Finn Lassen wrote:

Are you saying that a prop traveling through relatively soft air is
a bigger load than
a 2 ton car directly connected to the output shaft of the gearbox?

Finn

Finn,
 The short answer is YES. Of course it's not that simple. I would suggest
you check out the following web site for an explanation by persons far
more knowledgeable than myself as to some of the problems propellers
cause.
http://www.prime-mover.org/Engines/Torsional/index.html
Charlie Kuss
RV-8 wings

Looks like Charlie Kuss gets the credit for this and no Jim West.
Sorry Charlie.

Here is a little excerpt from the article that should open a few eyes.
Sorry I did not see this sooner.

Paul Lamar

http://www.prime-mover.org/Engines/Torsional/sport_av92/sport_av92.html

"The propeller's mass moment of inertia, a function of weight and diameter,can be
approximated by the following equation
(for a two-blade prop): 
                                    lo = .66667(m)(1)2

where "m" is the propeller's mass (weight divided by 32.17) and "l" is the length of
the blade from the output shaft's
centerline to the tip of the blade (propeller's radius). 

Substituting all the appropriate values we get an applied moment of over 11,000
ft.-lbs. to the end of that gearbox. If the
output shaft supports are about six inches apart, this moment translates to a radial
bearing load of over 22,000 pounds! 

Granted, this is momentary and a worst case condition, but in the life of an aircraft
loads of similar magnitude will occur quite
often due to turbulence or control input (the latter is especially true if flying
acrobatic maneuvers). The condition is critical in
selection of the bearings and design of the case, especially if the latter is
fabricated from an aluminum casting (very low
endurance limit - on the order of 4,000 psi for rough orgrooved material)."

That is one heck of a bending load on the shaft!!!!!! PL

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