I removed my Hushpower the other day to re-do the heat shielding around
it.
 It's submerged and does not get enough cooling air around it. I used an
 aluminum heat shield and some woven ceramic insulation  with aluminized
 mylar, I don't know what that particular heat shielding is called, but,
the
 aluminum burned through and the mylar melted. So, I'm doing a re-design
 where I have double stainless steel heat shielding with forced air going
 through the air space. Backing that up will be a layer of fiberfrax.

 But, back to the Hushpower. When I pulled it off, I shook it and it
sounds
 like a baby rattle. So, I'm going to use a bore scope and see what's
what
 with it. Hmmm....

 Brian Trubee

 Good idea Brian. Harbor Frieght has a cheap bore scope.

 I like the outer case design. I would cut it open and gut it
 and then weld it backup.


 Paul Lamar

Paul,

I tried one of these and it couldn't handle the heat.  Packing melted
within
the first hour.  (Maybe Brian could cut it open, stuff it full of SS
shavings, and weld it back together.  The outer shell is made of 304 SS,
but
the perforated cone appears to be made of mild carbon steel.  It melted
and disintegrated after about 25 hrs.

Mark

I am not sure I would put anything in it but shavings might
be small enough to be spited out :)

For the new guys this is what can happen if your cheap automotive
muffler fails. This one caused a crash. The pilot lived fortunately.

Rotary mufflers are best from Inconel if weight is important but
.064 thick SS 321 is OK too for a 30% muffler weight increase trade off.

Paul Lamar

Paul,

What material was the baffle made of?  The Hushpower II has a cone-shaped
baffle.

Mark

Looked like mild steel to me.

Here are some fail safe ideas.


Paul Lamar

Brian,


You might look into Aerogel insulation as it is the lightest and most
efficient stuff out there. Mylar is basically plastic. Fiberfax might
trap moisture.

Doug in Japan

Here are some pictures of Brian's muffler installation for the new guys.

Paul Lamar


So Doug, I looked up Aerogel, it sounds like it could be effective,
but is there a source that sells it in form that is usable and
affordable for my application? I don't think I'd worry about Fiberfrax
absorbing moisture too much- not where it would be situated and with
the conditions it would see. But I'm willing to look at anything that
you think might be better.
The heat of the exhaust is the only thing that really makes me a bit
nervous about my plane.

Brian Trubee



You might have another look at my muffler that I published on this web
site. It is quiet!

chris smale

I think I lost it Chris.
Can you send it again?

Paul Lamar