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FWIW, most (if not all) of the big tech companies working on flying cars or UAV are aware of the noise problem and have in-house teams working with research lab

FWIW, most (if not all) of the big tech companies working on flying cars or UAV are aware of the noise problem and have in-house teams working with research labs & consultant on the problem. Now whether or not they succeed is another issue because it's a hard problem. There is at least one prominent tech firm that appears to think they can mitigate these issues in a year or so, which is... unrealistic.

hanniabu 7y ago
Anybody familiar with how the military creates stealth choppers that aren't as noisy? I'm assuming it has to do with blade design, but would these changes be applicable at smaller scale and would it be enough of a sound reduction?
- Anechoic 7y ago
  From what I heard 3rd/4th hand/speculation, the "stealth" helicopters are quieter than normal helos but at the cost of efficiency and maneuverability. There are always tradeoffs. edit: what nradov said.
- nradov 7y ago
  There's no such thing as "stealth" really, but they can optimize blade shape for noise reduction and put mufflers on engines. Those measures reduce aircraft performance (no free lunch in aviation).
- yummypaint 7y ago
  Some first order guesses: -Have lots of blades on the same rotor so the assembly can turn slower -Put the tail rotor inside a shroud -Having a smaller rotor might help, since the spread in air speed across the length will have less variation (less sure if this would help) -Turbine engines can be pretty loud, I'm guessing the same is true of other powertrain components. Maybe put the loudest stuff on the roof.
- starpilot 7y ago
  The most promising theory is that the "stealth hawk" used actuated micro flaps on its blades' trailing edges to reduce noise and vibrations. I would put money on this being true. Flapped blades have been studied in academia for over a decade, it's definitely an engineering problem now and has clear benefits. http://www.helijapan.org/pdf/general/general05/Friedmann/Japan-05VF-notanimated_PART-1.pdf http://www.helijapan.org/pdf/general/general05/Friedmann/Jap...

hanniabu 7y ago

Anybody familiar with how the military creates stealth choppers that aren't as noisy? I'm assuming it has to do with blade design, but would these changes be applicable at smaller scale and would it be enough of a sound reduction?

Anechoic 7y ago
From what I heard 3rd/4th hand/speculation, the "stealth" helicopters are quieter than normal helos but at the cost of efficiency and maneuverability. There are always tradeoffs. edit: what nradov said.
nradov 7y ago
There's no such thing as "stealth" really, but they can optimize blade shape for noise reduction and put mufflers on engines. Those measures reduce aircraft performance (no free lunch in aviation).
yummypaint 7y ago
Some first order guesses: -Have lots of blades on the same rotor so the assembly can turn slower -Put the tail rotor inside a shroud -Having a smaller rotor might help, since the spread in air speed across the length will have less variation (less sure if this would help) -Turbine engines can be pretty loud, I'm guessing the same is true of other powertrain components. Maybe put the loudest stuff on the roof.
starpilot 7y ago
The most promising theory is that the "stealth hawk" used actuated micro flaps on its blades' trailing edges to reduce noise and vibrations. I would put money on this being true. Flapped blades have been studied in academia for over a decade, it's definitely an engineering problem now and has clear benefits. http://www.helijapan.org/pdf/general/general05/Friedmann/Japan-05VF-notanimated_PART-1.pdf http://www.helijapan.org/pdf/general/general05/Friedmann/Jap...