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