dumbest of all questions

[yancovitch]

why don't airplanes  have mufflers??? (props)....
not to mention the helicopters which fly over my place every day on the way to the hospital a block away.....something to do with back pressure reducing power? or? there are automobiles which have alot of power, which run reasonably quietly....just curious.....

[olderndirt]

[quote][b]why don't airplanes

[OVERLORD_CHRIS]

Special Ops helicopter do have a type of muffler, but you rarely see them, and if there are flying low, you will still hear the blades though.

[specter177]

Yep, most of the sound you hear is from the blades themselves, not the engines.

[Brett_Henderson]

It would vary bit, from airplane to airplane.. But for the most part, on a piston engine... a muffler would add weight, AND reduce horse-power..

[Hagar]

Depends on the type. A lot of British light aircraft with Gipsy engines have open exhausts. They're not particularly noisy.

WWII fighters with inline engines also have open exhausts. That's what gives the Merlin that lovely crackle. Noise nuisance was not a problem during wartime. Simply changing the exhaust stubs on the Spitfire Mk Vb to fishtail units increased the speed by 7 mph.

Here's some examples of Rolls-Royce Merlin exhausts fitted to different aircraft.

[SaultFresh]

Better to run the risk of looking like a fool for asking your question, than being a fool for not asking your question.

[yancovitch]

saultfresh ..................you mean, even on regular aircraft, most of the noise is from the blades?...

[DaveSims]

saultfresh ..................you mean, even on regular aircraft, most of the noise is from the blades?...

Aircraft with props and helicopters, yeah most of the noise actually comes from the blades.  Think of how much noise a ceiling fan makes on high, then figure how much larger and faster those blades are on an aircraft.  At full power, some aircraft (Bonanazas and Centurions come to mind), their blades make huge sounds as they are very near the speed of sound.

[olderndirt]

It would vary bit, from airplane to airplane.. But for the most part, on a piston engine... a muffler would add weight, AND reduce horse-power..

From the Continental C65 to the O145 and Lycoming A65 to O360 - with carburetors, all have a shrouded muffler for carb heat.

[Brett_Henderson]

Welll.. they don't muffle so welll .. 

Because the'yre about concentrating heat, not muffling..

[beaky]

Noise-abating mufflers are fairly common on typical light singles in parts of Europe, if I'm not mistaken. The drawbacks are pretty obvious, and I agree that it's usually the props which make the most noise, anyway.

[specter177]

Besides, airplane engines sound great, so what's the matter?

[Brett_Henderson]

Noise-abating mufflers are fairly common on typical light singles in parts of Europe, if I'm not mistaken. The drawbacks are pretty obvious, and I agree that it's usually the props which make the most noise, anyway.

Stand between two rows of hangars as a big C206 comes taxiing in under power, and the pilot hasn't pulled the RPMs back

[olderndirt]

Because the'yre about concentrating heat, not muffling..

And they're a real good source of carbon monoxide when you get a hole and the shroud brings it in with cabin heat  .