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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