It is believed that electrification will play an important role in the aviation of tomorrow, where fossil fuels are not used. But electric aviation grapples with a trade-off dilemma: The more energy efficient an electric airplane is, the louder it gets. Now, researchers at Chalmers University of Technology in Sweden have developed a method for optimizing propeller design that paves the way for quiet and efficient electric aviation.

In recent years, it has been announced that electrification plays an important role in reducing future aviation emissions. Due to long-range problems, more attention has been focused on electric propeller aircraft that can travel short distances. Propellers connected to electric motors are considered the most efficient power plant for regional and domestic flights. But when airplanes are electric, propellers cause another type of radiation – noise. The noise from the propeller blades will not only disturb the passengers in the air. Electric planes of the future will have to fly at relatively low altitudes, and the noise will disturb residential areas and animals.

Dealing with the compromise dilemma

This is where the research community faces a dilemma. The quest to develop electric airplanes that are both quiet and energy-efficient is hampered somewhat by the trade-off issue.

“We see that the more blades a propeller has, the lower the noise level. But with fewer blades, the engine becomes more efficient and an electric airplane can fly longer. Associate professor and researcher in fluid dynamics and marine technology at Chalmers University of Technology. “In this sense, there is a trade-off between energy efficiency and a kind of barrier for quiet and efficient electric aircraft,” explains Hua-Dong Yao.

Optimized design for quiet and efficient screws

But now Hua-Dong Yao and his fellow researchers may be one step closer to a solution. They were able to isolate and investigate the noise produced at the tip of the propeller blades, or “tip vortices,” a well-known but less studied source of noise. By isolating this noise, the researchers were able to fully understand its role in relation to other noise sources generated by the propeller blades. By adjusting a number of propeller parameters such as pitch angle, chord length and number of blades, the team found a way to optimize propeller design and smooth the balance between efficiency and noise.

The method is described in a study published in the journal Cell. aviationit can now be used in the design process of quieter propellers for future electric aircraft.

“Modern aircraft propellers typically have between two and four blades, but we have found that using six blades designed with our optimization system you can design a relatively efficient and quiet propeller. The propeller is noise up to 5-8 dBA with only 3.5 percent thrust loss compared to a three-bladed propeller. This is comparable to lowering the volume of a person moving from a normal conversation to the one you would hear in a quiet room,” says Hua-Dong. Yao.

A-weighted decibels (dBA or dB(A)) is an expression of the relative intensity of sounds perceived by the human ear. A-weighting places more value on frequencies in the mid-range of human hearing and less on frequencies at the edges, compared with an equal measurement of sound decibels. A-weighting is the standard for determining hearing damage and noise pollution.