Helicopters and fans have blades, why can helicopters fly and fans can't?

The helicopter can fly up the most important is to rely on a pair of special profile shape of the wing, and the need for a strong power to dominate.

The wing profile is also known as the airfoil shape. A typical airfoil has a convex top and a flat bottom, and is often referred to as a streamlined shape. According to the continuity of the fluid and Bernoulli's theorem, relative to the air far in front of the air flow through the upper airfoil is squeezed, the speed of the flow velocity is accelerated and the pressure is reduced, and even the formation of suction (negative pressure) and the flow of the lower airfoil flow velocity is slowed down. Thus a pressure difference is formed between the upper and lower airfoils. This pressure difference is the aerodynamic force. According to the law of decomposition of force, it is decomposed into upward lift and backward drag along the direction of flight. The drag force is overcome by the thrust provided by the engine. The lift is just enough to overcome its own gravity and hold the airplane up into the air. This is the mystery of why airplanes fly.

Fan blades have a different structure and only push the airflow.