It is customary to treat the rotor as if it had an infinite number of blades which form a disc. This imaginary rotor disk, lies in the plane of the blades with the radius equal to the length of the blades. The thrust that the rotor produces is always perpendicular to the rotor disc plane. When the helicopter is in axial flight, that is flying up, down or hovering, the lift of the
rotor is symmetrical around the rotor’s axis.