Hi, Paul....I have been discussing my muffler needs with Ed Klepeis. He can build
another VAM muffler for me, if I am willing to try it before final testing has
been accomplished, but he explained that "the VAM needs a muffler attached to
it to keep it muffled, and that the VAM is just a collection point for the 1700
degree exhaust, cooling it a bit and passing it on to other exhaust components
that can deaden the sound and not have to deal with the high temps" . Would you
say the same is true of a tangenial muffler?
Jury is still out. I suspect with the same down pipe diameter the VAM may
eventually prove to be quieter. Also pusher verses tractor is a consideration
on the noise generated. When the exhaust must pass through the prop things
change. So far we don't have any hard and fast data. We have a few data
points on different airplanes with different muffler systems. Much of the noise
is generated by the prop so it is hard to say one muffler is better than another.
Subjectively the tangential muffler that I have heard so far all seem to
be acceptable.
I also think a simple fish mouth on a VAM or tangential would quiet them further.
Fish mouths must be beefed up as they are prone to failure if not properly
designed. We also need to experiment with square pipes entering the VAM and
the tangential as well as a square down pipe out of the tangential.
Hopefully we can get some back to back noise and HP measurements when I get the dyno
going. Too early to make any hard and fast statements about mufflers.
I know Ed can make a quality muffler
for me....Unfortunately, I am unfamiliar with a tangenial muffler, and the
sound/muffling characteristics of a tangenial versus the VAM. If I do not need
another muffler behind the tangenial, that might be a better way for me to go.
I would, however be able to fit a muffler similar to Al Gietzen has on the end
of his, as shown in this picture. Thanks for taking the time to explain the
differences, and your recommendations? Paul Conner
The difference is subtle. The VAM and the tangential in theory work the same
way. Exhaust pulses are forced to spin around inside the muffler losing
energy in the process by friction with the outer skin. The VAM has an inner
pipe which adds additional skin friction surface area. It also introduces
cool air to reduce the temp of the exit air making it less damaging to a
prop or to any muffler added down stream.
The reason anything inside a muffler used on a rotary engine
is prone to failure is, unlike the skin of the muffler, it is not cooled by
outside air. This cooling effect applies to the center pipe in the VAM muffler.
Several people have tried various interior parts and lost them though the tail pipe.
Fortunately this happened on tractor airplanes so the failed parts did not go through
the props. I myself have had a similar experience with the muffler on my C182.
It happened on the ramp at Valdes Alaska greatly disturbing one of my
passenger that happened to be standing outside the 182 cabin. I just told
him not to worry.... the engine really did not need those parts :)
Unfortunately, as Jerry Bass has discovered, the VAM does not work well at idle.
Therefore it is essential to have a metal pipe coming out of the VAM
preferably pointed forward but oriented in such a way as to not direct hot
gases on any part of the airplane.
Paul Lamar
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