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

Brian,

Brian,


Try this company in Germany that a incorporated the substance  into some products.
http://www.cabot-corp.com/Aerogel/Building-Insulation/Products

I was going to use it as a lightweight insulation material for the cockpit, but in combinations with other material it could work for your application as well.

Download the spec. sheet on Thermo-Wrap and you will notice the nanogel is imbedded into a synthetic blend material,  and is only good for 230C.   That doesn't help directly against a red-hot muffler or exhaust pipe of course.  I believe you have a chamber on the belly of your airplane that could benefit from a layer of this stuff. Next, like a  turbo-charger, you need a infrared reflector shield say a thin stainless sheet.  Inside this shield is the  ceramic fiber mat, and perhaps a network of expanded metal to keep it in place.    Most importantly for your particular design is to get some air moving through that chamber.


The moisture issue concerns what happens when a hot item cools off in an ambient atmosphere with high humidity. Whether it is the inside your engine or right next to the exhaust pipes ferrous metals will rust.  If you used stainless exhaust pipes it's not an issue.


Doug