Mailing List flyrotary@lancaironline.net Message #5461
From: Tracy Crook <lors01@msn.com>
Subject: Re: [FlyRotary] Re: Torsionals
Date: Thu, 22 Jan 2004 18:46:20 -0500
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
True, my redrive is definitely not tight.  As Ed pointed out, it is much lower in cost to engineer the resonant point lower rather than higher like Powersport did.  It also made field replacement of many of the parts easy to do because I did not have to worry about the lash buildup due to splines in the system.  We changed the prop shaft on Chuck Dunlops drive in about 30 minutes when he was here during a fly-in.  I wanted to check out some axial play in his front prop shaft bearing.  Turned out it was normal.
 
 The exact resonant point will vary depending on prop weight, length, and even ignition timing at idle but generally it is around 800 rpm which is well below idle rpm on my installation.  Even when I intentionally drop engine speed down to the resonant point the "rattle" is much softer than what I had with the Ross drive.  This is due to the rubber damper and the hydraulic damping of the input shaft.  Most of the noise on the Ross was actually caused by the input shaft slaming back and forth between bearing in redrive and the crankshaft of engine. 
 
Tracy
----- Original Message -----
From: Al Gietzen
Sent: Thursday, January 22, 2004 10:39 AM
Subject: [FlyRotary] Re: Torsionals

 

Jim;

 

I realize that these are relative terms, but my opinion is that Tracy’s re-drive would not be called “tight” tolerance.  There is; what – ˝ back and forth play at the prop tip?  As I recall, Tracy had given this some consideration, and chose to keep the relatively “loose” tolerance.

 

Al

 

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.

 

Ed Anderson wrote:

 

> Hi Greg,

>

>    Welcome to the list.

>

>  Torsional vibrations and resonance are a fairly complex topic.  ..  In

> generally tighter tolerances raises the resonant frequency of an assembly

> and looser tolerances lower it.  Tighter tolerances are generally more

> expensive than looser.  ...By the way, since the rotary does not have a

> negative torque region in its

> power curve this problem is minimal and can generally be handled by some

> simple dampeners such as rubber disks, etc.

>

> Ed Anderson

 

--

Jim Sower  aka  Destiny's Plaything ...

Crossville, TN; Chapter 5

Long-EZ N83RT, Velocity N4095T

 

 

 

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