Toroidal Propellers Make Drones Less Annoying

A black quadcopter sits on a grey surface. In place of traditional propellers are four figure eight propellers with sharp tips where the top and bottom of the eight would be.

Despite being integral to aviation for more than a century, propellers have changed remarkably little since the Wright Brothers. A team at MIT’s Lincoln Lab has developed a new propeller shape that significantly reduces the noise associated with drones. [PDF via NewAtlas]

Inspired by some of the experiments with “ring wings” in the early 20th Century, researchers iterated on various toroidal propeller geometries until arriving at one that significantly reduces the sound produced by the rotors, particularly in the range of human hearing. The team suspects the reduction in noise is due to vortices being distributed over the whole propeller instead of just the tips.

Experiments show the drones can get twice as close before becoming a nuisance for human ears which should be great news for anyone hoping to launch Skynet commercial drone deliveries. Since the rotors are easily fabricated via 3D printing they should be easy to adapt to a number of different drones.

If you want to explore some more interesting drones, checkout this one that can fly and swim or this one that only uses a single propeller.

60 thoughts on “Toroidal Propellers Make Drones Less Annoying

        1. Based on the history of humans, it’s kind of automatic that if it can perverted, it will. Like Internet Rule 34: “If it exists, or can be imagined, there is Internet porn of it. ” and it’s corollary, Rule 35: “If no porn is found of it, it will be made”

        1. camera size isn’t a big deal if you wanna hit it. There are many many ways nowadays, even for camera modules much bigger than this. The problem is not the camera itself, but the supporting hardware, MCU, power source, etc.

  1. I don’t think the efficiency of the propeller is mentioned anywhere. If there’s less turbulence generated, maybe more efficient? If it’s a lot less efficient, we’re probably not going to see these everywhere except in special applications where noise is the critical thing (like indoor fans). For drones, cutting the range a lot would limit it’s use.

      1. Yeah, I saw that parallel as well. I found some photos of the propeller (Screw? What’s the proper maritime term?) spinning in water, both normal designs and this toroidal one—the normal designs have a spiral cavitation trail coming off the propeller tips, but not the toroidal. I wonder if that’s involved in making propeller noise in air as well? Pretty interesting.
        If it’s not dumping energy into making noise, I would assume that energy goes elsewhere. Hopefully into efficiency moving air around (but not in the high-frequency vibrating sense like before).

    1. I’m sure they limited the scope of their study to the sound aspect, aside from a passing claim of “achieves comparable thrust,” i.e., retains the ability to fly in a controlled manner.

  2. The curves appear to show that peak noise is reduced but not the level of average noise when integrated across the frequency spectrum. I guess that’s why there is no mention of these props being more efficient … apparently they are not. Still, quieter is good.

    1. Loudness is not perceived equally across the hearing spectrum. A 5kHz tone at 40dB SPL is as loud as a 125 Hz tone at 60 dB SPL (roughly). That is: low pitched noise needs more energy than its high pitched counterpart.

      1. Anyone with neighbours who like parties will tell you – low bass thumping travels a significantly longer distance.
        A lot of people exposed to Industrial Noise also find high pitch hearing is the first to go.

        Drone blades are generally small, and move at high speed. Spreading the resulting noise across the spectrum risks moving sound into a band some people find easier to detect. Not as irritating perhaps, but detectable.

        1. Part of what makes drones noisy IS the high frequency noises. The article talks about the released energy being absorbed by the atmosphere in less distance.

          The reason you can’t hear your neighbors treble is because of the walls. Odds are that drones operating near people will be line of sight, where this would help.

      1. True. I find it curious that they didn’t show the actual data for that, though, since in most situations a more efficient prop would be more important than a quieter one. My Mavic Air 2 drone doesn’t have to get very far away from me before the sound is negligible, but extending the flight time would be very nice. They had the data and could have easily compared the noise power.

  3. I have never favored the term “twice as close”; it makes no sense logically. 2x distance would provide a larger number, not a smaller one as the phrase implies. The more appropriate term would be “half as far” as it indicates an appropriate reduction in linear distance. Even that one has its problems; it implies a departure rather than an approach.

    1. Absolutely, that’s why scalpels dont work.


      In all seriousness though I am not seeing these as any safer. At the speeds they are going it doesn’t matter much. A speck of dust hitting the space station could be round like a marble or sharp and pointy, damage is similar.

      More contusions for less lacerations? I don’t want any of it.

      1. Of course they’re safer? It’s a flat edge/surface on the sides rather than a thin angled/sharp edge. Short of sticking your fingers into the actual inside part, just accidentally bumping up against it should be much safer.

        I still remember my dad slicing his leg open a couple times during his model aircraft (mostly helicopters) days.

  4. If its vortex shedding/distribution that’s the root of the reduced noise, then a straight-bladed prop with a bell-shaped (rather than oval) spanload should produce similar results at a lower blade mass and using conventional manufacturing techniques.

  5. There is an expired U.S. Patent 6,736,600 “Rotor with Split Blade” to Rudolf Bannasch that looks similar to the MIT toroidal propeller. Please see Figure 7 of U.S. Patent 6,736,600. I have no idea of Mr. Bannasch’s propeller has good performance or not, but it would be very interesting to see a comparison between MIT’s propeller and Mr. Bannasch’s propeller, especially since U.S. Patent 6,736,600 expired in 2020!

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