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From: "Ed Klepeis" <techwelding@comcast.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-813293@logan.com>
Subject: Re: [FlyRotary] New Muffler
Date: Fri, 4 Nov 2005 19:01:55 -0600
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Dear Larry
      Could you contact me off line I would like to take to you about 
muffler systems.thanks
                                                                Regards
                                                             Ed Klepeis
techwelding@comcast.net
----- Original Message ----- 
From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, November 03, 2005 8:55 AM
Subject: [FlyRotary] New Muffler


> Larry LaBeau sent me some excellent data on work he's doing with his 
> muffler.  Enjoy
>
> *****Begin*******
> Finally found a muff that works.  Similar to the tangential muffs.  Used a 
> two cycle model airplane design program by Martin Hepperle called 
> "Silencer Design Application".  You can input the exhaust tempreture, 
> engine rpm, type of fuel used, select the type of silencer and add them in 
> series, and then add the dimensions in millimeters.
>
> It plots out the DB vs Frequency with the peak rpm.  I found relationships 
> between the dimensions that gave a smooth curve without spikes.  My 
> thinking is this tunes the muff.  Sizing of the muff was also driven by 
> the volume I could put it in.  The material is off the shelf automotive 
> exhaust pipe of 16 gage.  For the large can I used two 3" pipes split on 
> one side longitudinally and welded the edges together.
>
> The can has two chambers, one to expand and swirl the incoming gas, and 
> the second to also expand and exhaust the gas.  The dimensions of the 
> center tube are critical as well as the dimensions for the exhaust pipe, 
> its length, dia, and how far it is inside the can.  Some of the dimensions 
> are multiples of other dimensions.  Like 204/102 = 2.  This keeps the 
> spikes down or tunes the muff.
>
> Flight test shows a back pressure or loss of rpm of from 200 to 300.  I am 
> planning to modify the center tube to a large diameter of from 2" to 
> 2-1/4".  If the back pressure is still present then I will make the 
> exhaust tube larger.  Unfortinatly this will increase the noise.  Took my 
> headset off during flight and the greatest noise was air noise, not the 
> muffler as before.  Results:
>
>            rpm               DB a                  DB c      measured 
> inside the cabin at pilots lap position.
> Idle       2K                  80                     100
> run up   3K                  88                     100.5
> climb    5.5K               96.5                   107
> cruise   5.3K               96                       104
> cruise   5.4K               96                       105
> taxi       1.7K              78                        97
>
> I flew for 46 min and the muff did not fall apart.  No real discoloration 
> except on the can's ends.  I thought I would see two discolorations where 
> the two tubes come from the engine and blast on to the cans skin, but it 
> did not happen.  Its a please to fly the airplane without that Mazda beat.
>
> The distance from the face of the engine to the cans edge is 12".  To 
> support the aft end of the can I added a tie rod from it to the engine 
> mount (see photo).  Weight of the muff is 11 pounds which is real good for 
> a nose heavy Dyke Delta.  Now to get it made of SS.
>
> TNX
> Larry La Beau
>
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>
> -- 
>         ,|"|"|,                                    |
> ----===<{{(oQo)}}>===----        Dyke Delta         |
>        o|  d  |o          www.ernest.isa-geek.org  |
>
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