----- Original Message -----
Sent: Friday, June 17, 2005 7:38 PM
Subject: [FlyRotary] Re: small muffler
suggestions for single rotor?
I have a muffler running
on my test stand for several hours. It is a tangential expansion type with
nothing inside so nothing will come out. I can stand next to the engine
running witout the need of ear plugs.
The only critical
issue is dimensions, which sometimes go against intuision.
Feel free to copy
it.
It would have to be a bit
different from yours to fit the Kolb. I suppose it could
run left to right in front of the engine, rather than under it.
In order to copy the non intuitive critical
dimensions, it would help to know what they are :-)
Thanks,
Rusty (I still owe you a
visit)
I never did any analytical work on this muffler
design, however, I followed the physics principals. The first muffler of this
design, I built for my SOOB in the AVID which is still flying very
quietly.
Considering exhaust noise to be the only issue, you
follow the principle of adiabatic cooling of the exhaust gases as much as you
can afford in the available space.
This means trying to keep the gases as long as
possible in the muffler container, which also will add radiation and
convection losses as a benefit.
If you consider a container of 6" dia and 24"
long physically acceptable, the muffler is built around it. Next, in the
single rotor is only one pipe input, this input pipe enters the container
tangential on one end. The exit pipe is located on the other end of the
container rectanular to the container C/L. The exit pipe must be smaller then
the inlet pipe since the gases have less volume because of the energy loss in
the container. This is very important for keeping the expansion noise inside
the container. Keep in mind when Bubba wants to give his truck a bigger sound
he puts in a bigger tail pipe.
The output pipe is between 50 and 75% of the input
pipe cross section. This will keep the back pressure in in a range where it
has no significant impact on engine power.
Using this design principle on a 13B you only have
to be aware of the fact that only one input pipe counts for dimensioning the
output pipe because only one pipe is flowing exhaust gases into the muffler at
any time.
BTW, the muffler size in the picture was driven by
the material I had, but it works anyway.
Richard Sohn
N-2071U