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Date: Sat, 12 Sep 2009 19:59:44 -0500
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: cockpit soundproofing
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Agreed. The extension idea was to just extend the pipes so the ends are 
behind the cockpit. I think that Tracy actually had something like that 
for a while & mentioned that it made the cockpit quieter.

I have no proof, but I suspect that turning the pipes down can, in some 
situations, actually add noise & heat to the floorboards due to the 
induced turbulence whipping the exhaust back against the floor & also 
causing drumming on the floor. My Lyc powered RV-4 has downturned pipes, 
& the floor is so hot I'm pretty sure I could cook pancakes on it.

Mike, Since you've flown RV's for a while, you may already be aware of 
this; a lot of the higher frequency noise can be minimized in the 
cockpit by just sealing up all the air leaks into the cockpit. The 1st 
-4 that I owned was painful, even with a Lyc. Sealing up the air leaks 
around the canopy made it easily tolerable, even with passive headsets.

FWIW,

Charlie

Mark Steitle wrote:
> Charlie,
>  
> You're correct, turning the pipe down does add drag, but so does 
> hanging a big square suitcase shaped box under the fuse.  It just 
> depends on how badly you want to quiet things down. 
>  
> Mark
>  
>
>
>  
> On Sat, Sep 12, 2009 at 3:03 PM, Charlie England 
> <ceengland@bellsouth.net <mailto:ceengland@bellsouth.net>> wrote:
>
>     Mark Steitle wrote:
>
>         Mike,
>          My first line of defense against the noise is an ANR headset.
>          That's a given.
>          I purchased some black foam from ACS that I installed on the
>         interior walls and floor.  From what I've read a lot of the
>         noise comes in through the firewall and windows.  Not much you
>         can do about the windows, but it seems that a generous amount
>         of soundproofing on the firewall will help the most.  Lastly,
>         you can turn the exhaust down so that it is directed away from
>         the occupants?  Or, run it back behind the pax, and fly faster
>         than the speed of sound so it can't catch up to you.  Mark S.
>
>         On Sat, Sep 12, 2009 at 10:15 AM, Mike Wills <rv-4mike@cox.net
>         <mailto:rv-4mike@cox.net> <mailto:rv-4mike@cox.net
>         <mailto:rv-4mike@cox.net>>> wrote:
>
>            I asked a few days ago and got no replies. Since things are
>         a bit
>            slow on the list now I'll try again. Anyone have any
>            recommendations for a decent soundproofing material that I
>         can add
>            to my firewall and floorboards to tame this racket? Maybe
>         the rest
>            of the world will have to deal with the noise, but at least
>         I can
>            try to make it a little more pleasant for me.
>                Mike Wills
>            RV-4 N144MW
>
>
>     Running it back past the occupants can actually be effective.
>     Turning it down adds drag.
>
>     I've often wondered why no one has tried carrying the pipes down
>     several inches below the fuselage before turning them aft, and
>     installing streamline inserts aft of the downpipes & between the
>     fuselage bottom & the horizontal run of pipe, to get smooth air
>     between the fuselage & the now-parallel exhaust stream.
>
>     Charlie
>
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