Those scientists at MIT didn't come up with anything, they just added the wrong name to the mobius strip propeller so no one would find other research. I found a publication dated 1996 on the subject of these propellers. You can find them by searching"Propellers And Fans Based On The Moebius Strip" or "Screws, propellers and fans based on the Moebius strip" A regular 5 blade propeller is much quieter than a 3 blade propeller. Noise reduction and greater thrust also improve with more blades, but the load on the motor increases. This seems to explain the effect of these propellers. It's just a different design doubling the number of blades, with more extra mass at the ends. On motors with a power reserve, thrust will increase, due to increased consumption and the efficiency of grams per watt will noticeably decrease
@@hesher. or a very cool trick to annoy people with their stupid and cheap video so the public would actually try and prove them wrong and develop this for them?
@@hesher. They may have copied the idea from the mobius strip boat propellers, but these propellers do have the potential to be far better than conventional ones. They just need to be perfected first. Look at how much more efficient Sharrow boat propellers are than normal boat propellers.
Thanks for summing it up. I was about to write something similar. 6 blade props are more quiet indeed. Also like you said because of motor load, you cant just replace a 3 blade with a 6 blade or toroidal in the same size/diameter, without overloading the motors. You need to go down like an inch.
@@Chris-hn4lp It is very likely we will not see the same benefits as the Sharrow propellers. Moving through water is much different than moving through air. Specifically the Sharrow propellers prevent water cavitation from forming at the blade tips which drastically reduces propeller efficiency. I'm not an expert but from my understanding there is not a direct equivalent of cavitation for propellers moving through air.
It might have been a good test to 3D print the Nazgûl prop so you could see a quantifiable amount of degradation due to printing. You could then somewhat speculate how much more efficient the toroidal props will be once they’re injection molded.
I have to say, with all the tests already out there, I’m not sure why Chris missed this detail. It gives it more of a even playing field to test the new tech.
I'm actually quite surprised that my V3 tri-loop managed to perform as well as it did considering how old it is now. Wish I had more time to explore the topic more, but thank you for doing this really solid testing. I casually theorised a lot on the possibilities and potential of toroidal designs, and your very thorough testing I think has brought us to very similar conclusions. I was never of the thought that toroidals would ever replace standard designs, since an aim for efficiency and more discreet operation is a bit of a clash with acrobatic flying, but I still think maybe the Cinewhoop space could benefit in some ways. Certainly the tri-loop looks less likely to cut us up 😅. If it's not too much to ask, I'd appreciate a tag - also helps me keep track of people who've tested my design as I've been maintaining a playlist on that as well. You might find that interesting, especially one of the videos by MoppelMat where he printed the V3 tri-loop out of Nylon-CF and made props lighter weight than equivalent 5" injection-moulded props he had lying around: czcams.com/play/PLYXuRA_sySbwa7FRot80kzEA_j4iqWQ_w.html Also, Foxeer just posted a teaser on their Facebook of a production injection-moulded bi-loop design which would be worth putting through its paces, I think. Proves that injection moulded the bi-loop is possible, now wondering if they might be able to work-out injection moulding the tri-loop. Exciting times, hehe.
@@chrisbee5481 Yeah it's delayed for some reason. I asked and they just said "soon", so I'm wondering what's up. Could be manufacturing, maybe. Or if they've sent out review samples maybe they want a bunch of influencers to post about it at the same time as release? I dunno, completely guessing 😅
I think the material of the prop is also really important. You can see printed props bend significantly when they spin. This can reduce their performance. I wonder how would they perform when made of polycarbonate.
Yeah, the deformation of the prop while spinning was quite evident, especially on the last one (strinkingfpv 3 loop) @6:00. The area inside each loop seems to be expanding (i.e. what would be the "tips" seems to be pulled towards the center as the "wings" of the loop are spread apart).
Polycarbonate can be printed on (generally only advanced) 3D-Printers, but it isn't trivial. They require exceedingly high temperatures for the hotend (~300°C) and relatively high for the bed (100+ °C). Even then, it remains to be seen if they behave differently due to their layer-based construction compared to injection molding, as stresses from high RPM might manifest differently despite them being the same material. Another way would be to print negative molds and construct them from CF+Epoxy or similar, but that again is a very different and extensive process.
negative, bad layer adhesion on PC, needs rebakiing, that warps a bit the shape, all goes bannanas, best is CF Nylon, or CF PPS for cheap money, for bigger money PEI or PEKK CF.
I'm just finding this now. It was neat seeing some of my designs get tested and that they worked as well as they did. When I was designing these I was just learning cad and used these as a challenge to improve my skills. I didn't use any special airfoils or anything. Just eyeballing these and slowly improving them. At the time I didn't even have a 3d printer so I had to rely on others to print and test them for feedback. Most of my designs were designed for easy FDM 3d printing so the bottom of the blades were flat to adhere to the print bed. I've since learned a lot more about prop design so it'd be neat to do some new designs meant for SLA printing.
This is important, because the 6 and even 8 blade props are substantially more quiet than even these toroidal props. Quadmovr had a great video showing this when MIT first put out their press release.
Just an FYI all the props he tested were made by non aerospace engineers who just made something that looked right. You honestly can't expect someone with no background in such a complicated field to make something better than what we currently have. Now seeing a toroidal prop made by someone with the proper engineering background would be quite interesting. However, even seeing that these props can bet a bit close to our current props shows that it will likely end up being something worth using.
As a prior AV Production Technician, thank you so much for using the 1 meter standard for measuring noise! So many you-tubers just hand hold their meter so close that the results can easily be skewed but an inch or two of distance.
I think to do an apples to apples comparison, you should CAD up the traditional blade and print it on an SLA printer (as close to the same process and finish) and see how much the performance diminishes and compare that. If you see more than a 10% drop in efficiency on either thrust, power or both, there's definitely something here. Best!
There was a testing of Toroidal propellers on out boards for 25 ft boats there abouts. The area where the Toroidal propellers excelled over conventional 3 blade propellers in terms of speed, fuel efficiency, noise was between a 3000- 4500 RPM range.
Thanks for posting this...fascinating. One thing I think would help you understand your perception of the dB SPL measurements. You are on the right track...but Human ears are more sensitive to 1k Hz and higher frequencies. In audiology we measure in dB HL (hearing level) not SPL (Sound pressure level) when measuring people's ability to hear different frequencies. We record the measurements in HL due to a concept called audiometric zero. Significantly more SPL is needed in the low frequencies for the average human to even hear the sound. So in dB HL we are actually experiencing lower sound intensity in the lowere pitches. This can be verified by googling "equal loundness curves in dB SPL) which will show the amounts of pressures needed for sounds to be audible in humans. I hope this helps....thanks again.
