> > > Keith Holm wrote:
Hi Paul, I talked with a Cozy Pilot at AirVenture who has had
failures of
two Ross drives in under 200 hrs. the nature of the failure was not
specified, only the disgust! I believe that Dave Atkins has
performed all
the prescribed thrust bearing and oiling mods, and is on his third
drive,
at relatively low power levels. Dave has ordered a Powersport
reduction.
Keith Holm [at Power Sport]
Well Keith pardon me for being a bit skeptical but when you guys get
500 hours on one of those things let me know :-) Jim Mederer and I
talked about mounting the redrive pinion on the end of the e-shaft and
he too was a bit skeptical. It is not as if this has never been tried
before
in aircraft engines. Allison did a lot of work on this arrangement
as did Rolls Royce back in the 30's and they were both six power pulses
per rev V12 engines. Rolls wound up using a quill shaft to isolate the
torsional vibrations. You guys need to get a lot more hours before I
will
be totally convinced.
Paul Lamar
Paul - The Powersport drive sounds a lot like the Marcotte (sp), is
there any relationship ? - Vance
They are both internal spur gears but the Marcotte, as you can see, has
a torsionally isolated spur gear pinion mounted with a separate bearing.
The rear main does take some side load but it is much reduced due to
leverage effects. Still not ideal but much better.
Paul Lamar
Paul
You are correct that Allan Tolle had a gear box failure at Sun and Fun.
What you did not state, or did not know were the operating conditions
before the failure, and the actual cause of the failure. The drive failed
during the sun 100 race @240+mph. Allan had just set a time to climb
record of 0-2000ft. in 42seconds while delivering 350hp on Nitrous! The
reduction that Allan ran utilized a flat bronze ring for a thrust bearing
which caused the ring gear to over heat during the high power climb. When
an internal ring gear becomes excessively hot, it warps, causing poor tooth
engagement, which can lead to a chipped pinion tooth. A chipped tooth is
what failed that box. Interestingly, the same pinion gear with the chipped
tooth was ground flat, and flown for over a year before Everett's accident.
Those who have looked closely at the Powersport website may recall that our
drive handles thrust loads in both directions through very efficient
Angular Contact bearings, eliminating the problem Allen experienced, and
making our drive usable in both pusher and tractor applications. This type
of of bearing is used in all our CNC machine spindles, and is designed to
handle extreme thrust and radial loads. The Powersport drive transmits no
side or end loading to the eccentric shaft, as a sliding outboard support
bearing supports the pinion and allows for thermal growth of the eccentric
shaft. As far as the engine knows, it is driving a torque converter.
There are very clear exploded view models and a detailed explanation of
the reduction drives operation found at <powersportaviation.com>.
There is no relationship between the Marcotte drive and the Powersport
reduction drive.
Keith
Everett told me the plain bearing failed next to the ring gear and
that is what it felt like to me. At Sun & Fun you could grab the
prop and move the shaft around. The teeth were indeed chipped but
I guessed that happened when they came out of mesh due to the
bearing failure.
To set the record Everett died 7 months after Sun&Fun in April 97 and it took
a month or more to get the airplane back to Oregon and fix the box so there
was quite a bit less than a year of use after the Power Sport box was fixed.
NTSB Identification: SEA98LA008.
Accident occurred OCT-26-97 at SCIO, OR
Aircraft: Beckham RV-4, registration: N160HB
Perhaps a drawing from Power Sport would help us understand your gear box
better.
Since there are only two pulses per rev of the 13B it is no trick to
grind the affected teeth flat and rotate the gear 90 degrees
relative to the e shaft and run it forever if the rest of the design
is corrected. I have a picture of that very pinion gear I took
at Everest's place.
You have not addressed my concerns with the alignment and wear of the
sliding outboard support bearing. I am not referring to the gear thrust
load as obviously straight cut gears as used in your gear box have no
thrust loads. As you can see in this picture of the Power Sport pinion
gear it is directly and rigidly attached to the e-shaft through
the taper in the flywheel hub.
I am not saying this is not going to work Keith. I am saying it needs more
hours on it to prove its integrity. I am also saying it is a very heavy
and expensive way to go. What is the weight of the box?
I would love to build a torsionally isolated planetary gear box around
your prop shaft, ball thrust bearings and ring gear. I think it would make
a fine gear box capable of handling a 900 HP turbo three rotor and still
not be overly heavy :-)
Paul Lamar
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