Why can the rotor of a helicopter take off? Is it its speed or something? Is its structure the same as that of electric fan blades? thank you

That thing in the helicopter is called the rotor. Its structure is different from that of an electric fan, but similar to that of an airplane wing. The upper side of the cross section is curved and the lower side is straight. The principle of generating lift is similar to that of fixed-wing aircraft. When this structure works, the air flowing up and down will generate upward pressure difference, so that the aircraft can get lift, except that the fixed-wing aircraft moves forward to make the air flow up and down along the wing surface, while the helicopter is realized by rotating the rotor. If the structure of electric fan is adopted, the helicopter can fly, but the advantages and disadvantages of that structure are that if the engine stops in the air, the helicopter will fall, at this time, the air resistance will make the rotor reverse, and it is almost impossible for the engine to ignite again, while the wing structure will not reverse due to resistance when falling, and at the same time, it can continue to provide some lift due to inertial rotation, which provides valuable time for the engine to ignite again.