Not that I'm going to jump on this right away, but it seems that it would be relatively easy to rosette weld the tips of the discs. Drill 1/8" (or slightly bigger) holes through the tube at the center of each disc tip.
Mark,
Since you have not gotten to the muffler part of your design, here are some thoughts (Yes, I did do 6 muffler experiments - don't ask me why)
The one design that was "almost" totally successful in achieving my goals is attached. Hard to make out the details, but enough to give you the general ideal.
My objective was trying to decided how to muffler the shock wave (which creates most of the ear problems) but let the exhaust gas flow freely. My conclusion was that reactive design muffler was the only acceptable choice given our constraints.
What I came up with was the idea of stuffing (I put five but I think three would make a considerable difference) disc with outer parts cut into blades and bent at a 45 deg angle into a tube. Looked a bit like an old farm windmill.
The idea behind this approach was if you looked head on at the fan-disc - you see basically a solid metal front. That is what the shock wave would see and most (a lot?) of the energy would be reflected back toward the engine (actually to the next disc in the tube). The bent blades on the other hand would permit exhaust gas to flow with minimum restriction.
It really did deaden the sound where folks could stand by the wing tip with no problem hearing someone else talk. I was thrilled. It also met my minimum restriction as I could still get my 6000 rpm static.
Ok, what went wrong - well, not being a welder I resorted to other methods - which ultimately failed.
Two things occurred -
one if the disc broke loose of the small 5/8" thread SS shaft from the Jam nuts on each side holding the disc, well, the disc could (and did) begin to spin inside the tube like the turbine wheel of a jet engine. This windmilling effect acted just like a windmilling prop on the exhaust gas and definitely impeded gas flow. So can not permit the disc to spin (the tips polished the inside of the tube where the spun)
Second because I donot weld, I did not secure the tips of the blades of the disc to the sides of the tube. Well the shock wave naturally causes those blades to flex and eventually break off.
The SS disc were 2" in diam 1/8 thick and fit really nice inside the 2 1/4" tubes. I cut slots in the outer part of the SS disc and then used pliers to bend the tabs to an approx 45 deg angle (see attached Jep).
So none of this was difficult to fabricate (tedious perhaps but not difficult).
I gave up on it because without welding skills I could not figure out away to secure the tips of the blades to the tube to give them better support. Perhaps better than disc would have been cones but couldn't find any {:>).
So since I couldn't see any way around my lack of welding (and too cheap to hire someone), I went the hushpower II route.
Just thought I would throw some fuel on your fire {:>)
FWIW
Ed