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Anonymous Mon 17 Aug 01:54:13 2020 No.12016529 View Reply Original Report

Quoted By: >>12016539 >>12016571 >>12017127 >>12022105

How much of the noise quadcopters make is mechanical, and how much is aerodynamic?
I'm curious about whether it'd be possible to make a drone with electromagnetically driven (and possibly even suspended) propellers, and if such a drone would be virtually silent.
Also, how come drone propellers are almost always 2-bladed?

Anonymous

Anonymous Mon 17 Aug 2020 01:56:26 No.12016539 Report

Quoted By: >>12016553

>>12016529
Magnetic bearings are totally a thing but don’t yield much efficiency unless you are operating at gas turbine tier RPMs and forces

Anonymous

Anonymous Mon 17 Aug 2020 01:59:08 No.12016553 Report

Quoted By: >>12016573

>>12016539
Do you mean they don't yield much additional efficiency compared to conventional bearings, or do you mean they're ridiculously inefficient at normal prop RPMs?

Anonymous

Anonymous Mon 17 Aug 2020 02:03:32 No.12016571 Report

Quoted By:

>>12016529
Air is a medium to carry the sound generated by the motor.

Anonymous

Anonymous Mon 17 Aug 2020 02:03:59 No.12016573 Report

Quoted By: >>12016653

>>12016553
>they don't yield much additional efficiency compared to conventional bearings

Yes.

Prop RPMs are only one parameter. You have to think about the force loading on those bearings as well. If your drone only weighs a couple pounds, it’s not worth it. Maybe If you had a big ass drone that had to lift big payloads.

Anonymous

Anonymous Mon 17 Aug 2020 02:27:03 No.12016653 Report

Quoted By:

>>12016573
>not worth it
well that depends how important silence is.
PI or military for example

Anonymous

Anonymous Mon 17 Aug 2020 04:11:04 No.12016982 Report

Quoted By: >>12017015 >>12017027

Noise is almost entirely due to the propellers disturbing the air. The only way to reduce it would be making quieter propeller blades. There's a 2016 paper from NASA about a lift distribution that could theoretically drastically improve efficiency in wings, and by extension reduce propeller noise if applied to propeller blade design. I hope to study exactly this for my master thesis.
t. Aerospace Engineer

Anonymous

Anonymous Mon 17 Aug 2020 04:23:27 No.12017015 Report

Quoted By: >>12017171

>>12016982
good luck anon

Anonymous

Anonymous Mon 17 Aug 2020 04:27:03 No.12017027 Report

Quoted By: >>12017171

>>12016982
Can you link to the paper? I can't find it. I can find articles on something called the "Prandtl-D" which sounds relevant though.

Anonymous

Anonymous Mon 17 Aug 2020 05:05:00 No.12017096 Report

Quoted By:

As said before, most of the noise is due to the air. This is called aeroacoustics and it is now a trending topic because it is expected to use drones for delivery in the recent future.

Instead of using EM propellers it would be better to improve its shape, but it is quite hard because you need to reduce noise but you can't lose lift, then it would be like a tradeoff when you have to win both.

Anonymous

Anonymous Mon 17 Aug 2020 05:21:39 No.12017127 Report

Quoted By:

>>12016529
>Also, how come drone propellers are almost always 2-bladed?
The short answer is because they are small and two blades is more efficient in that size and rpm range. The long answer is an entire course in fluid mechanics and props that I am not qualified to give.

Anonymous

Anonymous Mon 17 Aug 2020 05:47:20 No.12017171 Report

Quoted By: >>12017266

>>12017015
Thanks.
>>12017027
Yep, that's the one. I suggest you to look on YouTube the conferences held by Al Bowers on the subject: that's how I came to know about it, by mere chance of the almighty YouTube algorithm. In one of those he specifically mentions the application on fans and propellers but apparently there's no written document on that explicitly dives into this application.

It's really interesting because apparently everyone got stuck on Prandtl's elliptic lift distribution, which fair enough it's a good solution, but Prandtl after the elliptic distribution also published a really brief paper that everyone but Dr Bowers basically overlooked and that's what the Prandtl-D wing is all about. I haven't really had the time to dive into the matter but seems super cool and I want to apply it to propellers.

Anonymous

Anonymous Mon 17 Aug 2020 06:46:36 No.12017266 Report

Quoted By: >>12017276

>>12017171
If you want to do a test, print out some props and smooth them with acetone vapor. Unless you're living somewhere pretty underdeveloped, you should be able to find a 3D printer.

Anonymous

Anonymous Mon 17 Aug 2020 06:53:16 No.12017276 Report

Quoted By: >>12017281

>>12017266
For the time being I have neither the space nor the money for a 3D printer. Beside, I'm still a year away from having to do a master thesis, so I'm in no hurry.

Anonymous

Anonymous Mon 17 Aug 2020 06:55:50 No.12017281 Report

Quoted By:

>>12017276
I don't mean buy a personal one, I mean use one in a library or makerspace. Or failing that, ask to have something printed on Craigslist.

Anonymous

Anonymous Tue 18 Aug 2020 01:23:03 No.12019890 Report

Quoted By: >>12020597

What's some good study material for getting an overview of concepts in aerodynamics?

Anonymous

Anonymous Tue 18 Aug 2020 08:15:40 No.12020597 Report

Quoted By:

>>12019890
Unironically Wikipedia. If you want you can try and download the Anderson, which is written beautifully, but requires a certain familiarity with calculus.

Anonymous

Anonymous Tue 18 Aug 2020 18:05:48 No.12022105 Report

Quoted By: >>12023843

>>12016529

niggacopter

Anonymous

Anonymous Wed 19 Aug 2020 03:15:41 No.12023843 Report

Quoted By:

>>12022105
>gets shot down

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