Hey everyone, for the silver printed propellers, I should have spun them in the clockwise direction, since they are clockwise blades. But luckily the tones that I demonstrated stay the same.
Didn't you notice while measuring the wind speed that it pushes instead of pulling air? Or did you just flip it on the other side? (which would work just the same). I noticed that when you stopped the engine it appeared as spinning backwards and I thought the frame rate is to blame, or the engine had a kick-back before it stopped.
you should also have explained the formula at 2:19 -> 1240 revoltion per MIN means -> 20.67 per sec. * 4 blades and you get 82.67! Also there are some eroors in all the blade geometries: The frequency gets halved compared to a 4 blade prop because when you narrow the distance to two opposite pairs each pair basically acts like a single, hence half the frequency or the same as a 2blade prop at the same speed. Furthermore in the mit prop comparisson you show it is NOT a 2 blade prop (2 toroids), but a 4 blade prop with connected tips! And of course a 3 toroid= 6 blade prop would be quieter than a 2 blade prop, because it has to spin about only a third as fast to get the same lift, so it would be quieter anyway without considering the wing tip turbulence!
A similar concept is also used in car tires: The tread blocks have slightly different sizes to spread out the rolling noise over a wider frequency range.
True when tires were first introduced the were quite loud so engineers had to make treads in a specific pattern to combat the high frequency noise generated by the tire
As a submarine sonar tech we would analyze the effects except the propeller or screw is in water. One of the first things you learn is how to turn count a merchant using just aural and then using the equipment on board to pick out the individual frequencies, so you can see how many blades the ship has and it's rpm and with some rough turns per knot calculations you can get an estimate of speed
sub screws/props are covered in bags/tarps/etc while they're in dry dock to conceal the acoustic signature of the sub. i bet the US, if they havent been using toroidal props, is scrambling to silence their new subs or existing fleet with toroidal props soon ;)
I knew that from reading papers on audio principles and playing some sub simulators. Destin from SmarterEveryDay made a video IN a submarine asking the crew about just that, and he was stamped with the [Confidential] seal. That led me to ask "Wait,... how is this 'confidential'? It's out there everywhere... why you so worried about disclosing it?" and then it hit me: if they admit to doing that specifically, anyone running a hostile military operation would intentionally alter their sound profiles to fool submarines. the navy would be listening to the mistakes an enemy would make when trying to avoid the navy's sonar... but if they're specifically using sonar by-the-book, then the enemy would outright avoid the sonar principles and try something else.
A lot of this discovery and research was done way back in the 40s, but the only thing that was important was efficiency and thrust, not noise. Now it's being re-researched and re-discovered all over again because the focus has now changed to noise :) interesting
Not just that, but manufacturing capabilities and analysis/optimization techniques have caught up, and now you can win on all three at the same time vs conventional.
That's what my thoughts were with all these 'new' blade discoveries and invention claims popping up everywhere. I swear I have seen the oval and halo blades years and years ago because of the reduced turbulence being researched, same goes with the counterweighted looking set zipline drones have. It always boils down to money and I guess we have electric motors that are now efficient enough that the losses in lift/thrust don't outweigh the luxury comforts of noise. My guess is it has something to do with the patent expiring?
i accidentally noticed this while making my first rc plane when i had to stack 2 double props to the motor.I had to find a good angle between those blades ,so i just held the motor in my hands and feel the vibration and noise. some how a 15 degrees angle works best for the least noise and vibration
@@TheZombieSaints Leaf branches and insect wing veins often show up around 15 degrees. Also crystals like calcite and quartz have internal angles close to 15 degrees apparently. Don't know if that means much in context, but it's something. :) Divides evenly into 45 and 90 so it makes sense there's probably some correlation between 15 and what we typically engineer at 90 and 45.
Interesting. I don’t know a thing about aerodynamics but 15 degrees is 1/24 of a circle and 24 has lots of ways to factor it so intuitively I wonder if this allows for a lot of different harmonics.
Very interesting. Birds flying in a V formation use the lift from the lead birds wing tip vortices to conserve energy. Makes me wonder if the birds sit at a 15 degree angle behind the lead bird similar to the double stacked props 🤔
The 13 1/2 foot diameter, four-blade propellers used on the Convair 580 airliner's two Allison enginess had a synchronization feature that matched more than the exact speed of the two propellers. In cruise flight, it would adjust the passage of the blades so that the blades on the right engine propeller rotated fifteen degrees behind the blades of the left propeller, all as the props spun at 1,020 rpm. This was done to--you guessed it--reduce propeller noise in the passenger cabin. Each time a propeller was removed and replaced the mechanics would re-time the angle between the two propellers by adjusting tachometer generators on the reduction gear boxes. As far as I can recall some fifty years later, nobody ever asked why the phase angle that worked best was fifteen degrees.
Aerospace propulsion Phd student here. The video was pretty good but I wanted to really highlight the elephant in the room. The big thing us propulsion engineers care about is THRUST. There’s about a million ways to make jet engines and propellers quieter but all of them so far DRAMATICALLY impact thrust. For example, you can make a equivalent size propeller to a classic 4 blade propeller (same pitch and diameter etc) that is wayyy quieter like over 10-20 decibels quieter at 10-m, but a lot of times when you then compare the thrust that new propeller makes you realize it doesn’t make enough. So logically you design your novel propeller geometry to generate more thrust… but then once you get to the thrust output of the classic 4 blade you realize it’s only 1-2 decibels quieter and is significantly less efficient at converting mechanical energy into thrust since you’re doing things to mess with the flow… So, all that to say I REALLY want MIT and Zipline to actually release their white papers on their novel propeller concepts to see how useful they actually are (Thrust vs noise curves). Zipline I understand why they haven’t released anything, since they have a market advantage if it’s legit (and it seems legit), but I am a little frustrated with MIT since they’re a research institution (and they’ve only released a hype video and 1 page of real info)…. But anyway still really cool stuff but it really remains to be seen if it’s the game changer that everyone has hyped them up to be…
That is true. You can see how much less air it moves towards the end of the video. But it would take some more in-depth testing of the full frequency profile to see if the added speed makes it sound louder or not. I didn't have to increase the speed much more to get the same wind speed, so it seems like you would still get the reduced tones with the higher speeds, but then broadband noise is slightly higher as well
@@TheActionLab Be careful not to conflate speed with power. The goal is to get the most efficient air movement for the lowest power. MD Helicopters no longer offer either the "Scissor Blade" tail rotors or the Notar because of efficiency and other issues. The Notar was quieter than any of these, but also used more power and offered less control (i.e. tail rotor authority), which would have required even more power to fix. Many large helicopters, especially Russian, have quite a large distance between the two rotor blade pairs of the tail. This is because in a helicopter ~1/3 of the power is used for the antitorque tail rotor and with larger helicopters the tail rotor diameter approaches that of large WWII fighter and some bomber aircraft, which are very loud. I suspect the MIT toroidal propeller is very inefficient and weighs a lot, especially scaled up, so it will never be used in production aircraft. More of the usual MIT "look what we can do" impractical BS.
@@TheActionLab I think it was a good educational tool. Doing proper propeller acoustic testing correctly is usually pretty expensive even for the little guys… And I’ll tell you that even if you duplicate the setup from a published paper people will almost always complain about your acoustic setup. They’re a pretty particular group of folks…
I think the MIT toroidals were a exposure/funding "scam". No one could see any benefits yet of any toroidal design tried. They didn't release any files and the video is also more of an ad then anything else, very sad. I don't think we'll be hearing anything, except maybe more lies in the future
Actually, while M.I.T. is getting the credit, I believe Sharrow Marine (Gregory Sharrow - 2012) invented the design. He has a very fascinating story of why and how he developed it. He was a videographer and wanting to video an orchestra, quietly, while using a drone - he developed the Sharrow prop. Look him up.
@@roberterbes Indeed. The real-world results on the boats are impressive. I know it is a massive process to manufacture propellers for large cargo vessels, and was trying to imagine a Sharrow Marine prop on a vessel like Ever Given. From what I have read, the fuel savings due to efficiency gain is something like 5-8% - that would be a lot of fuel savings for the shipping industry.
@@roberterbes TY - I follow Titans of CNC (I'm from CA and knew of him before he moved to TX). I took a road trip (to visit family in TX and stopped by his new shop. Great people. That is a good video.
MIT is also trying to take the credit for the first ion propelled aircraft without an externally tethered power supply. On my channel there are more than 40 videos of a previously patented version, with onboard power, that is also much more efficient.
The issue I'd imagine with the counterbalanced propellers is that there would be an uneven torque on the bearings caused by unequal "lift", even though there is a balanced centripetal force.
