<P> These rotations are produced by torques (or moments) about the principal axes . On an aircraft, these are intentionally produced by means of moving control surfaces, which vary the distribution of the net aerodynamic force about the vehicle's center of mass . Elevators (moving flaps on the horizontal tail) produce pitch, a rudder on the vertical tail produces yaw, and ailerons (flaps on the wings that move in opposing directions) produce roll . On a spacecraft, the moments are usually produced by a reaction control system consisting of small rocket thrusters used to apply asymmetrical thrust on the vehicle . </P> <Ul> <Li> Normal axis, or yaw axis--an axis drawn from top to bottom, and perpendicular to the other two axes . Parallel to the fuselage station . </Li> <Li> Lateral axis, transverse axis, or pitch axis--an axis running from the pilot's left to right in piloted aircraft, and parallel to the wings of a winged aircraft . Parallel to the buttock line . </Li> <Li> Longitudinal axis, or roll axis--an axis drawn through the body of the vehicle from tail to nose in the normal direction of flight, or the direction the pilot faces . Parallel to the waterline . </Li> </Ul> <Li> Normal axis, or yaw axis--an axis drawn from top to bottom, and perpendicular to the other two axes . Parallel to the fuselage station . </Li> <Li> Lateral axis, transverse axis, or pitch axis--an axis running from the pilot's left to right in piloted aircraft, and parallel to the wings of a winged aircraft . Parallel to the buttock line . </Li>

The movement of an aircraft about its normal axis is called