Thank you, this is very good information. I would love to see an audio spectrogram or FFT for the sound produced by the toroidal vs traditional props. Also, I agree that the efficiency of these new designs will improve fairly quickly.
Great video! A couple notes: It would be very interesting to see the noise power over frequency. Also SLA still has tiny layers which still could or could not impact efficiency and noise.
Thanks for cutting through the hype, Chris. It's interesting to have seen GemFan's comment on JB's livestream the other day. The message was something along the lines of them wanting to move forward, but not necessarily knowing how to work out the credit / attribution to the MIT team. The fact that there is very little technical information available from that team, and that folks have to reverse engineer the dimensions and parameters is frustrating, to say the least.
You are brilliant, thank you for sharing this. I'm sure you already know but lower frequencies get attenuated in air more than high. Would have been interesting to see the spectrum from the mic.
It's getting kind of clear that toroidal will be used for cinewhoops, places where you dont want to disturb anybody and maybe for bigger drones since 7' and forward apparently make tons of noise; while standard will still be used for freestyle, racing and probably tiny whoops for the weight difference. Great informative video
- also for "safe" props - if the tops are very circular - as has been done with outboard motor props - it could reduce (perception too) potential for harm.
I am curious as to strike applications in Ukraine. They brag about how maneuverable the FPVs are, but I suspect it is not needed. A toroidal prop being quieter may give them an offset ability to get closer before detection.
Also, traditional props change profile as you go from center to tip to accomodate relative velocity changes with radius. I noticed the toroidal props shown here, seem to keep a high attack angle at the tips where the loop returns. This suggests to me that at least some of the noise reduction is happening because of stalling and loss of lift.
Its interesting to compare the sound frequencies spectrum Of the props incompare and not only dB as there is more sensitive freq to Human ear than other
Thanks for the info on these. I'd have loved to see how the do on a safety point of view. Our traditional props are dangerous around skin but I feel like these wouldn't draw blood if they made contact. Would be interested in a short video on, maybe see how each do vs a tomato or banana?
i garuntee 100 percent they will draw blood. i dont think your realizing how powerful fpv motors are and how ridiculously fast they spin. may be slightly less damaging yes. but i garuntee it will still cut your finger to the bone in the right moment.
Very interesting and informative video. Well done demo and explanation. The other issues that are top priorities to fpv pilots. Cost, I'd wager these will cost more. And durability, good props I can just bend back and keep on ripping. I have a feeling these toroidal props won't be so forgiving. Happy flying everyone. 🤓
Maybe different use cases? For the toroidal props, I would be using them in situations where I want to fly close to people, and also introduce as little 'annoying' noise as possible. Where, when I'm just rippin', and really pushing my limits as a pilot, I don't care as much about the noise, I am all about power and efficiency.
There's also less corners to get stuck behind the propellor, everything is rounded off. but yeah, they probably wont bend back with the same characteristics
I was waiting to see when you were going to pull this thing apart. More practical applications I would guess would be for commercial jobs but like you said need to get some more refinements, and it would be nice if MIT would share...
@ChrisRosser Your analysis are really inghtful, could I propose a few more tests? Would be great to test comparison with toroidal prop and "iFlight F5 propeller like 3D printed" to remove the material out of the equation In the same way would be great to test Zipline props, what borthers me most is the noise that quadcopeters produce, I would happily sacrifice a little of performance to have a quieter one
Im wondering when they decide a single blade with a weighted balance is the best prop for efficiency. Stiffness of the prop is also important like glass fibre APC props or carbon fibre/wooden props. The plastic props have the toughness for crashing but deform under load. 5 inch racing/freestlye quads, plastic 3 blade is best. APC props for model aeroplanes or mejzelik carbon if you can afford them. Torroidal props have their place but wont re-invent the wheel
Amateur designed 3d printed props aren’t really a valid comparison. Now what Foxeer are releasing next week would be more exciting to see a comparison of.
Personally, I don't see traditional props going away for the one simple reason that is ease of manufacturing. Even if there was a marginal performance increase, it would be offset by the additional cost to retool production lines. This would be particularly true with upscaled applications such as aircraft parts, where factories would have to be retrofitted and the new propeller design would have to be FAA approved, which are both incredibly expensive endeavors.
I’ve been expecting to hear a fluid dynamics interpretation of this MIT toroidal prop stuff from you so this video is most welcome. Sounds like that cold has taken a toll on your voice, I hope you’re on the back end of it now though, get well soon Chris. 🤕 Great video, thank you.😊
And why not try the usual three-bladed propeller with the blades united by a ring. Not rotating inside, but a one-piece design and work with the corners of the ring, the upper edge is wider than the bottom and vice versa.
A ducted propeller addresses tip losses and a ring propeller (and more commonly as a fan) has effectively zero tip clearance. These blades may also have forward and backward curving blade sweeps. These designs have similar advantages and limitations as a toroidal prop.
I think it's pretty obvious that loop blades can never be as efficient as single blades. The ones we see today are also having completely wrong angle close to the tip. I'm sure you can find traditional props with vortex management optimized for noise reduction but if you optimize for noise reduction you will get less efficiency than if you optimize for efficiency which is pretty obvious...😆 So my take on the concept of torodial props ... It's just a hype. The current patent I think was from 2017 and they still haven't been able to show any better performance except possibly noise but even that I think is probably better using traditional blades optimized for noise reduction.
Very helpful testing and explanations. I think a lot of the noise of the prop (or any fan blade) comes from interaction of its shock wave with the elements of the frame supporting the motor. I would like to know how much of the noise reduction of toroidal (or any non-straight blade) prop comes from spreading out the impact of each blade's shock wave in time by making it curved, vs a reduction in tip vortices (which I assume are there regardless of what the supporting frame geometry is.) I think a lot can be done to reduce prop noise on drones by more clever design of elements close to the props that their shock waves bounce off of. An easy test would be to put a long prop axle on your test rig to move the prop away from the supporting structures, and then move objects near the blades while spinning and recording sound and displaying its frequency components using FFT.
I suspect improvement will come with larger diameter props due to reduced wing tip velocity, I'd expect drag to have less effect on a slower spinning prop and therefore more efficient.
