How Do Zipline's Silent Propellers Work?
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- čas přidán 13. 04. 2023
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The paper used in this video: escholarship.org/uc/item/9q75...
In this video, I show you why uneven blade spacing makes propellers sound quieter.
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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.
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.
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
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
Aerospace propulsion Phd student here. The video was pretty good but I wanted to really highlight the elephant in the room.
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
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.
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.
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.
I want this but for my fan by my bed 👍
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!
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'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.
Channels like yours are the best part of CZcams. I always learn cool stuff from you!
Car manufacturers have known this for a long time, radiator cooling fans often have uneven spacing on the blades for noise reduction.
You missed a cool feature of the Zipline propellers: The counter weight.
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.
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.
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.
Cannot tell you how bad I've been wanting a detailed review of this! You read my mind!