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Date: Wed, 09 Sep 2009 10:11:52 -0400
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Muffling
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Lynn Hanover wrote:
>
> Lynn,
>
> Some speculation going on here.  When you run the exhaust thru a 
> turbo, will it break up the pulses enough for a fishtail to work? I'm 
> hoping to use a fishtail to create an augmentor out the back of my 
> plane. Should I reinforce the fishtail to insure rigidity?
>
> Bob Tilley
> Albany, Ga
> temporarly on loan to Baton Rouge
>  
> I would just based on what I did to myself trying to put a form of 
> fishtail on my Fiat racer. Not to form a muffler but to get the 
> exhaust pipe under the Fender seam. So I decided that if I maintain 
> the cross sectional area the same as the main pipe, I should loose 
> nothing, flow wise.
>  
> So I cut a length of pipe down the centerline and add triangular 
> pieces top and bottom, in .062" mild steel the same as the pipe. Then 
> I squished the opening down to 1" tall in the vise. Then three 
> weekends later the bottom triangle is split in the center. The top 
> would have failed as well but it had a bracket welded on at 90 degrees 
> to bolt it to the car.
>  
> So I started to notice how others had done the same thing, and guess 
> what? each installation had  a few virtical walls between the top and 
> bottom flat areas, and no cracks. Now I am smart too............
>  
> I would add these to you fish/mouth/tail..........
>  
> Lynn E. Hanover
>
Just a suggestion of something to try that might be easier and lighter:  
Put a 90 degree bend on the very last bit of that .062" mild steel.  
Even a 1/8" flange does an incredible job of increasing the rigidity of 
a section, and it moves the most common origins of stress risers (sheet 
edge cuts) into a much cooler and less stressful area.