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.
Al