Vance Jaqua wrote:

Bunch of snips.................

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

I vigorously dispute Mr Husa's numbers - I have cross
checked the expression for precession forces with a
couple of machine design texts and come up with a much
lower value. The expression for the force - if you
rigidly resist movement in the direction of the force
is: moment(ft lbs)= mass X radius of gyration squared
X  rotation in radians per second X displacement from
axial direction in radians per second
The radius of gyration of an ellipse is 1/4 the major
dim (6 ft/ 4 = 1.5ft) and a propeller has mass much
more centered than an ellipse. using those numbers
with
his heavy prop and excessive pitch rate 0f 360 deg/sec
(6.28 radians/sec) the numbers compute to 4148 ft lbs.
Still a big number but much less than "over 11,000 ft
lbs", and if you got pitched at that rate you are
riding in a broken airplane anyway, and it certainly
did not resist the resulting yaw. I think 1 radian per
second is a more realistic maximum. I do not know
where his "Mass moment of inertia" came from, all
references seemed to use "radius of gyration" and
suggested that the derivation was the square root of
(the moment of inertia divided by the area).- Vance

 
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