Alan Tolle wrote:

Brian

The .049 wall 321 simply will not live in the first bend out of the block.
If you weld on patches cracks will develop right at the weld.

To my knowledge ceramic coatings have never been approved for certified
aircraft application.  Exhaust systems for certified aircraft are
engineered to dissipate as much heat as possible (hence the use of thin
wall stainless tubing) into the cowl.  Wrapping or coating is prohibited
because it would oppose heat dissipation.  I really don't think that we
rotary engine enthusiasts should ignore proven practice in this regard.

That said, the much higher exhaust gas temperatures of the rotary engine
must be accommodated.  The simple solution is heavier wall tubing and slip
joints.

For what it is worth I used 0.125 wall 304 stainless with 1.5 inch inside
diameter for the first foot out of the engine.  I made a 0.375 thick steel
plate to bolt to the engine, then welded a 1 inch long stub of straight
tube to that.  Then came a 90 degree bend followed by 10 inch piece of
straight tube.  Slip joints were  used between each piece.  After that came
a slip joint to as much .035 wall 321 stainless of 1.75 inch outside
diameter as was necessary to get out of the cowl.

The slip joints sound like a lot of work but if you don't put them in now
the system will break at those points  and you will end up putting them in
later.  The slip joints in the heavy wall stuff were made by welding a one
inch collar of 1.75 i.d. pipe to the down stream member in the joint.
Three tabs were welded above and below each joint and laced together with
.035 stainless safety wire.

The entire system turned out to be 32 inches long.  Though this is
sometimes mentioned on this news letter as a tuned length for a 13B exhaust
system, such was not the case.  It was dyno tested and as noted earlier, it
hurt the power, but less than anything else.  It was flown for 400 plus
hours with no repairs.

Note that I am simply giving here an accurate account of history and saying
"this is what worked for me."  No attempt is made to advocate anything and
the opinions of others may vary.

Hope this helps.

Alan Tolle

Thanks for the input Alan. I followed you and Mr. Hatches progress in the past. I'd be comfortable with a .125 thick pipe for the first 12" out of the engine followed by some flex tubing( It's
worked for Tracy Crook for 1300 + hours so far) clamped with some stainless exhaust band clamps and from there to .049 321 and then to a Moroso  muffler. #2 inches from the exhaust to a two to one
merge and then the muffler. The entire exhaust system to be enclosed with 316 stainless with a blast tube. Any input is welcome.

Brian Trubee

 
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