This is only true if the counterbalance is only balanced in the horizontal dimension - meaning, its weight is meant to replace the weight of the blade. But this doesn't have to be the case here. While the mass needs to be equal to the blades on the other side to avoid vibrations, the distance doesn't matter. So you can counterbalance the uplift "tilt" created by the blades in hover by moving the weight inwards making the blades (if you think in a tilting motion) look heavier than the weight on the other side. But as the mass is equal they will rotate without any vibrations.
I suggest you consider measuring power consumption to windspeed, rather than rpms to windspeed, since different sound profiles also have different efficiency profiles. A quieter blade may not provide as much force per rotation, but it may also spin up more easily due to less turbulence.
I was thinking also about “less efficient” due to needing to spin faster. If less efficient means draw less current, it seems to me that a faster blade with the same amount of resistance would require the same amp draw by the motor. Wouldn’t the resistance be the same to reach the same wind velocity? Of course, there could be a change in resistance if the motor creates more internal friction at higher speed, or other incidental differences at higher speed, but it seems to me that it would be very insignificant. Why do wind generators have only 2 blades, and turn slowly? First thought would be to have many blades, like the old farm windmills, and spin faster. But speed doesn’t generate electricity, the 2 blades generate enough torque(?) to spin the generator at its optimum speed through gearing. I’m not an expert engineer, so I might have used incorrect words, but overall am I right?
@@jazzdad52less efficient means it has to work harder to do the same work. Thus spinning faster to move the same air. Most likely using more current to move the same air. Normally spining a motor faster requires more current. No matter the resistance of the prop it still requires more current.
I’d actually do power consumption to thrust as well as wind speed, since thrust is the factor actually defining the performance of the propeller. From wind speed and thrust, mass flow rate can be calculated. Since mass flow rate is one of the few constants in a propeller, it’s the best way to quantify performance absent of this test environment, and it can be used to recalculate thrust in different circumstances.
I'd be interested to see a staggered toroidal blade, just to see if there's any benefits. Toroidal blades themselves are nothing special, they're just a duct integrated into the blades themselves. But there may be interesting occurrences when the toroid is staggered, due to how the blade contorts in 3D space. I'd also be curious to see both the uneven and staggered blades within a normal duct. Maybe Tom Stanton could eventually do a video or series on these.
everything is a trade off... power, efficiency, stability. we had similar results with large RC helicopters. the fastest most aerobatic helicopters were all 2 blade designs... but the heavy lifting quiet models were always multi bladed rotors with up to 5 or 6 blades... which meant they ran slower rpms but generated less tip vortices, but since they had more blades within the same rotor diameter they had more lift. There was once an experimenter that used a single rotor blade with a counter weight as well, it can be found here on YT. the toroidal design is simply merging two blade types ... swept back tip with a lead tip... if there was any benefit to the design dont you think the NAVY would be using it on their Subs? There is also another YTuber that has a drone that uses multi bladed rotors that resemble computer fans... very quiet and very effective... he too tried the toroid design... but it couldn't compete with the multi blade. a more current test of these blades is an eye opener... toroidal are not more efficient power wise and they are heavier, they are just quieter compared to high performance rotor blades... check out: Toroidal Prop Testing: Is this the future of FPV propellers?! by Chris Rosser
@@igrim4777 if you really look a it... a multi blade toroidal is no different than a ducted fan with both forward swept and backward swept blades... with the duct spinning with it
@@renaissanceman5847 - many single blades have been used on all types of craft (air and water)- it is the most efficient, though the lower the rotor solidity the lower the maximum power absorbed by the disk. More blades (in the same or adjacent planes) cause more wake interference drag, reducing efficiency - as you said, everything is a tradeoff. Usually, if the diameter can be increased more power can be transferred to the system more efficiently, otherwise using wider blades, increased pitch or higher numbers of blades - and fancy tip treatment is the answer (heavily loaded tips (nearly always) increase noise - prime numbers reduce harmonics. Yes the "toroid" is a spinning duct - check out some patents from edit: 1890s (sorry I remembered wrong) and 1960s to see how the concept was developed. (Charles Meyer+ J. Davies and David Sugden are some names to use in patent searches.US467322A US467824A US3504990A - may be defined as prior art to the more recent designs. (David B Sugden did a bit of work with a certain - number of- Boring machine(s) totally tedious -jk....)
@@kadmow "check out some patents from the 1860's" is not typically the type of research task one sends another to embark upon without giving the other a place to start haha. Could you maybe link one especially good example?
Yep, distinctly remember the asymmetric 7 blade fan bolted to the engine of my first car.. In my first year learning mechanics I was so curious I had to ask about it, and discovered the reason was for noise/harmonics. Now more than a decade later I'm left still wondering why it isn't used in other situations - like bathroom exhaust fans, kitchen stove extractors or even PC cooling fans.
@@MotoCat91 Especially so in cases where power and efficiency aren't really a limit, like with all of those examples you gave. There I would I happily give up some extra space and power to reduce noise.
I just started looking up information on how to make quieter propellers as well as for air fluid dynamics sim programs for testing propellers a few hours ago. Impressively good timing.
Brilliantly presented. I have read several explanations of uneven spacing and torodial props, but none of them mentioned the crucial relationship between frequency and perceived noise level. This was highly useful, as my favourite UAV is deal breakingly noisy. Thank you!
Something that would probably help more to reduce noise from drones would be to have variable pitch blades. This would allow all the rotors to be run at the same speed and have them phased in a way to achieve best cancellation of noise between them. The downside is that it defeats the simplicity of conventional multirotors in which the only moving parts are the motor armatures. Another approach could be to go the opposite way and have a rotor with many more blades, as in a turbine. With enough blades you could have a fundamental frequency above audible. It will however only work for rather small rotors as even with 50 blades you would need to run at 24,000 RPM which somewhat limits the allowable diameter. The efficiency will probably not be too good either but the sound would be like whooshing rather than buzzing or screaming, which might be less annoying even at the same sound level. Dogs and other animals may have a different opinion though. There are also ways of combining with stators with different number of blades that allows a much higher fundamental frequency for a given number of blades, a technique used in many gas turbine engines to reduce noise, at least the noise that is audible to us humans.
I watched a video last night of an fpv freestyle guy testing different prop designs on his 5” prop quad. When he put 8 blade 3” diameter props it was relatively very quiet while remaining agile and able to accelerate and maintain high speeds. The sounds did go higher in pitch but it wasn’t unpleasant. With two blade 5” it was terrifyingly loud, very high acceleration and top speed, but a little sloppy cornering. Six blades had less power and was noisier than 8. Prop design is interesting.
I remember as a kid, we had a toy, that had a pistol grip winder, where you put a propeller on it, that had a ring going all the way around the outside of the blades, you wound the spring up using the propeller as it clicked while you were turning it, once the spring was tight, you pointed it up in the air, and pulled the trigger, the propeller would fly off for some distance, but I noticed how quiet the propellers were, most likely because of the ring around the outside edge of the blade tips, the propellers also had like a saw tooth shape, on the trailing edge of the blades, that made it quieter as well, perhaps we should revisit these old school toys.
I've been thinking about Zipline's weird propellers since I saw that same video. It would be awesome if they decided to make their propeller design open source. It looks like a lot of time and engineering went into it.
I'm sure it's patented, but anyone could run a similar fluid dynamics analysis/ai and come up with another shape with similar sound profile if they wanted too. Also, anyone can see what the shape looks like and copy it with a 3d printer if they want too.
@@takanara7 Well, my definition of the word "anyone" might not be the same as yours, haha. But if you do that, more power to you. You will have done the R&D that they did developing their prop design. As for copying the design based on visual inspection and 3D printing it, let me know how that works out. I suspect you'll be doing a lot of trial and error there, too. These guys didn't invent or discover the principles these props are based on. They took known concepts and adapted them to their needs to come up with a design. Others are free to do the same (you're probably in for a good amount of work), but I can't see any reason Zipline would have an incentive to give the world their IP by making it open source. The engineering work is non-trivial.
Dude, i'm a big fan of your work in broadening knowledge and increasing understanding of, at times, complex issues. Thank you. What may also aid comprehension is a standardisation of terms: RPM is an abbreviation of Revs Per Minute. It is colloquially referred to as Rev(olutions)s - revs - but never is it correct to call them RPMs. And, as they are measured in Minutes, your description of '...to measure the RPMs, s 'how many times is it spinning around per second...' could be clearer to your audience. Thanks for making time to read this, and keep up the good work.
