From alanbernstein's link...
Quote:
Schempp refers to the propeller as being "noise optimized" and you can see that the blades are free to flap (forward) like helicopter blades (which flap up) so that the asymmetric thrust axis from having the propeller disc offset from the rotational axis doesn't place bending loads on the hub.
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What? Helicopter blades
do not flap up, it couldn't fly if they did. The blades are flexible so the tips will droop at slow rotational speed, and bend under heavy load, however they're firmly attached to the pitch control at the hub which acting like a brassiere will stopemfromflapen.
Of course you can eliminate blade questions by going jet.