[HN Gopher] Toroidal propeller allows a drone to operate more qu... ___________________________________________________________________ Toroidal propeller allows a drone to operate more quietly [pdf] Author : lxm Score : 108 points Date : 2023-01-29 19:12 UTC (3 hours ago) (HTM) web link (www.ll.mit.edu) (TXT) w3m dump (www.ll.mit.edu) | monocasa wrote: | Sort of reminds me of the design of Navy submarine propellers | (there known as 'screws'), optimizing for similar noise dampening | properties. For a very long time the design of modern submarine | screws was one of the closest guarded secrets of submarine | design, with submarines docked having cloth shrouds over the | screw even in classified facilities. | | AFAIK, those weren't torodial, but they had similar long arcs of | the blades. | | For more information: | https://americanhistory.si.edu/subs/anglesdangles/taming.htm... | mLuby wrote: | IIRC submarine screws use prime-numbered blades (5, 7, 9) to | cut down on harmonics. Perhaps the same would be useful here, | though I don't see many prime-numbered turboprops, which you'd | expect to benefit from similar noise reduction. Related, I | highly recommend HI Sutton's youtube channel if you're into | submarines. https://www.youtube.com/watch?v=ugSEIiTZ1Pg | | A magnus effect drone may have a decent chance at being quiet. | IANAAeroEng but I'd guess that the moving part's interaction | with the fluid can be made laminar or at least non-turbulent, | and also unlike some propellers, the moving part shouldn't be | approaching or interacting with the sound barrier. | https://youtu.be/hlmvHfIAszo?t=16 | | However my money's on ionic propulsion drones since they have | no moving parts to make noise. I wonder if the air accelerated | through the grids produces an audible hiss. | https://youtu.be/UGM4JXVB5FM?t=126 | WirelessGigabit wrote: | That's funny, because I remember watching a documentary about | some form of caterpillar drive. | ChrisMarshallNY wrote: | That was the one that was "narrated" by Sean Connery? | froh wrote: | the hishtorically accurate shientific account of a rushian | boat being reshcued? | BuckyBeaver wrote: | And all the while, the captain had a mouthful of shtew. | jonstewart wrote: | The order ish, engage the shilent drive. | petee wrote: | I believe they still shroud them. And I vaguely recall reading | about a museum that received a retired prop design; they had to | vertically mount it for display partially underground, as the | Navy wouldn't let them cut the bottom blades since there was | something still secret in the construction of the casting. My | guess is it was hollow like jet fan blades | dsfyu404ed wrote: | Even if the design principals are known the acoustics of a | particular sub are not and can be inferred from the design. | finnh wrote: | Also today: https://news.ycombinator.com/item?id=34571282 | | and a couple months ago: | https://news.ycombinator.com/item?id=33949895 | moistly wrote: | These previous discussions have links to papers and videos that | are convincing. The sound reduction is astounding. The power | graphs are impressive. The price of the boat propellers is | gobsmacking... but if the efficiency claim holds true, will | easily pay the upgrade, and the dolphins & whales will be ever | thankful. | zawy wrote: | Be careful of the boat propellor claims. For example, they | filmed the regular prop in slow motion to hide that it was | going at a much faster speed that caused more cavitation to | make it look worse. Also when they claimed it needed a LOT | less steering, I'm extremely skeptical because that should be | mostly caused by the boat riding higher in the water at a | faster speed. Also they disabled comments on videos. | https://youtu.be/_KkIqC7arnU?t=74 | zawy wrote: | Quieter means more energy is possibly available for more thrust. | I noticed SpaceX rockets sound a LOT more quiet and smooth | compared to older rocket videos. Notice upward tilting winglets | on the tip of large airplane wings these days are to reduce the | same vortices that are seen on propellers (wings work on same | principle as propellers) in order to be more efficient and more | quiet is just a side effect. | anigbrowl wrote: | _INTERESTED IN ACCESSING THIS TECHNOLOGY? Contact the Technology | Ventures Office tvo@ll.mit.edu_ | | LOL good luck trying to corral that. These will be an $11.99 | upgrade on Banggood within 3 months. | DennisP wrote: | Especially since they've barely started optimizing it. Should | be pretty easy for other people to achieve similar or better | performance. | | > the team's best-performing B160 design was not only quieter | at a given thrust level than the best standard propeller they | tested, it also produced more thrust at a given power level - | pretty remarkable given that standard props have more than a | century of development behind them and these toroids are at a | very early stage, with plenty of optimization yet to come. | | https://newatlas.com/aircraft/toroidal-quiet-propellers/ | | This article also suggests that 3D printing would be the best | way to manufacture these. Just need a file on thingiverse. | nabla9 wrote: | It seems to have smaller diameter and more surface area than same | sized normal propeller. This means it could have lower RPM for | same power and generate less noise. | | Are they better than long-screw propeller with the same diameter, | area and RPM? | pacbard wrote: | I was wondering about performance, but I cannot find any data on | how these toroidal propellers are preforming compared to | traditional airblades. | | The two-pager just says: | | > Achieves thrust comparable to that of a multirotor drone | propeller | | which isn't saying anything. | | My