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I'd be real quick to duplicate someone's successful exhaust design.
Keeps the risk items to minimum. This failure could have easily occurred in
first flight. PRETEND IT DID. You would have no prop remaining. Weld tab on your
tail pipe, safety wire to aircraft. Control the failure modes.
I'd give strong consideration to eliminating the figure 8 welds at muffler.
I would have tail pipe be a slip fit at that point. So your tail pipe floats.
That would require safety wire and clamp on tail pipe to prevent it from
departing plane, but would eliminate mechanical moment on those welds.
I'm not all that familiar with rotary characteristics. Puzzled why tail
pipe is such large diameter (2 pipes seam welded together). I would think that
exhaust pulse at any one moment is no greater than a single tube diameter. Maybe
someone can explain to me.
I’m still struggling with tuning
my rotary/microtech. I spent an hour or so running it yesterday and ended up a
little closer on the tuning front but also ended up with a blown out
exhaust/muffler. It’s come apart at a bunch of places – not the welds but the
Inconel itself next to the welds.
The exhaust pipe coming out of the
“tangential tube” is/was in the profile of an “8” without the connection in
the center. An engineer friend of mine who looked it over said it makes sense
- after the fact - that the exhaust pulses were causing the tube to flex at
the center joint. It appears to have started at the outboard end and
went all the way to the center tube and then, perhaps from vibration, cracked
out the pipes except for about ˝” from the center
connection.
The main manifold – runners and
the tangential tube – are all sound with no signs of
stress.
So, be careful out
there!
Pics
attached.
Thanx,
Joe
Hull
Cozy Mk-IV #991 (Done Building! In
Phase1 Flight Test - 0 hrs flown)
Redmond (Seattle), Washington
-al wick
Artificial intelligence in
cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on
engine/airframe from Portland, Oregon
Prop construct, Subaru install, Risk
assessment, Glass panel design
info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
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