Dave Arbogast wrote:

        I had an idea concerning your hollow prop shaft PSRU. The

idea of welding

 pinion shafts onto the hollow prop shaft has always bothered me. In

fact,

I know of aircraft manufacturers that would never allow a part with

the

kinds of stresses on a prop shaft to be held together with a weld.

Still

yet I liked the idea. I think I found a solution that would not only
eliminate the weld but also make it much simpler to mass-produce.
Unfortunately it would make it heavier, but not that much. Instead

of

 welding pinion shafts to the prop shaft simply thicken the walls,

then

drill out and tap holes in the end of the thicker walls in the ends

and

use bolts to hold the planet gears on one end and the prop flange

and

prop on the other. I think this would increase the reliability,

cause

fewer problems with the prop shaft becoming imbalanced, and mass

production

much simpler. It would be slightly heavier due to the increased

metal

in between where the pinion shafts were on your original design.
This way it could be made very easily with a lathe, drill press,
and tap, and eliminate welding.
        Just an idea, Tell me what you think.

Thanks,
Mark

When I did die design, we would solve this problem with an interference

fit of

several thousands of an inch. You'd have a small radius on the outside

of the

shaft. You'd freeze the shaft with a CO2 extinguisher, bake the gear to

500 F in

an oven (not hot enough to distort it) and press them together. You
need to do the calculations on how much the IO & OD change with the temp

delta...

Once together, it may as well be a weld, w/o the stress & metal crystal

changes.

Thoughts?

Yep! feed- back to me is that the weld is the weak link.
My suggestion would be pressure injection casting.

I'm unsure if the above mentioned bolt-in method would be strong enough, I
somehow doubt it!!
George (down under)

We have an FEA and it indicates the bolts/pinion shafts would be plenty 
strong enough. Each of the six bolts/pinion shafts is about .4 inch in dia. 
With a conservative prop shaft torque of 800 foot pounds or 9600 inch pounds 
the shear load on each bolt would be about 948 pounds. The bolt/shaft circle
diameter on the six pinion planet carrier is about 3 3/8 inch in diameter.
A .4 inch dia. bolt/shaft has an area of .126 square inches so the shear stress 
is about 7,500 psi. Well below the max stress on a 100K psi grade eight bolt.
Check my math.

Paul Lamar
 
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