Aircraft principal axes

An <a href="/facts/Aircraft/EhC4mBep">aircraft</a> in flight is free to rotate in three dimensions: <a href="/facts/Yaw_(rotation)/6u8PKjRW">yaw</a>, nose left or right about an axis running up and down; pitch, nose up or down about an axis running from wing to wing; and roll, rotation about an axis running from nose to tail. The axes are alternatively designated as vertical, lateral (or transverse), and longitudinal respectively. These axes <a href="/facts/Moving_frame/3jNPLngL">move with the vehicle</a> and rotate relative to the Earth along with the craft. These definitions were analogously applied to <a href="/facts/Spacecraft/YQqQaUw0">spacecraft</a> when the first crewed spacecraft were designed in the late 1950s.
These rotations are produced by <a href="/facts/Torque/KcrcvNtV">torques</a> (or <a href="/facts/Moment_(physics)/WvgxtdhP">moments</a>) about the principal axes. On an aircraft, these are intentionally produced by means of moving control surfaces, which vary the distribution of the net <a href="/facts/Aerodynamics/Cn6Lnl3H">aerodynamic</a> force about the vehicle's <a href="/facts/Center_of_gravity/n4Lr9GAz">center of gravity</a>. <a href="/facts/Elevator_(aeronautics)/LPMxWDXk">Elevators</a> (moving flaps on the horizontal tail) produce pitch, a <a href="/facts/Rudder/w675HJUP">rudder</a> on the vertical tail produces yaw, and <a href="/facts/Aileron/700JRzbo">ailerons</a> (flaps on the wings that move in opposing directions) produce roll. On a spacecraft, the movements are usually produced by a <a href="/facts/Reaction_control_system/YfqBrd7h">reaction control system</a> consisting of small rocket thrusters used to apply asymmetrical thrust on the vehicle.

Aircraft principal axes open-in-new

Aircraft principal axes