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
Alan Tolle wrote:
Brian
Just a little more history. On the first exhaust system we built for the
RV-3 with the 180SL engine installation the 12 inch long primaries (the
0.125 wall stuff) were run separately into a mild steel Flowmaster
muffler. Two things happened. First, after about 20 hours there was
nothing left inside the muffler shell. So we cut the end out of a second
Flowmaster muffler and lined the input chamber with 601 inconel. That one
held up pretty well and had a really sweet sound, sort of like a P-51.
But that installation always had a glitch. There was a flat spot in the
engine at about 4000 rpm. Acceleration from idle to 4000 rpm was smooth
and positive either on take off or in the air. But at 4000 rpm the engine
seemed to hit a brick wall for a few seconds, then it would continue right
on up to 5000 rpm for climb or 6000 rpm for cruise. Nothing we could vary
(mixture, timing, etc) seemed to inprove the situation. Some time later we
talked with another rotary engine pilot with a similar exhaust system and
similar experience, but I don't have any notes about who it was. Someone
who reads this news letter may chime in here.
The two individual pipes out never experienced any such phenomenon. As I
have stated earlier, any muffler we tried hurt the horsepower out. The
stainless steel shroud around he exhaust system fed by a blast tube will
keep 90% of the exhaust heat out of the engine cold air plenum.
Alan Tolle
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