Probably the greatest effect on the BSFC is the capacity to lean
with
> altitude so as to keep the EGT's as high as possible all the
time. This
> occasions two things --- a very robust first foot or so of the
exhaust
> system and careful attention to how you are going to get the
additional
> heat out of the cowl. Both are do-able.
I 've been thinking about using the Schedule 40 304 stainless for the
first foot or so of my exhaust system, but I can't bends that tight -2"
inside diameter with 2.35 OD pipe. What I have now is
2"Diameter .049 321 Stainless bends. I'm a little concerned that the
bending stretched the material to an unacceptable thinness right where the
pipes are the hottest.
Of course I am going to have a SS heat shield completely surrounding my
exhaust system, but I was wondering if ceramic coating the pipes would help
keep the pipes intact.
Anyone?
Brian Trubee
I think you would be better off welding a conformable patch on the pipe.
Ed Anderson 304 SS .140 wall exhaust pipes don't even discolor :)
Paul Lamar
The Rotary Engine NewsLetter. Powered by Linux.
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Copyright 1998-2004 All world wide rights reserved.
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
By definition if 32 inch hurt the power less than anything else it obviously
was tuned. Coincidentally Racing Beat sells two into one headers with 32
inch pipes. The trick is knowing the speed of sound in the hot exhaust gas.
Smith MSAE and Morison Ph.D. in ME in their book the "Scientific Design of Exhaust
& Intake Systems" seem to think it is 1700 feet per second while as I recall
the speed of sound in intake air is around 1100 FPS. Also coincidentally
they came up with a tuned exhaust pipe length for 6000 RPM of 2 ft 10 inches or
34 inches. Page 83. BTW the brits are very good at building Formula One racing
engines.
Paul Lamar
The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/
Copyright 1998-2004 All world wide rights reserved.