gut reaction is that these propellers require more material | than traditional ones, which makes them weigh more, which should | make them perform differently than traditional propellers. At a | minimum, they should spin slower and/or strain the motor more for | the same RPM. Maybe I'm completely off base. | | I found this other website [1] which reports thrust differences | between traditional and toroidal propellers _for boats_. At least | under the conditions reported in the graph, it seems that | toroidal propellers might outperform traditional boat propellers. | | Again, I'm not sure how much air behaves like water. My layman | understanding of fluid dynamics tells me that air is different | from water just because air propellers don't look like water | propellers (e.g., they require longer, thinner, blades; air | engines need to spin way faster than water ones; water probably | requires more torque) and you can't turn a boat into a helicopter | if you turn it sideways. | | [1]: https://newatlas.com/aircraft/toroidal-quiet-propellers/ | p_l wrote: | The main difference is compressibility, to the point that | liquids are commonly used as air analogs in wind tunnels. | | Ship propellers end up working in different density material, | with also different speed requirements and that's why they are | differently shaped even if the equations are the same. | chrisdalke wrote: | Related thread from a few months ago discussed the Sharrow | propeller mentioned in this article, which applies the same | concept to boats: https://news.ycombinator.com/item?id=33949895 | | The difference in geometry for air vs. water propellers has a | lot of complicated reasons but above all the fluid density of | water is about 1000x air: ~1000kg/m3 for water vs ~1kg/m3 for | air. Air propellers are optimized for very high-speed operation | which is needed to produce any significant thrust in low- | density fluid. Boat propellers are very "built up" and | physically sturdy since they are used in low-speed operation | with high torque. | | I have seen people use RC airplane propellers in water for | small autonomous boats -- They do work but look very comical | (think 10x the size of a boat propeller, running at 1/10 | intended speed) | | Cavitation effects -- microscopic bursts of vacuum at low- | pressure boundaries along the propeller -- come into play much | sooner than with air propellers. | someweirdperson wrote: | > Cavitation effects -- microscopic bursts of vacuum at low- | pressure boundaries along the propeller -- come into play | much sooner than with air propellers. | | In liquids vapor-bubbles of the liquid (not vacuum) are | caused by low pressure (or high temperature, boiling), and | cavitation is the collapse of the vapor back to liquid state | when pressure rises (or temperature drops). | | Propellers in air do have issues with the speed of sound, but | that's a different matter than cavitation in liquids. | SkyPuncher wrote: | > At a minimum, they should spin slower and/or strain the motor | more for the same RPM. Maybe I'm completely off base. | | Only when adjusting RPM. At constant RPM, a heavier properly | will actually reduce impulses to the motor. | someweirdperson wrote: | Someone simply needs to invent a motor that provides constant | torque through a full revolution. | | To control the amount of thrust changeable rpm is needed, or | a changeable geometry, like pitch. I imagine the latter | wouldn't be easy with the toroidal propellers. | peepeepoopoo3 wrote: | They should produce more thrust per a given unit of energy than | a conventional propeller by eliminating induced drag. Winglets | on jet airliners work by the same principle, converting the | wingtip vorticity, due to the pressure difference above and | below the wing, into an apparent forward thrust. | mschuster91 wrote: | In some applications warfare and anything in residential areas | (e.g. thermal or roof damage inspection), I'd expect that | pilots will gladly go for the lower noise even if it means a | bit less flight time. | morcheeba wrote: | I too was also expecting a same-thrust controlled study. | | From the fundamental frequencies in the two graphs, we can see | the toroidal propeller (72 Hz) is spinning slower than the | traditional (88 Hz). Assuming, of course the same fundamental | vs. rpm relationship -- the toroidal has twice the number of | "blades" as standard, but I'm not sure how that manifests | sonically. I wonder how a 3-blade or 4-blade propeller would | compare to the standard 2-blade. | | Also, a big difference between quadcopter and other propellers | (boat, plane, heli) is that they use change speed to carefully | control thrust - most quadcopters use fixed pitches. Adding | mass to the propeller can reduce responsiveness, which means | less stability ... but I don't know enough about the magnitude | of this effect to know if that's a problem. | Eddy_Viscosity2 wrote: | Propeller efficiency (both and air and water) are factors of | torque, RPM, and advance speed (effectively the speed of the | vehicle). You can't be efficient for all conditions. For | example, a tug boat needs really high thrust at low and even | zero advance speeds as it pushes up against a giant ship like a | tanker. That design would be very different from what you'd | need for a high speed boat with high advance speed. Similarly, | props for drones can be designed for efficiency at hover (zero | advance speed), or for going fast. Designing for noise will | also have trade-offs for different conditions. Like it might be | really quiet AND efficient in hover, but then be crap at when | moving forward at high speed. Efficiency is always about trade- | offs. | Havoc wrote: | I can