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Date: Wed, 09 Feb 2005 09:12:15 -0500
From: Ernest Christley <echristl@cisco.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: PSRU - reaction bearing
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George Lendich wrote:

>Ernest,
>This is something I'm familiar with, but can you tell me who makes this
>particular PSRU and how is the sun gear attacked to drive shaft.
>  
>
This is a one-off design done at Lakeridge (8NC8) by Joe Hunt a few 
years ago.  The sun gear apears to be a integral part of the input drive 
shaft.  The propeller shaft is driven from inside splines on the planet 
gear carrier.

> **** Firstly plain ball bearings DO take some thrust. Tracy does use 
> one in
>
>the front ( of his PSRU) I believe.
>I can't say how much thrust it will take but it appears to be quite large -
>take the size to your local bearing supplier and they will identify it and
>give you a thrust rating.
>
>I know there's a 1,000 ft/lbs of thrust there, but how much is carried
>rearward I'm not sure.
>
>  
>

I have a bearing supplier that I've worked with in the past.  I will get 
them in the loop.
The sun gear is a tight slip fit into and rides on the inside of the 
ball bearing housing, which is 3/4" high.  The balls are 1/2" diameter 
as close as I can measure, but I'm unable to get the calipers down into 
the housing for a really accurate measurement.

I was thinking about this last night when I should've been sleeping, but 
I would think that the reaction forces would be a simple vector based on 
the helix angle of the gears and the input torque.  Assuming a 3" sun 
gear with a 30degree helix and 150ft/lb of torque, the reaction force 
would be:

150ftlb*12in/ft / 1.5in = 1200lb of force across the helix teeth
The part absorbed by the rear thrust bearing would be:
sin(30) * 1200  =  600

I didn't take the time to measure the helix angle this morning like I 
meant to, but if the angle is 20degrees, the force at the rear bearing 
will drop to around 410, and 10 degrees will take it down to 208.

>Question - is the rear teeth of the sun gear turned down before being
>pressed into the bearing - I'm assuming it is.
>George ( down under)
>
>  
>
I took a picture last night, but didn't get around to uploading it to 
the computer.  The rear of the sun gear is turn down to be a tight slip 
fit into the ball bearings inner race.