Propeller design paves way for quiet, efficient electric aviation

Electrification may have an important role in reducing emissions from future aviation, and propellers connected to electric motors are considered the most efficient propulsion system for shorter-range regional and domestic flights.

However, propellers cause another kind of emission – propeller blade noise that could disturb passengers. Future electric aircraft will need to fly at relatively low altitudes, so noise disturbance could also reach residential areas and animal life.

A dilemma

The ambition of developing quiet, energy-efficient electric aircraft faces a trade-off.

“The more blades a propeller has, the lower the noise emissions. But with fewer blades, propulsion becomes more efficient, and the electric aircraft can fly longer. There’s a trade-off between energy efficiency and noise,” explains Hua-Dong Yao, associate professor and researcher in fluid dynamics and marine technology at Chalmers University of Technology, in Gothenburg, Sweden.

But now, Yao and his colleagues may be one step closer to a solution. They’ve succeeded in isolating and exploring the noise that occurs at the tip of the propeller blades – tip vortices – a known but less well-explored noise source. In isolating this noise, the researchers could fully understand its role in relation to other noise sources generated by propeller blades. By adjusting propeller parameters, such as pitch angle, chord length, and number of blades, the team found a way to optimize the propeller design and equalize the trade-off between efficiency and noise. The method can now be used to design quieter propellers for future electric aircraft.

“Modern aircraft propellers usually have two to four blades, but we’ve found that by using six blades designed using our optimization framework, you can develop a propeller that’s both relatively efficient and quiet. The propeller achieves a noise reduction of 5dBA to 8dBA with only a 3.5% thrust penalty, compared to a propeller with three blades. That’s comparable to the noise reduction of someone going from speaking in a normal conversation voice to the sound you would perceive in a quiet room,” Yao says.

Chalmers University of Technology