Ed Anderson wrote:

Yvon,

    Here are a couple of photos of my "holey" mufflers. Finn's and mine are
conceptually the same, just the details differ.   Mine are out of 18" long,
2" dia,  0.035, Stainless Steel and have 60 5/16" dia holes with the tip
squeezed down to a "fishtail". The holes then are "louvered" by working a
rod back and forth so that a bit of the hole lip sticks up to catch the gas
flow.  There is one muffler for each rotor.   Originally I squeezed the
"fishtail" down to a 1/2" wide slot, but found that by squeezing it down to
1/8" I got much reduced volume of sound and I still get 5600 rpm static.
While much improved, it is still a bit on the loud side at WOT.

   I am currently constructing another set of two pipes, but making these
40" long and will drill smaller holes (probably 1/8" dia) along the half of
the cylinder that points away from the belly of the aircraft.  I believe I
can get even lower volume of sound and less back pressure.  I intend to
insert a plug on the end such that by rotating the plug I can increase or
decrease the back pressure in the pipe and hopefully be able to "tune" it
for optimum.

   I have the material ordered and want to try and get it finished before
Sun & Fun.

Ed Anderson

 
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