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Rich, I totally agree. My comment is based on personal experience on several racing engines on which I used the coating. The highest temps I saw are probably slightly lower than rotary exhaust temperature, but Jet Hot or similar cermet coating is just about the only thing with a chance of lasting. Otherwise I would go inconel with shielding. Bill
Just a thought,
Jet hot is a great idea as it lessens the heat exchange from the exhaust gasses to the outside due to IR radiation. It also may look great. However there may be a problem here in that the rotary (especially non-renesis) is quite hot and restricting its loss through the pipe by coating might quicken the demise of the pipes from the inside (which you won't be able to see). If you are going to coat, coat both the inside and outside of the pipes. (slip joints may be a problem here but they are inspect-able). Of course then there is the problem of the muffler.
In an aircraft application, these pipes are subject to higher sustained temperatures than our cylinder loving brethren.
Rich
-----Original Message-----
From: William Jepson wrjjrs@gmail.com < flyrotary@lancaironline.net>
To: Rotary motors in aircraft < flyrotary@lancaironline.net>
Sent: Thu, Jan 23, 2020 12:29 am
Subject: [FlyRotary] Re: mufflers
Guys, no paint is going to hold up. Look up Jet Hot. They have a very high temp cerment coating that is really rated to 1800 deg F. I’ve used it on several race bikes. No flaking or degradation. Much higher temperature than paint. For mufflers try looking up the Iannetti patent. Yes the same guy doing the tip seals. He built a very effective muffler that he leased to the rotary engine racers. At least until most racing groups banned the rotary.
Bill
Ok that makes more sense. I also painted my exhaust with supposedly 2000☀️F paint. Didn’t last long.
Finn, Correct, but I possibly confused everyone as the 28% only
allows the gas to "rub" and does not in any way totally exit
completely through the holes, it acts like a cheese grater
together with the packing. The exhaust gas exits unrestricted
through a 2.5 inch pipe A bigger pipe may eliminate the slight
power loss?? Originally just a straight through muffler, now a
"closed circuit" for want of a better description. THe muffler
runs red hot, so Chris shrouded it and put an air cooling blast
onto it which eliminated that problem. IN the photo you can see a
horrible paint job. That started out as top of the line high heat
resistant paint --- soon cooked that off, so that it looks like it
does
Neil.
Well, any reports on the power loss
with the muffler with 28% holes?
Obviously the most quiet installation of all is the one that
doesn't produce any power at all :)
Finn
On 1/22/2020 10:42 AM, Matt Boiteau mattboiteau@gmail.com
wrote:
What did you mean by
" The 3 inlets
fire directly onto the opposite side of the center tube."
So the 3 primary tubes are welded to the center tube,
which blows out into the outer tube (that has the
packing), then out the 2.5" pipe. How does the packing not
blow out the 2.5"?
I'm curious
about hard welding the 3 inlets to the outer can without
any??expansion??joints. I was worried so I made all 3
expansion joints.
Darn, I'm thinking I put way to many holes in the
perforated center tube.
- Matt Boiteau
Mat,
?????????????????????????????????? Here again I am just
the messenger.?? The guru is Kevin Davis from Active
Exhaust Systems?? (AES). (woolongong Aust)?? Yes 28% is
the magic number as is the size (dia) of the holes at
just over 1/8"(critical apparently).?? Packing is
Innox?? wool which is fine S/S.?? Too much and too
little, both affect the result. Kev, claims that he
weighs the muffler when packing to get the right
amount,?? says that although not packed precisely even
from end to end, it will even out as it works.
The big can has the perforated tube running end to end
which is hollow (perforated tube) and the outer can is
packed with Innox between the inner perforated tube and
the solid outer tube.?? The muffler shown, began life as
a straight through muffler which was mounted under the
RV.?? Chris then as usual adapted the muffler by cutting
3 x inlet holes right into the hollow center tube, then
welded it to the manifold plate.?? The 3 inlets fire
directly onto the opposite side of the center tube.?? I
tried to see what that has done to the "wool"opposite,
and it appears to have blasted some away. Hard to tell
looking through 1/8" holes, Only way to find out is to
disassemble it.?? Then to get the noise out, he again
simply cut another hole halfway between the back 2
exhaust inlets and welded a 2.5" outlet.?? Has done many
successful hours Chris says.?? Chris cut off the 3"
inlet and outlet tube and welded a plate over both ends
to seal the whole muffler.?? It fitted in the small
space available and worked which is what matters
Kev. seems happy with a 2.5" exhaust tube, so is up to
you if you chase 2.75".?? Here again I have no idea, and
I suspect most others have little idea as well.?? really
a dyno is the only evidence.?? Watched many Utube videos
of blokes putting different mufflers on their cars to
get a lovely "quiet" exhaust.?? All terribly successful
according to the operators, but IMHO the results ranged
from little difference to actually louder.?? Perception
and fact can be totally different.,?? AS they say if
your baby cries it is music, if it is someone elses you
want to kill it!
Neil.
Only 28%.
Geesh, I just drilled mine and did about 200%, I guess
that is way to much. I guessed the drill area to be
double the size of the pipe. Did make design so I can
drill out one cap and switch out the inner pipe full
of holes to test different back pressure.?? Neil, can you confirm
28%? ??
Is the big can stuffed full of wool, so the primary
tubes fire right into it? How does it exit out that
bottom pipe?
In RX8, they (car forum) say 2.75" is the best (but
hard to find) exhaust size. But since we are taking
large harsh pulses and bring them down to a small
constant flow, they say you can run smaller size. I
did my downpipe as 2.75" and will do the long exhaust
underneath plane in 2.5"
- Matt Boiteau
Second
time with 1 photo each to get past the editor!!
Photo of modified straight through muffler to
attach directly to the RX8
engine.?? The science apparently is to have approx
1/8" holes that amount
to 28% of the area of the through pipe.?? This one
is 3 inch but the
Manufacturer claims that?? 2.5" is better. Dia is
5 " and the space
between is packed with fine S/S "wool". THis is
the first bloke that can
tell me the science in mufflers as he has made
them all his working life.
JUst passing this on as I am totally ignorant as
usual.?? Still trying to
mount my turbo if I live long enough.
More photos to follw for those interested.?? Neil
--
Regards
Andrew Martin
Martin Ag
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