Question about GA airplanes


#1

First off, I am not a pilot so that is why I’m asking. Just returned from Venice, Florida and stayed close to the Venice airport. I noticed how loud many of the smaller planes are on takeoff which brings me to my question. Do these planes run straight pipes?

Denny


#2

In the US the answer is generally yes, however the really loud ones at full power have prop tip speeds approaching supersonic which produces a lot of the noise you hear. After the pilot reduces the RPM you should notice the same airplane a mile after takeoff is much quieter.
In Europe most light airplanes have to have a muffler in order to meet noise standards. I don’t know how much difference they make.


#3

Thanks. Don’t know about Europe either but will be over there in awhile so maybe I will listen in if I see a small airport. I do notice than many smaller planes are louder than a jet on takeoff. While in Florida, I noticed you can not even talk as small planes take off yet a car with as big or bigger engine running next to you is quiet. I guess I will also assume no emission requirements on small aircraft. I’m not complaining, just curious.


#4

In general, the planes that do have mufflers are much lighter, simpler and less restrictive than a car muffler. You can’t hang a 20 lb car muffler on a plane where weight is critical to performance. It’s easy to hang a heavy muffler on a car and have it whisper quite with very little weight penalties. All aircraft manufacturers strive to reduce weight wherever they can. It means the difference between having a plane that gets off a shorter runway and climbs at a greater rate, than just struggling off the ground and barely climbing over the trees off the end of the runway. That means a safer plane overall.

Like porterjet said, many times the loudest noise you hear is the prop tips making that loud rasping or bark that you hear. Certain planes have louder prop noise,
like a T-6 which you might see at an airshow, or float planes which generally have longer props, which means those tip speeds make noise. Once you pull the RPM’s back a few hundred from the take off setting, the noise reduces greatly.


#5

Besides the weight, mufflers and silencers restrict the exhaust gas flow thereby reducing the maximum horsepower that the engine would otherwise be capable of producing. In any situation in an airplane when you need all the horsepower you can get the noise factor isn’t even a consideration.

And yes the deafening noise is caused by the prop tips approaching the sound barrier, not the engine.


#6

Thanks, I appreciate knowing all that. I wasn’t complaining just curious. I know I replaced my nissan truck muffler which weighed 30lbs with a Flowmaster.