You missed a cool feature of the Zipline propellers: The counter weight. It's pretty cleverly designed: It's moved inwards, so while the mass of the counter weight is equal to the propellers on the other side, the propellers are rotating downwards - as they are further away from the center. (Their weight has more leverage on the rotation due to a larger distance from the center) This is necesary because the counterbalance generates no lift. The blades on the other hand will create a upward lift and thus a tipping motion on the bearing. So the counter balance needs to be moved inwards to counter the tipping motion the two blades of the propeller are generating when in hover. By counter I mean, that the propellers create a tipping motion towards them when not hovering. This is equalled out when hovering.
Wow, very impressive in so many ways! Thanks! Two sideways questions -- with all the talk about the noise, the actual generated "lift force" (at a given rotational speed) got a bit a brush-off until some quick attention at about the 8:40 to 9:45 mark, where the "wind speed" was measureed. Similarly, the electrical input power kind of got the brush-off, meaning for a given rotational speed, when e.g. comparing traditional blades with "offset" blades, were the motors using the same volts and same amps vis a vis power? Comparisons might be unfair if the electrical power input was higher for one case than the other (at a given rotational speed.) This is one of the best channels on all of RUclips...wish our high school science classes were far more like the Action Lab.
You sped up the quieter blades to match the air flow by increasing voltage, but the actual power consumed is what you need for calculating efficiency. You'd also need the current, which will depend on the load on the propellers. It could be that both approaches use very similar power because the quieter versions disturb the air less and thus have lower load for a higher rate of spin.
These bench top power supplies operate in either constant voltage or constant current mode. Given he changed the voltage, it's safe to assume he was in constant current mode. Therefore, more voltage equals more power, since current is held constant.
@@Panda_Gibs If he's varying voltage manually, it's in constant voltage mode. Specifically, the voltage he is selecting is held constant. Some benchtop supplies (I have one) can do both, but then the current setting is an upper limit and it'll drop the voltage (regardless of what voltage you select) until a desired current is drawn, in accordance with Ohm's law. The point I was getting at is that the resistance of a motor can vary with the load it is experiencing, so just because the voltage goes up doesn't mean the power goes up.
As a U-Controle & R/C hobbyist one of the perks is the propeller noise but the bane of those living close by. I'm fascinated by the sound reduction for our model aircraft and also for boating propeller efficiency and not the sound which is buried in the water. Fishermen may be more interested in the sound reduction though.
@@darrellcook8253 I looked at a video about it, and the toroidal props are hideously expensive for your average boater. I'd love the idea for my R/C boats and the sub, but no-one makes them... YET. One can only hope...
Scimitar-shaped propellers are a widely-used intermediate solution between conventional straight props and the toroidal designs that you showed. As with winglets and wing extensions on airliner wings, they work by reducing the energy of the tip vortex.
Thank God someone finally got the explanation and examples both RIGHT and easily UNDERSTOOD. Lol the toroidal craze has thrown a wrench in the hobbyist drone industries understanding of blade noise reduction. Chris Rosser is makingg and demonstrating more accurate resin prints to test toroidal props, and it would be amazing to see a colab between you guys on testing the zipline prop!
The big blades at the front of turbofan engines are typically designed and limited by the speed at its tip, which is also where most of the noise comes from. Previously the limit was around mach 1, but these days it can be exceeded with careful design of transonic airfoils. The big difference these blades bring to the table of drones is the noise. Blade spacing is one of the factors affecting that, but it also has to do with the wake interaction of the second blade in the series, which is both affected by the radial and vertical spacing between the two blades. Just slapping two props one after the other without careful consideration can make the second blade sit in the wake of the first blade. This may cause the second blade to stall reducing its lift and increasing its drag, in a similar fashion how airplanes can get into a deep stall. An issue these blades may have is damage tolerance, since now only one side of the rotor can take damage, reducing its weight and throwing out its balance. This would lead to vibrations which could take the whole airframe down.
A single piece of propeller blade on one side suppresses the airflow made by the other two and provides stability to the flying wing. The reason for the excitement and shaking may be due to the weight of the material and it is not smooth! it needs to be polished, there should be laminar flow on the propeller blades
Brilliant Video. Thank you Sir. Your videos are excellent at quickly distilling to real terms for understanding. I applaud your hands on demos for sure! Cheers
Lose efficiency? Measure the current comparison between the even spaced blades and the uneven spaced blades spinning at a higher RPM. If the current is the same when forcing an equal 3.1 FPS of air flow then efficiency is the same with improved perception in sound reduction.
Instead of counter rotating props, the noise reduction may work with an uneven number of stationary blades under the working blades forcing air pressure under stationery blades that act like wings.
Without hearing any more, I think it's to do with interrupting the cumulative oscillation (superposition, phase reinforcement, whatever you want to call it). The same reason marching soldiers step out of time when crossing a bridge.
I think these Zipline propellers are awesome. So is their idea of lowering their payloads with a retractable line! The brilliant video about these new propellers is much appreciated. I wanted to mention that toroidal propellors have been patented and used to propel commercial boats for many years, so despite their statements, the MIT students didn't invent the idea. On my channel there are a series of ion propelled aircrafts with onboard power that fly almost silently. They are patented for lifting their power supplies against Earth's gravity and for the required efficiency improvements. Please take a look. Thanks for the info!
Frore Systems is selling their first generation Air Jet, solid state computer fans. There are no rotating blades. PC World has two in depth videos with their president. MORE importantly, ACTION LABS made a video on this around July 2022, called "Solid State Piezoelectric Fans". Check it out!
MIT did not create the toroidal propeller a few months ago. The design has existed since the 70s and has been known to be more efficient for that long too. Due to manufacturing difficulty it hasn't been mass produced in all the years though. With the rise of better and more accessible advanced machining capabilities like multiple axis CNCs we might just see them become more common.
"and has been known to be more efficient for that long too." It has been around a lot longer and no, they are known for being INefficient but quieter. They have also been in use for nearly that long too.
Owl Wings have amazing structures for reducing/countering sound & these are being researched in order to build biomimicry technology - designed by nature, synthesized by us. There are several companies trying to recreate the Stiff Comb Structures along the leading edges of Owl Wings. These structures generate counter-vortices over the top of the wings, which act as inverted/offset soundwaves to significantly nullify the sounds that the wings generate as they fly. (There are many factors why this is as yet in production, with lifespan being at the top. Then the comb's overall structure, tine length, tines/cm, gap size/shape, etc. - all which changes with blade use & rotational frequency) Owl Wings also have highly fractal / fluffy shaped edges along the trailing edge feathers, (along with most body feathers). These act much like the acoustic foam in studio sound booths, trapping several sound frequencies within their structures - making everything much quieter. (Unfortunately, these kinds of structures tend to only work at low frequencies, hence the Owls slow, low flying hunting technique.) These evolutionary adaptations make Owls the quietest flyers in existence, capable of producing less than 15dBa in noise as they fly through testing facilities. This is far less than human ears are capable of hearing (with perhaps some pressure waves on your skin being the only sign an Owl is about to fly past you). [ I can actually attest to this myself as one chased a bat past my where I was sitting one very quiet evening (bush property). I heard the frantic fluttering of the tiny bat as it flew past, then nearly jumped out of my skin as an Owl with a pure white underside & huge 80cm wingspan, silently ghosted out of the night past my face... ]
Sadly it doesn't actually check out like you think. The fan showdown showed these designs may be quieter, but at the cost of less airflow or being heavier. Its a cool principle for attached fans, but not for drones.
Independent testing found the toroidal props so far are far less efficient than regular props, and the noise isn’t actually better either from memory - their video was a bit dishonest.
Well.. not quite true. Maximum air pressure is not lower, but that was never the claim the over frequency are. About efficency we still need the real model to test it.
*What d'you mean by they aren't SUPPOSED to be there?* Are you implying that they shouldn't use these for *medical purposes?* That they aren't meant for *AFRICAN PEOPLE?*
i suppose your phd revolved around sounds? why are we not yet able to have sound cancelling guns? need this to shup up the club playing loud music in my estate at night.
@peterkamakia7284 Noise canceling is a complex problem, but it is possible to have a speaker that tries to cancel the noise it receives from behind. It won't work in all directions, and unfortunately, the current approach to noise cancellation does not work too well with music and low frequencies. It's a consequence of physics + signal processing (adaptive filtering). Passive sound suppression (better insulation) and them to be quieter may be the best current option.
