[Jaydee]

The main reason a helicopter blade can't be curved is they first require a coning angle. Second the centrifugal force of the heavy blade means it's trying to straighten out, so a curved blade would put to much stress on the blade. You can't lift a helicopter by the blades if they were stationary, you can then imaging the force of them straightening out to be able to support a helicopter.
I tried several fans, 2 davie craig fans drew around 18 amps and the air flow was half of a single genuine commodore drum type electric fan drawing around 10 amps in a shroud, and quieter. Having the blades staggered makes it quieter also. The circular type fan roar because the blade width is so narrow, and have to many blades.
JD