Just like most recent developments I think cinematic FPV will benefit the most here. Less awkward noise and also increased safety from not having sharp blades - especially when flying closely around people. In those applications the additional weight and lost efficiency won't outweigh the benefits, as those drones are flying slowly anyway. For classic freestyle and racing it seems we may be sticking to standard props for quite a bit longer :)
I am curious of performance and durability. Are they going to be louder when damaged? Are they going to still be mostly functioning at close to normal performance when damaged? Are they going to be flyable when damaged?
Let me Enlighten us guys as for the sound perspective. The dbs that we get from a db meter is not corresponding all times to how loud a human ear will experience it. Let me explain why: Human hearing is not flat n has emphasis to mid range while decreasing n getting unnoticeable (most of times) close to our limits, below 20Hz and above 20Khz. In simple words we hear louder mid FRs. DB Meters measure the Peak n not the overall summing. On top of that DB meters has 3 different types of measurements, called weightings. A, C ,Z that effects the results. Mics also varies in sensitivity through the FR band. A quality balanced DB meter will have more accurate measurements. Let's also consider on scenarios like propellers that noise can be spreaded to different directions (depending the design) versus for ex. an exhaust that has only one way out, is prefered in my opinion to have multiple measurements like from Front Side n Rear. Last but important factor when recording is to isolate from any maybe reflecting sound that will increase or decrease some frs n disturb the rec. Last, 3db difference is quite noticeable n can be an important factor when u need to be less disturbing or even undercover. As my quick measures from those recs, the FR Hertz Peaks are: (k=khz=kilohertz) 1. 1k 2k 5k 2. 500Hz 1k 5k 3. 50Hz 170Hz 1k 4. 150Hz 2.5k 5. 50Hz 180Hz 800Hz 2.5K V3 3Loop sound preference for me as i prefer Low FRs , is less peaky n more wide spreaded
I noticed that the traditional propeller has a narrower tip which is bad to generate lift. It's more wider closer to the center which doesn't do the lifting but adding more weight. Also because of the flimsy tips, they tend to bend or tilt during lifting due to cantilever effect. This will reduce vertical lifting force.
Some new designed military helicopters have the propeller tips bent in such a way to compensate the lose of lift due to bending. Also since all parts of the propeller are spinning in contact rpm. But the tips are having the fastest velocity (not rpm) which should be wider to generate more lift. Conclusion reducing bending of tips because of cantilever effect, reducing the inner blade weight and shifting it to the tips for better lift.
For my personal opinion, toroidal propellers should be able to generate more lift because of increasing of surfaces which will produce more lift. Provided with bigger motors because more such design requires more power. More efficient lift means more power required.
I am very interested in ICE VTOL. This is impossible to many people because all existing ICEs are heavy and bulky. The ratio of power over weight is much too low. This is because of the piston rings which created high friction to the engine, hugely reducing the efficiency of the engine. I'm talking about new frictionless high efficiency ICE. With higher ratio of power over weight.
I suggest you to do the test again with all propellers in same weight. Meaning the toroidal will be much smaller in diameter due to greater surfaces. This is to rule out the weight issue. I'm sure you will notice that the toroidal is more efficient in lifting as compared to traditional propellers even though the former is a lot smaller.
Currently all commercial aircraft manufacturers attempt to remove the vortex by fitting winglets, as a props profile is basically the same as an aircraft wing surely the same could be tried on props thus adding less weight.
I just saw a video on "Zipline drone silent propeller" they use staggered propellers that look like a 'V' with a little counterbalance. He goes into the science about why the propeller make noise in lower frequencies and it's quite. Toroid propellers are neat but these other props are really weird.
In a word: no. These have limited use for small aircraft. Just because the marine version actually does work as good or better than a standard screw doesn't mean the concept translates to drone use. The fluids are vastly different, as is the rpm; the scale involved must be considered, as well. The initial presentation looked more like a student's assignment paper than an actual results report, this makes the whole thing suss, kinda like room-temperature fusion in a beaker.
I think it is better to compare props with the same blade surface area. I.e. compare a 2 loops prop with a 4 blade traditional prop, what do think about this?
Great video, thanks for the effort. I'd love to see a traditional prop but 3Dprinted, to really check the manufacturing effect. And maybe two staggered conventional tribades, six blades would also be more whoosy" than 3
Not in its current form but some form of toroidal prop might be good in an EDF where the drawbacks of being less efficient and heavier are somewhat mitigated.
Nice video. Thx. I wonder why the hell no one printed traditional props together with those toroidal ones?! Seems like this way we would compare "apples to apples" cuz manufacturing process is the same.
I did actually, but not scientific just a test hover. Funnily, my printed hex-blade drew more amps than my printed tri-loop, but it was just a hover test so no idea what the performance would be like for the rest of the thrust range.
These toroidal propellers can be made by injection moulding, first you would need to smooth off the toroidal the best you can before making a cast. The next part would be choosing the right plastic for your needs whether it would be light in weight or durability or both. Obviously the surface of the blades that was injection moulded would give a much different result on toroidal than a rough 3d printing, weight and type of plastic would also have some bearing on the results. As it is there is too many variables between normal blades and toroidal to make for a fair test, as you mentioned it is literally 3d printing against injection moulding.
The name toroidal is misleading and started with the boat prop. Looking at the boat prop you can see the real design philosophy: it is a tandem wing with the benefits of winglets, the leading wing (sort of extra big leading edge flap) has a downward winglet which is joined with the upward winglet from the other wing. This accelerates the medium (here air) twice and because the prop circle area is limited it gives more thrust. ;-)
I think the toroidal props has more of a future in water appliances than in the air. Boats for example are suffering a lot more of vorticies and cavitation than an airplane due whipping around the much more dense water than in air.
It is worth noting that a 3 dB decrease is half as loud, so in theory the three blade Willow toroidal prop is half as loud as the two blade Willow. When you were testing the props did you notice a significant difference in volume or was the perceived difference less due to the different sound profiles?
it should be a significant difference in volume, saying 2-3 dB different "isn't much" is completely ignoring that it's a logarithmic scale, I don't know if he's oblivious to that or just being facetious
Could you look at doing these tests with a counterweigh prop ie the propeller is only on one side and a counterweight is on the other thus would remove the proppelor wake issues and also make it more comparable to a two blade proppelor
The archaic way math\geometry is taught globally has us 5,000 years behind what the Ancient Africans already knew. If Vortex Math was taught in high school many new inventions would be produced that would revolutionize every industry. It makes one think.
