Jerry Hey wrote:

Paul,  I want to drop a 2.25inch  o.d. section of tube into the
S-beam
to allow direct air flow into the cool tube. The tube i.d should
allow
a piece of 2" scat to run through it.   I think if this is done
properly, the  s-beam's integrity will be enhanced, certainly not
weakened in any way.  By properly, I mean the hole cut in the
S-beam
would provide a tight fit around the tube, the tube would be
either
4130 or 304 SS.  It would be Tig'd into the s beam. I will build
a
prototype so we can prove its strength.      Your thoughts?
Jerry

That would probably be OK. Max stress on the beam is in by the
mounting
bolts. I would stick to 4130. No telling what can of
worms you might get into by welding stainless to 4130.

Paul Lamar

Good on the structure.  I and many others  have been welding 304
SS to
4130 for a long time.  No problem at all.  Just be sure to use 304
rod.
   That is TIG welding of course.    Jerry

Jerry Hey wrote:

Here is a photo of what I have in mind.  The tube is 2.75 o.d. mild
steel exhaust tubing because that is what was laying around but I
bet
it is more than adequate.  I have not found the same size in 4130.
It
is available in 304.   I just want a large enough hole to feed a
section of scat through.       Jerry

Not exhaust tubing. The top flanges are in compression. Exhaust
tubing will
collapse. You need at least 1/8 thick wall tubing here or better yet
box it in up
over top of the tube. You should also static test it by turning it
upside
down and hanging 900 pounds off it at the motor mount.

What is the matter with the S bend? Two 45 bends back to back will
clear the
beam. I did a 3D on this  awhile back but I can't find it. You need
to trim
the tube going into the muffler flush with the front face of the
muffler
to get enough room for the S bend.

Paul Lamar

Here it is.

Paul Lamar

Aubrey Thompson wrote:

Jerry,
I would not do this.  That location is near the position of maximum
bending stress in the S-beam.  You will be substituting a "springy"
structure for a rigid one.  The resulting flexure could result
in fatigue cracks in the welds along the top of the beam and in the
tube at the 12 o'clock and 6 o'clock positions.  The benefit here is
not worth the risk.  I think Paul's idea is a better
solution.

Aubrey Thompson

Aubrey,  thanks for your comments.  I disagree that the insert will
create a "springy" structure.  In fact I think it will be  stiffer than
the normal beam but I will test the resulting structure to make sure.
The insert will be 2.5" x .120" 4130.   Jerry

Don't use this in an airplane Jerry. It is a needless risk.

Paul Lamar
 
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