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Reinventing aviation

Travelling by air considerably shortens travel times – albeit it comes at a high price: aircraft noise, pollutants and greenhouse gases are emitted. At the German Aerospace Center, researchers have some ideas how travelling by air could be made more environment-friendly and more humane.

Heading towards the zero-emission aircraft

Aviation without kerosine? DLR is addressing this issue. DLR’s “Electric Flight Demonstrator” is a study for electrically driven aircraft for a test aircraft with 19 seats based on a Dornier Do-228 – with an electric propeller drive featuring an engine power of 500 kilowatts. The project is funded by the Federal and Bavarian ministries for Economic Affairs. The required energy comes from an on-board storage battery. During the flight, this storage battery can be charged with power from a hydrogen fuel cell or a gas turbine. Hydrogen can be obtained from renewable energies, for instance, from solar energy or wind power. Or will other gaseous synthetic energy sources win the race? Or synthetically generated liquid fuels? DLR conducts research on alternatives for kerosine – open and unbiased in terms of technology. For clean, sustainable aviation.

© DLR/Hendrik Weber, www.wda.de

The first four-seater hydrogen aircraft

Hydrogen as energy storage, a fuel cell as power generator, a storage battery, and an electric engine with 120 kilowatts – there you go:
the drive for HY4, the worldwide first four-seater airliner featuring a
battery-fuel cell drive. The maiden flight of the aircraft with a maximum
speed of 200 kilometres per hour took place in 2016, the range
is up to 1,500 kilometres. The drive is continuously further developed, it is already in the sixth generation and works well. The overall concept also includes hydrogen tanks which have to be extremely safe and lightweight in aircraft – DLR is conducting research in this field as well. In the project, DLR is collaborating with the Slovenian aircraft manufacturer Pipistrel, the fuel cell manufacturer Hydrogenics, the DLR spin-off H2FLY and the University of Ulm. As early as 2009, DLR presented the first aircraft capable of taking off exclusively with the drive from a fuel cell in the pioneering project DLR-H2. Hydrogen research is closely related to space flight: in the USA, the first rocket with hydrogen drive was launched in 1966, and today, the European Ariane launcher carries along the huge amount of 25 tons of hydrogen. The hydrogen propulsion units are developed and tested in cooperation with DLR.

© H2FLY GmbH

In the future, such small aircraft will be used as air taxis. Subsequently, the technology can be scaled even for larger aircraft.

© H2FLY GmbH

In the project “ZEROe“, Airbus is working on hydrogen aircraft for up to 200 passengers. In 2035, the first hydrogen large aircraft might take off.

© Airbus

DLR is setting the pace in hydrogen research: Europe’s first hydrogen vehicle originated from DLR in 1978. In 2020, DLR presented the concept of the hydrogen vehicle “Safe Light Regional Vehicle“ (SLRV), featuring a weight of 450 kilogrammes with production cost of just about 15,000 euros in series production.

© DLR

Flying with solar energy or storage batteries


Solar aircraft are very quiet and they “fuel“ themselves via solar cells in the wings. Today, the
Elektra Two solar aircraft from Elektra Solar GmbH, a spin-off from the DLR Institute of Robotics
and Mechatronics, is capable of being airborne more than 18 hours nonstop, for example to autonomously collect geographic data. The aircraft can even take off or land automatically. In the future, missions lasting several days should be possible at an altitude of up to 20,000 kilometres. The automatic flight control and propulsion components were developed in cooperation with DLR.

© elektra-solar.com

Thanks to continuously improving storage batterie technology and intelligent lightweight construction, even electric aircraft are possible that store the energy in a storage battery – if the purpose of application fits. For flight schools, Elektra Solar developed the “Elektra Trainer“, an ultralight training aircraft. It features a total weight of 400 kilogrammes only, a 35-kilowatt storage battery included. With the usual timing of 90 minutes, hardly any idling periods occur: during the 35-minute preparation time on the ground, the aircraft is charged – a full charge enables a flight duration of 50 minutes. The electric propulsion pays off: the cost for the aircraft amounting to 200,000 euros are twice as high as for a traditional training aircraft, but a flight school will save 500,000 euros of operating cost during the service life of the aircraft.

