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Message-ID: <005b01c50e35$b21bf780$9e731fd3@george>
From: "George Lendich" <lendich@optusnet.com.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-720313@logan.com>
Subject: Re: [FlyRotary] PSRU - reaction bearing
Date: Wed, 9 Feb 2005 09:27:02 +1000
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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.

See comments below Marked ****:-

> Continuing with the theme in my previous email, I spent some time to
> dis-assemble my PSRU, to see what it was really made of.  The design
> boils down to a planetary gear set welded to the wheel hub of a NASCAR
> racing car, and held to the engine with custom cast aluminum (LOTS of
> custom cast aluminum).
>
> This was put together several years ago, and loosely based on the Ross
> unit.  There have been several lessons learned since the Ross units
> started flying, and I want to make sure I incorporate those lessons into
> any modifications I make.
>
> The first question I have concerns the reaction forces from the
> planetary gear set.  If I understand the mechanism correctly, as the
> helix teeth on the sun gear engage and turn the planets, there is a
> considerable force trying to push the sun gear out the back of the
> unit.

**** Yes!

This force will be taken up by the eccentric shaft and destroy
> bearing in the engine unless steps are taken to  handle it in the PSRU.

**** Yes! the engine bearings are not designed to take this thrust!

> Tracy's solution has been to add a properly rated bearing at the back of
> the sun gear, if I'm not mistaken.

**** That's correct, other options have served to fix the Ross gearbox.
>
> The unit I have has a set of ball bearing at the rear of sun gear.  They
> look to be really heavy duty bearings, but I couldn't find a part number
> and didn't want to take the chance of damaging them while removing them
> from the housing.  Any guesses from the group on whether this setup will
> stand up to the reaction forces or not?

**** 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.

>
> The first picture below shows the back of the PSRU with it's rear cover
> removed.  The shaft engages the clutch plate.  The second picture is
> from the other side, and depicts how the sun gear sits in the center of
> the ball bearing housing.

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)


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