What Makes GA Planes So Loud?

[Jay Honeck]

GA planes are incredibly loud. Is what we are hearing primarily engine noise? Or prop noise?

I'm guessing it's engine noise. Given that, is there some reason no one has marketed a plane with real mufflers placed behind the crew cabin, like an automobile?

True, this would add weight, on the order of 20 pounds (estimated), and (unless designed for it from the get go) would be ugly as sin -- but wouldn't it be nice to have an airplane as quiet as my Lexus on the freeway?

Flexibility also presents a challenge. I remember the first time I saw my engine decowled and running, and the astonishment I felt upon seeing how much the engine moved at shutdown.

Still, flexible heat pipe exists. This is not insurmountable.

I seem to remember seeing antique aircraft with long exhaust pipes, similar to what I'm describing, so apparently this has been tried. It just seems so...logical...

Another thought: Eliminate Hell's Hammers, and we might have a better chance of attracting new generations to GA. I suspect gals who have grown up in Beemers think even "modern" GA sound like Indy cars, and don't want any part of them.

 

[Jim Logajan]

GA planes are incredibly loud. Is what we are hearing primarily engine noise? Or prop noise?

I'm guessing it's engine noise.

Engine noise.

 

[Jim Logajan]

Prop noise is the loudest. Our local C-180 is deafening when he takes off and that same engine in many planes, including a couple twins, is comparably silent.

While that is an interesting observation, consider that airplanes with electric engines of comparable power are quieter than their IC engine equivalents. In all the small single engine planes that Jay and many others fly, I believe engine noise dominates. While props cause noise too, and a poorly chosen prop can cause a lot of noise, noise from the engine appears to dominate.

 

[Jim Logajan]

I found the following 124 page NASA document on the CAFE Foundatio website titled:

An Assessment of Propeller Aircraft Noise Reduction Technology

http://cafefoundation.org/v2/pdf_tech/Noise.Technologies/NASA.1995.Metzger.Prop.Noise.pdf

It is long and I haven't read through it, but appears to be a review of existing literature on sources of noise and experiments on reducing noise. It seems to indicate that prop noise is indeed significant ( contrary to my own assertion, which I based on other sources) and things like reducing prop rpm can yield much reduced noise.

 

[Jim Logajan]

Well, I did say I was Pre-Private.

I am very weary of the speed though (Vx). I'll take Vy any day. BTW, I had Vx nailed that day...and i was DESCENDING. I was going to be a small news story and a fiery end to a nice lake house if I didn't do what I did...speed up and miss my appointment with death.

Ya'll tell me. Whats you're VSI say at Vx an whats it say at Vy?

Is it possible you were flying through descending air and your application of higher lateral speed simply flew you out of that downdraft? (Edit: I assume this is what you mean when you asked about VSI.)

The vertical speed component of Vx is lower than Vy, so Vx is more likely to cause problems where air is descending.