Solve the noise problem of electric aircraft

Preferably using propeller-driven aircraft powered by electric motors instead of aircraft that use polluting fuels is the best way to achieve clean aviation in the not too distant future. But electric aviation faces a seemingly insurmountable dilemma: the more energy efficient an electric plane is, the noisier it becomes.

The more blades a propeller has, the less noise it will make. But with fewer blades, the propulsion is more efficient and the electric plane can fly longer. In that sense, energy efficiency and silence tend to be mutually exclusive. This is an obstacle to achieving electric aircraft that are both efficient and quiet.

The noise from the propellers of energy efficient electric planes would not only disturb the passengers, but also the people in the places flown over by those planes. Regarding the latter, it must be borne in mind that future electric planes will have to fly at relatively low altitudes, so noise will be heard more easily than if they flew at high altitudes.

Now, Hua-Dong Yao’s team at Chalmers University of Technology in Sweden has developed a propeller design optimization method that paves the way for quiet and efficient electric aviation.

These scientists have succeeded in isolating and exploring the noise produced at the tip of a propeller blade. It is a known but little investigated source of noise. By isolating this noise, the researchers were able to understand its role in relation to other noise sources linked to propeller blades. By adjusting various characteristics of the propellers, not just the number of blades, the team found a way to optimize the propeller design and greatly mitigate the mutually exclusive relationship between efficiency and quietness. The method can now be used in the process of designing quieter propellers for future electric aircraft.

Plane propellers. (Photo: NASA/Christy Hansen)

Modern aircraft propellers typically have two to four blades, but Hua-Dong Yao and colleagues have found that using six blades designed with their optimization method can create a propeller that is both relatively efficient and quiet enough. . The propeller designed in this way achieves a notable reduction in the noise it emits, while its energy efficiency is only reduced a little.

Hua-Dong Yao’s team discusses the technical details of their design method in the academic journal Aerospace, under the title “Blade-Tip Vortex Noise Mitigation Traded-Off against Aerodynamic Design for Propellers of Future Electric Aircraft.” (Fountain: NCYT by Amazings)