One thing you forgot mention, these props with increase of rotative speed they will stretch out and impossible to fit on tight build , if someone try them careful they might touch each other and explode
Now we just awaiting propellers with wingtip's =) .... as a soaring pilot i have learnt wingtips is only good for one thing. Reducing the wingspan. Same length just flatten out is better.... however on a propeller the end is spinning faster so might be slightly different here....
My AOS Cine35 is absolutely SCREAMING loud. I hope these toroidal props find their way to the consumer, from an injection molded form. Would really love to be able to fly my Cine35, without waking the devil.
For boats, the toroidal is a win win, for plane and drones, more needs to be done. One idea I have is a hybred, one normal blade to counter balance one loop. ???
Shouldn't you print a traditional design prop using the same technique as the toroidal props being tested? I'm not 100% convinced the differences in manufacturing process and materials is negligible.
Hi Chris, your tests are briliant, but as far as I can tell, you are missing one super important thing. In the results you show us the level of sound in dB recorded by same microphone at specific distance. I am assuming that your equipment is capable to record 20Hz-20kHz. Can you add one more test focusing on "buzz" frequency of each prop? Because what I believe, that new design of props resonate at higher (for human less noticable) frequency. I would likely to see spectrum for each prop. Graph based rpm(frequency) and dB level at last for hearable sound that props make. I can probably extract it from this video 😁 but .. thanks for your awesome work.
it would be fun to look at a comparison of the same characteristics if use 2-blade props with winglets as classic, and not a three-blade iflight. The addition of winglets makes it sound similar to toroids, precisely because winglets are used to reduce turbulence at the tip due to the right of the flow at the transition of high and low pressure areas. Also, in terms of efficiency, a 2-bladed one would overtake even more toroidal ones. 4, 6 bladed propeller cannot be effective. Much easier to add winglets to 2blades if you need efficiency. Never propellers with the same pitch and diameter of the propeller if addition of x2 blades will be more effective only in reducing stall at the tips. Winglets decide this.
Fact is, toroidal props equals(if not worse) prop that has doubled blade counted, thus should also be compared to doubled blade count props. e.g. Tri toroidal props should be compared to 6-blade normal prop, not 3-blade normal prop. That's why toroidal props tends to be lower on frequency and also lower on efficiency - just like props with doubled blade has lower rpm and less efficiency when hovering.
Why are there no traditional props with a 'winglets' or 'sharkfins' like they added to modern airplane wings? Those are also added to reduce the wing's tip vortex, AFAIK.
I like that they also seem not to be likely to cut someone, like it has a cage built into the prop. They would be perfect for a tinywhoop flying indoors imo. I bet the efficiency of a tinywhoop with a cage is the same as toroidal with none, and you get the quiet part as a bonus. I'd be curious to see if a tinywhoop gets sucked into a wall like a normal drone without a cage, and what its dynamics are near walls and are in crashes you know?
I'm not into drones or RC , but right off the top I'm going to guess the extra mass of a toroidal prop will significantly degrade performance of aerobatics because of the gyroscopic effects, and throttle response.
It wasn't mentioned the toroidal props are less dangerous when dron hit a soft target. It might be an option when you need to fly you 5" relatively close to people
Really excellent examination of the propellers for the key properties of interest! Perhaps I missed it, but was there a comparison of the noise level for the same thrust/power, or was it only at the same speed? I imagine it would be more important to consider the noise level vs. the amount of thrust you can achieve ultimately if you are optimizing for that. I guess a frequency analysis of the sounds could also help in determining why they seem quieter/less annoying.
I would like to see what effect it would have to add a ring to the outer edge of a 5 or 6 blade prop. It should similarly reduce the tip vortices and add strength to the props
At the tip of the toroidal blade, what would happen if holes were drilled to let the air escape the cupping of the air? Would this allow the blade to speed up with less resistance?
Chris, get better soon! Thanks for great video! Did you one Zipline propeller design with 2 blades on a side being counterbalance with droplet-style weight on another. It seems ever more quiet. Can you test that shape for FPV as well?
Those scientists at MIT didn't come up with anything, they just added the wrong name to the mobius strip propeller so no one would find other research. I found a publication dated 1996 on the subject of these propellers. You can find them by searching"Propellers And Fans Based On The Moebius Strip" or "Screws, propellers and fans based on the Moebius strip"
A regular 5 blade propeller is much quieter than a 3 blade propeller. Noise reduction and greater thrust also improve with more blades, but the load on the motor increases. This seems to explain the effect of these propellers. It's just a different design doubling the number of blades, with more extra mass at the ends. On motors with a power reserve, thrust will increase, due to increased consumption and the efficiency of grams per watt will noticeably decrease
This is just yet another empty hype crap to collect sponsorship money
@@hesher. or a very cool trick to annoy people with their stupid and cheap video so the public would actually try and prove them wrong and develop this for them?
@@hesher. They may have copied the idea from the mobius strip boat propellers, but these propellers do have the potential to be far better than conventional ones. They just need to be perfected first. Look at how much more efficient Sharrow boat propellers are than normal boat propellers.
Thanks for summing it up. I was about to write something similar.
6 blade props are more quiet indeed. Also like you said because of motor load, you cant just replace a 3 blade with a 6 blade or toroidal in the same size/diameter, without overloading the motors. You need to go down like an inch.
@@Chris-hn4lp It is very likely we will not see the same benefits as the Sharrow propellers. Moving through water is much different than moving through air.
Specifically the Sharrow propellers prevent water cavitation from forming at the blade tips which drastically reduces propeller efficiency.
I'm not an expert but from my understanding there is not a direct equivalent of cavitation for propellers moving through air.
It might have been a good test to 3D print the Nazgûl prop so you could see a quantifiable amount of degradation due to printing. You could then somewhat speculate how much more efficient the toroidal props will be once they’re injection molded.
I have to say, with all the tests already out there, I’m not sure why Chris missed this detail. It gives it more of a even playing field to test the new tech.
The drag might equalise them both though. I think something better is to use body filler on the props and sand them smooth and balance them after
@@Athiril Or use the acetone-vapour smoothing method.
Ah, just got to the part where he adress this point
Would a resin 3d printer be better?
