Paul,

What is the ID and length of that plain bearing?

Without the rest of the Lycoming crank bearings is that one bearing enough to handle the "rocking" of the shaft caused by prop gyro loads?


Ken Bauman


Yes I think so as the crankshaft is not very stiff in bending due
to the jogging back and fourth for the rod journals. IMHO that is
why Lycoming made the front main so long.  Also the planet gears
being captured in the ring gear adds stiffness. The gyro loads
are momentary by nature. How many times do you stall the airplane at 60
degrees per second? Maybe in a spin at one turn in six seconds. Or ten
turns per minute. What is the spin rate of your aircraft?

I am not sure on the length. I would guess around ten inches.
The diameter as I recall is around 2.3 inches. Ron might know.

At 60 degrees per second yaw or pitch rate the rocking load is 650
foot pounds with a CS metal prop. If it were one foot long that is
330 pounds on the front and and 330 pounds on the rear. Nothing for
a 2.3 inch diameter plain bearing. Plain main bearings usually absorb
thousands of pounds of force. In line piston engines and V piston engines
are trying to jam the crankshaft out the bottom of the block continually.
That is why they use steel four bolt main bearing caps or steel
crankshaft girdles.

A copper-lead with a tin or silver overlay plain bearing shell will
handle 3,000 to 4,000 psi. Also in the case of the rotary 100 psi
oil pressure is typical as opposed to 40 psi in the Lycoming. That
should also help. That is not to say that is the hydrodynamic oil pressure
inside the bearing. That can be thousands of psi due to a pumping or flying
effect. For more info goto:

http://www.hexagon.de/lg2_e.htm


BTW I notice the Allison planet carrier has only four planets.
A new planet carrier can be machined up to accept six Allison planets
for a 50% further increase in torque capacity. Here is such
a planet carrier machined by one of our subscribers (John Moran)
long ago before the Ford six planet unit was available.

Paul Lamar ...No rotor no motor.

What prop RPM are you using for your gyroscopic load calcs?

Ken Bauman

The calcs came from the Sky Ranch Engineering Manual page 436 437.
1500 RPM and five foot diameter 20 pound blade.

Paul Lamar ...No rotor no motor.

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