Paul,
Don't you have to add the thrust of the prop to the thrust bearing load as
well?
Doug Fir
Not in a Ross or Tracy PSRU. There are separate bearing that take
the prop load. Needle bearing six takes tractor thrust in the 2.17 in
the Ross and a bearing between the prop shaft and the planet carrier
takes prop thrust in a pusher configuration. Not shown. The planet
carrier is locked to the outer housings. This needle works because it is
going only prop RPM. Needles don't like high RPM. The engine thrust
bearing is subjected to engine RPM which is the killer. That is why three
of them back to back are used in Tracy's PSRU to take the helical
gear thrust only. Each needle is going one third engine RPM.
In the case of Tracy's PSRU all prop thrust both pusher and tractor
is taken by the large ball bearing just behind the prop flange
shown in these pictures.
------------------------------------------
BTW note that the tooth force calculated above is 2,100 pounds and assumes
there
is only one mating gear. With a planetary you have six mating
gears so the tooth force is only 350 pounds per tooth.
The helical gear thrust force on the bearing is the same.
It would be interesting to lock the planet carrier and the ring
gear together and see how much static torque the Ford planet
set will really take. I have a four pinion set I will donate
to a person in a position to try this.
Paul Lamar ...No rotor no motor.
Paul,
Wouldn't the thrust loads between the sun gear and planet gears/ housing be
equal and opposite, with some ( if not half) of the thrust going to the prop
shaft bearings.
George ( down under)
Yes in the Tracy tractor they would add to the prop thrust bearing
loads. In the Tracy pusher they would add or subtract from the prop
trust loads on the prop thrust bearing depending on which was greater.
There is only one large (3.35" OD ~ 1.6 ID) ball bearing that takes prop thrust.
In the Ross 2.17 there are two needle thrust bearings. One ahead
of the ring gear bulkhead and one behind it. In a tractor the
loads would add to the front prop thrust bearing. The back prop thrust
bearings would see the helical gear loads. In a pusher the
loads would add to the back prop thrust bearing. If the helical
loads exceeded the thrust loads the remaining loads would go into
the front prop thrust bearing.
In the Ross 2.85 tractor there is only one needle thrust bearing.
The one ahead of the planet carrier. In the Ross 2.85 tractor
the helical gear loads would again add to
the prop thrust bearing as the ring gear is fixed.
In the Ross 2.85 pusher there is only one prop thrust bearing ahead
of the planet carrier as mentioned. The helical gear thrust
bearings will take both prop thrust and helical gear thrust. If the
helical loads exceeded the thrust loads the remaining loads would go into
the front needle thrust bearing.
BTW The use of that large front ball bearing pays a price in
PSRU weight. As I recall it weighs well over a pound while
needle bearings used in the Ross are ounces.
I am going to try a light weight thin section non metallic plain
bearing called Rulon and feed it with high pressure oil. Best of both
worlds if it works. At low start up speeds it is low wear and low friction.
Once the oil pressure comes up it works like a metallic plain bearing
found in all engines with even lower friction losses and the oil can
cool it.
Paul Lamar ...No rotor no motor.
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