© elektra-solar.com

The next generation of storage battery aircraft is currently being developed, for example,
6- or 10-seaters from Elektra Solar‘s subsidiary SCYLAX with a range of
300 kilometres and an airspeed of 300 kilometres per hour. Typical application areas for such aircraft are short-haul flights to islands in the North Sea, as a “bush plane” or an air taxi. Electric aircraft are also well-suited in case of strong crosswind and short take-off or landing runways. Currently aircraft are used for these flights that are equipped with two 6-cylinder engines each with a cylinder capacity of 8.9 litres. Together, they consume up to 100 litres of aviation fuel. A conversion to electric propulsion would protect the environment and save money.

© elektra-solar.com

Alternative fuels: what alternative type of energy will replace kerosine in the future, or what mixture of kerosene and synthetically generated fuel will be well-suited? These questions are tackled by simulation with DLR’s own engine synthesis programme GTlab, and optimised fuel-saving turbines are tested under realistic conditions at the DLR turbine test rig. The aim: reducing fuel consumption and exhaust emissions. The advantage of synthetic fuel is that it can be perfectly adapted to the application by “fuel design“. DLR’s cross-sectional project “Future Fuels” is conducting research on synthetic fuels.

© DLR

Flying smoother: “please remain seated and fasten your seat belts, we have turbulences ahead of us.” In the best of cases, it is just unpleasant when aircraft have to fly through a thunderstorm. But why do they not just avoid it? The answer is quite simple: the overview of weather conditions for air traffic controllers is a complex task – until now. However, DLR’s project MET4ATM (Meteorology for Air Traffic Management) is intended to solve the problem. Current and forecasted weather data regarding thunderstorms and hail – for instance, based on the information from weather satellites – are specially processed for air traffic controllers to support the planning of evasion and circuit routes during final descent. The project was funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK) within the scope of the second call of the National Aviation Research Programme (LuFo V-3).

© DLR

Quieter landing: in flight tests with the Airbus A320 ATRA (Advanced Technology Research Aircraft) in Braunschweig, DLR scientists are testing new automatic landing procedures and satellite-based position determinations – without the need of expensive instrument landing systems to be installed at airports. The technical prerequisites for that are precise satellite position data, for instance from the European Galileo system, and the European “precision enhancer“ EGNOS, consisting of ground stations and transponders on satellites. Curved final descents and high-precision landings can reduce noise and protect the environment. With the help of satellite navigation and the use of state-of-the-art aircraft systems, curves with fixed radii between two waypoints can be exactly planned; in this way, precisely flown curved final descents are rendered possible. A continuous descent requires lower engine performance, which makes it quiet and fuel-saving. In addition, better “circuiting“ of regions plagued with noise is made possible.

© DLR

Safer landing: aircraft have to maintain a security distance between each other during flight and landing of up to ten kilometres in order not to get into “wake turbulences“ – which means unavoidable turbulences in the air and at airports that are mainly caused by the wings and can result in a crash. A construction patented by DLR ensures that these wake turbulences dissipate faster on the ground. Huge plates act as “swirl devices“ for wake turbulences. In this way, the safety distance can be reduced, and more aircraft can land on the same runway at the same time. This renders new construction of airports and runways partly obsolete and holding patterns in final descent are avoided. Therefore, the stress on humans and the environment is reduced, since holding patterns cause unnecessary aircraft noise, and increase fuel consumption and exhaust emissions.

© DLR

Tediousness on board – broadband internet comes from space: online even on board? Streaming one’s own entertainment programme from the internet during a flight instead of using on-board entertainment provided by the airline? This is only possible thanks to internet via satellite transmission, far away from any smartphone radio mast, for example when flying over the high seas. Data rates of up to 100 Mbit/s per aircraft are possible today. In the future, 10 Gbit/s per aircraft will definitely be possible through the use of laser technology for data transfer between satellite and aircraft. At DLR, ground-breaking research results regarding this technology could be achieved.

