of online teaching. ‘Using online content helps automate many aspects of teaching. It also opens up more time and opportunity for interaction and engagement with students. Online education does not replace on-campus teaching. It basically creates new avenues to disseminate knowledge to different groups of people.’ The ‘Mechanics of Materials’ lecture course for which Calvin was nominated provided a completely blended teaching experience. ‘All of the lecturing was done with online videos that I had made, opening up more class time to discuss the connection of the theory to aerospace applications. The first-year students really appreciated getting this extra context behind what they were learning.’ Second-year students complimented Calvin on his redesign of the ‘Structural Analysis and Design’ course: a heavily mathematical course with a huge failure rate. ‘I completely changed the focus to understanding the underlying concepts hidden underneath the complex math. One of the changes we made was to create an exam not based on individual questions but questions that followed a design process. All the questions were related to a specific application, providing a unifying context for the exam. However, each question was formulated in such a way that the numerical answers did not depend on one another, minimizing the risk of continuation errors. This allowed the students to reflect on their answers and to make connections with their previous learning activities to see how concepts are actually related to applications.’ Magic trick Calvin’s ‘magic trick’? ‘I always try to show the connection between theory and practice. I use my own research projects, case studies or even certain projects being addressed in other courses. Sometimes I bring in some very interesting, complex organic shapes that have been 3D-printed to give an idea of the direction in which we are going. We then break it down so that the students can get a better idea of the structural elements they have been studying. It gives them something to connect with.’ Being an entertainer is also crucial. ‘It helps to get people in a relaxed state of mind so that they can reflect and think about things. That’s why I bring cartoons into my class. And when I do a presentation of bending deflection, I bring in hockey sticks and we do an analysis of a hockey player doing a slapshot. These little things make it fun and encourage students to interact.’ Calvin has always been interested in figuring things out. ‘And I found that the easiest way to really figure something out is to be able to explain it to someone else. So, for me, teaching became a way for me to learn.’ For education in the future, he foresees classroom environments full of challenges and problems to be solved in which students have access to small online modules or lectures for what they need to learn. ‘Of course, this will require a different type of teacher: a mentor who guides students toward what they need to learn. Some universities are already playing with this idea.’ The TU Delft DreamTeams composed of students who work on a project for a year are a fantastic example of this approach. ‘In this case, the university gives these students access to the information they need for their project, but they are not learning just to pass an exam; they are trying to make their project work. This tends to be the most useful education experience for them. I hope universities will be heading in this direction in the future.’ Teaching became a way for me to learn.

Using plasma forces to improve airplane fuel efficiency

In a breakthrough experiment Marios Kotsonis used plasma to actively interfere with the airflow on the wings of jet airliners.

Aerospace student Nadine Duursma chosen to receive IAWA Scholarship

Text by: Heather Montague The International Aviation Womens Association (IAWA) has chosen bachelor’s student Nadine Duursma as its 2018 TU Delft scholarship recipient. This scholarship is given annually to support women pursuing studies in aviation or aerospace related fields. Since 2004, IAWA has worked with four designated universities in the US and Canada, awarding one scholarship per year to a student from each school. Last year, TU Delft was chosen to join that group of universities. “We work with the universities to identify candidates with good grade point averages, financial need and a passion for a career in the fields of aviation and aerospace,” said Lisa Piccione, IAWA Director-at-Large and Immediate Past President. Confidence and creativity One such candidate, Duursma, saw the IAWA announcement for scholarship applications last year on Brightspace. “I thought, well, I’m a first-year student but I still meet all of the requirements and I thought if you never try you never win,” she said. The application involved writing a motivation letter and doing a creative assignment explaining why she chose to study at TU Delft. “They gave examples like making a video or a pitch or a poster. But I thought those examples were what everyone would do so I needed to find something else,” she explained. “So, I wrote a poem and made a timeline about how I chose Delft, including photos of me with aircraft when I was younger.” Despite her sense of confidence, Duursma was very pleasantly surprised when she got the news in June that she had won. Choosing a career Growing up, she always liked math and science and recalls being good at these subjects from a young age. And although Duursma’s father studied at TU Delft and her mother studied mathematics, they didn’t push her into science. She says they encouraged her to freely make her own choice about her studies. “But I was completely sure that I don’t like history or languages so for me it was an easy choice,” she said. After briefly considering a career as a pilot, Duursma decided what really inspired her was the idea of design and the opportunity to make something new. She began looking at different fields, including life sciences and medicine, but felt that they focussed too heavily on memorisation. “Then I came here to the aerospace faculty and fell in love with the aircraft,” she said. “It was something you could really think about and that’s why I decided to apply. It was also one of the most challenging programmes at Delft and I really liked that.” Looking to the future Although it’s still early in her academic career, Duursma has some clear ambitions for the future. She dreams of studying abroad one day, she sees herself working for a company for a while and then later possibly setting up her own business. “I think it would be interesting to try and make aircraft as a means of public transportation,” she said. “So instead of going to work by train, I hope in the future we can all go by plane.” She also has a great respect for astronauts because, as she explains, they have to be smart, physically fit and work really hard. “If I ever get the opportunity to apply to be an astronaut in the future, I will. I will always try. I don’t expect that, but why not try?” Supporting the next generation Through their scholarship awards, IAWA continues to support the development of women who are passionate about careers in aviation and aerospace. And Duursma certainly fits that description. “Nadine’s lifelong interest in aviation and her commitment to her aerospace engineering studies really make her a great role model and someone who will be a future leader in the industry,” said Piccione. “We look forward to working not only with Nadine, but really with all of the women studying in the field.” Piccione emphasised IAWA’s commitment to the next generation and helping those who are seeking to join the industry. Having worked for many years in aviation, she also stressed the importance of developing a professional network, having contacts, and building your presence in the industry. “We hope all of the young women pursuing careers in aviation and aerospace will add their names to our mailing list,” she said. “We have IAWA events happening all over the globe throughout the year.” On Thursday 11 October, Piccione will be at TU Delft to present Duursma with the official IAWA scholarship award. The event will take place immediately following the first lecture in a new initiative called Diversity Talks at the university. In addition, Duursma and the scholarship winners from the other universities will be honoured on stage at the 30 th annual IAWA Conference in Memphis, Tennessee from 24-26 October. See also Humans of TU Delft: Nadine Duursma in Delta Nadine Duursma Lisa Piccione, IAWA Director-at-Large

