Aircraft powered by hydrogen and fuel cells could help to meet climate targets. This is because they do not produce any greenhouse gases, only water is emitted.

Flying could be so nice if only it weren't for the CO2 emissions. There are many new ideas for the future on how to make flying more climate-friendly. One promising approach is to use hydrogen as a fuel instead of kerosene, as is currently the case. This would then be used to power fuel cells installed on board. Their task is to generate electrical power in the form of electricity. This works in such a way that electric motors drive propellers to generate thrust. No carbon dioxide or nitrogen oxide emissions are produced during this process or during the flight; only water is produced.

The Institute of Aircraft Systems Technology (FST) at Hamburg University of Technology is currently working on various such climate-neutral aviation research projects. In cooperation with their partners, the engineers are developing concepts and technology modules that should lead to viable hydrogen concept aircraft. Two of them are Thimo Bielsky and Vivian Kriewall. They are researching electric flight with partners Airbus and the German Aerospace Center (DLR). "We have designed the overall system architecture for a fully electric passenger aircraft and investigated and virtually tested the interaction of all relevant individual systems," says engineer Thimo Bielsky, describing the project.

Climate-neutral flying for 70 passengers

The concept aircraft itself was developed by DLR and corresponds to a regional aircraft with a design range of around 1000 nautical miles. This corresponds to 1,852 kilometers. With this range, almost all current missions can be covered by the aircraft, which can carry around 70 passengers. The concept aircraft has a total of ten drive units, known as "pods", each of which contains fuel cells, buffer batteries and the electric drive train. Each drive unit can generate an output of around 400 kilowatts. This is how much is needed to charge an electric car in three minutes for a range of 100 kilometers. Vivian Kriewall explains the main difference in the design compared to a conventional aircraft: "The hydrogen tanks are not housed in the wings, but in the rear of the aircraft. To avoid losing too much space, the fuselage of the aircraft is wider and the cabin is shorter".

Hydrogen is an ideal source of energy, but in its natural form the gas has a comparatively low density and requires a lot of volume when stored. In order to provide the required drive energy, the pressure tanks would require as much space as a second airplane fuselage if the gas were stored. The scientists are therefore using a trick and cooling the hydrogen in the concept aircraft to -253 °C as liquid hydrogen in vacuum-insulated tanks. This means that much less volume is needed.

The aircraft becomes heavier, but more efficient

"In the next step, we position the components in the aircraft and connect them to hydrogen pipes, hydraulic lines, air ducts or electrical cables," explains Thimo Bielsky. The scientists carry out various studies: For example, they can change parameters such as the number of components, their position, a pressure level or an electrical voltage level. The aim is to evaluate the influence on the systems themselves, but also on the overall aircraft. In the case of the hydrogen concept aircraft, studies were primarily carried out in relation to the energy supply in the aircraft. For example, it was investigated whether the fuel cells with the batteries in the pods are sufficient or whether systems are required to supply the on-board systems in an emergency - the hydrogen supply would fail. "Compared to a conventional aircraft, the hydrogen concept aircraft would be around five tons heavier," calculated Vivian Kriewall. "However, the overall efficiency increases by around 30 percent thanks to the fuel cells and batteries, as their efficiency is significantly higher than that of conventional engines."

Finally, the scientists still have to solve a safety problem, as hydrogen itself is highly flammable. They want to avoid routing hydrogen lines through the printed area of the cabin. In addition, the engineers at the FST Institute still have to investigate how large the distances to other systems such as the electrical or hydraulic system need to be in order to be safe. Once these tasks have been completed, the vision of electric flight, in which the aircraft glide through the air quietly and in a climate-friendly manner, can quickly become a reality.

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