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Date: Wed, 01 Dec 2004 09:19:18 -0700
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
From: Bill Dube <bdube@al.noaa.gov>
Subject: Re: [FlyRotary] Re: Muffler design
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>
>
>I believe (have not done the calculations) that if you put both exhaust into
>the same tube that you may find 24" is sufficient to get some good noise
>reduction.  However, in order to handle double the exhaust gas flow that
>putting both exhaust ports into one tube, you might find that   a 2"DIA tube
>might be on the small size.  I would probably think about at least a 2 1/2"
>perhaps 3" dia tube.  Unfortunately, I had little success in finding 3" dia
>SS discs at least .062 thick.  So I did not go down the 3" path.

         A cross-over pipe is significantly different than combining the 
two tubes with a wye. Its length and positioning provide a set of 
resonances that can help damp the sound. The length of the cross-over 
itself combined with the length of pipe between the engine and the 
cross-over tee, and the length of pipe from the tee to the first muffler 
baffle all play a role. Not a simple system by any means.

         Perhaps one could nickel plate a section of 4130 airfoil shaped 
tubing for the cross-over.