Bill, the muffler did have the long tailpipe.  I am disappointed by the
test.   Was it too loud or not?  In testing Chuck Dunlop's plane
outdoors, Paul stood about 20 feet away with the sound meter.  Also,
why not make a power run when we had the chance?   I was looking for
info that would with the design.........Jerry

Jerry,

 123 db is loud. If that  is at 2 feet then it may be tolerable. One thing I was going to mention was that we should be trying to make the muffler at least optically dense. By that I mean that the exit hole needs to be unable to "see" the inlet pipes. One of the basic tennets has always been to make the shock wave reflect at least once on the way to the exit. The swirl effect of the tangential muffler does help, but if the cannister is full of exhaust gas the bark of the rotaries initial shock wave is an even wavefront dipersing from the tubes entry into the can. If the shock wave runs directly across the canister there will be a loud exit bark. The design could probably be made slightly quieter by enlarging the diameter of the cool tube to pervent a straighline path from the inlet tube to the exit.

 

Bill Jepson