MIT’s propeller innovation can make your drone less whiny

low noise drone propeller

Researchers at the Massachusetts Institute of Technology (MIT) have developed new low-noise propellers that can make current multirotor drones much less of an acoustic annoyance.

A team working at the MIT Lincoln Laboratory says it has come up with a closed-form propeller design that can significantly cut down the loud noise commonly associated with consumer drones. The configuration that the facility has gotten patented almost makes the propellers sound more like a rushing breeze rather than high-pitched buzzing — and it does so without sacrificing thrust.

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Named after their donut-like shape, MIT’s quieter toroidal propellers consist of two blades looping together so that the tip of one blade curves back into the other. This closed-form structure minimizes the drag effects of swirling air tunnels (i.e., vortices) created at the tips of blades and strengthens the overall stiffness of the propeller. The result is that the acoustic signature of the propellers comes down considerably.

Researchers say that when they tested prototype toroidal propellers on DJI drones, they found thrust levels comparable to those of regular props at similar power levels. But reduced sound levels on the drones fitted with toroidal props meant they appeared only half as annoying as a regular drone. Or in other words, the drone sounded as if it were twice as far away.

Dr. Thomas Sebastian, a senior member of the Lincoln Lab’s structural and thermal-fluids engineering group, explains that the design for these low-noise propellers comes from experimental airplanes in the early 1900s and those operated during World War 2. “There were a couple of designs that were basically these ring wings. So, I wondered what it would look like if you took a ring wing and turned something like that into a propeller.”

After a few attempts, the team zeroed in on the design that would go on to win an R&D 100 Award in 2022. Researchers also found that the propellers could be 3D printed and customized to a range of vehicles, making them suitable as drop-in replacements on current drones.

Quieter, low-noise propellers are important because the noise impact of drones can become a barrier to their adoption, especially when operations are to be conducted near people or in urban areas. The European Union Aviation Safety Agency (EASA) has even published guidelines explaining how UAS manufacturers and government agencies can measure the noise level of drones, ensuring they are not a nuisance to people and wildlife.

Related: Annoyed by its buzzing noise, Dutch vacationer fires multiple shots at high-end DJI drone

Image: Glen Cooper/MIT

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