I have a practical problem with the theoretical mathematic harmonic series. I'm never going to do a video on this so, have at it. When I was learning electronics, specifically antenna design and operation, the literature and course work stated infinite harmonic frequencies are produced at multiples by the initial frequency. I pointed out this was impossible because it would require an infinite amount of power to produce any given frequency. I was told to just go along with the course material if I wanted to pass. This problem seems similar in nature to Zeno's Paradox of Dichotomy, the "half the distance" problem. Divide the remaining distance by half and you will never reach the end. I am fairly certain there are not infinite harmonics produced or an infinite distance between points that can be observed. Quantum collapse of duality seems of interest here. Cheers, Tom
Electrical Engineer here. There is no mathematical void waiting in the infinite harmonics produced, such as by a signal generators interpretation of a square wave - this seems like it should be familiar to you - as each progressive harmonic becomes less powerful proportional to it's distance along the frequency axis from the fundamental. Infinite infinitesimal energy is not infinite energy, nor do these contradict. It sums to unity (- in our case, the original energy output of the signal generator). The mathematics proves this unequivocally. If it doesn't make sense looking at a energy vs frequency plot, look a little longer. At a large enough harmonic (~30 or so, typically) the magnitude of the harmonics will be so small as to be undetectable to conventional sensors, but that doesn't mean they don't exist.
@@titusbaumgartner7579Thank you for responding. I assume from your certainty you do not know my theoretical point has not been resolved, even though practical applications work well enough. I know theories postulate solutions that infinity sums to unity. The initial state power is somehow a limiting factor, although infinite harmonics are theoretically produced? That the magnitude is so small it can not be detected does not prove it does not exist. If you are right, actual infinity would not exist, which I disagree with. How is "Infinite infinitesimal energy is not infinite energy" since it never reaches a point of non-exitance across infinite time? Unless it's detection has an effect on it's existence? But here lays the practical and my disagreement with theory unbounded, and why I bring up quantum physics. We are ignorant, and it is a good thing.. I did review the infinite series must "Sum to unity" to save us arguments because it makes sense with what we see, on the macro.
Hi, interesting video, Just a note, in your test (min. 4:00), you raised the blades and overlapped them, so you basically changed 2 variables at the same time, so we don't know how much the overlapping or raising of the blades could have affected the overall change in noise.
THANK YOU!!! I was trying to find where I saw that prop a couple weeks back and I couldn't find it, I was skimming through Mark's videos, Veritasium and a few other channels I subscribe to.
Which chemical defuses the bulb of a torch from a distance of 6 inches? In detail: A person switched on the torch and kept it at a distance of 6 inches from the chemical vessel, after a minute the torch bulb (2.4v) automatically switched off. What could be the chemical used in the utensil?
I know right, this other guy just dropped an ultra quiet propeller like it is nothing and expected nobody would notice. Thanks for digging in and sharing this information
6:57 you can tell that the high pressure points on the right model come when blades face one another straight. that's because the air density in between them is less than everywhere else, because they're both sweeping the same area. turn the props 90º to each other so they never face the same line, and that should cut the buzzing even more. MORE to it, put a funnel around them so the air is contained and bounced around, it'll help dissipate shockwaves. your sound would go up and down instead of sideways. bend the blades like in high performance propellers, from AC fans or turbines, and that would smooth the transition from high to low pressure. basically... you're using a piston engine propeller... use a submarine propeller instead.
I'd love to print stuff for you if you need. I've been tinkering and tuning 3d printers to where I can get stuff off the bed that doesn't even look printed. I'm not talking down on your print or anything but it looked like a first timer. *EDIT* Oh and I'm not talking about for money, you've paid me enough with all of the knowledge and entertainment you've given me.
My question about the design, comes down to the counter weight. Because you're using a counter weight, would it make a difference for the RPM vs. the weight? Or is the counter weight and RPM independent of each other?
Respect! We just started looking into this with our science outreach program, following playing bagpipes with helium. Thank you for giving us an INCREDIBLE head start! You Rock.
One thing not discussed here are the surface areas exposed to air as it rotates, plus the pitch of each blade. Think of surface area as the size of a bird's wing. It takes an equal amount of energy for more surface area to create the same amount of lift. Think of it as the difference between a hawk's wing versus a hummingbirds. That is what makes the "hum" from a hummingbird. But all we hear from a hawk is a whoosh. In fact, the most silent bird is an owl because of the owl's wing design. So, using the same analogy for propellers, a prop with a large surface area can rotate slower than one with less surface area rotating faster. The faster blade will create a buzz or a hum whereas the slower one will create a "whooshing" noise. On a helicopter, the amount of lift generated isn't created by the speed of the blades as it is by the pitch of each blade. The surface area doesn't change nor does the rotational speed. The speed stays constant but the blade pitch changes. This is why we hear a doppler sound as the helicopter approaches and recedes and also depends on where we are in relation to the blades.
I can't help but shiver at the quality of those prints. I know they don't have to look pretty, but i'm 99% sure the bad surfaces mess up the test data significantly.
Awesome that you made this video - I've been thinking about those props since I saw the video and was also surprised there wasn't more detail about them. This is revolutionary.
Excellent demo. Some food for thought: I know normalizing by rpm is more practical, but I am inclined to believe it should be normalized by airflow or lift/thrust.
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Hey everyone, for the silver printed propellers, I should have spun them in the clockwise direction, since they are clockwise blades. But luckily the tones that I demonstrated stay the same.
Didn't you notice while measuring the wind speed that it pushes instead of pulling air? Or did you just flip it on the other side? (which would work just the same). I noticed that when you stopped the engine it appeared as spinning backwards and I thought the frame rate is to blame, or the engine had a kick-back before it stopped.
You should also have equalised the current draw, not the speed. The wider spaced propeller would produce more lift for a given speed.
you should also have explained the formula at 2:19 -> 1240 revoltion per MIN means -> 20.67 per sec. * 4 blades and you get 82.67! Also there are some eroors in all the blade geometries: The frequency gets halved compared to a 4 blade prop because when you narrow the distance to two opposite pairs each pair basically acts like a single, hence half the frequency or the same as a 2blade prop at the same speed.
Furthermore in the mit prop comparisson you show it is NOT a 2 blade prop (2 toroids), but a 4 blade prop with connected tips! And of course a 3 toroid= 6 blade prop would be quieter than a 2 blade prop, because it has to spin about only a third as fast to get the same lift, so it would be quieter anyway without considering the wing tip turbulence!
Recommendation for better 3D printed Finnish
-Increase temperature of the nozzle
-Slow down print speed
-Smaller layers
@@christmassnow3465 99
A similar concept is also used in car tires: The tread blocks have slightly different sizes to spread out the rolling noise over a wider frequency range.
Very interesting, thanks! 🇦🇺
I remember this being mentioned, now it all makes sense now
And running over different road surfaces can create music.
True when tires were first introduced the were quite loud so engineers had to make treads in a specific pattern to combat the high frequency noise generated by the tire
@@freetolook3727 totally unrelated to the comment and the video, but true. It depends on more factors than the road tho
As a submarine sonar tech we would analyze the effects except the propeller or screw is in water. One of the first things you learn is how to turn count a merchant using just aural and then using the equipment on board to pick out the individual frequencies, so you can see how many blades the ship has and it's rpm and with some rough turns per knot calculations you can get an estimate of speed
Wow, that's amazing!
Now leak some confidential document to prove your claim.😂
@@rakib9420 😮😂 lol
sub screws/props are covered in bags/tarps/etc while they're in dry dock to conceal the acoustic signature of the sub. i bet the US, if they havent been using toroidal props, is scrambling to silence their new subs or existing fleet with toroidal props soon ;)
I knew that from reading papers on audio principles and playing some sub simulators.
Destin from SmarterEveryDay made a video IN a submarine asking the crew about just that, and he was stamped with the [Confidential] seal.
That led me to ask "Wait,... how is this 'confidential'? It's out there everywhere... why you so worried about disclosing it?"
and then it hit me: if they admit to doing that specifically, anyone running a hostile military operation would intentionally alter their sound profiles to fool submarines.
the navy would be listening to the mistakes an enemy would make when trying to avoid the navy's sonar... but if they're specifically using sonar by-the-book, then the enemy would outright avoid the sonar principles and try something else.
A lot of this discovery and research was done way back in the 40s, but the only thing that was important was efficiency and thrust, not noise. Now it's being re-researched and re-discovered all over again because the focus has now changed to noise :) interesting
Not just that, but manufacturing capabilities and analysis/optimization techniques have caught up, and now you can win on all three at the same time vs conventional.
@@microcolonel He showed the thrust output was less.
That's what my thoughts were with all these 'new' blade discoveries and invention claims popping up everywhere. I swear I have seen the oval and halo blades years and years ago because of the reduced turbulence being researched, same goes with the counterweighted looking set zipline drones have.
It always boils down to money and I guess we have electric motors that are now efficient enough that the losses in lift/thrust don't outweigh the luxury comforts of noise.
My guess is it has something to do with the patent expiring?
