Exhaust Heat Wrap

[Mike Davis]

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To: murphy-rebel@dcsol.com
Date: Thu, 26 Feb 1998 07:37:26 -0800
Subject: Re: Exhaust Heat Wrap
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From: rbartman@juno.com (Richard H Bartman)

Rich

What was the failure mode of the exhaust wrapped with insulating
material? Corrosion? overheating?

I think it would be informative to hear your description on this as
insulating the system would seem to make sense (and indeed is used in
some automobile racing applications).

Thanks

Dave R.

The thero wrap caused the metal underneath it to disintegrate. While
flying I noticed a change in the sound of the exhaust. Upon landing an
inspection revealed a hole had blown through the wrap.

After removing all of the wrap a large hole was found on the right side
at the "Y" where the two pipes meet.

All of the exhaust pipe covered with exhaust wrap was flaking. I could
take a knife and scrape off a layer of metal.

I returned a piece of the damaged pipe to Thermal Wrap and they said my
engine was running too rich and that flames were traveling down the pipes
and causing excessive heat. They also said that although automotive
racers use soft steel for ther headers that they would not recommend
using anything but stainless steel in an airplane.

An interesting comment in the last issue of Contact Magazine for a man
converting a large block Corvette engine. After a few hours of test stand
running his system cracked under the thermo wrap. He replaced the pipes
and ran it with no further problems.

Rich

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[Mike Davis]

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Hi Rich,
Curt Martin with #426. That was a very interesting comment in your e-mail.
We
also have the crossover system from MAM, and after only 3hrs we also had
flaking, a crack at the wye. After that was repaired, at 15hrs. total time
we
found an additional crack further up the #3 cylinder stack. Not only do we
lean, we have an electronic ignition system installed . It burns much
cleaner.
The other cylinders are all fine. We too found the problem by looking
closely
at the flaking. What happens if this cracking problem continues into the
area
of the heat muff??? !!!!!!! MAM will be getting a call from Me!!!!! (We did
not recieve instructions either!!)





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[Mike Davis]

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To: <murphy-rebel@dcsol.com> (Murphy Rebel)
From: Greg Board <normarin@winshop.com.au>
Subject: Re: Exhaust Heat Wrap
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Rich:

Heat wrap does a good job keeping the heat out of the engine compartment.
It also does an even better job keeping the heat IN the exhaust pipe so
nuch in fact that the pipe reaches enornous temperatures that will destroy
the integrity of the metal in the pipes.....as you have seen.

Heat wrapped exhausts should be in the order of 3/16" wall thickness on up
to 1/2" (Marine use) depending on engine size but the weight will not be
welcome in our airplanes. 316 Stainless steel exhaust may be a little less.
Exhaust pipes need to have the maximum amount of cool air flowing over the
metal as possible. Rolls Royce silent cars have heat wrapped 1/4" wall
stainless in many models.

If sound is the problem use mufflers, also with cool air flowing over them.
Keep the expansion joints free to slide and attach the outer pipes to the
ENGINE, not the mount or the airframe. The engine and the airframe vibrate
at different frequencies and direction. Use a semi flexible attachement
such as a thin steel strap allowing movement of the tail pipe. This strap
served two purposes (1) It limits
the amount of movement of the tail pipe thus reducing fatigue and (2) It
stops the tail pipe falling on peoples heads when it breaks off.

GREG




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