>
> Hello All,
>
> Here's a question to the group for those who own a Ross PSRU. I
own a
> Ross 2.17 to 1, and I am tying to solve one of the issues
regarding the
> "drive shaft" from hitting or bouncing off of the thrust bearing
I'm
> sure people who own such a unit knows what I mean. I found some
> solutions on the net but I'm wondering if anyone else in this
group has
> a suggestion, possibly a simpler solution.
>
> I've heard comments of "just sell the unit and get another one"
but I'm
> not sure that I need to go to that extreme. My primary two
reasons are
> 1 The unit is an integral part of my engine mount and 2 A
> replacement would probably cost me two to three thousand dollars
(if not
> more to redesign my engine mount) just to note, I purchased the
plane
> from someone else, so it's not my original idea
.
>
> I've included a few pictures of my setup.
>
> Cheers,
>
> Burck Hantel
>
> FYI:
>
> A fellow named Phillip Johnson explains what is going on a little
better
> then I can so I am reiterating his explanation here:
>
>
http://www.canardzone.com/members/PhillipJohnson/Engine/psru.htm
>
> "Breaking open the PSRU reveals the working parts, namely the
planetary
> drive. Under load conditions the input shaft is drawn towards the
output
> shaft to which the propeller is attached. A thrust race, takes
this load
> quite satisfactorily. When in a decent the propeller drives the
engine
> and the input shaft is forced to move in the direction of the
engine.
> The ROSS design does not provide a true thrust bearing to support
this
> load, moreover the load is taken by a conventional sealed ball race
> contained within the lightweight flywheel. This bearing is there to
> accommodate the slight differential rotational rocking motion
> encountered as a result of the torsional isolator mounted on the
> flywheel. A resonant condition is set up when operating near idle
when
> the engine drives the propeller followed by the propeller driving the
> engine. There is considerable chatter at that point and the input
shaft
> is hammered back and forth between the thrust race illustrated
below,
> and the conventional bearing previously described. The bearing
begins to
> break down and the end movement increases only exacerbating the
problem."
>
> ---------------------------------------------------
Burck,
Here is another solution that Al Wick described at some time in the past
on his web site. His Ross PSRU is a 1.85:1 unit on a Subaru engine. He
fabricated a zero clearance bearing cap that acts as a spring to load
the input shaft thrust bearings.
I agree with you that the Ross PSRU is a viable unit to use. I would
guess that the Ross units have collectively accumulated a lot more
flight hours than any other type. The most notable example is the
Maynard gyrocopter with the rotary and the 2.85 Ross that logged more
than 2500 trouble free hours as a training vehicle. One other
modification that I have considered making to the Ross installation is
to design a resilient drive plate similar to Tracy's. The operating
history, at least as far as I know it, of the Ross units would suggest
that this modification is not mission critical, but, it may reduce
vibration. Or, it may not.
Aubrey
Aubrey we don't do .doc :) Please send as jpg and txt.
Not everybody has office. Worst comes to worst as a pdf
file as pdf viewers are free on all platforms.
Paul Lamar
Thanks for the info; this was one of the designs I was reviewing last
weekend. I tried to wrap my head around how the cage cap would actually
work, my conclusion was that it would interfere with the ring gear that
meshes with the planetary gear (on my box that is). -- but I could be
wrong... The suggestion that Paul posted looks like it will give me
enough room to put in the thrust bearings. Now I have to find a metal
lathe in and around Athabasca, Alberta (one that will be reasonable in
cost)....
Thanks Aubrey and Paul for your help!
Burck
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