@@microcolonelexactly q😅😊
@@JFirn86Q ...on that one.
i accidentally noticed this while making my first rc plane when i had to stack 2 double props to the motor.I had to find a good angle between those blades ,so i just held the motor in my hands and feel the vibration and noise. some how a 15 degrees angle works best for the least noise and vibration
That's really cool. I reckon a lot of things were discovered like that. Accidentally. Thanks for sharing your experience and knowledge 👍
@@TheZombieSaints Leaf branches and insect wing veins often show up around 15 degrees. Also crystals like calcite and quartz have internal angles close to 15 degrees apparently. Don't know if that means much in context, but it's something. :) Divides evenly into 45 and 90 so it makes sense there's probably some correlation between 15 and what we typically engineer at 90 and 45.
Interesting. I don’t know a thing about aerodynamics but 15 degrees is 1/24 of a circle and 24 has lots of ways to factor it so intuitively I wonder if this allows for a lot of different harmonics.
Very interesting. Birds flying in a V formation use the lift from the lead birds wing tip vortices to conserve energy. Makes me wonder if the birds sit at a 15 degree angle behind the lead bird similar to the double stacked props 🤔
The 13 1/2 foot diameter, four-blade propellers used on the Convair 580 airliner's two Allison enginess had a synchronization feature that matched more than the exact speed of the two propellers. In cruise flight, it would adjust the passage of the blades so that the blades on the right engine propeller rotated fifteen degrees behind the blades of the left propeller, all as the props spun at 1,020 rpm. This was done to--you guessed it--reduce propeller noise in the passenger cabin. Each time a propeller was removed and replaced the mechanics would re-time the angle between the two propellers by adjusting tachometer generators on the reduction gear boxes. As far as I can recall some fifty years later, nobody ever asked why the phase angle that worked best was fifteen degrees.
Aerospace propulsion Phd student here. The video was pretty good but I wanted to really highlight the elephant in the room.
The big thing us propulsion engineers care about is THRUST. There’s about a million ways to make jet engines and propellers quieter but all of them so far DRAMATICALLY impact thrust.
For example, you can make a equivalent size propeller to a classic 4 blade propeller (same pitch and diameter etc) that is wayyy quieter like over 10-20 decibels quieter at 10-m, but a lot of times when you then compare the thrust that new propeller makes you realize it doesn’t make enough. So logically you design your novel propeller geometry to generate more thrust… but then once you get to the thrust output of the classic 4 blade you realize it’s only 1-2 decibels quieter and is significantly less efficient at converting mechanical energy into thrust since you’re doing things to mess with the flow…
So, all that to say I REALLY want MIT and Zipline to actually release their white papers on their novel propeller concepts to see how useful they actually are (Thrust vs noise curves).
Zipline I understand why they haven’t released anything, since they have a market advantage if it’s legit (and it seems legit), but I am a little frustrated with MIT since they’re a research institution (and they’ve only released a hype video and 1 page of real info)….
But anyway still really cool stuff but it really remains to be seen if it’s the game changer that everyone has hyped them up to be…
That is true. You can see how much less air it moves towards the end of the video. But it would take some more in-depth testing of the full frequency profile to see if the added speed makes it sound louder or not. I didn't have to increase the speed much more to get the same wind speed, so it seems like you would still get the reduced tones with the higher speeds, but then broadband noise is slightly higher as well
@@TheActionLab Be careful not to conflate speed with power. The goal is to get the most efficient air movement for the lowest power. MD Helicopters no longer offer either the "Scissor Blade" tail rotors or the Notar because of efficiency and other issues. The Notar was quieter than any of these, but also used more power and offered less control (i.e. tail rotor authority), which would have required even more power to fix. Many large helicopters, especially Russian, have quite a large distance between the two rotor blade pairs of the tail. This is because in a helicopter ~1/3 of the power is used for the antitorque tail rotor and with larger helicopters the tail rotor diameter approaches that of large WWII fighter and some bomber aircraft, which are very loud.
I suspect the MIT toroidal propeller is very inefficient and weighs a lot, especially scaled up, so it will never be used in production aircraft. More of the usual MIT "look what we can do" impractical BS.
@@TheActionLab I think it was a good educational tool. Doing proper propeller acoustic testing correctly is usually pretty expensive even for the little guys…
And I’ll tell you that even if you duplicate the setup from a published paper people will almost always complain about your acoustic setup. They’re a pretty particular group of folks…
I think the MIT toroidals were a exposure/funding "scam". No one could see any benefits yet of any toroidal design tried. They didn't release any files and the video is also more of an ad then anything else, very sad. I don't think we'll be hearing anything, except maybe more lies in the future
agreed
I love that you are comparing FDM printed props to FDM printed props. Surface finish also plays a role in perceived loudness of a propeller.
Actually, while M.I.T. is getting the credit, I believe Sharrow Marine (Gregory Sharrow - 2012) invented the design. He has a very fascinating story of why and how he developed it. He was a videographer and wanting to video an orchestra, quietly, while using a drone - he developed the Sharrow prop. Look him up.
I believe TiTans of CNC recently did a video on the company that actually machines those propellers for him as well.
Video is called "nobody in the world could machine these difficult parts"
@@roberterbes Indeed. The real-world results on the boats are impressive. I know it is a massive process to manufacture propellers for large cargo vessels, and was trying to imagine a Sharrow Marine prop on a vessel like Ever Given. From what I have read, the fuel savings due to efficiency gain is something like 5-8% - that would be a lot of fuel savings for the shipping industry.
@@roberterbes TY - I follow Titans of CNC (I'm from CA and knew of him before he moved to TX). I took a road trip (to visit family in TX and stopped by his new shop. Great people. That is a good video.
MIT is also trying to take the credit for the first ion propelled aircraft without an externally tethered power supply. On my channel there are more than 40 videos of a previously patented version, with onboard power, that is also much more efficient.
I want this but for my fan by my bed 👍
Oooohhh. You're one of those weirdos.
It's not a good idea to blow a fan on you while you're sleeping. It can suck out the oxygen and cause you to suffocate and die in your sleep.
@@kg4boj Ok
fr but i lowkey enjoy the sound of it, it sounds so weirdly quiet when it’s not on
@@kg4bojbro your logic doesn't make any sense
The issue I'd imagine with the counterbalanced propellers is that there would be an uneven torque on the bearings caused by unequal "lift", even though there is a balanced centripetal force.
for a tiny drone its not a problem, but probably thats why you wont see it on a helicopter
Is the counter weight a lifting surface at all? I feel like it would have to be for efficiency reasons but I don't know offhand
@@WhoIsTheEdman The counterweight does not appear to be a lifting surface.
I wonder if gyroscopic precession could reduce the force you’re talking about?
This is only true if the counterbalance is only balanced in the horizontal dimension - meaning, its weight is meant to replace the weight of the blade. But this doesn't have to be the case here.
While the mass needs to be equal to the blades on the other side to avoid vibrations, the distance doesn't matter. So you can counterbalance the uplift "tilt" created by the blades in hover by moving the weight inwards making the blades (if you think in a tilting motion) look heavier than the weight on the other side. But as the mass is equal they will rotate without any vibrations.
Channels like yours are the best part of RUclips. I always learn cool stuff from you!
I suggest you consider measuring power consumption to windspeed, rather than rpms to windspeed, since different sound profiles also have different efficiency profiles. A quieter blade may not provide as much force per rotation, but it may also spin up more easily due to less turbulence.
I was thinking also about “less efficient” due to needing to spin faster. If less efficient means draw less current, it seems to me that a faster blade with the same amount of resistance would require the same amp draw by the motor. Wouldn’t the resistance be the same to reach the same wind velocity? Of course, there could be a change in resistance if the motor creates more internal friction at higher speed, or other incidental differences at higher speed, but it seems to me that it would be very insignificant. Why do wind generators have only 2 blades, and turn slowly? First thought would be to have many blades, like the old farm windmills, and spin faster. But speed doesn’t generate electricity, the 2 blades generate enough torque(?) to spin the generator at its optimum speed through gearing. I’m not an expert engineer, so I might have used incorrect words, but overall am I right?
Bingo
@@jazzdad52less efficient means it has to work harder to do the same work. Thus spinning faster to move the same air. Most likely using more current to move the same air.
Normally spining a motor faster requires more current. No matter the resistance of the prop it still requires more current.
I’d actually do power consumption to thrust as well as wind speed, since thrust is the factor actually defining the performance of the propeller. From wind speed and thrust, mass flow rate can be calculated. Since mass flow rate is one of the few constants in a propeller, it’s the best way to quantify performance absent of this test environment, and it can be used to recalculate thrust in different circumstances.
