Flying more climate-friendly with hybrid-electric drives

November 22, 2021 // By Christoph Hammerschmidt
Flying more climate-friendly with hybrid-electric drives
The climate crisis has increased the pressure on aviation to develop and deploy technologies that are more climate-friendly and suitable for everyday use. Electric and hybrid-electric propulsion systems have the potential to reduce emissions from aviation through innovative aircraft configurations. The use of alternative propulsion systems impacts the entire aerodynamic concept of the aircraft.

As part of the joint project SynergIE, scientists from the German Aerospace Center DLR, together with partners Airbus, Rolls-Royce and Bauhaus Luftfahrt e.V., have investigated the overall system of a hybrid-electric short-haul aircraft for up to 100 passengers with distributed drives on the wing. With this technology, the drives are distributed over the span of the entire wing and thus lead to a more efficient flow around the aircraft.

"In classic regional aircraft, the wings are often oversized in order to achieve good take-off and landing performance," explains Dr Martin Hepperle from the DLR Institute of Aerodynamics and Flow Technology. "These aircraft then fly at too high an energy consumption in cruise flight." Highly accurate flow simulations showed that electric drives allow the thrust to be distributed over many smaller propellers. When these then overflow the wing, they provide increased lift and more efficient aerodynamics. This effect allowed the project partners to reduce the wing area and wing mass, and to reduce drag through the interaction of the propeller jets with the wing's edge vortices.

As a final design for an aircraft with distributed hybrid-electric drives, the researchers selected and evaluated a concept with turbo generators in the fuselage and ten electric motors along the leading edge of the wing as the best solution from a number of different approaches. By optimally designing and installing the propellers, it is possible to reduce the wing depth and rudder size and thus reduce energy consumption by about 10%. "The special arrangement of the propellers allowed us to compensate for the weight disadvantages of the hybrid-electric propulsion system," says Hepperle. "We were also able to design the vertical stabiliser smaller and thus lighter and with less drag in our multi-engine concept," Hepperle continues. "This concept can even compensate for the failure of two electric motors, so it also offers greater operational reliability."

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