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Date: Thu, 10 Feb 2005 18:29:26 -0500
From: Ernest Christley <echristl@cisco.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: PSRU - hub/prop end
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George Lendich wrote:

> Tracy,
> I guess that was directed at me, and that's a Yes!
> I had requested that info from the Chief Engineer at Timken Australia, 
> who provide those figures. If memory serves me I quoted 3,000 RPM.
>  
> Butch suggested that 250,000 hrs was way overkill !
> That's not to say they are the best bearing for the job, but they are 
> a very robust bearing - that's for sure.
>  
> The big problem for any bearing is cooling, so a TRB with much larger 
> surface area than ( for instance) a plain ball bearing, requires more 
> cooling.
>  
> I had originally wanted to use TRB on my own Aussie design, as an 
> engineer mate explained - their so robust, but have been since coerced 
> by Butch to consider other options. 
> George ( down under)
>
I'd like to share as much of the details of this design with y'all as I 
can.  The more I look at it, the more I realize how ingenious and how 
much overkill it is.  I think it would probably drive a B-52 to an 
aerobatic championship.  It's heavy at around 45lbs, but a lot of that 
weight was for cosmetic purposes.  Joe was trying to emulate the center 
section of a radial, AND need to add weight to the nose for CG purposes, 
so the housing is about 2" thick at the rear.  The wheel axle 'thingy' 
(feel free to correct my terminology) is welded directly to the gearset 
housing, and carries ALL of the flight loads.  The prop shaft does 
nothing but actually turn the propeller (not that that is a small job).  
The hollow shaft that the hub rides on is 1.98" in diameter and has a 
.2010" thick wall.

The ball bearing at the rear can probably handle the reaction thrust, 
but I'm going to add a plain bearing anyway.  I have to supply oil to 
the center of the sun gear, and the easiest way for me to do that is to 
pump it forward through the sun gear shaft (vs backward through the prop 
shaft as Tracy does).  I'll only have to drill about 1" through a 
hardened shaft, vs the 10" to do it the other way.  I'll drill an oil 
gallery in the plain bearing, and make it just large enough to backup 
the inner race of the ball bearing.

I'll feed oil at the rear in this method, and then I'll block off the 
oil gallery at the other end so that it's supply will only feed 
forward.  It will be forced to travel down the inside of the hub and 
return back between the propeller drive shaft and it's housing to a 
single return at a low point in the planet gear housing.  The front 
bearings will ride in an oil bath about 1/3 of it's diameter; oil that 
has just come through the cooler.  This, combined with the hub spinning 
out in the 200mph wind, should keep it cool.

The only part that worries me is that it uses a 3-planet gearset.  I 
believe I can swap in a 4-planet set without further modification, but 
that is still under investigation.