totally see this taking off (pun intended) - has sufficient | weirdness factor that marketing teams can leverage it as a | "stealth" design while actually being somewhat credible | | Wouldn't be surprised if we see this on a major commercial drone | soon | compumike wrote: | Video demo (with audio) comparing side-by-side with a | conventional propeller at timestamp 1:12 - 1:22: | | https://twitter.com/MITLL/status/1611438712683958306 | cush wrote: | Wow it's so much quieter in volume, but also less harsh | sounding without those high frequencies | O__________O wrote: | Appears primary source of sound in helicopter blades is from | blade-vortex interaction: | | https://wikipedia.org/wiki/Blade-vortex_interaction | | Likely that even a non-toroidal half-crescent shaped tips would | significantly reduce sound levels. Here's comparable design: | | https://youtube.com/watch?v=dBS1NRsYuF8 | | Possible even a vortex diffuser similar to those found on | submarines might help too. | jbay808 wrote: | This also makes me wonder whether, instead of an entirely | toroidal propeller, you could just put a small, appropriately- | shaped toroidal loop at the tip of the prop. | falcolas wrote: | At least this PDF shows dB graphs, but the graphs are so noisy | that you can't make much out of them. They have fewer harmonic | peaks, and the peaks do seem to be up to 10 dB smaller. But the | average appears to be pretty similar. Again, hard to be concrete | on the differences given the noisy data. | | 10 dB is a lot (2x the sound pressure) since dB is an exponential | scale, but at the peak of 55dB, you're still below the range of a | "normal conversation". | ec109685 wrote: | They claim where the peaks are is less annoying to humans. | bbhi wrote: | I wonder how the acoustic measurements were taken. From my own | experience propeller noise is highly direction-dependant. For a | fair comparison a lot of angle-dependant measurements would have | to be considered. | hdevalence wrote: | Unfortunately for those who care about noise reduction, LL | patented the design, preventing its widespread use. | digdugdirk wrote: | This seems to be the patent in question: | | "Claims: | | 1. Toroidal propeller comprising: a hub supporting a plurality | of elongate propeller elements in which a tip of a leading | propeller element curves into contact with a trailing propeller | element to form a closed structure with increased stiffness and | reduced acoustic signature. | | 2. The toroidal propeller of claim 1 having two or more | propeller elements." | | That's it. Honestly, that's pretty easy to get around, even | without arguing against its validity from prior art in the | submarine world. | IshKebab wrote: | How would you get around it? Sounds fairly solidly written to | me. | superjan wrote: | Perhaps if your design does not improve stiffness? The way | it's phrased suggest that that is a necessary part of the | design. | beambot wrote: | Very curious, since there were commercialized versions reported | back in 2019. | | https://www.boatindustry.com/news/32122/sharrow-amazing-prop... | | https://boattest.com/Sharrow-Propeller | | And there are examples from online forums dating back to 2012: | | https://www.boatdesign.net/threads/strange-propeller.44740/ | BuckyBeaver wrote: | All of those differ from the one in this ad. | beambot wrote: | They are very similar, just with more toroids attached to the | central shaft. They also render the patent completely invalid | by way of prior art. | stareatgoats wrote: | The flying cars that are in development currently are largely | mega-sized drones. Noise is one of the major obstacles to | acceptance. Rather than reshaping the propellers I'm thinking | active noise reduction might be the solution. | | Flying cars that whisk back and forth with a whisper? Could be! | cush wrote: | Exactly. Drones are so useful, but they screech like banshees, | making them effectively useless for consumer applications | within 200ft of any humans. Basically only aerial photography. | klipt wrote: | I assume jetpacks have similar issues | BuckyBeaver wrote: | "The flying cars that are in development currently are largely | mega-sized drones." | | Mmmm, I'm not aware of any that are. The Terrafugia wasn't, but | it has been abandoned apparently. The Samson Switchblade is a | three-wheeled car with a pusher-prop design: | https://www.samsonsky.com/models/ | | The three-wheel strategy is pretty smart, because the vehicle | can be licensed as a motorcycle and doesn't have to have all | the heavy safety equipment of a car. | cush wrote: | > I'm not aware of any that are | | 1. BCL | | 2. Boeing AFS | | 3. Kittyhawk | | 4. Ehang | | 5. Workhorse | | The list goes on... | | You might not have heard of them as they're absolutely | unmarketable because of the unbearable noise they make | keizo wrote: | Wow like Sharrow boat props. | [deleted] | moffkalast wrote: | Was about to say this too, didn't they already have a patent | for this already or does it only cover boats? | b3morales wrote: | Interesting development, but I'm not certain that I want drones | to be quieter. They're not that noisy now, and making them silent | would be sort of like taking the bell _off_ the cat. | macintux wrote: | I was at a ceremony a few years ago for victims of a workplace | shooting. There was a drone overhead, I assume one of the local | news organizations taking photos, and the noise was quite | distracting for such a somber occasion. | | Whether or not there _should_ have been a drone overhead, if | there 's going to be one at a memorial service I'd want it to | be quiet. ___________________________________________________________________ (page generated 2023-01-29 23:00 UTC)