So you are correct that friction is used in tranferring torque in
wooden props. They also use counterbored drive bushings to transfer
the torque. I'd be willing to bet that the bushings transfer most of
it, but that is only a guess.

Thanks.
--
Jim in NC

I spent some time talking today at lunch with some friends who are
structural engineers, about this issue of friction delivering torque
to the prop. They said that if the strength of the attachment of the
prop to the flange had been determined through experience, then
eliminating the friction load path for the engine torque to be
tranmitted to the prop could result in failure of the junction of the
flange and prop, but that it wasn't likely.

I'll bet that you structural engineer friends are not experienced with wood
props, and their failure modes. It seems to be their own unique circumstance.
It has been found that the props fail, not the bolts.
--
Jim in NC