Good luck, Mike, on the absorption muffler with a rotary. I have tried a number of different approaches including mufflers with ceramic packing that can withstand 2000F+. The heat is no problem, the problem is the exhaust shock wave pulverizes the ceramic/fiberglass/stainless steel/etc into small pieces in a relative short time. Its true they were good in suppressing sound while they lasted, but two weeks – 1 month was about the limit.
I still dream of doing a remake of a muffler design I came up with which had 3” 1/8” stainless steel discs (about 4-5) in a 36” tube. The disc were slotted and “blades” bent until the disc looked a bit like a fan. The blades were bent at an approx 45 deg angle. If you looked down the tube with the disc in it all you saw was solid metal – however the blades provide room for exhaust gas to flow around them. The theory was the shock wave would see basically a solid disc and reflect some/most of its energy back and forth between discs, whereas the gas could more or less freely flow around and through the blades.
The concept worked well in that my hangar neighbors were all remarking how quite the engine sounded and I could still get a static rpm of 6000.
The problem was I am not a welder and while I had the disc clamped with Jam nuts to a SS thread rod through their center – it was not sufficient to keep the exhaust from loosening the nuts and causing the discs to spin like a turbine wheel. IF I could have welded the tips of the blades to the tube then it may have been viable. But, not a welder and got tire of messing with exhaust so I hung two Hushpower mufflers and went flying.
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered