Anaircraft in flight is free to rotate in three dimensions:yaw, nose left or right about an axis running up and down;pitch, nose up or down about an axis running from wing to wing; androll, rotation about an axis running from nose to tail. The axes are alternatively designated asvertical,lateral (ortransverse), andlongitudinal respectively. These axesmove with the vehicle and rotate relative to the Earth along with the craft. These definitions were analogously applied tospacecraft when the first crewed spacecraft were designed in the late 1950s.
These rotations are produced bytorques (ormoments) about the principal axes. On an aircraft, these are intentionally produced by means of moving control surfaces, which vary the distribution of the netaerodynamic force about the vehicle'scenter of gravity.Elevators (moving flaps on the horizontal tail) produce pitch, arudder on the vertical tail produces yaw, andailerons (flaps on the wings that move in opposing directions) produce roll. On a spacecraft, the movements are usually produced by areaction control system consisting of small rocket thrusters used to apply asymmetrical thrust on the vehicle.
Normally, these axes are represented by the letters X, Y and Z in order to compare them with some reference frame, usually named x, y, z. Normally, this is made in such a way that the X is used for the longitudinal axis, but there areother possibilities to do it.
Theyaw axis has its origin at the center of gravity and is directed towards the bottom of the aircraft,perpendicular to the wings and to the fuselage reference line. Motion about this axis is calledyaw. A positive yawing motion moves the nose of the aircraft to the right.[1][2] Therudder is the primary control of yaw.[3]
The termyaw was originally applied in sailing, and referred to the motion of an unsteady ship rotating about its vertical axis. Itsetymology is uncertain.[4]
Thepitch axis (also calledtransverse orlateral axis)[5] passes through an aircraft from wingtip to wingtip. Rotation about this axis is calledpitch. Pitch changes the vertical direction that the aircraft's nose is pointing (a positive pitching motion raises the nose of the aircraft and lowers the tail). Theelevators are the primary control surfaces for pitch.[3]
Theroll axis (orlongitudinal axis[5]) has its origin at the center of gravity and is directed forward, parallel to the fuselage reference line. Motion about this axis is calledroll. An angular displacement about this axis is calledbank.[3] A positive rolling motion lifts the left wing and lowers the right wing. The pilot rolls by increasing the lift on one wing and decreasing it on the other. This changes the bank angle.[6] Theailerons are the primary control of roll. The rudder also has a secondary effect on roll.[7]
These axes are related to theprincipal axes of inertia, but are not the same. They are geometrical symmetry axes, regardless of the mass distribution of the aircraft.[citation needed]
In aeronautical and aerospace engineering intrinsic rotations around these axes are often calledEuler angles, but this conflicts with existing usage elsewhere. The calculus behind them is similar to theFrenet–Serret formulas. Performing a rotation in an intrinsic reference frame is equivalent to right-multiplying its characteristic matrix (the matrix that has the vectors of the reference frame as columns) by the matrix of the rotation.[citation needed]
The first aircraft to demonstrate active control about all three axes was theWright brothers'1902 glider.[8]