Question about prop sounds...

A general, non-powerplant specific, discussion on airboat technology, ie., hulls, rigging, polymer, etc..
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SWAMPCRACKER
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Question about prop sounds...

Post by SWAMPCRACKER »

I was outside the other day and heard a cessna flying over head and thought to myself...Why do airplanes with props sound different in the air than airboats do on water with a/c motors ? I always wondered this...Is it because of thinner air in higher altitudes or prop designs ?...Would any of you know? I hope i'm not the only one with this crazy question ! lol I hope i'm not going crazy but i swear there's a difference in sound...
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Whitebear
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Re: Question about prop sounds...

Post by Whitebear »

Outside of different prop design and muffler design, the airplane dissipated noise in a 360 degree pattern up down, forward and backward. An airboat has a different prop that typically is spinning a bit faster than an airplane prop but also the airboat has a table of water right under the engine and prop to reflect sound off of. The sound of an airboat is dissipated in only about a 180 degree pattern but it has the same intensity in that half pattern as an airplane does in the full 360 degrees.

Thats just my take on it anyway. Good observation.
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SWAMPCRACKER
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Re: Question about prop sounds...

Post by SWAMPCRACKER »

Thanks for the knowledge I did'nt think about how the prop on an airboat reflects its sound off the water vs just air alone...Makes sense to me...It was just something I always wondered about...
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ROBERT JAMES
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Re: Question about prop sounds...

Post by ROBERT JAMES »

Whitebear wrote:Outside of different prop design and muffler design, the airplane dissipated noise in a 360 degree pattern up down, forward and backward. An airboat has a different prop that typically is spinning a bit faster than an airplane prop but also the airboat has a table of water right under the engine and prop to reflect sound off of. The sound of an airboat is dissipated in only about a 180 degree pattern but it has the same intensity in that half pattern as an airplane does in the full 360 degrees.

Thats just my take on it anyway. Good observation.
all of wich i have to agree with except that an airboat prop is spinning faster than a airplanes. i would say a typical a/c airboat cruises around the lake at anywhere from 1300-2000rpm depending on the load and water depth while a typical cessna 172's cruise rpm is between 2300-2500rpm. now at WOT yes and airboat is runniin 3grand wich a cessna rarely if ever will see
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SlowRide
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Re: Question about prop sounds...

Post by SlowRide »

WB I think I hear an echo
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Duece
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Re: Question about prop sounds...

Post by Duece »

Doppler effect, how often are you below an airboat to listen to the sound it makes.

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CactusJack
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Re: Question about prop sounds...

Post by CactusJack »

^Deuce, only sometimes when the driver has had a bit much beer :drunken: and he aint looking where he's going :lol:
I was told I was wrong, once (not sure I believe it though)
If you can't blind 'em with brilliance, baffle 'em with BS
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