I'm actually quite surprised that my V3 tri-loop managed to perform as well as it did considering how old it is now. Wish I had more time to explore the topic more, but thank you for doing this really solid testing. I casually theorised a lot on the possibilities and potential of toroidal designs, and your very thorough testing I think has brought us to very similar conclusions. I was never of the thought that toroidals would ever replace standard designs, since an aim for efficiency and more discreet operation is a bit of a clash with acrobatic flying, but I still think maybe the Cinewhoop space could benefit in some ways. Certainly the tri-loop looks less likely to cut us up 😅.
If it's not too much to ask, I'd appreciate a tag - also helps me keep track of people who've tested my design as I've been maintaining a playlist on that as well. You might find that interesting, especially one of the videos by MoppelMat where he printed the V3 tri-loop out of Nylon-CF and made props lighter weight than equivalent 5" injection-moulded props he had lying around:
czcams.com/play/PLYXuRA_sySbwa7FRot80kzEA_j4iqWQ_w.html
Also, Foxeer just posted a teaser on their Facebook of a production injection-moulded bi-loop design which would be worth putting through its paces, I think. Proves that injection moulded the bi-loop is possible, now wondering if they might be able to work-out injection moulding the tri-loop. Exciting times, hehe.
I can't find that foxeer post on facebook. Can you confirm it's still there? Any date?
Still waiting for foxeer to release.
@@chrisbee5481 Yeah it's delayed for some reason. I asked and they just said "soon", so I'm wondering what's up. Could be manufacturing, maybe. Or if they've sent out review samples maybe they want a bunch of influencers to post about it at the same time as release? I dunno, completely guessing 😅
I think the material of the prop is also really important. You can see printed props bend significantly when they spin. This can reduce their performance. I wonder how would they perform when made of polycarbonate.
Yeah, the deformation of the prop while spinning was quite evident, especially on the last one (strinkingfpv 3 loop) @6:00. The area inside each loop seems to be expanding (i.e. what would be the "tips" seems to be pulled towards the center as the "wings" of the loop are spread apart).
Polycarbonate can be printed on (generally only advanced) 3D-Printers, but it isn't trivial. They require exceedingly high temperatures for the hotend (~300°C) and relatively high for the bed (100+ °C). Even then, it remains to be seen if they behave differently due to their layer-based construction compared to injection molding, as stresses from high RPM might manifest differently despite them being the same material.
Another way would be to print negative molds and construct them from CF+Epoxy or similar, but that again is a very different and extensive process.
They could be cut out of a solid block with a multi axes laser cutter, perhaps.
@@putteslaintxtbks5166 nope, but with a 5 axis mill it can be done
negative, bad layer adhesion on PC, needs rebakiing, that warps a bit the shape, all goes bannanas, best is CF Nylon, or CF PPS for cheap money, for bigger money PEI or PEKK CF.
I'm just finding this now. It was neat seeing some of my designs get tested and that they worked as well as they did. When I was designing these I was just learning cad and used these as a challenge to improve my skills. I didn't use any special airfoils or anything. Just eyeballing these and slowly improving them. At the time I didn't even have a 3d printer so I had to rely on others to print and test them for feedback. Most of my designs were designed for easy FDM 3d printing so the bottom of the blades were flat to adhere to the print bed. I've since learned a lot more about prop design so it'd be neat to do some new designs meant for SLA printing.
You should test this 'three' blade moebius strip propellers with 6 blades regular propeller, because this design just doubles number of blades
This is important, because the 6 and even 8 blade props are substantially more quiet than even these toroidal props. Quadmovr had a great video showing this when MIT first put out their press release.
Indeed. HQProp offers 8-Blade Props (in 2.5", 3" and 3.5" I think). They are indeed quieter and also have a similar windy sound.
Just an FYI all the props he tested were made by non aerospace engineers who just made something that looked right. You honestly can't expect someone with no background in such a complicated field to make something better than what we currently have. Now seeing a toroidal prop made by someone with the proper engineering background would be quite interesting. However, even seeing that these props can bet a bit close to our current props shows that it will likely end up being something worth using.
This is what I've been thinking since this whole toroidal prop craze started.
@@thirtythreeeyes8624 not to mention 2 dB is almost twice as quiet, not much of a difference my a**, it's a freaking logarithmic scale
As a prior AV Production Technician, thank you so much for using the 1 meter standard for measuring noise! So many you-tubers just hand hold their meter so close that the results can easily be skewed but an inch or two of distance.
Logically, I think the 2 loop toroidal prop is equivalent to a 4-bladed prop, 3 loop == 6-bladed, etc
I think to do an apples to apples comparison, you should CAD up the traditional blade and print it on an SLA printer (as close to the same process and finish) and see how much the performance diminishes and compare that. If you see more than a 10% drop in efficiency on either thrust, power or both, there's definitely something here. Best!
There was a testing of Toroidal propellers on out boards for 25 ft boats there abouts. The area where the Toroidal propellers excelled over conventional 3 blade propellers in terms of speed, fuel efficiency, noise was between a 3000- 4500 RPM range.
Thanks for posting this...fascinating. One thing I think would help you understand your perception of the dB SPL measurements. You are on the right track...but Human ears are more sensitive to 1k Hz and higher frequencies. In audiology we measure in dB HL (hearing level) not SPL (Sound pressure level) when measuring people's ability to hear different frequencies. We record the measurements in HL due to a concept called audiometric zero. Significantly more SPL is needed in the low frequencies for the average human to even hear the sound. So in dB HL we are actually experiencing lower sound intensity in the lowere pitches. This can be verified by googling "equal loundness curves in dB SPL) which will show the amounts of pressures needed for sounds to be audible in humans. I hope this helps....thanks again.
Thank you, this is very good information. I would love to see an audio spectrogram or FFT for the sound produced by the toroidal vs traditional props. Also, I agree that the efficiency of these new designs will improve fairly quickly.
Great video! A couple notes: It would be very interesting to see the noise power over frequency. Also SLA still has tiny layers which still could or could not impact efficiency and noise.
Thanks for cutting through the hype, Chris. It's interesting to have seen GemFan's comment on JB's livestream the other day. The message was something along the lines of them wanting to move forward, but not necessarily knowing how to work out the credit / attribution to the MIT team. The fact that there is very little technical information available from that team, and that folks have to reverse engineer the dimensions and parameters is frustrating, to say the least.
Foxeer will be selling toroidal props later next week. I'm guessing they just bypassed MIT entirely to get them made.
You are brilliant, thank you for sharing this. I'm sure you already know but lower frequencies get attenuated in air more than high. Would have been interesting to see the spectrum from the mic.
