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dumbest of all questions (Read 913 times)
May 30th, 2010 at 11:29am

yancovitch   Offline
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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.....
 
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Reply #1 - May 30th, 2010 at 11:36am

olderndirt   Offline
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yancovitch wrote on May 30th, 2010 at 11:29am:
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.....
Internal combustion engines do have mufflers (very expensive to replace) and, on smaller aircraft at least, they're shrouded to capture heat which is directed to the carburetor, on demand, and to the aircraft interior.  Most helicopter noise is from the blades.
 
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Reply #2 - May 30th, 2010 at 12:12pm

OVERLORD_CHRIS   Offline
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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.
 
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Reply #3 - May 30th, 2010 at 12:18pm

specter177   Offline
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Yep, most of the sound you hear is from the blades themselves, not the engines.
 
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Reply #4 - May 30th, 2010 at 1:31pm

Brett_Henderson   Offline
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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..
 
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Reply #5 - May 30th, 2010 at 1:35pm

Hagar   Offline
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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.
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Reply #6 - May 30th, 2010 at 1:45pm

SaultFresh   Offline
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Better to run the risk of looking like a fool for asking your question, than being a fool for not asking your question.
 
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Reply #7 - May 30th, 2010 at 7:19pm

yancovitch   Offline
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saultfresh Smiley..................you mean, even on regular aircraft, most of the noise is from the blades?...
 
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Reply #8 - May 30th, 2010 at 8:50pm

DaveSims   Offline
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yancovitch wrote on May 30th, 2010 at 7:19pm:
saultfresh Smiley..................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.
 
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Reply #9 - May 30th, 2010 at 10:23pm

olderndirt   Offline
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Brett_Henderson wrote on May 30th, 2010 at 1:31pm:
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.  Interior heat is a bonus.  What really reduces horsepower is when the baffles in the muffler go bad  Smiley.
 
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Reply #10 - May 30th, 2010 at 11:03pm

Brett_Henderson   Offline
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Welll.. they don't muffle so welll ..  Cheesy

Because the'yre about concentrating heat, not muffling..
 
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Reply #11 - May 30th, 2010 at 11:58pm

beaky   Offline
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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.
 
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Reply #12 - May 31st, 2010 at 12:53am

specter177   Offline
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Besides, airplane engines sound great, so what's the matter? Grin Wink
 
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Reply #13 - May 31st, 2010 at 7:22am

Brett_Henderson   Offline
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beaky wrote on May 30th, 2010 at 11:58pm:
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  Cheesy

Even that big, grumpy, IO-540 is quiet at 15-inches, compared to prop tips near supersonic  Angry
 
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Reply #14 - May 31st, 2010 at 10:33am

olderndirt   Offline
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Brett_Henderson wrote on May 30th, 2010 at 11:03pm:
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  Cheesy.
 
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Reply #15 - May 31st, 2010 at 4:47pm

beaky   Offline
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specter177 wrote on May 31st, 2010 at 12:53am:
Besides, airplane engines sound great, so what's the matter? Grin Wink

Exactly... some call it noise, I call it music.  Smiley
 
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Reply #16 - Jun 5th, 2010 at 11:08pm

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beaky wrote on May 31st, 2010 at 4:47pm:
specter177 wrote on May 31st, 2010 at 12:53am:
Besides, airplane engines sound great, so what's the matter? Grin Wink

Exactly... some call it noise, I call it music.  Smiley

It's why I went to the Reno air races in 2008 and will go again this year if time avails. Hearing those Mustang engines at full bore is something to be experienced...
 
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Reply #17 - Jun 9th, 2010 at 11:42pm

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olderndirt wrote on May 31st, 2010 at 10:33am:
Brett_Henderson wrote on May 30th, 2010 at 11:03pm:
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  Cheesy.


Sounds just a bit dangerous. Tongue
 
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Reply #18 - Jun 10th, 2010 at 11:23pm

TacitBlue   Offline
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Here's a typical installation on a Cherokee. Two cylinders exhaust into one muffler, the other two exhaust into the other. They are bright and shiny because I had just replaced the old leaking ones with these brand new ones right before I took the pic.
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Reply #19 - Jun 11th, 2010 at 1:46pm

OVERLORD_CHRIS   Offline
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Slight update, yesterday an AH-64D was doing loops around field for what every reason, and 1000ft, that thing is pretty quiet, you could only hear it when it was really low and flaring.
 
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