Wouldn't the moment of inertia of the prop be a significant factor? 
Perhaps not since most props will fall into a small window in that regard.
Where is George Graham?  How would one get hold of him? ... Jim S.

Tracy Crook wrote:

> The torsional resonant point is highly dependant on how smoothly the
> engine idles.  If you have no misfires, the RD-1C hits resonance at
> around 800 rpm.  If you have any misses at idle, this immediately
> introduces a much higher amplitude and lower frequency excitation to
> the system and it will show up at a higher rpm.
> 
> In summary, the "rattle point" is more dependant on idle quality than
> absolute rpm.   Do not be too concerned about this however.  It will
> cause no harm to the drive or engine.  The drive has been torture
> tested for over an hour running on one rotor over the full range of
> throttle settings.  If you've ever run a twin rotary on one rotor, you
> know how violent this is.  George Graham ran his Mazda transmission
> redrive on one rotor for about 2 seconds before every gear tooth on
> one gear was stripped off.
> 
> Tracy  (now canoeing to the post office one last time before
> departing for S'nF)
>
>
>     Greetings,
>     
>     I asked this a couple times, but it was always buried at the end
>     of long messages, which gives me a clue how few people make it to
>     the end of those :-)
>     
>     IIRC, the RD1 drives have a low rpm point where they're known to
>     rattle.  I guess this is torque reversals, or something like that
>     from the engine.  Anyway, can someone confirm that this is true,
>     and tell me what rpm this is supposed to happen at?  I've never
>     been able to idle below 1500 or so, but now, I could probably idle
>     down to 1000 easily.  The problem is that I seem to hit this
>     rattle mode at 1100-1200 rpm, so I've got my idle set at 1400 for
>     now.
>     
>     Thanks,
>     Rusty (wondering if I should have inspected the redrive following
>     the oil out)
>     
>     
>     PS- TIG and Plasma machines both got 1.5 inches of water before I
>     picked them up, but I dried them out yesterday, and they both work
>     now (thank goodness).  Fortunately nothing expensive was damaged
>     in the flood, assuming we don't have to replace the carpet in the
>     great room.
>

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