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Ernest, There is no question that using jam nuts to try to restrain the "turbine discs" was woefully inadequate - even welding on that small arm just prolonged the event as you correctly pointed out. I still think with some work that approach might have ended up with a good working muffler. I think the theory was proven sound - but the fabrication was certainly inadequate to the task.
Rosette welds on the outer perimeters would undoubtedly have been much more effective. However, not being a welder (and not going to risk my one good eye ball, I am never going to become a welder {:>)) - also should mention retired and too cheap to hire one - I decided to abandon the project in order to take a whack at some of other To-Do projects.
Finally finished the software for my AOA (it took me several weeks to discover a long vexing problem that turned out to be an unnoticed, not readily apparent(is that redundant?) and certainly unintended loop within an loop which was throwing off the wave-form timing and therefore shape that I used to measure pressure from the pressure transducer used for the AOA.
So with that problem now solved, I am proceeding on my single axis autopilot using some of the latest (and reasonably priced) MEMS gyros and accelerometers- got the board designed, now "just" have to write the software {:>).
There is just too many projects and not enough time (even when you are retired - or perhaps especially when you are retired {:>).
Ed
Ed Anderson wrote:
The rotary is also pretty sensitive to back-pressure, so what kills the noise generally does the same to the power. There was one design I tired that used 3" dia SS disc in a tube with "Paddles" bent on the outer permimeter. The ideal was that the shock wave would see solid metal and be reflected - but the exhaust gas would cruve and flow around the paddle blades.
It worked (while it worked) , I flew from NC to Florida and it measurably reduce the exhaust note (by something like 8 db), the problem was the discs and the jam nuts I had holding them on a 3/8" dia SS rod (I don't weld) I had through their center. At some point, some of them (I had 5 discs in each tube) worked loose under the pounding . They then began to act like a windmilling propeller (yes, they were spinning at high speed). The effect was to expotentially increase the drag on the exhaust gas and imped gas flow.
Tracy was kind enough to use his arc welder to weld the discs to the rods (that lasted for about two weeks).
I think you gave up to early on that one Ed, but I can see how you felt like you did your part with so many others under your belt. The way I'm seeing it, the 3/8" torque arm was just way to small for the 3" disks torque arm. What you needed was some rosette welds on the perimeter of the discs to tack them to the will of the tube.
Make the discs last, and we can feed the exhaust through that Swiss muffler that Neil is talking about.
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