@@ProteinFromTheSea It seems the long way around, to me. Slapping a Kill-A-Watt inline seems infinitely easier unless you're setting up a full lab.
I'd be interested to see a staggered toroidal blade, just to see if there's any benefits. Toroidal blades themselves are nothing special, they're just a duct integrated into the blades themselves. But there may be interesting occurrences when the toroid is staggered, due to how the blade contorts in 3D space. I'd also be curious to see both the uneven and staggered blades within a normal duct. Maybe Tom Stanton could eventually do a video or series on these.
everything is a trade off... power, efficiency, stability. we had similar results with large RC helicopters. the fastest most aerobatic helicopters were all 2 blade designs... but the heavy lifting quiet models were always multi bladed rotors with up to 5 or 6 blades... which meant they ran slower rpms but generated less tip vortices, but since they had more blades within the same rotor diameter they had more lift. There was once an experimenter that used a single rotor blade with a counter weight as well, it can be found here on YT. the toroidal design is simply merging two blade types ... swept back tip with a lead tip... if there was any benefit to the design dont you think the NAVY would be using it on their Subs? There is also another YTuber that has a drone that uses multi bladed rotors that resemble computer fans... very quiet and very effective... he too tried the toroid design... but it couldn't compete with the multi blade. a more current test of these blades is an eye opener... toroidal are not more efficient power wise and they are heavier, they are just quieter compared to high performance rotor blades... check out: Toroidal Prop Testing: Is this the future of FPV propellers?! by Chris Rosser
Toroidal blades are not the same as ducted propellers which is what a naive person could easily be mislead into believing by your statement.
@@igrim4777 if you really look a it... a multi blade toroidal is no different than a ducted fan with both forward swept and backward swept blades... with the duct spinning with it
@@renaissanceman5847 - many single blades have been used on all types of craft (air and water)- it is the most efficient, though the lower the rotor solidity the lower the maximum power absorbed by the disk. More blades (in the same or adjacent planes) cause more wake interference drag, reducing efficiency - as you said, everything is a tradeoff.
Usually, if the diameter can be increased more power can be transferred to the system more efficiently, otherwise using wider blades, increased pitch or higher numbers of blades - and fancy tip treatment is the answer (heavily loaded tips (nearly always) increase noise - prime numbers reduce harmonics.
Yes the "toroid" is a spinning duct - check out some patents from edit: 1890s (sorry I remembered wrong) and 1960s to see how the concept was developed. (Charles Meyer+ J. Davies and David Sugden are some names to use in patent searches.US467322A US467824A US3504990A - may be defined as prior art to the more recent designs.
(David B Sugden did a bit of work with a certain - number of- Boring machine(s) totally tedious -jk....)
@@kadmow "check out some patents from the 1860's" is not typically the type of research task one sends another to embark upon without giving the other a place to start haha. Could you maybe link one especially good example?
I remember when cars had (engine driven) radiator fans with uneven blade spacing in the '70's. As is so often the case- what's old is new!
Yep, distinctly remember the asymmetric 7 blade fan bolted to the engine of my first car..
In my first year learning mechanics I was so curious I had to ask about it, and discovered the reason was for noise/harmonics.
Now more than a decade later I'm left still wondering why it isn't used in other situations - like bathroom exhaust fans, kitchen stove extractors or even PC cooling fans.
Yeah, I’ve seen that on my dad’s impala and wondered why it was like that!
@@MotoCat91 Especially so in cases where power and efficiency aren't really a limit, like with all of those examples you gave. There I would I happily give up some extra space and power to reduce noise.
@@MotoCat91 maybe the design was patented?
Car manufacturers have known this for a long time, radiator cooling fans often have uneven spacing on the blades for noise reduction.
Yea.. I have noticed that. But they still have very rought edges.. I guess they are ducked so it don't matter
I just started looking up information on how to make quieter propellers as well as for air fluid dynamics sim programs for testing propellers a few hours ago. Impressively good timing.
Cannot tell you how bad I've been wanting a detailed review of this! You read my mind!
Brilliantly presented. I have read several explanations of uneven spacing and torodial props, but none of them mentioned the crucial relationship between frequency and perceived noise level. This was highly useful, as my favourite UAV is deal breakingly noisy. Thank you!
Something that would probably help more to reduce noise from drones would be to have variable pitch blades. This would allow all the rotors to be run at the same speed and have them phased in a way to achieve best cancellation of noise between them. The downside is that it defeats the simplicity of conventional multirotors in which the only moving parts are the motor armatures.
Another approach could be to go the opposite way and have a rotor with many more blades, as in a turbine. With enough blades you could have a fundamental frequency above audible. It will however only work for rather small rotors as even with 50 blades you would need to run at 24,000 RPM which somewhat limits the allowable diameter. The efficiency will probably not be too good either but the sound would be like whooshing rather than buzzing or screaming, which might be less annoying even at the same sound level. Dogs and other animals may have a different opinion though.
There are also ways of combining with stators with different number of blades that allows a much higher fundamental frequency for a given number of blades, a technique used in many gas turbine engines to reduce noise, at least the noise that is audible to us humans.
I watched a video last night of an fpv freestyle guy testing different prop designs on his 5” prop quad. When he put 8 blade 3” diameter props it was relatively very quiet while remaining agile and able to accelerate and maintain high speeds. The sounds did go higher in pitch but it wasn’t unpleasant. With two blade 5” it was terrifyingly loud, very high acceleration and top speed, but a little sloppy cornering. Six blades had less power and was noisier than 8. Prop design is interesting.
I remember as a kid, we had a toy, that had a pistol grip winder, where you put a propeller on it, that had a ring going all the way around the outside of the blades, you wound the spring up using the propeller as it clicked while you were turning it, once the spring was tight, you pointed it up in the air, and pulled the trigger, the propeller would fly off for some distance, but I noticed how quiet the propellers were, most likely because of the ring around the outside edge of the blade tips, the propellers also had like a saw tooth shape, on the trailing edge of the blades, that made it quieter as well, perhaps we should revisit these old school toys.
I watched Rober’s video and thought the blades were extremely interesting. Thanks for making this video.
FINALLY someone is talking about the propellers.
Iv been scrolling reddit and youtube and twitter to find someone speculating about the propellers.
I've been thinking about Zipline's weird propellers since I saw that same video. It would be awesome if they decided to make their propeller design open source. It looks like a lot of time and engineering went into it.
That time and engineering work is probably why they won't make it open source. They sure are cool, though!
I'm sure it's patented, but anyone could run a similar fluid dynamics analysis/ai and come up with another shape with similar sound profile if they wanted too. Also, anyone can see what the shape looks like and copy it with a 3d printer if they want too.
@@takanara7 Well, my definition of the word "anyone" might not be the same as yours, haha. But if you do that, more power to you. You will have done the R&D that they did developing their prop design. As for copying the design based on visual inspection and 3D printing it, let me know how that works out. I suspect you'll be doing a lot of trial and error there, too.
These guys didn't invent or discover the principles these props are based on. They took known concepts and adapted them to their needs to come up with a design. Others are free to do the same (you're probably in for a good amount of work), but I can't see any reason Zipline would have an incentive to give the world their IP by making it open source. The engineering work is non-trivial.
@@swissfreek lol these are industry secrets and you can bet on them never being shared
Maybe its all just bs? Like they're the first to ever research fan blade design before and found a way to make them silent, yeah ok 😂
Dude, i'm a big fan of your work in broadening knowledge and increasing understanding of, at times, complex issues. Thank you.
What may also aid comprehension is a standardisation of terms: RPM is an abbreviation of Revs Per Minute. It is colloquially referred to as Rev(olutions)s - revs - but never is it correct to call them RPMs. And, as they are measured in Minutes, your description of '...to measure the RPMs, s 'how many times is it spinning around per second...' could be clearer to your audience.
Thanks for making time to read this, and keep up the good work.
You missed a cool feature of the Zipline propellers: The counter weight.
It's pretty cleverly designed: It's moved inwards, so while the mass of the counter weight is equal to the propellers on the other side, the propellers are rotating downwards - as they are further away from the center. (Their weight has more leverage on the rotation due to a larger distance from the center)
This is necesary because the counterbalance generates no lift. The blades on the other hand will create a upward lift and thus a tipping motion on the bearing. So the counter balance needs to be moved inwards to counter the tipping motion the two blades of the propeller are generating when in hover. By counter I mean, that the propellers create a tipping motion towards them when not hovering. This is equalled out when hovering.
Just like certain tree seeds when they fall.
Definitely one of the best channels on youtube. Could watch these videos all day.
We appreciate your effort and hard work on this channel. God bless you.
Wow, very impressive in so many ways! Thanks! Two sideways questions -- with all the talk about the noise, the actual generated "lift force" (at a given rotational speed) got a bit a brush-off until some quick attention at about the 8:40 to 9:45 mark, where the "wind speed" was measureed. Similarly, the electrical input power kind of got the brush-off, meaning for a given rotational speed, when e.g. comparing traditional blades with "offset" blades, were the motors using the same volts and same amps vis a vis power? Comparisons might be unfair if the electrical power input was higher for one case than the other (at a given rotational speed.) This is one of the best channels on all of RUclips...wish our high school science classes were far more like the Action Lab.
This is a perfect video for teaching the dynamics of sound!!!
Wow! A video sponsor that's not genuinely involved with the video, but offers a service I might be interested in. Incredible.
You sped up the quieter blades to match the air flow by increasing voltage, but the actual power consumed is what you need for calculating efficiency. You'd also need the current, which will depend on the load on the propellers. It could be that both approaches use very similar power because the quieter versions disturb the air less and thus have lower load for a higher rate of spin.
These bench top power supplies operate in either constant voltage or constant current mode. Given he changed the voltage, it's safe to assume he was in constant current mode. Therefore, more voltage equals more power, since current is held constant.
@@Panda_Gibs
If he's varying voltage manually, it's in constant voltage mode. Specifically, the voltage he is selecting is held constant.
Some benchtop supplies (I have one) can do both, but then the current setting is an upper limit and it'll drop the voltage (regardless of what voltage you select) until a desired current is drawn, in accordance with Ohm's law.
The point I was getting at is that the resistance of a motor can vary with the load it is experiencing, so just because the voltage goes up doesn't mean the power goes up.
How does this new propeller compare in terms of "pulling-power" as compared to old fashion ones?
As a U-Controle & R/C hobbyist one of the perks is the propeller noise but the bane of those living close by. I'm fascinated by the sound reduction for our model aircraft and also for boating propeller efficiency and not the sound which is buried in the water. Fishermen may be more interested in the sound reduction though.
Torodial trolling motor propellers are something to invest in. I wonder how they would preform in weedy conditions.
@@darrellcook8253 I looked at a video about it, and the toroidal props are hideously expensive for your average boater. I'd love the idea for my R/C boats and the sub, but no-one makes them... YET.
One can only hope...
Scimitar-shaped propellers are a widely-used intermediate solution between conventional straight props and the toroidal designs that you showed. As with winglets and wing extensions on airliner wings, they work by reducing the energy of the tip vortex.
It's so convenient having guys like you around to teach me things I didn't know I needed to know. Thanks
You are the best science teacher I've ever had.
Thank God someone finally got the explanation and examples both RIGHT and easily UNDERSTOOD. Lol the toroidal craze has thrown a wrench in the hobbyist drone industries understanding of blade noise reduction. Chris Rosser is makingg and demonstrating more accurate resin prints to test toroidal props, and it would be amazing to see a colab between you guys on testing the zipline prop!
THANK YOU. These propellers not getting explained in the Zipline video was the only downside of said video.
The big blades at the front of turbofan engines are typically designed and limited by the speed at its tip, which is also where most of the noise comes from. Previously the limit was around mach 1, but these days it can be exceeded with careful design of transonic airfoils.
The big difference these blades bring to the table of drones is the noise. Blade spacing is one of the factors affecting that, but it also has to do with the wake interaction of the second blade in the series, which is both affected by the radial and vertical spacing between the two blades. Just slapping two props one after the other without careful consideration can make the second blade sit in the wake of the first blade. This may cause the second blade to stall reducing its lift and increasing its drag, in a similar fashion how airplanes can get into a deep stall.
An issue these blades may have is damage tolerance, since now only one side of the rotor can take damage, reducing its weight and throwing out its balance. This would lead to vibrations which could take the whole airframe down.
A single piece of propeller blade on one side suppresses the airflow made by the other two and provides stability to the flying wing. The reason for the excitement and shaking may be due to the weight of the material and it is not smooth! it needs to be polished, there should be laminar flow on the propeller blades
Props to you on this analysis 😊
Noise is not the entering argument for a propeller, it is the lift or thrust generated. This is great basic science!
Brilliant Video. Thank you Sir. Your videos are excellent at quickly distilling to real terms for understanding. I applaud your hands on demos for sure! Cheers
Excellent video. I love being able to dip into a 10 minute video on things like this on RUclips, keep it up.
Lose efficiency? Measure the current comparison between the even spaced blades and the uneven spaced blades spinning at a higher RPM. If the current is the same when forcing an equal 3.1 FPS of air flow then efficiency is the same with improved perception in sound reduction.
Instead of counter rotating props, the noise reduction may work with an uneven number of stationary blades under the working blades forcing air pressure under stationery blades that act like wings.
Because of the speed of a movement of the blades it would also create low pressure above the stationery blades if designed correctly
Without hearing any more, I think it's to do with interrupting the cumulative oscillation (superposition, phase reinforcement, whatever you want to call it). The same reason marching soldiers step out of time when crossing a bridge.
I think these Zipline propellers are awesome. So is their idea of lowering their payloads with a retractable line! The brilliant video about these new propellers is much appreciated.
I wanted to mention that toroidal propellors have been patented and used to propel commercial boats for many years, so despite their statements, the MIT students didn't invent the idea.
On my channel there are a series of ion propelled aircrafts with onboard power that fly almost silently. They are patented for lifting their power supplies against Earth's gravity and for the required efficiency improvements. Please take a look.
Thanks for the info!
I think this thing is not well researched. Snake oil it is.
Awesome analysis. I'm curious whether this would work with cpu or gpu fans given the constraint with the listening position.
Frore Systems is selling their first generation Air Jet, solid state computer fans. There are no rotating blades. PC World has two in depth videos with their president.
MORE importantly, ACTION LABS made a video on this around July 2022, called "Solid State Piezoelectric Fans". Check it out!
Cutting down on fan noise would be cool.
Now I get why the Apache's tail rotor is designed as it is.
wow that was on my mind looking for a video
This is really interesting. The noise has always been an issue to me. Very well presented.
Now we need to try a single counterbalanced toroid prop
MIT did not create the toroidal propeller a few months ago. The design has existed since the 70s and has been known to be more efficient for that long too. Due to manufacturing difficulty it hasn't been mass produced in all the years though. With the rise of better and more accessible advanced machining capabilities like multiple axis CNCs we might just see them become more common.
"and has been known to be more efficient for that long too."
It has been around a lot longer and no, they are known for being INefficient but quieter. They have also been in use for nearly that long too.
you mean the 1870s.. - lol, - oops sorry 1890s, I misspoke..
US467323A US467824A United States Patent
Owl Wings have amazing structures for reducing/countering sound & these are being researched in order to build biomimicry technology - designed by nature, synthesized by us.
There are several companies trying to recreate the Stiff Comb Structures along the leading edges of Owl Wings. These structures generate counter-vortices over the top of the wings, which act as inverted/offset soundwaves to significantly nullify the sounds that the wings generate as they fly. (There are many factors why this is as yet in production, with lifespan being at the top. Then the comb's overall structure, tine length, tines/cm, gap size/shape, etc. - all which changes with blade use & rotational frequency)
Owl Wings also have highly fractal / fluffy shaped edges along the trailing edge feathers, (along with most body feathers). These act much like the acoustic foam in studio sound booths, trapping several sound frequencies within their structures - making everything much quieter. (Unfortunately, these kinds of structures tend to only work at low frequencies, hence the Owls slow, low flying hunting technique.)
These evolutionary adaptations make Owls the quietest flyers in existence, capable of producing less than 15dBa in noise as they fly through testing facilities. This is far less than human ears are capable of hearing (with perhaps some pressure waves on your skin being the only sign an Owl is about to fly past you).
[ I can actually attest to this myself as one chased a bat past my where I was sitting one very quiet evening (bush property). I heard the frantic fluttering of the tiny bat as it flew past, then nearly jumped out of my skin as an Owl with a pure white underside & huge 80cm wingspan, silently ghosted out of the night past my face... ]
Another amazing informative video! Keep it up! 💯 ✨
Sadly it doesn't actually check out like you think. The fan showdown showed these designs may be quieter, but at the cost of less airflow or being heavier. Its a cool principle for attached fans, but not for drones.
I love that you watched the same video I did and thought the same thing I did and I'm *really* glad you decided to do a video on it; thank you!
Independent testing found the toroidal props so far are far less efficient than regular props, and the noise isn’t actually better either from memory - their video was a bit dishonest.
Well.. not quite true. Maximum air pressure is not lower, but that was never the claim the over frequency are.