Compare the StrikingFPV triloop to a 6 blade prop.
It's getting kind of clear that toroidal will be used for cinewhoops, places where you dont want to disturb anybody and maybe for bigger drones since 7' and forward apparently make tons of noise; while standard will still be used for freestyle, racing and probably tiny whoops for the weight difference. Great informative video
- also for "safe" props - if the tops are very circular - as has been done with outboard motor props - it could reduce (perception too) potential for harm.
I am curious as to strike applications in Ukraine. They brag about how maneuverable the FPVs are, but I suspect it is not needed. A toroidal prop being quieter may give them an offset ability to get closer before detection.
Great information. Thank you Chris for this video!
Also, traditional props change profile as you go from center to tip to accomodate relative velocity changes with radius. I noticed the toroidal props shown here, seem to keep a high attack angle at the tips where the loop returns. This suggests to me that at least some of the noise reduction is happening because of stalling and loss of lift.
Its interesting to compare the sound frequencies spectrum
Of the props incompare and not only dB as there is more sensitive freq to
Human ear than other
Chris - thanks for putting the drawing files with details on the AOS page - loving my 3.5" AOS O3 Freestyle!!
Thank you, that was a great review of a new technology in props, with very interesting results.
A set for your (my) experimental--test bed AOS7 would be perfect!!
Interesting data. What happens if the airflow is not perpendicular?
Thanks Chris!
Thanks for the info on these. I'd have loved to see how the do on a safety point of view.
Our traditional props are dangerous around skin but I feel like these wouldn't draw blood if they made contact. Would be interested in a short video on, maybe see how each do vs a tomato or banana?
i garuntee 100 percent they will draw blood. i dont think your realizing how powerful fpv motors are and how ridiculously fast they spin. may be slightly less damaging yes. but i garuntee it will still cut your finger to the bone in the right moment.
4s 2500kv. thats 2500rpm per volt. max voltage of 16.8v thats 42,000 rpm.
@@wubforceone Yeh, but I still want to see for myself if it does...
It makes sense that the thrust from the cordial props would be less efficient because there is more surface area, therefore more drag.
Very interesting and informative video. Well done demo and explanation. The other issues that are top priorities to fpv pilots. Cost, I'd wager these will cost more.
And durability, good props I can just bend back and keep on ripping. I have a feeling these toroidal props won't be so forgiving.
Happy flying everyone. 🤓
Maybe different use cases?
For the toroidal props, I would be using them in situations where I want to fly close to people, and also introduce as little 'annoying' noise as possible. Where, when I'm just rippin', and really pushing my limits as a pilot, I don't care as much about the noise, I am all about power and efficiency.
There's also less corners to get stuck behind the propellor, everything is rounded off. but yeah, they probably wont bend back with the same characteristics
@@Inertia888 or they may act like cheese graters instead of knives. 🧀😋
Thanks Chris.
I was waiting to see when you were going to pull this thing apart. More practical applications I would guess would be for commercial jobs but like you said need to get some more refinements, and it would be nice if MIT would share...
Great video. I really liked it. Keep up the good work.
@ChrisRosser Your analysis are really inghtful, could I propose a few more tests?
Would be great to test comparison with toroidal prop and "iFlight F5 propeller like 3D printed" to remove the material out of the equation
In the same way would be great to test Zipline props, what borthers me most is the noise that quadcopeters produce, I would happily sacrifice a little of performance to have a quieter one
similar to a QUADMOVR design minus the other worldy flight regimes he enters!! great video here for sure!!
Thanks. Test the new Foxeer toroidal props.
Will do
yeah we would need to see thrust-vs-noise curves to make a judgement on noise levels though
Im wondering when they decide a single blade with a weighted balance is the best prop for efficiency.
Stiffness of the prop is also important like glass fibre APC props or carbon fibre/wooden props.
The plastic props have the toughness for crashing but deform under load.
5 inch racing/freestlye quads, plastic 3 blade is best.
APC props for model aeroplanes or mejzelik carbon if you can afford them.
Torroidal props have their place but wont re-invent the wheel
Amateur designed 3d printed props aren’t really a valid comparison. Now what Foxeer are releasing next week would be more exciting to see a comparison of.
Personally, I don't see traditional props going away for the one simple reason that is ease of manufacturing. Even if there was a marginal performance increase, it would be offset by the additional cost to retool production lines. This would be particularly true with upscaled applications such as aircraft parts, where factories would have to be retrofitted and the new propeller design would have to be FAA approved, which are both incredibly expensive endeavors.
With small drones, there is also foldability. Current small drones use foldable prop blades for compact storage.
Welp, that seals the deal for me, for the near future anyway. Thanks!
Even if they were better. we'd still have to fly off our old stock of props😜
7:50 Brooo you're amazing, will definitely be checking out your sit, appreciate your video comprehension and website
I’ve been expecting to hear a fluid dynamics interpretation of this MIT toroidal prop stuff from you so this video is most welcome. Sounds like that cold has taken a toll on your voice, I hope you’re on the back end of it now though, get well soon Chris. 🤕 Great video, thank you.😊
Funny what doubling the surface area of a propeller does. I would like to see it's efficiency compared to conventional props of the same surface area.
And why not try the usual three-bladed propeller with the blades united by a ring. Not rotating inside, but a one-piece design and work with the corners of the ring, the upper edge is wider than the bottom and vice versa.
Great video! Thanks for the great information. I think, toroidal props vs cinewhoop test will be a great test.
A ducted propeller addresses tip losses and a ring propeller (and more commonly as a fan) has effectively zero tip clearance. These blades may also have forward and backward curving blade sweeps. These designs have similar advantages and limitations as a toroidal prop.
good watch, thanks again. you are a saint.
I think it's pretty obvious that loop blades can never be as efficient as single blades. The ones we see today are also having completely wrong angle close to the tip. I'm sure you can find traditional props with vortex management optimized for noise reduction but if you optimize for noise reduction you will get less efficiency than if you optimize for efficiency which is pretty obvious...😆 So my take on the concept of torodial props ... It's just a hype. The current patent I think was from 2017 and they still haven't been able to show any better performance except possibly noise but even that I think is probably better using traditional blades optimized for noise reduction.
