Good luck, Mike, on the absorption muffler
with a rotary. I have tried a number of different approaches including
mufflers with ceramic packing that can withstand 2000F+. The heat is no
problem, the problem is the exhaust shock wave pulverizes the
ceramic/fiberglass/stainless steel/etc into small pieces in a relative short
time. Its true they were good in suppressing sound while they lasted, but
two weeks – 1 month was about the limit.
I still dream of doing a remake of a
muffler design I came up with which had 3” 1/8” stainless steel discs
(about 4-5) in a 36” tube. The disc were slotted and “blades”
bent until the disc looked a bit like a fan. The blades were bent at an
approx 45 deg angle. If you looked down the tube with the disc in it all
you saw was solid metal – however the blades provide room for exhaust gas
to flow around them. The theory was the shock wave would see basically a
solid disc and reflect some/most of its energy back and forth between discs, whereas
the gas could more or less freely flow around and through the blades.
The concept worked well in that my hangar neighbors
were all remarking how quite the engine sounded and I could still get a static
rpm of 6000.
The problem was I am not a welder and
while I had the disc clamped with Jam nuts to a SS thread rod through their
center – it was not sufficient to keep the exhaust from loosening the
nuts and causing the discs to spin like a turbine wheel. IF I could have
welded the tips of the blades to the tube then it may have been viable.
But, not a welder and got tire of messing with exhaust so I hung two Hushpower
mufflers and went flying.
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Mike Wills
Sent: Tuesday, October 06, 2009
12:58 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: engine
runup video
Thanks. Read through it yesterday. Nothing too earth
shattering here. What the article really didnt discuss and what I think is
the major problem we face in aircraft which is less of a problem in a car is
the need to get sufficient muffler volume. Finding space for a muffler that
actually has sufficient volume to do any good on an airplane is
problematic.
Havent yet seen the muffler that relies on
"reflective" (aka passive cancellation) that really works. Tried a
variety of them on various cars over the years, and of course the homebrewed
"spiral flow" muffler on my airplane currently. Still waiting for
someone to come up with one that actually works and will fit on my airplane.
Meanwhile I am intrigued by the absorptive design which I
posted here the other day. Its the only thing I've seen that actually provides
plenty of volume, appears to be capable of both muffling and lasting, and wont
look too terrible. I'm thinking about trying to throw together something cheap
and easy to try out before committing a bunch of time and effort.
----- Original Message -----
Sent: Sunday, October
04, 2009 11:38 PM
Subject: [FlyRotary] Re:
engine runup video
The address is right, but it didn't work when I tried it
also.
What I did was use up to Miscellaneous on the address and
clicked on exhaust etc on the LHS of the screen - OK.
----- Original Message -----
Sent: Monday, October
05, 2009 11:45 AM
Subject: [FlyRotary] Re:
engine runup video
That link didnt work for me George.
----- Original Message -----
Sent: Sunday, October
04, 2009 3:45 PM
Subject: [FlyRotary] Re:
engine runup video
Here's a good site for general info on mufflers, mine and
Bill Jepson design is around deflection.
----- Original Message -----
Sent: Monday, October
05, 2009 2:34 AM
Subject: [FlyRotary] engine
runup video
For anyone who hasnt had that first engine run and is
looking for some motivation. A buddy visited the hangar a few weeks ago and
shot some video of an engine runup. He posted it to his website and you can
find it here:
This was shot right after I re-installed my original muffler
after the aborted DNA muffler test. Noticeable in the video is the big staging
bog. I had this tuned out about 15 minutes after he shot the video.