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Can airplane engines be differentiated and identified by what noises they make? If so, what does each engine sound like? How would you be able to tell between a low-bypass and high-bypass turbofan? How could you tell between turboprops and aviation piston engines?

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  • $\begingroup$ Please see if the answers here give you a good answer to your question. $\endgroup$
    – Ralph J
    Aug 20, 2023 at 19:28
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    $\begingroup$ @RalphJ I was wondering if you could tell what type of engine is being used, like turbofans or turbojets $\endgroup$
    – Mateo
    Aug 20, 2023 at 21:09
  • $\begingroup$ Yes, but it's not something you can just easily explain, you have to listen yourself to discern differences. $\endgroup$ Aug 20, 2023 at 21:38
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    $\begingroup$ One of the more subtle running gags in the movie Airplane! was the piston engine airliner background sound even though they were in a jet. $\endgroup$
    – John K
    Aug 21, 2023 at 1:58
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    $\begingroup$ @JohnK, it isn't always an intentional gag; in one of the latest Jurassic Park movies they dubbed a piston engine sound into a 208 Caravan. Because, you know, that's what prop planes sound like, right?! $\endgroup$ Aug 26, 2023 at 22:34

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Regarding only piston engines: with practice you can identify 4-cylinder engines, 6-cylinder engines, 2-blade props, 3-blade props, horizontally-opposed engines, and radial engines.

There are certain classic piston engines that have unique characteristics, like those used in the twin bonanza, which are readily recognizable because they were geared (turning faster) and had "augmentor" exhausts (distinctive exhaust note).

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  • $\begingroup$ True. You can always recognise a Merlin engine. $\endgroup$
    – Chenmunka
    Aug 24, 2023 at 9:01
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To a certain extent, yes.

As per your question, low and high bypass ratio engines are quitw easy to learn to tell apart. From close(ish) low bypass engines are stupid loud, and the sound spectrum is quit even, offering deafening experience in all frequencies. High bypass engines tend to be clearly less noisy, the bypass fan contributing a "swooshing" note to the sound.

Another way to describe the difference from close range would be to call low bypass engines' sound "raw" and that of high bypass engines softer. Also some passenger plane high bypass ratio engines have a noticeable "growl" at high power setting, sorry to say I can't tell which make/model it is off the top of my head.

Further away low bypass engines will be audible as a low rumble, and high bypass ones as a more even noise.

As for the piston vs. turboprop part: this really is a no brainer once you learn to distinguish the propeller noise from the engine noise, since a lot of the noise of propeller driven planes actually comes from the propeller itself. The exhaust "purr" of a piston engine is easy to tell apart from the high pitch whine of a turbine engine, which also has a distinct exhaust "swoosh" similar to that of a high bypass jet engine.

Combined with the "aerodynamic noise" made by the airframe creates more or less unique sound footprint which in turn can be used to narrow down the specific engine, on a further note on that: I live near an active military base. I can tell by sound alone which of the few "domestic" types is flying by, even at miles away. During joint excercises I can also distinguish visiting types from the usual ones. Determining the engine would then be a matter of looking up what engine is run in which airframe.

I'm confident an algorithm would be able to quite accurately recognice most of current engine/plane combinations if it had a large enough database to reference.

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I know that there is technology that analyzes the sound signature of submarines and traces their locations and what country they're made by, as designs differ between countries. I would assume that a similar model could be applied to aircraft, where an ML model could be trained to make the comparison between engine type and sound profile, and then pair that with a list of possible aircraft.

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