Unlike an aeroplane, helicopters have moving wings in the shape of spinning rotor blades. Air currents passing over the upper and lower surfaces of the spinning blades create low pressure above it and generate lift. So, a helicopter does not have to taxi on a runway to get the lift. The lift can be controlled by varying the pitch (angle) of the rotor blades. By increasing the pitch of the main rotor blades lift is increased and the craft climbs. Lowering the pitch of the blades reduces lift and gravity causes the helicopter to descend. Similarly, if the pilot holds the rotors pitch in such a way that the blades produce just enough lift to counteract gravity, the helicopter remains stationary in mid-air.