Peter wrote:
Doesn’t that assume that the uppermost layer of the wood of the propeller – a layer of wood of a miniscule thickness and comparable in thickness to any irregularities on the surface of whatever the prop is screwed against – has a sufficient shear strength to withstand not just the average torque but the peak torque pulses from the engine?If that was true, then gluing the prop to the flange with any glue that is stronger than the wood (e.g. epoxy) would be sufficient – in terms of mechanical strength.
The glue case is not comparable. By virtue of the compression of the wood due to the crush plate (the clue is in the name), it is not simply the “miniscule thickness” of the wood that is being mobilized in shear. I would say LeSving is correct. If installed correctly with the correct amount of tension in the bolts, the lugs should not be subject to any shear loading….they are there as a safety precaution. IMO…
A picture of the back of the old crush plate:
