Overheating?

[alffie]

"Curved" blades have more surface area and varied angle of attack from root to tip so therefore can move more air. The blades are shaped so as to not have the blade tip reach the speed of sound.

[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