Very helpful testing and explanations. I think a lot of the noise of the prop (or any fan blade) comes from interaction of its shock wave with the elements of the frame supporting the motor. I would like to know how much of the noise reduction of toroidal (or any non-straight blade) prop comes from spreading out the impact of each blade's shock wave in time by making it curved, vs a reduction in tip vortices (which I assume are there regardless of what the supporting frame geometry is.) I think a lot can be done to reduce prop noise on drones by more clever design of elements close to the props that their shock waves bounce off of. An easy test would be to put a long prop axle on your test rig to move the prop away from the supporting structures, and then move objects near the blades while spinning and recording sound and displaying its frequency components using FFT.
Yo know, I've had people complain about my 3 inch quad noise, I think I would consider them, as I'm not yet a high performance flyer.
I suspect improvement will come with larger diameter props due to reduced wing tip velocity, I'd expect drag to have less effect on a slower spinning prop and therefore more efficient.
The faster tip speed of a bigger prop was more suited to the toroidal in the MIT testing.
I would think for thrust testing it would make more sense to compare looped props with 4 and 6 bladed conventional propellers.
toroidal props will be useful in tethered drones, that get power from the cable and operate 24/7 over a UN base/hospital or military bases.
Just like most recent developments I think cinematic FPV will benefit the most here. Less awkward noise and also increased safety from not having sharp blades - especially when flying closely around people. In those applications the additional weight and lost efficiency won't outweigh the benefits, as those drones are flying slowly anyway. For classic freestyle and racing it seems we may be sticking to standard props for quite a bit longer :)
I am curious of performance and durability. Are they going to be louder when damaged? Are they going to still be mostly functioning at close to normal performance when damaged? Are they going to be flyable when damaged?
Durability is a good point. But i think those would be more for Longrange + Autopilot applications than for freestyle
Let me Enlighten us guys as for the sound perspective.
The dbs that we get from a db meter is not corresponding all times to how loud a human ear will experience it.
Let me explain why:
Human hearing is not flat n has emphasis to mid range while decreasing n getting unnoticeable (most of times) close to our limits, below 20Hz and above 20Khz. In simple words we hear louder mid FRs.
DB Meters measure the Peak n not the overall summing.
On top of that DB meters has 3 different types of measurements, called weightings. A, C ,Z that effects the results.
Mics also varies in sensitivity through the FR band. A quality balanced DB meter will have more accurate measurements.
Let's also consider on scenarios like propellers that noise can be spreaded to different directions (depending the design) versus for ex. an exhaust that has only one way out, is prefered in my opinion to have multiple measurements like from Front Side n Rear.
Last but important factor when recording is to isolate from any maybe reflecting sound that will increase or decrease some frs n disturb the rec.
Last, 3db difference is quite noticeable n can be an important factor when u need to be less disturbing or even undercover.
As my quick measures from those recs, the FR Hertz Peaks are: (k=khz=kilohertz)
1. 1k 2k 5k
2. 500Hz 1k 5k
3. 50Hz 170Hz 1k
4. 150Hz 2.5k
5. 50Hz 180Hz 800Hz 2.5K
V3 3Loop sound preference for me as i prefer Low FRs , is less peaky n more wide spreaded
I noticed that the traditional propeller has a narrower tip which is bad to generate lift. It's more wider closer to the center which doesn't do the lifting but adding more weight.
Also because of the flimsy tips, they tend to bend or tilt during lifting due to cantilever effect. This will reduce vertical lifting force.
Some new designed military helicopters have the propeller tips bent in such a way to compensate the lose of lift due to bending. Also since all parts of the propeller are spinning in contact rpm. But the tips are having the fastest velocity (not rpm) which should be wider to generate more lift.
Conclusion reducing bending of tips because of cantilever effect, reducing the inner blade weight and shifting it to the tips for better lift.
For my personal opinion, toroidal propellers should be able to generate more lift because of increasing of surfaces which will produce more lift. Provided with bigger motors because more such design requires more power. More efficient lift means more power required.
I am very interested in ICE VTOL. This is impossible to many people because all existing ICEs are heavy and bulky. The ratio of power over weight is much too low. This is because of the piston rings which created high friction to the engine, hugely reducing the efficiency of the engine.
I'm talking about new frictionless high efficiency ICE. With higher ratio of power over weight.
I suggest you to do the test again with all propellers in same weight. Meaning the toroidal will be much smaller in diameter due to greater surfaces. This is to rule out the weight issue. I'm sure you will notice that the toroidal is more efficient in lifting as compared to traditional propellers even though the former is a lot smaller.
Currently all commercial aircraft manufacturers attempt to remove the vortex by fitting winglets, as a props profile is basically the same as an aircraft wing surely the same could be tried on props thus adding less weight.
I just saw a video on "Zipline drone silent propeller" they use staggered propellers that look like a 'V' with a little counterbalance. He goes into the science about why the propeller make noise in lower frequencies and it's quite. Toroid propellers are neat but these other props are really weird.
In a word: no. These have limited use for small aircraft. Just because the marine version actually does work as good or better than a standard screw doesn't mean the concept translates to drone use. The fluids are vastly different, as is the rpm; the scale involved must be considered, as well. The initial presentation looked more like a student's assignment paper than an actual results report, this makes the whole thing suss, kinda like room-temperature fusion in a beaker.
I think it is better to compare props with the same blade surface area. I.e. compare a 2 loops prop with a 4 blade traditional prop, what do think about this?
Great video, thanks for the effort. I'd love to see a traditional prop but 3Dprinted, to really check the manufacturing effect. And maybe two staggered conventional tribades, six blades would also be more whoosy" than 3
Not in its current form but some form of toroidal prop might be good in an EDF where the drawbacks of being less efficient and heavier are somewhat mitigated.
Nice video. Thx.
I wonder why the hell no one printed traditional props together with those toroidal ones?! Seems like this way we would compare "apples to apples" cuz manufacturing process is the same.
I did actually, but not scientific just a test hover. Funnily, my printed hex-blade drew more amps than my printed tri-loop, but it was just a hover test so no idea what the performance would be like for the rest of the thrust range.
These toroidal propellers can be made by injection moulding, first you would need to smooth off the toroidal the best you can before making a cast. The next part would be choosing the right plastic for your needs whether it would be light in weight or durability or both. Obviously the surface of the blades that was injection moulded would give a much different result on toroidal than a rough 3d printing, weight and type of plastic would also have some bearing on the results. As it is there is too many variables between normal blades and toroidal to make for a fair test, as you mentioned it is literally 3d printing against injection moulding.
The name toroidal is misleading and started with the boat prop. Looking at the boat prop you can see the real design philosophy: it is a tandem wing with the benefits of winglets, the leading wing (sort of extra big leading edge flap) has a downward winglet which is joined with the upward winglet from the other wing.
