Smaller wings, smaller rudder, more propellers. According to a DLR concept, regional aircraft should become more efficient. But there are still challenges.

Aircraft manufacturers, start-ups and research institutes around the world are working on the aircraft of the future. They should be quieter, more efficient and run with as few fuel and emissions as possible. The Brazilian regional aircraft manufacturer Embraer has just presented concepts for four alternative aircraft that could become a reality from 2030.

Now the German Aerospace Center (DLR) is also presenting a new type of regional aircraft. It is a hybrid-electric plane with ten propellers. The research center developed the concept for the aircraft, which can accommodate up to 100 travelers, together with Airbus, Rolls-Royce and Bauhaus Luftfahrt in a state-funded project.

The area and mass of the wings decrease

The propellers are distributed over the entire length of the blades. This leads to a more efficient flow around. “The wings of classic regional aircraft are often oversized in order to achieve good take-off and landing performance,” explains Martin Hepperle from the DLR Institute of Aerodynamics and Flow Technology. “These planes then fly when they are cruising with excessive energy consumption.”

Simulations showed that electric drives enable the thrust to be distributed to many smaller propellers. “If these then flow over the wing, they provide increased lift and more efficient aerodynamics,” writes DLR. In this way, the researchers were able to “reduce the wing area and the wing mass and reduce drag through the interaction of the propeller jets with the tip vortices of the wing”.

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The vertical stabilizer is also significantly smaller

As the final design for an aircraft with distributed hybrid-electric propulsion systems, the researchers considered a concept with turbo generators in the fuselage and ten electric motors along the leading edge of the wing to be the best solution. For example, the wing depth and the size of the rudder unit could be reduced, which, according to DLR, cuts energy consumption by up to ten percent.

Bild: DLR, CC BY-NC-ND 3.0

Aerodynamics expert Hepperle explains that the special arrangement of the propellers made it possible to compensate for the weight disadvantages of the hybrid-electric drive system. “With our multi-engine concept, we were also able to make the vertical stabilizer smaller and therefore lighter and with less resistance,” says Hepperle. The concept can compensate for the failure of two electric motors.

Still open challenges

However, this also led to new challenges, as shown in virtual flights in the flight simulator, especially when approaching the aircraft. The lower effectiveness of the smaller rudder and rudder had to be compensated for. For this purpose, a research team developed a flight control regulator that enables yaw control – control around the vertical axis – by means of rudder and differential thrust.

And there are still unanswered questions, for example about the acoustics of the distributed propellers. The researchers also still have to find the optimal flap system for the landing approach.

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