Emission-free electric flight – current projects and technologies

The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is a pioneer in the field of electric flight. It is unique in Europe in the way it combines fundamental and application-oriented research in this field. DLR brings together all the expertise required for the electrification of air transport. This includes battery and fuel cell technologies, expertise in electric propulsion, the integration of alternative propulsion systems into aircraft, and flight testing and overall system assessment.

E2Flight – the industry's specialist conference

The 'E2Flight' symposium, organised by the DLR Institute of Engineering Thermodynamics in cooperation with the Institute of Aircraft Design at the University of Stuttgart, is the industry's specialist conference. It has en eye on the pulse of the latest developments and this year brought together the international community to discuss the theme of electric flight for the fourth time. On 28 and 29 March 2019, more than 120 representatives from research institutions and industry exchanged information on the topic of electric flight in Leinfelden-Echterdingen, near Stuttgart. This year's symposium focused on concepts for for electric flight, hybrid propulsion systems, technical and certification aspects, and propulsion integration based on current projects.

Why electric flight?

Andreas Klöckner, the coordinator for electric flight at DLR explains its three advantages. "First of all, purely electric flight is locally emission-free, which means that the aircraft itself does not emit any pollutants. Second, both production and maintenance of electric propulsion systems are expected to cost less, thanks to the reduced number of moving parts. And the third advantage is that electric propulsion enables completely new aircraft configurations, which should further reduce fuel consumption, emissions and noise levels." Against this backdrop, completely new transport services, such as air taxis, will also be possible in the near future.

A growing industry

"The industry has definitely recognised the potential of electric flight, as is very clear at present," says Josef Kallo, a DLR researcher and co-founder of the symposium. For the next few years, he expects to see strong growth: "Almost all the major manufacturers of aircraft, propulsion systems and turbines are already active in this area. Funding agencies in Germany and Europe have also recognised the potential, and are authorising and providing support for various projects." According to Kallo, the focus is on projects with outputs of between one and two megawatts. This would make it possible to develop aircraft capable of carrying 20 to 40 or 50 passengers on short and regional routes. In this sector, the DLR scientist is counting on new ideas, technologies and projects to emerge from Europe and America. "There is certainly a palpable sense of optimism," he says. "Science and industry are investigating the possibilities of existing technologies, investing in their development, and intensifying and professionalising their work beyond small research projects."

Kallo himself is responsible for the DLR’s Hy4 – the world's first four-seat passenger aircraft powered by a hydrogen fuel cell took off for the first time in 2016. His team is currently equipping the research aircraft with a completely new propulsion system in order to begin further flights in the autumn of 2019. The plan is to at least double the performance of the fuel cell over time, and to store hydrogen three times more efficiently. Corresponding research projects have already started, and the team has already completed several laboratory tests, with positive results.

Electric flight – a new look, and therefore quieter

Aircraft noise will be one of the limiting factors for the air transport system of the future. There are already restrictions at most airports, for example at night. Quiet aircraft eliminate the negative health effects of noise and make it possible to meet the ever-increasing demand for mobility. In flight, regardless of the type of propulsion, noise is mainly due to aerodynamic factors: sound is generated by the propeller rotors or jet engines and by the airflows around the airframe. "Electric propulsion systems are not in themselves always quiet. Nevertheless, there is considerable potential for noise reduction – although this will require intensive research over the next few years," explains researcher Jan Werner Delfs from the DLR Institute of Aerodynamics and Flow Technology in Braunschweig. "With electrically powered aircraft, the arrangement and distribution of engines on the plane, and their operation, can be rethought from scratch," adds Delfs. The aircraft can be designed much more freely together with many small, distributed electric engines. For example, the shape of the wings could be optimised and the rudder made substantially smaller or completely eliminated. DLR researchers are already investigating what such alternative aircraft architectures could look like. They are currently using digital modelling to develop and evaluate innovative concepts for hybrid electric propulsion aircraft operating on short and regional routes.

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