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A question on another SE site prompted me to search for 'Aircraft engines untrasonic noise dogs', but with not much success. The OP's dog barked like crazy at turboprops, but was not bothered at all by 'louder' noises from light GA planes with piston engines, even when led next to them as the engines ran up on the ground.

Does anyone know how much ultrasonic noise does a small turboprop put out? I suspect that it may be worse, in proportion, to that from the large turbofans on airliners since the hp shaft revs so high on those little engines.

Maybe that noise that is merely an annoyance to humans is actually painful to dogs etc?

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    $\begingroup$ Unfortunately, I'm only a software engineer with a liking for dogs. $\endgroup$ – Martin James Aug 23 '17 at 18:38
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    $\begingroup$ The question is also then if the dogs are barking because it's loud/painful, or it sounds like a howl (e.g. sirens), so they're responding to that. $\endgroup$ – Nick T Aug 23 '17 at 22:13
  • $\begingroup$ Your dog might hate electric vehicle and induction cooker, too, together other modern "quite" high power electric equipment. They are all designed to operate at a frequency to appear to be quite to humans only, e.g. 20-40kHz range, and 25kHz is a common choice. $\endgroup$ – user3528438 Aug 23 '17 at 22:33
  • $\begingroup$ I don't expect that the dogs can sense the electromagnetic field, so the only audio outputs would be magnetostrictive etc. vibrations from inductors and the like. Probalby not vey loud, (?) Gas turbines, however, have little, if any, EM radiation, but a LOT of sound emissions. $\endgroup$ – Martin James Aug 23 '17 at 23:10
  • $\begingroup$ You often hear switched mode power supplies drop into the audible range when under light load. Not very loud but nevertheless highly irritating. $\endgroup$ – Peter Green Aug 24 '17 at 4:12
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This answer lists a number of RPM values for different aircraft engines. A typical small turboprop engine, the PT6, runs its core at 45,000 RPM and the power turbine at 30,000 RPM, which should produce sounds in the ultrasonic region.

The picture below shows a cutaway of a PT6 (source); if you count the blades and take the result times 3 (the cutaway spans 120°), the high pressure turbine disc shows 54 blades and the power turbine 42 blades.

PT6 cutaway

Each time one of those blades runs through the wake of a stator blade ahead of it, it will create a pressure change with a frequency of 30,000·42/60 = 21 kHz and 45,000·54/60 = 40.5 kHz. At idle power, the speed is a bit lower, but not by much.

So, yes, the dog might very well have heard a noise inaudible to humans.

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