________________________________
 From: rotaryeng <rotaryeng@earthlink.net>
To: AAAA Put this in the To box <rotaryeng@earthlink.net>
Sent: Thursday, September 6, 2012 5:10 PM
Subject: Hushpower autopsy



We'll I finally got some time off to check out my airplane after the round trip from
Everett to Medford. The heat cooked my left brake line, and I suspected the muffler
had too much back pressure, so I resolved to investigate. Here's what I found when I
removed my Hushpower from the airplane. There is way too much heat coming off my
muffler- the powder coating on my engine mount is cooked near the exhaust pipes, even
though I coverd them with fiberfrax and placed a SS heat sheild to cover the tubes
from view of the exhaust. The muffler was making like a baby rattle so I cut it open
and this stuff came out of the inlet side. I'll send more pictures of the innards.

What I have is an RV-4 with the radiators and oil cooler hung underneath the plane in
a scoop that is reminiscent of a P-51. I had the muffler submerged under the
fuselage. I"m thinking that it would be better to have the exhaust pipes exit the
side of the cowl, in a reverse scoop that would vent a huge amount of heat from the
cowl. The muffler would be a straight 6 foot muffler like the one Paul outlined about
a week ago. It would be mounted along the side of the fuselage. I hate to ruin the
clean lines of an RV-4, but nothing would ruin it more than having a mechanical
failure due to excessive exhaust heat bringing the plane down. My biggest worry about
this rotary conversion is excessive exhaust heat and how to manage it effectively.

Here is the muffler cut open. The red chunks are what is left of the melted
insulation material between the perforated inner case and outer. The outer case
showed signs of bulging. The perforated inner case was split on the seam closest to
the camera. The inner cone material which is also perforated was mostly gone, but big
chunks were still left inside the muffler and undoubtedly were causing some obstruction.

Here's the split in the inner perforated case. Not real confidence inspiring.


Crap that I shook out of my baby rattle/Hushpower muffler.


Brian Trubee

That will work out OK but I would put it on the bottom like Mike did.
I think you could get the rad under the engine.

Either that or use a narrower rad and put it next to the rad under the fuse.

Paul Lamar


I'd better take some time to think about it- running the exhaust under the fuselage,
around engine mount tubes, near the coolant lines, near the radiator, making
allowances for cooling duct considerations, etc, not to mention momentary cash flow
situation etc. I'm inclined to just exit out the side of the cowl- makes all those
considerations other than $ easy to address.

Brian Trubee

I am not sure you have enough room to do it this way but it is  sort of what Mike
wound up with. He had the advantage of his motor mount being further back. These are
two inch tubes with 3 inch CL radius bends. If you have Wagner pipes the bend CL
radius is bit tighter and the OD is 1 7/8" as I recall. Under the engines the tubes
can be side by side. I'll modify the 3D for that.

BTW we might make it up there next week. We will try to go from SFO to SEATAC
on Monday. I put your number in my cell.

Paul Lamar
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