© lightpoet/fotolia.com

Chances for small airports

There is a tower at every airport. But only if highly qualified air traffic controllers are working there, aircraft can take off and land. A major problem for small airports, especially in rural areas: no personnel – no airport. DLR’s idea: the tower is “remote-controlled“, with the technology on site and air traffic controllers at another airport. In the project “Remote Tower for Multiple Airports“ it is investigated how this vision can become a reality.

© DLR

Navigating indoors: made in Munich

We stay in closed buildings for 90 per cent of the time. Some of them are rather complex: shopping malls, car parks – or airports. Unfortunately, the usual satellite navigation works hardly at all here.

The ground-breaking idea behind NavVis: such interiors are photographed with 90 megapixels through a camera dolly and measured via laser scanning (LIDAR). In this way, a digital twin of reality is created. The idea to develop NavVis emerged from TU Munich; in 2011, DLR became aware of that – and looked for a technology to generate maps on uncharted territory like, for example, on Mars, by means of a robot so that automatic minidrones can find their way with the help of these data. DLR funded the idea, and in 2013, NavVis was founded as a spin-off. From this, a real success story emerged: in 2021, the company is staffed with 200 employees and present in 30 countries.

On Earth, the NavVis app then combines the live images of the smartphone camera with the NavVis data for orientation. So, the smartphone recognises where its owner actually is in the building. At the airport or at the university, travellers or students are shown where they actually are and how they have to move to reach their destination.

© NavVis GmbH

Will robot swarms soon explore Mars?

The project VaMEx – CoSMiC (Valles Marineris Explorer ‒ Cooperative Swarm Navigation, Mission and Control), funded by the German Space Agency at DLR, demonstrates that swarms of autonomous rovers, drones, and robots can explore distant worlds, for example to search for traces of life in the huge canyon system Valles Marineris on Mars. The challenge: the swarms are supposed to act autonomously and make decisions. To this end, the individual swarm members have to explore the terrain, exchange information with each other, jointly make measurements – and, first of all, navigate. Navigation in an unknown world? The NavVis technology assists in fully autonomous mapping.

© DLR

Hello Charlie: the ape robot could become part of an exploration swarm on Mars. It is developed at the Robotics Innovation Center (RIC) at the Bremen site of the German Research Center for Artificial Intelligence (DFKI) GmbH. A robot capable of climbing is ideally suited to work in canyons or caves – both on Mars and on Earth. The swarm should be given the capability of deciding on its own what task to take over.

© DFKI

Protection for engines and spaceships at 1,700 degrees Celsius

Turbine blades and spaceships have one thing in common: they have to withstand extreme temperatures – and should be as lightweight as possible at the same time. With turbines, high combustion temperatures are ideal since the fuel is burned more efficiently and cleaner. Space vehicles need heat shields for re-entry into the Earth’s atmosphere. Carbon fibre compounds, known as carbon, are basically ideal since they are very lightweight and solid. However, they cannot stand temperatures of 1,700 degrees Celsius. The solution: a protective coating. With the HOSSA project, researchers from Fraunhofer IISB had the idea to apply cost-efficient high-temperature coatings to carbon by means of powder coating. In this way, the components – for example, a turbine blade or the outer shell of a space probe – are effectively protected. In 2020, this idea won third place in the DLR Challenge at INNOspace Masters.

At the DLR Institute of Materials Research in Cologne, turbine blades for aircraft engines are developed that can stand higher temperatures. The heat resistance improved by 100 to 150 degrees Celsius is achieved by a thermal barrier coating made of zirconium oxide featuring a thickness of 0.002 millimetres only.

© DLR

Experiments are also conducted with new metal alloys: titanium aluminide alloys (titanium aluminides) are – at lower density – more lightweight as well as harder and more heat-resistant than customary alloys. This material can even be used in powder form in special 3D printers working with temperatures of 1,000 degrees Celsius. In this way, heat-resistant structural components for aerospace applications or turbine blades can be manufactured quickly. The melting and solidification behaviour of these alloys can partly only be investigated under space conditions. The respective experiments were conducted, for example, on board the research rocket MAXUS-8.

© DLR

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