We tried using thicker pipe wall (600 series stainless
in incremental
increases in thickness up to almost 1/8" wall ) and even
those would
eventually crack. The problem was not cracking at the
flange, but rather
cracking of the pipe wall itself itself whenever pipes
from each port were
merged outboard of the exhaust ports without any
provision for a slip
joint
or other. Before we came up with the idea of the ball
joint welded
directly
to the port, we first used short stub stacks welded to
the four stud
flange,
with a slip fit pipe over that and it completely
eliminated the cracking
problems even using .035 wall...but we never came up
with anything close
to
elegant in terms of securing the stub pipe to the slip
tube. To test the
approach we retained the exhaust tube to the stub stack
using safety wire
looped through small 'L" brackets welded to the outboard
tube with a hole
drilled in the 90degree leg for the safety wire...and
the other inboard
"L"
brackets held on the stub end by each of the four nuts
that secured the
exhaust flange/stub stack to the rotor housing. Looked
cheesy and not
meant
for long term but the approach did work and led us to
the ball joint. It
is simple and cheap if you could come up with an
effective, safe way to
retain the tubes.
Steve Beckham
Steve,
Thanks for the response, I agree the pressed exhaust flanges
are the most
elegant option, but there are a degree of complexity for the
average
builder - whereas just welding may be easier. See attachment
for what may be
options. This isn't as you described (but similar) with a
heavier tube as
the stub I believe it would be quite robust- drawing by Bill
Jepson.
George (down under)
George, I apologize for not being able to tell from this nice
drawing by
Bill....is the downstream tube allowed to expand and contract
independent of
the short stub stack?
Steve Beckham
YES Steve,
The short header tube has the collar (with dog leg or L shape)
welded to it.
The exhaust pipe has a collar and small extension welded to it.
The exhaust pipe is also flared to accommodate the short header tube.
The L shaped ( dog leg) holds the two together. There would be movement
between the two pipes which would allow for differential expansion and
contraction, which I believe is your primary concern.
This could design could have many variations, like more than one dog
leg and
springs, but I've never liked springs around that sort of heat.
I believe it's a simple yet quite effective design that can be
handled by
the novice.
Here is another by Bill Jepson, if you were concerned about gas leakage.
Could be considered simpler.
George (down under)
Paul,
Why not just drill the holes in the bracket a size or two larger than
the bolt to allow for expansion, but still be secured? Dave D
Dave, and Group,
On the bolt secured exhaust stub the securing bracket is made of the
same material as the pipe so it expands at the same rate. No need to
slip fit it. The toughest problem on that system is that you need to use
a aerospace "jet" or "K" nut to secure the bolt or it will loosen due to
heat cycles. I have used much simpler dog-leg brackets on piston engine
exhausts. They don't see the really high temps that the rotary exhausts
do though. I really like the pressed spherical joint Idea though. I
would have loved to have had the chance to work with you and Everett, Steve.
Bill Jepson
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