The torsional stuff is BS. We don't have any torsional problems. The
tooth
with the hole in it was simply over loaded. We have tens of thousands of

accumulated hours behind Ford based planetarias over a period of twenty
years
and that is far far more than Power Sport can claim with your over
priced
over weight product.

Al Gietzen wrote:

Paul;

I would be a bit less sanguine (ah; confident, optimistic) in this
regard until we have a little more proof.  When Chuck was having his
problems with the Ross drive on the 3-rotor, my preliminary analysis
suggested that at the power levels he had been running, it should not
have been a problem with the gear set, certainly not in so short a time.
So I suspected a torsional resonance issue.   I 'suspect' that could be
a contributing factor in Tom's case as well.

An important factor there is that the Ross drive has no damping.  The
resonant frequency may be lowered by the flexibility, but the springs in
the coupling conserve all the energy and put it back into the system.
The drive has worked reasonably well on the 2-rotors, but the 3 rotor
would likely have a different torsional frequency response.

Tracy's drive is a clear improvement over the Ross in a number of
respects; the damping in the coupler being important to this particular
issue.  The added flexibility in the system, and the damping, gets the
resonance frequencies low enough for the two-rotor so the issue goes
away.  And whatever energy is dissipated in the damping donuts is low
enough that it is not an issue.  Is this also true for the 3-rotor??  I
think so; but we don't know yet for sure.  I'll find out, and I would
really like someone to be ahead of me on that one.  Tom, get an RD-1B on
your plane ASAP!

Al

I think you are on to something there Al. Rubber works better as there is
more damping. Tracy takes this one step further by using a bit of friction 
damping in the metal and plastic washers clamping the rubber bushings.

BTW looking closely at the 2.17 sun gear with the small lube hole in it
appears the hole is designed to lie outside the gear engagement area.
In other words there would be very little cantilever beam bending
on the tooth in the area of the small hole. The differences is about
.1 to .2 inches of engagement. In other words if the sun gear is
inserted into the planet carrier too far the small hole then becomes
a factor. I find it hard to believe the Ford engineers were unaware
of the inadvisability of drilling a small hole at the base of a loaded
gear tooth.

Chris Ross may have missed this subtle point and machined the box
incorrectly. Usually the gear unscrews itself moving the small
hole away from engagement. If a thrust bearing was installed
in Tom's gear box the gear could have been positioned incorrectly
or if no thrust bearing the gear could slid back and fourth
within the planet carrier. Also there is some sort of thrust bearing
installed ahead of the sun gear limiting its travel into
the planet carrier. If this thrust bearing is incorrectly dimensioned
the same scenario could happen.

As I said before this failure mode has been unheard of up until now.
Bottom line is I am still not convinced the four pinion is unsuitable
for a 3 rotor. We will probably never know as I am sure all you
three rotor guys will switch to the six pinion.

Paul Lamar
 
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