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Date: Tue, 6 Jan 2009 14:54:48 -0700
From: Bob White <bob@bob-white.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Cc: "Ed Anderson" <eanderson@carolina.rr.com>
Subject: Re: [FlyRotary] My Muffler experiments (long) was  [FlyRotary] Re:
 Mistral muffler.
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Hi Ed,

I'm glad you reminded me of this experiment.  For the Alpine, I
currently I have a Racing Beat presilencer that I'm going to put in
front of a Hushpower II.  I'm not at all convinced that this system is
going to keep me from getting tickets for too much noise. :)
http://www.racingbeat.com/resultset.asp?partnumber=16404

If it's still too loud, I may add your design to see if it's
acceptable noise wise.  I have a much better chance of it lasting in
the car than you did on the airplane.  

Bob W.


On Tue, 6 Jan 2009 15:13:21 -0500
"Ed Anderson" <eanderson@carolina.rr.com> wrote:

> Contrary to intuition - two parallel mufflers actually reduce the sound less
> than one of the same type.  If you have both rotor pulses going through a
> single muffler you have a dominant high energy frequency (at 6000 rpm) of
> 200 Hz to filter.  If you have a single rotor exhaust port with its separate
> muffler then the dominant freq for each muffler is now 100Hz rather than
> 200Hz.  The dimensions for two mufflers of equivalent effectiveness would
> need to be approx twice as large for the 100Hz  pulse of which you are
> required to hang TWO of these twice as larger hummers underneath to get the
> same effectiveness in sound suppression as using one muffler half the
> dimensions - or something along those lines.
> 
>  
> 
> So a single muffler (for sound suppression) appears to be a better way to go
> - now if you are looking for power instead of sound suppression then the
> story can be different.
> 
>  
> 
> Having experimented with several different approaches, the one that seemed
> to have the most promise was the one in which I placed 3" diameter 1/8"
> thick Stainless Steel discs.  The discs had vanes cut from the outer
> perimeter down to within 3/8 - 1/2" of the center.  Then each vane was bent
> approx 45 deg to the plane of the disc.  These then had a 3/8" dia hole
> drilled down the center and a rod on which 5 discs were strung and first
> locked in using jam nuts (don't bother trying) and later welded to the rod.
> 
>  
> 
> The idea was that the pulse in the exhaust would in effect see (straight on)
> an almost solid metal disc and bounce back what pulse go through the first
> disc would find a 2nd and 3rd and 4th etc, where as the exhaust gas would
> fairly easily flow around the blades and through the discs - relatively
> unimpeded (so the theory went {:>)).  
> 
>  
> 
> The first one I made I used a 2" dia tube and discs - it was tremendously
> effective in suppressing the sound - unfortunately it was equally effective
> in suppressing power.  So I concluded I needed a larger tube - so went to
> the 3" dia tube and six discs.
> 
>  
> 
> This one I thought was really the solution (and may have been if I had
> continued development) as it was very effective in suppressing the sound
> (although not quite as much as the 2" tube) and I got 6000 rpm static.  Ah
> ha! I thought - this is it!!! I have succeeded.  So I buckled up and ran the
> engine up to 6000 rpm and launched.  The only unfortunate aspect of the
> flight is that I never got over 6000 rpm static {:<(.   
> 
>  
> 
> I then cut the number of disc back to 4 and that appear to do the job.
> However, my next flight was down to Tracy's Crook.  I was later told by a
> witness to my take off that it sound like I had a turbine engine under the
> cowl (more on that later).  In any case, I noticed about 20 minutes into the
> flight that the EGT on one exhaust was up into the 1700 + range whereas my
> normal EGT was more like 1550 -1600 max.  After landing at Tracy Crooks, I
> decided to determine what the problem was.
> 
>  
> 
> It turns out that the discs in one tube  had broken loose of their jam nuts
> and were free wheeling like a turbine blade inside the tube. Not only were
> the tips of the discs burnished but you could clearly see the polishing
> effect of their rubbing against the inside of the 3" tube.   So that
> explained the high EGT on the one tube (and the turbine sound reported) the
> discs were acting like a freewheeling prop and impeding the flow of exhaust
> gas.
> 
>  
> 
> So I decided to reduce the number of discs down to 3 and Tracy was nice
> enough to weld the disc to the rod.  Well, that seem to be the answer.  I
> was getting good power and good sound suppression still.  However, the discs
> only stayed welded to the rods for approx 2-3 weeks, and then I began to
> find pieces of disc back by the end of the tube.  The pulse was too powerful
> and were slowly beating the stuffings out of the SS blades on the discs and
> they were breaking off and leaving the tube .
> 
>  
> 
> By that time the expense (and more telling - the work) of six
> experimentation with mufflers had taken their toll.  I decided to have my
> two tube header modified into one tube - turns out it cost twice to modify
> the header   as two hushpower mufflers. So I just kept my old 10 year old
> header of stainless steel pipe and put on two hushpower mufflers.  Not as
> quite as my experimental design - but they have lasted.
> 
>  
> 
> So good luck folks, I'm eagerly awaiting the magic muffler design.
> 
>  
> 
> Ed
> 
>  
> 
> Ed 
> 
>  
> 
> Ed Anderson
> 
> Rv-6A N494BW Rotary Powered
> 
> Matthews, NC
> 
> eanderson@carolina.rr.com
> 
>  <http://www.andersonee.com/> http://www.andersonee.com
> 
>  <http://members.cox.net/rogersda/rotary/configs.htm>
> http://members.cox.net/rogersda/rotary/configs.htm#N494BW
> 
>  <http://www.dmack.net/mazda/index.html>
> http://www.dmack.net/mazda/index.html
> 
>   _____  
> 
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
> Behalf Of Mark Steitle
> Sent: Tuesday, January 06, 2009 10:57 AM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: Mistral muffler.
> 
>  
> 
> Dennis, 
> 
>  
> 
> Thanks for the suggestion, but I initially felt that the Hushpower 2 was too
> heavy (10#/ea).  I used it anyway out of desperation.  So, I really don't
> want to be dragging two of them around with me everywhere I go if I can help
> it.  I'm ready to give Al's design a try.
> 
>  
> 
> Mark S.
> 
> On Tue, Jan 6, 2009 at 9:52 AM, Dennis Haverlah <clouduster@austin.rr.com>
> wrote:
> 
> Mark:
> 
> Have you thought of splitting the exhaust and running it through two
> Hushpower's in parallel.  If you had room for this I would think it would
> work.
> 
> Dennis H.
> 
> Mark Steitle wrote:
> 
> Lynn,
> 
> Thanks, I'll check the Mistral site.  At least what I'm running now is
> durable, not the quietest on the field, but durable.
> 
> Mark
> 
> 
> 
> 
> --
> Homepage:  http://www.flyrotary.com/
> Archive and UnSub:
> http://mail.lancaironline.net:81/lists/flyrotary/List.html
> 
>  
> 
> 


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