What flying robots can teach us

Fruit fly is not the first association that comes to mind when looking at the 30cm wingspan of the Delfly Nimble. The aerial acrobatics of it do, however, very much mimic fruit fly behaviour. This allowed its developers to test important assumptions about how these flying insects perform their evasive manoeuvres. Their recent publication in Science is only the beginning of what flying robots can teach us about insect flight. The Nimble is the newest in a line of micro-air vehicles developed by researchers at the TU Delft MAVLab. “It is our first insect like robot that doesn’t have a plane-like tail,” said Dr Matěj Karásek, post-doctoral researcher at the MAVLab. “Just like insects, our robot uses only its wings to initiate rotations around any of its three body axes.” According to Dr Guido Croon, scientific director of the MAVLab, “Nimble is an important step towards our ultimate goal of lightweight, safe and smart drones. Because of its agility, Nimble can operate effectively in much harsher wind conditions than our previous tailed drones.” Inspired by nature Imagine the Nimble standing up, like a person. For rotations around its head-to-foot axis (known as yawing), the Nimble pushes the ‘bottom’ of both wing pairs in opposite directions, angling both wings pairs with respect to each other. For rotations around its left-to-right axis (known as pitching), it pushes both wing pairs towards its back or belly. “Both strategies are similar to the method used by fruit flies and many other insects,” Karásek said. “Rolling is an exception. For a sideways rotation (around their front-to-back axis), a fruit fly varies the amplitude of its wing motion, while we change the flapping frequency on one side of Nimble’s body. We don’t copy nature, we are inspired by it.” The Nimble is controlled by a tiny 2.8-gram programmable autopilot unit that also houses sensors for estimating body orientation and rate of rotation. According to Karásek, “the control algorithms are comparable to what we believe insects use.” At the press of a button Unless instructed to do otherwise, the Nimble will return to a hovering position, its body hanging vertically in the air and its wings flapping about seventeen times per second. But it can also use its sensors and wing motion adaptation to follow pre-programmed commands, initiated through a remote controller. “These pre-programmed manoeuvres include aerial tricks such as 360-degree flips, but also turns inspired by the escape manoeuvres of real fruit flies,” Karásek said. “We press a switch to initiate the motion, and only when the Nimble recovers do we get back control.” Nature’s code “Fruit flies can drive us crazy when they manage to repeatedly escape our attempts at swatting them,” Karásek said. “Scientists have tried to explain how fruit flies perform these manoeuvres, based on observations made with high-speed cameras. But for confirmation one would need to look into the animal’s brain. Our insect-like Nimble provides an alternative approach.” In a collaboration with Florian Muijres, biologist and assistant professor at Wageningen University & Research, MAVlab researchers programmed the robot to replicate the fruit fly manoeuvres. When they compared its flight trajectories to those of fruit flies, there were remarkable similarities. Capturing insect flight “Our most important finding may be the discovery of a new aerodynamic effect assisting the fly in making turns,” said Karásek. “For both fruit flies and our robot, we observed rotations around the head-to-foot axis. But for our robot we were certain this was a passive phenomenon as we had disabled its yawing mechanism. This rotation is initiated by a combination of body translation and the adjusted wing motion, necessary to initiate rotations around the other axes.” The researchers were able to capture this complex mechanism, assisting the fly in turning its body into the escape direction, in a surprisingly straightforward equation. Nimble as a bee Their research with Nimble has already resulted in a publication in Science. But, according to Karásek, “there is so much more that our robots can teach us about insects. And there is so much more that we can learn from insects to improve our robots.” In their NWO-funded project, “To be as nimble as a bee”, they are again collaborating with Wageningen University & Research. They will look at how insects handle sudden wind gusts. They also want to understand why different insects have different sensory systems. “Fruit flies use so-called ‘halteres’, biological gyroscopes, to provide information about their body rotation during flight. The gyroscopes in our autopilot unit are actually based on the same principle. But certain flying insects do not have halteres, and yet they are flying perfectly fine. What sensors are involved and how do they use them?” asked Karásek. Smaller and smarter The current Delfly Nimble has only limited autonomy. Sure, it flies wirelessly, but its behaviour is completely governed by a few hundred lines of code and by external commands. The Nimble is also blind. It has to be steered or it will bump into objects. “Nimble will have the onboard intelligence to fly autonomously using only a single camera,” said Croon. “And we have already developed the wireless technology to have our drones operate in swarms.” Karásek expects to be able to scale down the size of the robot. He explained that “at small scales, flapping wing robots fly more efficiently compared to traditional quadcopter drones.” When asked for a futuristic application for such agile, small and smart drones, Karásek said, “imagine a swarm of miniaturized Nimbles, flying autonomously in a greenhouse, pollinating flowers.” More information: - Here you can see a movie of Delfly Nimble . - The publiciation in Science is available here.

The AerGo: When an airplane modeling exercise takes off

“Do you also want to build it?” project leader Julian Kupski had asked.