laugh at me if you want... dumb question about plane engines

[Mustaine]

why are they loud? (not jet engines, but normal planes)


engines in cars with straight headers are about as loud, but passenger cars have mufflers, for sound, and if i am not mistaken back pressure on the engine to help it run better (i dont quite understant it fully but thats what i have been told)

so why dont cessnas have mufflers? wouldn't it:

A: make the flight more enjoyable for passengers
B: reduce noise around the airfields
C: help the engine run better or more efficent


i mean yeah the rumble of an old warbird zooming by is cool, but i am talking about new / newer planes. i know you can get boosts of HP or something with better exhaust. why wouldn't the same apply to a plane engine?

[Maverick]

Actually some do have mufflers. They have enough exhaust pipe and or manifold to maintain sufficient back pressure for optimal combustion.

The loudest noise for small aircraft is usually the prop at max RPM's. With the prop turning at about 2600 to 2800 rpm the tips are getting supersonic and are louder than the pipes are. Putting too much muffling will reduce the HP from the engine so the least is best. Most of the small AC manufacturers do not tune their pipes as they are only concerned with fitting them in the cowling. A company is making some decent bucks designing custom exhaust systems for light AC and helping performance with a tuned system. It's a boost to HP but sometimes even louder.

I was told my plane got definately quieter when I switched from the old 2 blade Hartzel to a 3 blade MacCauley Scimitar. I was wearing headsets the entire time but folks on the field said they noticed the difference.

[Mustaine]

hmmm the prop thing makes sense, that would be like a bullwhip snapping over and over and over.

i guess i just don't know jack about engines and exhaust, i was just thinking about luxury cars and how quiet yet powerful they can make them. some of them you almost can't hear the engine.

it is kind of like the construction equipment outside of where i work. these loaders and stuff seem to have straight pipes like a semi, and loud engines. how detrimental to the machine would it be to make a quiet engine?

same for planes i guessed. how would it be a "bad" thing?

if i owned a plane i would want either a warbird / warbird replica that was loud as a muscle car, or a sleek smooth silent plane. hard choice.

[dynamt]

Originally posted by Maverick
Actually some do have mufflers. They have enough exhaust pipe and or manifold to maintain sufficient back pressure for optimal combustion.

The loudest noise for small aircraft is usually the prop at max RPM's. With the prop turning at about 2600 to 2800 rpm the tips are getting supersonic and are louder than the pipes are. Putting too much muffling will reduce the HP from the engine so the least is best. Most of the small AC manufacturers do not tune their pipes as they are only concerned with fitting them in the cowling. A company is making some decent bucks designing custom exhaust systems for light AC and helping performance with a tuned system. It's a boost to HP but sometimes even louder.

I was told my plane got definately quieter when I switched from the old 2 blade Hartzel to a 3 blade MacCauley Scimitar. I was wearing headsets the entire time but folks on the field said they noticed the difference.

I have the Poweflow tuned exhaust on my plane, it did add some HP. It sounds different not really louder, just different. You definitely get less noise after a switch to a 3 blade prop. Less speed at the tips. You also normally get a better climb at the expense of reduced cruise speed. You get better ground clearance but, The extra drag is a hindrance if you lose the engine.

Everything in aviation is a trade-off

[Debonair]

Aircraft sound loud in part because there is nothing between you & the plane except the 1/r squared rool to damp the sound

[Chairboy]

There's another thing, those quiet cars produce max power very infrequently.  Once you're cruising at highway speeds, you might not need more than 10-20 horsepower to maintain your speed.  An airplane engine is putting out 75%+ power most of the time.  Even a Cadillac is loud when you're drag racing it and revving the motor, ya know.

In my plane, I'm going to use a rotary engine (which is often louder than a piston engine) but it'll also have a turbo, which will soak up most of the noise.  My muffler needs will be minimal after that, but the plane will still make plenty of noise because of the prop.