----- Original Message -----
From: "Jim Sower" <canarder@frontiernet.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, January 22, 2004 10:16 AM
Subject: [FlyRotary] Re: Torsionals


> Ed,
> Assuming (key word here) that Tracy's PSRU can be regarded as "tighter
> tolerances", mightn't rubber bushings effectively "loosen" the tolerances
and
> get us INto more trouble than they get us OUT of?
> Just wonderin' .... Jim S.
>
 >
>  Actually, Jim

    After looking at the pros and cons of both approaches, Tracy went with
the looser tolerance route and that is why you get a 42 lb gear box rather
than a 60 lb gearbox.  The resonant frequency for his drive is down low in
RPM.  So the rubber bushing actually help push it lower.  An example of the
other approach is PowerSports Spur drive gear box.  They went to tighter
tolerances (more precision machining required) and stiffer components which
raised the resonant freq above our normal operating range. Both approaches
work.  PowerSport had their own CNC machining company so its not surprising
they took that route.  Tracy had considerably less machining capability -
but more smarts {:>) IMHO

Ed Anderson