Given the recent interest in mufflers, I thought I would
throw in my experience with home made muffer. I could hit
6000 rpm on take off with my 13B with the 2.18:1 Gear ratio.
You could stand within a wing width with the engine idling and
bearly hear it. At 6000 rpm it was about 1/2 as loud as an
unmufflered lycoming.
The basic idea was to break up the shock wave while
minimizing gas flow impedeance. I used 1/8" thick 2"1 /2
Dia stainless steel disc inside of a 2 1/8" dia stainless
steel tube. The disc has slits cut from the outer edge
approx 1/2" toward the center in 8 regions as shown in the
diagram. Then each "tab" was twised 45 deg from the plane
of the disc. If you looked at the disc front on it look
almost as a solid disc with just a small slot area showing
through. The idea was that the shock wave would basically
see a "solid or mostly solid" disc where as the gas could
still flow through the slots around the tabs. I had a
threaded rod extending the length of the tube with jam nuts
on each side to hold the disc in place.
The reason for the rod and nuts was not being a welder-
I used jam nuts - welding it turns out would have been much
better as the nuts eventually became loose. That was not
good, when one of the disc came lose it started to spin and
greatly impeded the gas flow. Although folks told me it
sound cool - like a turbin winding up.
In any case, I decided that not being a welder there was
no way I could remedy the defects. I think if there were
some way to "spot weld" the outer part of the tabs to the
tube and perhas to a rod in the center the muffler would
have extend it useful time. I flew approx 12 hours
including one trip to Tracy Crook (first extended flight
with muffler) by the time I got there at least one disc had
broken loose and was spinning. Tracy was kind enough to use
his welding skills to weld the discs to the rod on one of
the mufflers (had two one for each exhaust), but within
another 6 hours or so disc in the other muffler started to
spin. Also I found that the shock wave pounding eventual
would break off a tab or two since they were not anchored
and could flex.
Just thought I would throw the idea out there in case it
has any merit.
Best Regards
Ed