RE: Speed props – a difficult task
Indeed. The outside layer is fabric to increase torsional stiffness.
I would think crank flex is a major issue at these speeds. Making it longer than it needs to be would probably mean that you have to make it a whole lot more massive.
As for reducing prop load: I usually work at making the airfoil near the tip thinner. I don't actually "clip" the prop down a whole lot. The more you reduce blade area, the more you reduce acceleration out of the turns. So my goal is to try to lighten the prop load while trying to keep the thrust up.