Don Dunbar wrote:

Hi Paul and group,
Attached the Velvet drive drawing, This can be found at www.marinegears.com/index.html

The bearing spread does look marginal for an aircraft Don.
As much as 600 ft pounds due to prop gyro torque can be applied
to the output flange of an aircraft PSRU.

A boat PSRU never sees anything like that much torque.

What is the distance between those output shaft bearings?

Paul Lamar

I'm not an engineer & I didn't stay at a Holiday Inn last
night. But marine abuse has always seemed much more severe
than the a/c environment. What's the bending load on the
output shaft when 480hp worth of torque drives the tips of a
20" (or bigger?) prop into the surface of the water after
the boat hull & prop get airborne? Also, some racing boats
run continuously with only 1/2 the prop in the water.

Wouldn't these bending loads approach the gyro loads of a
prop?

Charlie England

Those are torque loads Charlie. Bending loads are what happens when
you set the prop vertical and grab the bottom and top blades.
Pull out on the bottom and push in at the top blade. This is the
kind of forces you get on a spinning gyroscope. Same thing happens
on a prop. Worst case scenario is stalling the airplane at full
power. The nose can drop 60 degrees in one second. Aerobatics
engines have a lot of trouble with this. That is why the last
part of an aircraft engine crankshaft is so long and straight.

Paul Lamar

Let me try again. The a/c gyro loads occur because the prop
tries to stay in the same plane while the shaft axis
changes.

The boat shaft axis stays more or less the same while the
assymetric load on the prop (from driving against the water
on only one side of the shaft axis) tries to change the
plane of the prop. Gyro forces counteract some of this, but
it seems that the assymetric loads on the shaft would still
be pretty brutal.

Remember, I'm not talking about torque load, but the pushing
action of each prop blade against the water parallel to but
offset from the shaft axis.

ce

These boxes are not used without out some sort of shaft
bearing down near the prop.

Paul Lamar
 
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