Fan wings, also called blades, are slightly curved in shape, they are not straight. The possible reason behind why are fan wings slightly curved is the proper air circulation.
Scientific Explanation behind why are fan wings slightly curved ?
Fan blades are curved for optimum air circulation which is determined by solidity ratio. Solidity ratio is the ratio of area of the blades to the area of the disc swept by them. well if the blades are flat, it will provide air circulation no doubt but the volumetric flow rate will be less compared to blade which is suitably curved based on aerodynamic principles.
In layman words, if the blades of the fan are not curved then they will not be able to produce a good amount of air as compared to the curved blades fan.