Mailing List flyrotary@lancaironline.net Message #28922
From: george lendich <lendich@optusnet.com.au>
Subject: PSRU Ratios
Date: Wed, 4 Jan 2006 08:56:14 +1000
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
A question for Tracy.
What problems would you envisage using a 3.21 ratio instead of the 2.85.
 
One of the Lads on the other site has found this 'U-beaut' Planetary out of a Cummings Diesel ( overdrive).
There are two 5 planet arrangements, one with angle cut ( opposite to the Ford unit) whereby the thrust is between the sun gear and planet ( internal thrust gear arrangement).
The other is a straight cut 5 planet arrangement ( no thrust).
 
The beauty of this planetary is that the sun gear has a spline at the aft end with a matching female splined flange ( for bolting to the damper plate).
 
The ring gear is externally notched as in the Ford  2.17.
The planet housing is similar in design and size to the Ford 2.85.
 
Advice from people in the industry are that the Dodge units are superior to the Ford units, however that would have to be confirmed. 
 
Originally you were opposed to going from the 2.17 to 2.85 for a number of reasons - can quite remember why? Was it because of higher RPM ( engine workload)? overspeeding the water pump and alternator? Anything else ?
 
What problems do you envisage with a 3.21:1 ratio?
George ( down under)
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