Subject: [FlyRotary] Re: 20B - torsional vibration

Powersport tests = were found to be faulty by dint of the fact that they used a piston engine = coupling to the dyno. The shaft excited itself and busted several times, and they = blamed the engine. Torsional reversals are not a problem on a rotary-there aren’t any, but there is some harmonic vibrations, easily tamed. Completely different animal. Mazda did have some flexing problems on the = early 20 shafts, they were all recalled or replaced. The forgings, metallurgy, = and some details were changed.

Marc Wiese

Obviously = I’m hopeful as well that we won’t run into any problems, but in spite = of Paul Lamar’s dismissal; I know just enough about vibration analysis, = and the risk of resonances to suggest we be wary until proven we’re in the = clear. I guess you are referring to Powersport tests that were done 8-10 years ago. The coupling to a dyno is pretty much independent of engine = type, however it is possible to have a shaft/coupling/brake system that could = have a resonance frequency with the engine in either case, and break = something. They had no such problems with the 20B tests. A shaft can’t = excite itself; it has to have a driving frequency.

Torsional = reversals are not required for a torsional vibration resonance – torsional = vibration is there regardless, and a resonant frequency in the system can cause = things to break. Torque reversals do aggravate the situation. = Vibration by itself isn’t the issue – it’s the potential for = exiciting a resonance that can multiply forces by large factors that is the = concern.

Barney, = you’re right; harmonic dampers (especially non-viscous types) need to be tuned = to the specific system, so the powersport unit isn’t of much = interest.

Fluidampr.com = (used to be part of vibratec) makes viscous dampers for a number of engines (none = for a rotary), including one for Honda which may be adaptable. But as = you say, there isn’t data that says we need it, so I guess we’ll wait = and see. I’m just suggesting that we proceed with some caution, = and hopefully avoid any unpleasant surprises. When I get my engine = running on the plane I’ll be watching for the behavior I saw on the dyno on = the drive belts; and will try to find some means for measuring the = deflection in the elastomer bushings in the drive. That could provide some good = info.