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Date: Wed, 09 Dec 2009 20:36:47 -0600
From: Phil White <philwhite9@aol.com>
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To: Rotary motors in aircraft grp <flyrotary@lancaironline.net>
Subject: Re: Exhaust Manifold material
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Al: Are there pictures of your exhaust available?

2. What thicknesses of Inconel did you use, and were did you buy the 

materials?
3. If I may ask, what was the cost of an Inconel tangential muffler?

Knowing how heavy the RB flange is, I am amazed that your whole muffler 
system is only 12 pounds!

Phil
> Subject:
> RE: [FlyRotary] Exhaust Manifold material
> From:
> "Al Gietzen" <ALVentures@cox.net>
> Date:
> Sun, 6 Dec 2009 07:58:28 -0800
>
>
> Phil;
>
> I know youre asking Ed, but hope you dont mind another opinion.
>
> Both 304 and 321 SS are subject to inter-granular stress corrosion at 
> the temps were talking about. 321 is a better choice and will last 
> longer, and could be lighter by some reduction of thicknesses.
>
> Yes, making it thicker will make the 304 last longer by lowering 
> stress, but it is still subject to limited life, and at the 
> thicknesses you suggest, my estimate is your system will be rather 
> massive at close to 30 lbs.
>
> I dont know the details of his design, But Dave Atkins had a SS 
> tangential man/muff that basically crumbled to pieces within a couple 
> hundred hours.
>
> Id also suggest a larger diameter for the tangential muffler; like 
> 5+. This allows for more expansion which lowers both temp and pulse 
> strengths. Flat ends would definitely be a failure point. Reinforcing 
> with a central tube would be a big help, but I would still make them 
> conical, or concave inward.
>
> I know that inconel kicks up the cost a fair amount, but it gets you 
> away from the stress corrosion issue and allows a system of about 1/3 
> the weight of what your considering. When you consider the overall 
> time, effort, cost, risk, and weight, I still think inconel comes out 
> on top. My inconel tangential muffler weighs in at about 12#; 
> including the rather massive RB exhaust flange. The 321 secondary 
> muffler and exit pipe add another 3 ½#. It has now been running for 
> 170 hours; and as far as I can tell, is about as sound as when it started.
>
> Al
>