This accelerates the medium (here air) twice and because the prop circle area is limited it gives more thrust.
;-)
Thank you for outlining the myths about these props so I can save some money
I think the toroidal props has more of a future in water appliances than in the air. Boats for example are suffering a lot more of vorticies and cavitation than an airplane due whipping around the much more dense water than in air.
I'm guessing the material used to make the prop would have a wide range of differentiates.
It is worth noting that a 3 dB decrease is half as loud, so in theory the three blade Willow toroidal prop is half as loud as the two blade Willow. When you were testing the props did you notice a significant difference in volume or was the perceived difference less due to the different sound profiles?
it should be a significant difference in volume, saying 2-3 dB different "isn't much" is completely ignoring that it's a logarithmic scale, I don't know if he's oblivious to that or just being facetious
Could you look at doing these tests with a counterweigh prop ie the propeller is only on one side and a counterweight is on the other thus would remove the proppelor wake issues and also make it more comparable to a two blade proppelor
The archaic way math\geometry is taught globally has us 5,000 years behind what the Ancient Africans already knew.
If Vortex Math was taught in high school many new inventions would be produced that would revolutionize every industry. It makes one think.
Damn, bad timing with the Foxeer props coming soon
One thing you forgot mention, these props with increase of rotative speed they will stretch out and impossible to fit on tight build , if someone try them careful they might touch each other and explode
Now we just awaiting propellers with wingtip's =) .... as a soaring pilot i have learnt wingtips is only good for one thing. Reducing the wingspan. Same length just flatten out is better.... however on a propeller the end is spinning faster so might be slightly different here....
My AOS Cine35 is absolutely SCREAMING loud.
I hope these toroidal props find their way to the consumer, from an injection molded form.
Would really love to be able to fly my Cine35, without waking the devil.
For boats, the toroidal is a win win, for plane and drones, more needs to be done. One idea I have is a hybred, one normal blade to counter balance one loop. ???
It would be interesting to compare with a traditional prop featuring a circular rim.
I think noise is the most important thing for me. But I heard a fanless drone is call ion something i forgot the actual name.
Shouldn't you print a traditional design prop using the same technique as the toroidal props being tested? I'm not 100% convinced the differences in manufacturing process and materials is negligible.
Hi Chris, your tests are briliant, but as far as I can tell, you are missing one super important thing. In the results you show us the level of sound in dB recorded by same microphone at specific distance. I am assuming that your equipment is capable to record 20Hz-20kHz. Can you add one more test focusing on "buzz" frequency of each prop? Because what I believe, that new design of props resonate at higher (for human less noticable) frequency. I would likely to see spectrum for each prop. Graph based rpm(frequency) and dB level at last for hearable sound that props make. I can probably extract it from this video 😁 but .. thanks for your awesome work.
He is seemingly forgetting that dB's are a logarithmic scale, 2-3 dB is roughly half as loud, saying it's not a big difference is kind of wild to hear
@@13374me I absolutly agree
$50 "reference" mic would've helped a lot. It would show you exactly the frequencies and the decibels.
What is the traditional refinement process for an FPV prop? Is it (1) computer simulation or (2) making 50 versions with a thrust stand?
Maybe you can try to obtain some of the wishbone props from Zipline for testing, too?
it would be fun to look at a comparison of the same characteristics if use 2-blade props with winglets as classic, and not a three-blade iflight. The addition of winglets makes it sound similar to toroids, precisely because winglets are used to reduce turbulence at the tip due to the right of the flow at the transition of high and low pressure areas.
Also, in terms of efficiency, a 2-bladed one would overtake even more toroidal ones. 4, 6 bladed propeller cannot be effective. Much easier to add winglets to 2blades if you need efficiency.
Never propellers with the same pitch and diameter of the propeller if addition of x2 blades will be more effective only in reducing stall at the tips. Winglets decide this.
You are awesome!
Fact is, toroidal props equals(if not worse) prop that has doubled blade counted, thus should also be compared to doubled blade count props. e.g. Tri toroidal props should be compared to 6-blade normal prop, not 3-blade normal prop. That's why toroidal props tends to be lower on frequency and also lower on efficiency - just like props with doubled blade has lower rpm and less efficiency when hovering.
Planes have curved tip wings. Why don't drones use that?
Why are there no traditional props with a 'winglets' or 'sharkfins' like they added to modern airplane wings? Those are also added to reduce the wing's tip vortex, AFAIK.
There are. The EMAX scimitar, for example. Great props.
I like that they also seem not to be likely to cut someone, like it has a cage built into the prop. They would be perfect for a tinywhoop flying indoors imo. I bet the efficiency of a tinywhoop with a cage is the same as toroidal with none, and you get the quiet part as a bonus. I'd be curious to see if a tinywhoop gets sucked into a wall like a normal drone without a cage, and what its dynamics are near walls and are in crashes you know?
toroidal props have been in use on boats for a while
Sharrow.
I'm not into drones or RC , but right off the top I'm going to guess the extra mass of a toroidal prop will significantly degrade performance of aerobatics because of the gyroscopic effects, and throttle response.
It wasn't mentioned the toroidal props are less dangerous when dron hit a soft target. It might be an option when you need to fly you 5" relatively close to people
would the injected mold make a weight difference if you had them made the materials are not the same
cant you just lower the angle of attack right at the tip of a standard prop to stop the low pressure meeting high air pressure issue?
Really excellent examination of the propellers for the key properties of interest! Perhaps I missed it, but was there a comparison of the noise level for the same thrust/power, or was it only at the same speed? I imagine it would be more important to consider the noise level vs. the amount of thrust you can achieve ultimately if you are optimizing for that. I guess a frequency analysis of the sounds could also help in determining why they seem quieter/less annoying.
I would like to see what effect it would have to add a ring to the outer edge of a 5 or 6 blade prop. It should similarly reduce the tip vortices and add strength to the props
Cool video. Toroidal propellers would be very use fell in the Ukraine war because the sound of a drone is very distinctive sound cheers
At the tip of the toroidal blade, what would happen if holes were drilled to let the air escape the cupping of the air? Would this allow the blade to speed up with less resistance?
Chris, get better soon! Thanks for great video! Did you one Zipline propeller design with 2 blades on a side being counterbalance with droplet-style weight on another. It seems ever more quiet. Can you test that shape for FPV as well?