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Uh, that wasn't me. :-)
But I've heard the case made that exactly what you describe is
what happened (dyno designed for V-8s at 4per-rev; twice the
excitation frequency). I didn't stay in a Holiday Inn last night,
but those who did tell me that *in resonance*, power level doesn't
really matter much; stuff is going to break. I'd love to see that
same driveshaft & dyno hooked to something like a big 4cyl
engine (2per-rev) capable of the same HP & rpm where their
failure occurred. Doesn't it make you wonder if the results would
have been the same?
One of our former members (since deceased due to natural causes)
flew successfully for years using a Mazda transmission as a
reduction drive. Worked great until one day when the engine
started on only one rotor (1per-rev) & *at idle power* it
destroyed the gearbox.
I can't help but wonder if that dyno incident took them down an
unnecessary rabbit hole of expensive zero-clearance gears &
extra weight.
Charlie
On 3/21/2017 3:51 PM, William Jepson wrote:
Charlie,
In terms of simple vibration caused by out of balance you
are correct. It terms of torsional vibration though the rotary
is a tough customer. Part of the problem is that the e-shaft
on the rotary is so stiff. I have been working with Steve
Beckham from the original PowerSport. Steve told me about how
a 200 HP rotary just blew up the input shaft on a dyno that
was regularly used to test 600+ HP V8 piston engines. This is
the torque pulses of the engine, not out-of-balance. It is
likely that in that case the rotary hit a amplifying couple or
harmonic frequency with the dyno causing the failure. That
said Steve and Everett Hatch did a LOT of work to be sure
their "stiff" model reduction drive placed all the frequencies
above the normal operating range. If you hit one of those
frequencies with one of the rubber couplings or the
bushing-around-bolt dampers it will fail period. Most of those
systems try to push the first order frequency below the
operating range. That is why you will often hear the engine
shut down rattle with a planetary. Typically the energy in the
system is low enough to pass through that RPM without damage.
Usually. But if not planned for those pulses can be a
disaster.
Bill Jepson
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