Are high-frequency flapping wings efficient and scalable at high Reynolds numbers?
Some English University researchers studied the tiny helicopter Black Hornet versus Colibri-wings as efficiency. It was shown that rotating wings have LESS LOSS as the flapping ones because the latter must surpass the inertia of the wings at each flap. The insect wings have little weight and so small inertia.  So high-frequency flapping is only for small devices. What is better in the animal wings is the aerodynamic itself> Search "leading-edge vortex" on Google. Why animals have no rotating wings? >there is no rotating device in animals, because they must be fully articulated, by design... Only maple-seeds have a sort of autogyro.