In aeronautics, the roll moment is the product of an aerodynamic force and the distance between where it is applied and the aircraft's center of mass that tends to cause the aircraft to rotate about its roll axis. The roll axis is usually defined as the longitudinal axis, which runs from the nose to the tail of the aircraft. A roll moment can be the result of wind gusts, control surfaces such as ailerons, or simply by flying at an angle of sideslip. See flight dynamics.