Over the past 8 years, drone noise levels have shown no improvement

[hank970]

There was an article in Popular Mechanics recently that referenced recent findings on Leonardo Da Vinci’s screw bladed helicopter. They seemed to think that his design was more efficient and quieter for the same amount of lift. Perhaps it’s time some CFD was applied along with modern manufacturing to see if we can get away from what is essentially driven windmills.

Maybe the folks at Popular Mechanics should take DaVinci's idea and run with it. Then they could compare the noise level, efficiency, and usefulness of their contrivance with a conventional helicopter or quadcopter. If nothing else, by trying to reinvent the wheel, they'd learn why multiple helicopter manufacturers over multiple decades haven't adopted Da Vinci's screw-blade rotor.

In fact, any of us with a bit of mechanical aptitude and a 3D printer could fabricate some screw-blades, attach them to a drone, and give it a try -- a revelatory experience. As with any drone, maneuvering would rely solely on varying the RPMs of each motor, since there'd be no way to adjust the pitch or tilt of the rotor blades, as on a helicopter.

 

[anotherlab]

There was an article in Popular Mechanics recently that referenced recent findings on Leonardo Da Vinci’s screw bladed helicopter. They seemed to think that his design was more efficient and quieter for the same amount of lift. Perhaps it’s time some CFD was applied along with modern manufacturing to see if we can get away from what is essentially driven windmills.

The study referenced in the Popular Mechanics article (Leonardo da Vinci’s 500-Year-Old Invention Might Fix the #1 Problem With Drones) noted that the Da Vinci design had a lower lift coefficient, but required less power and generated less noise.

The study cites “the screw’s large wetted area and lower rotational speed” as the primary reason for these advantages, while conceding that “the design is not optimized for performance.”

 

[WanderLost]

Hey mate, could you do a hover noise comparison between the M30, M3, and Mini 4 Pro?

I don’t have access to M30 but I’m really curious about its noise level. According to DJI’s Euro certification, the M30 is 7-8 dB louder than the M3, which actually makes it quieter than the Phantom 4 — I found that hard to believe. I thought the M30 was at least 10 dB louder than the M3. If you can, please hover the drones and check the noise from 5-10 meters (or yards) away, either outdoors or indoors. Thanks!

Just saw this now. Sure - It would be interesting to compare them side by side and make a video. I think I'll include by Neo for fun as well. I'll have to wait for a windless quiet day here to run the experiment.

 

[AeroJ]

I'm not surprised prop noise hasn't decreased much in 8 years - it's not a priority in most commercial builds and nor would most of us want it to be - stealth is not usually much of a factor in our flyings I would imagine, and making these things much quieter would involve a performance hit none of us really want.

Lastly I would speculate that the fact prop noise has remained relatively consistent in all that time suggests users are OK with the current levels. I certainly am, though still find the discussion interesting...

 

[WanderLost]

Hey mate, could you do a hover noise comparison between the M30, M3, and Mini 4 Pro?

I don’t have access to M30 but I’m really curious about its noise level. According to DJI’s Euro certification, the M30 is 7-8 dB louder than the M3, which actually makes it quieter than the Phantom 4 — I found that hard to believe. I thought the M30 was at least 10 dB louder than the M3. If you can, please hover the drones and check the noise from 5-10 meters (or yards) away, either outdoors or indoors. Thanks!

Here is a link to a video of all 4 drones tested. I measured the sound level at 1 meter. The camera was about 6 feet away. Neo - 71 dB, Mini 4 Pro - 67 dB, Mavic 3E - 71 dB and Matrice M30 - 80 dB.

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[nswsyw]

Here is a link to a video of all 4 drones tested. I measured the sound level at 1 meter. The camera was about 6 feet away. Neo - 71 dB, Mini 4 Pro - 67 dB, Mavic 3E - 71 dB and Matrice M30 - 80 dB.

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Thanks a lot for doing this test and sharing the results!
It’s really helpful to see all four drones compared side by side. That said, because the drones vary so much in size, measuring at just 1 meter can introduce a lot of variability — even a small shift in position can change the readings noticeably. For a more accurate comparison, it’s usually better to measure from at least 3 meters away. Also, the obstacle avoidance warning beeps on the Mavic 3E and Mini 4 Pro can influence the readings, which makes the sound levels look a bit higher than they actually are.

 

[Droning on and on...]

The pitch and volume of the sound are determined by the size and width of the propellers and how fast they are spinning. Until someone comes up with a way to keep a drone in the air without props, you are not going to see a "stealth drone".

And the number of blades. This is directly proportional. 4 blades will be twice the pitch of a 2 blade prop spinning at the same RPM -- one octave.

This is especially noticable on the loudest, most annoying FPV drones. Switch a neo from the DJI 3-blade props to a 5 blade aftermarket, and the pitch goes up by 5/3.

 

[hank970]

And the number of blades. This is directly proportional. 4 blades will be twice the pitch of a 2 blade prop spinning at the same RPM -- one octave.

This is especially noticable on the loudest, most annoying FPV drones. Switch a neo from the DJI 3-blade props to a 5 blade aftermarket, and the pitch goes up by 5/3.

All things being equal, the higher the RPMs, and/or the greater the number of blades biting into the air per unit of time, the higher the frequency. But all things aren't equal. If you increase the angle of attack of a prop's blades or increase the number of blades, you increase resistance, and your drone's motors wouldn't have enough power to spin them at the same RPMs as the supplied props.

Something like that, anyway. I have no idea how frequency relates to decibels, but a higher frequency of sound is probably be more intrusive and irritating to bystanders.

Frankly, my AIR 3 doesn't seem to be very loud when aloft, and I don't perceive the sound it emits to be a problem.

 

[WanderLost]

Thanks a lot for doing this test and sharing the results!
It’s really helpful to see all four drones compared side by side. That said, because the drones vary so much in size, measuring at just 1 meter can introduce a lot of variability — even a small shift in position can change the readings noticeably. For a more accurate comparison, it’s usually better to measure from at least 3 meters away. Also, the obstacle avoidance warning beeps on the Mavic 3E and Mini 4 Pro can influence the readings, which makes the sound levels look a bit higher than they actually are.

I doubt the beeping from the controller had much of an effect on the measurement since I measured the noise at 1 meter, which is standard for measuring noise from sound systems since it reduces the effects of ambient noise and reflections.
The controller was at least 10 feet away from the testing and the fast response setting I was using on the sound meter did not show any fluctuations from ambient noise.
The biggest difference I noticed was in the level of annoyance from the pitch, and the huge increase in dB with the M30. The Neo seemed louder compared to the Mavic 3E which actually measured the same dB.
A point to consider is that these measurements aren't A-weighted to compensate for the actual sensitivity of human hearing - they are unweighted (Z weighted).
This may explain the greater perceived noise from the NEO, since it's sound falls right in the range where our ears are most sensitive, unlike lower frequencies that we are less sensitive to.
I've attached a graph of A weighting that shows how we perceive sound levels.