yancovitch wrote on May 30^th, 2010 at 11:29am:
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.

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

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

Brett_Henderson wrote on May 30^th, 2010 at 1:31pm:
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  .

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.

beaky wrote on May 30^th, 2010 at 11:58pm:


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

Even that big, grumpy, IO-540 is quiet at 15-inches, compared to prop tips near supersonic