Asymmetry of lift describes an aspect of the nature of aerodynamic lift generation along the length of an individual rotor blade of a helicopter. The phenomenon is most easily envisaged when a helicopter is hovering, that is, maintaining a fixed position above a fixed point, and with no wind in the atmosphere. Helicopter manufacturers try to reduce this differential effect (that is, aim for more equality of lift along the blade length). This has two main aspects: When the helicopter is travelling forwards with respect to the atmosphere, a further phenomenon comes into play, dissymmetry of lift.