About efficency we still need the real model to test it.
gives audio test, plays music over test. GENIUS!!!!!!!!!!!
I like peanut butter
Glad you like peanut butter 👍
No jelly. Jelly is gross.
@@joshuagibson2520 jelly da best fr
@@Random15Yr it does taste good. It's the texture that gets me.
@@joshuagibson2520 skill issue
Incredibly seamless advert. I was just wondering software what was used to make those simulations.
Are they worried about noise because they are flying in areas that they aren't supposed to be there?
???
What are trying to say??
No it's just a small island and the Zipline drones deliver a ton of supplies across it constantly
*What d'you mean by they aren't SUPPOSED to be there?*
Are you implying that they shouldn't use these for *medical purposes?* That they aren't meant for *AFRICAN PEOPLE?*
I wonder if you added whale inspired lumps to the propeller, it would increase the performance in thrust efficiency & noise reduction.
first
Ah dude, it was close
Is your boyfriend impressed?
I did my Ph.D. at UC Irvine in the same lab as the thesis you showed, with Dimitri Papamoschou. Thanks for citing! Those were great explanations.
i suppose your phd revolved around sounds? why are we not yet able to have sound cancelling guns? need this to shup up the club playing loud music in my estate at night.
@peterkamakia7284 Noise canceling is a complex problem, but it is possible to have a speaker that tries to cancel the noise it receives from behind. It won't work in all directions, and unfortunately, the current approach to noise cancellation does not work too well with music and low frequencies. It's a consequence of physics + signal processing (adaptive filtering).
Passive sound suppression (better insulation) and them to be quieter may be the best current option.
@@andresa7781 well apparently the loud music is what they need to make money. May be a real gun can work better than a sound gun.
I have a practical problem with the theoretical mathematic harmonic series. I'm never going to do a video on this so, have at it. When I was learning electronics, specifically antenna design and operation, the literature and course work stated infinite harmonic frequencies are produced at multiples by the initial frequency. I pointed out this was impossible because it would require an infinite amount of power to produce any given frequency. I was told to just go along with the course material if I wanted to pass. This problem seems similar in nature to Zeno's Paradox of Dichotomy, the "half the distance" problem. Divide the remaining distance by half and you will never reach the end. I am fairly certain there are not infinite harmonics produced or an infinite distance between points that can be observed. Quantum collapse of duality seems of interest here. Cheers, Tom
Welcome to higher education! Lol...
Electrical Engineer here. There is no mathematical void waiting in the infinite harmonics produced, such as by a signal generators interpretation of a square wave - this seems like it should be familiar to you - as each progressive harmonic becomes less powerful proportional to it's distance along the frequency axis from the fundamental. Infinite infinitesimal energy is not infinite energy, nor do these contradict. It sums to unity (- in our case, the original energy output of the signal generator).
The mathematics proves this unequivocally. If it doesn't make sense looking at a energy vs frequency plot, look a little longer.
At a large enough harmonic (~30 or so, typically) the magnitude of the harmonics will be so small as to be undetectable to conventional sensors, but that doesn't mean they don't exist.
@@titusbaumgartner7579Thank you for responding. I assume from your certainty you do not know my theoretical point has not been resolved, even though practical applications work well enough. I know theories postulate solutions that infinity sums to unity. The initial state power is somehow a limiting factor, although infinite harmonics are theoretically produced? That the magnitude is so small it can not be detected does not prove it does not exist. If you are right, actual infinity would not exist, which I disagree with. How is "Infinite infinitesimal energy is not infinite energy" since it never reaches a point of non-exitance across infinite time? Unless it's detection has an effect on it's existence? But here lays the practical and my disagreement with theory unbounded, and why I bring up quantum physics. We are ignorant, and it is a good thing.. I did review the infinite series must "Sum to unity" to save us arguments because it makes sense with what we see, on the macro.
Hi, interesting video,
Just a note, in your test (min. 4:00), you raised the blades and overlapped them, so you basically changed 2 variables at the same time, so we don't know how much the overlapping or raising of the blades could have affected the overall change in noise.
THANK YOU. I couldn't find any info on this, and I was thinking that this could *literally* be revolutionary for propellers.
Is it the best quality we can expect from 3D prints? Looks pretty rough. :(
THANK YOU!!! I was trying to find where I saw that prop a couple weeks back and I couldn't find it, I was skimming through Mark's videos, Veritasium and a few other channels I subscribe to.
Been waiting for a long time for someone to make a video on this after the referenced video!😅
Great video, I've been very curious about this since first coming across Ziplines shorts a year or so ago. Very neat stuff.
Which chemical defuses the bulb of a torch from a distance of 6 inches?
In detail: A person switched on the torch and kept it at a distance of 6 inches from the chemical vessel, after a minute the torch bulb (2.4v) automatically switched off. What could be the chemical used in the utensil?
Wow! This is something I would never consider to look into. Thank you for keeping me engaged in science.
I know right, this other guy just dropped an ultra quiet propeller like it is nothing and expected nobody would notice. Thanks for digging in and sharing this information
6:57
you can tell that the high pressure points on the right model come when blades face one another straight.
that's because the air density in between them is less than everywhere else, because they're both sweeping the same area.
turn the props 90º to each other so they never face the same line, and that should cut the buzzing even more.
MORE to it, put a funnel around them so the air is contained and bounced around, it'll help dissipate shockwaves.
your sound would go up and down instead of sideways.
bend the blades like in high performance propellers, from AC fans or turbines, and that would smooth the transition from high to low pressure.
basically... you're using a piston engine propeller... use a submarine propeller instead.
Thank you for addressing this! I've been curious about that ever since I watched Mark Rober's video.
This is quality content. Thanks for asking interesting and niche questions and giving us well read answers. Your videos get me thinking.
Someone needs to turn this into a fan for the fan showdown on major hardwares channel
haha yes!
does it require more energy to spin the uneven blade faster, even if producing the same thrust?
I'd love to print stuff for you if you need. I've been tinkering and tuning 3d printers to where I can get stuff off the bed that doesn't even look printed. I'm not talking down on your print or anything but it looked like a first timer.
*EDIT*
Oh and I'm not talking about for money, you've paid me enough with all of the knowledge and entertainment you've given me.
Just like offset tread on car tires
The AH-64 tail rotor blades are offset like this.
Dude if you were just one of my teachers growing up I know my future would have been brighter.
I saw those in the video and wondered why they were shaped like that. Thanks for the video
Thank you for this video! I've been waiting for someone to notice and tell me how it works!
My question about the design, comes down to the counter weight. Because you're using a counter weight, would it make a difference for the RPM vs. the weight? Or is the counter weight and RPM independent of each other?
What about the uneven blade efficiency? Torque and lift? Great Video!
Respect! We just started looking into this with our science outreach program, following playing bagpipes with helium.
Thank you for giving us an INCREDIBLE head start! You Rock.
One thing not discussed here are the surface areas exposed to air as it rotates, plus the pitch of each blade. Think of surface area as the size of a bird's wing. It takes an equal amount of energy for more surface area to create the same amount of lift. Think of it as the difference between a hawk's wing versus a hummingbirds. That is what makes the "hum" from a hummingbird. But all we hear from a hawk is a whoosh. In fact, the most silent bird is an owl because of the owl's wing design.
So, using the same analogy for propellers, a prop with a large surface area can rotate slower than one with less surface area rotating faster. The faster blade will create a buzz or a hum whereas the slower one will create a "whooshing" noise.
On a helicopter, the amount of lift generated isn't created by the speed of the blades as it is by the pitch of each blade. The surface area doesn't change nor does the rotational speed. The speed stays constant but the blade pitch changes. This is why we hear a doppler sound as the helicopter approaches and recedes and also depends on where we are in relation to the blades.
I can't help but shiver at the quality of those prints. I know they don't have to look pretty, but i'm 99% sure the bad surfaces mess up the test data significantly.
Thank you! I was really curious about efficiency comparison.
Awesome that you made this video - I've been thinking about those props since I saw the video and was also surprised there wasn't more detail about them. This is revolutionary.
Action lab is right on the dot. I really wanted to know how these propellers work. Fast work Sir.
ive said it before and ill say it again. channels like action lab are the only reason i still use youtube. the only social media that i use
Excellent demo. Some food for thought: I know normalizing by rpm is more practical, but I am inclined to believe it should be normalized by airflow or lift/thrust.
Would the toroidal propellers be combinable with the other designs for minimum sounds?
My '92 Jeep YJ's 4.0L engine also has unevenly spaced blades. Now I understand why. Thank you.
Excellent and direct explanation of the sound suppression in just 3 minutes! Keep up the good work!
Always mind blowing videos man, unreal.