Quick Noise question

[Mtns2Skies]

Not entirely sure where to post this but out of Curiosity I was wondering, when you hear a piston propeller plane overhead, are you hearing the propeller, engine, or a solid mixture of both?

 

[denverpilot]

Not entirely sure where to post this but out of Curiosity I was wondering, when you hear a piston propeller plane overhead, are you hearing the propeller, engine, or a solid mixture of both?

Both.

To isolate "what's the engine" vs. "what's the prop" listen to the difference between a turboprop (jet engine turning a propeller) vs. a reciprocating engine turning a prop (your typical airplane), vs. a big radial engined warbird turning a prop, vs. say... a Merlin 12 cylinder turning a prop (P-51 Mustang).

The prop isn't all that noisy in cruise, but during climb-out at high power setting when you get that "biting" very loud noise (hard to describe) that's often the tips of the prop going above super-sonic speed, and that makes quite a racket.

 

[Ted]

It is both, however I would say that most of it is really prop noise. The big difference is one of RPM, and the bigger aircraft tend to have lower RPM props in cruise. The engines are actually not all that loud, but turbo pistons tend to be a bit quieter because the turbo acts as a muffler.

But Austin, come now... you know that there's no such thing as a "quick" question on PoA.

 

[Henning]

Yes..

 

[COFlyBoy]

My buddy's Mooney has a much louder exhaust note than my Cherokee 6 despite mine having more horsepower. I think his engine has a less restrictive muffler.

 

[Ted]

My buddy's Mooney has a much louder exhaust note than my Cherokee 6 despite mine having more horsepower. I think his engine has a less restrictive muffler.

Which model Mooney? The angle valve Lycomings are louder than the parallel valve ones in my experience. If it's a 200 HP Mooney, it should have an angle valve IO-360 in it.

Remember than on an airplane, the muffler is not typically the same as in the traditional sense as we know them on our cars. Typically, the "muffler" only serves to pull heat off the exhaust for cabin heat in a single.

Look at a twin, and you see the true meat of the exhaust construction: pipes connecting all the cylinders and dumping out the back. That's it.

 

[COFlyBoy]

Which model Mooney? The angle valve Lycomings are louder than the parallel valve ones in my experience. If it's a 200 HP Mooney, it should have an angle valve IO-360 in it.

Remember than on an airplane, the muffler is not typically the same as in the traditional sense as we know them on our cars. Typically, the "muffler" only serves to pull heat off the exhaust for cabin heat in a single.

Look at a twin, and you see the true meat of the exhaust construction: pipes connecting all the cylinders and dumping out the back. That's it.

Yeah, he has a 20J with the angle valve 200hp IO-360. I've got a carb'd O-540 with parallel valves.

The difference in exhaust note is a lot more than I would have thought for just the valve arrangement though. I've heard my plane at high power settings (like full power) on the ground while standing behind it, and I'd say the prop noise and the exhaust noise are about the same.

But my buddies bird, from idle on up, the exhaust is much louder than the prop...maybe he's got a better prop than I do.

 

[denverpilot]

The props and engines on the LSAs are super quiet. Eerie quiet even. FWIW.

 

[Skylane81E]

Also wind noise over the airframe.

and those Rotax powered planes need a horn for taxiing.

 

[denverpilot]

Also wind noise over the airframe.

and those Rotax powered planes need a horn for taxiing.

The ATR-42/72 has one. Technically it's there to get the rampies attention, but more than one wag has honked at another airplane on the taxiway.

 

[Jaybird180]

I have a similar question:

For passengers sitting in a single does the sound typically reduce sitting further back? Are there any airplanes where the front seat is quieter than the rear?

 

[Skylane81E]

I have a similar question:

For passengers sitting in a single does the sound typically reduce sitting further back? Are there any airplanes where the front seat is quieter than the rear?

Perhaps a Skymaster

 

[maddog52]

I have a similar question:

For passengers sitting in a single does the sound typically reduce sitting further back? Are there any airplanes where the front seat is quieter than the rear?

Sky Arrow and FK 12 Comet come to mind but the difference is fairly small.

What I meant was in the Sky Arrow, it's quieter in the front. In the Comet, it's quieter in the back.