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From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: [FlyRotary] Re: Torsionals
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
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Date: Fri, 23 Jan 2004 21:41:52 -0500
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>>>Just to add my 2d, if the firing impulses  are halved by cutting down to
one rotor, is not the torsional frequency also halved? Or am I missing
something. If so, to what effect?<<<


I don't possess the engineering vocabulary to properly address this, but in 
layman's terms, I'd tend to look at this a little differently.  I would think 
that when you're talking about torsional issues, the firing pulses are simply 
the "exciters"... the resonant system is the structure in question.  I would 
think that in the single rotor the resonant frequencies would actually be 
raised rather than lowered, due primarily to the reduction in mass of the 
system.  Think about a guitar or piano string... the big fat ones, with more 
mass, have resonant frequencies that are far lower than the little skinny 
ones.  I propose that a power system is no different, and that its total mass 
is also a part of the equation.  The single rotor e-shaft is a little stubby 
thing, with much more torsional rigidity than that of a 2-rotor.  Ergo, its 
resonant torsional frequency is probably considerably higher than the 
2-rotor's.  Further, if you consider the resonance of the total system, if any 
one component has a higher resonant frequency then the total system's 
resonance goes up with it.  Think about the discussion here to date... if the 
drive coupling (one component) is tight and stiff, the system's resonant freq 
is raised.  Loosen up or soften that coupling, and the system's resonant freq 
is lowered, which, as Tracy has so eloquently explained, is the reason that 
his drive system works so well.

I don't know if I've gotten the point across, but this is how I understand it. 
 I hope it helps.

  <Marv>