Aircraft principal axes

This article is about yaw, pitch, and roll as symmetry axes of an aircraft. For meaning in mechanics, seeMoment of inertia § Principal axes.For Euler angles with the same names, seeEuler angles § Tait–Bryan angles.For aircraft design coordinates, seeLofting coordinates.

Anaircraftin 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), andlongitudinalrespectively. These axesmove with the vehicleand rotate relative to the Earth along with the craft. These definitions were analogously applied tospacecraftwhen the first crewed spacecraft were designed in the late 1950s.

The position of all three axes, with theright-hand rulefor describing the angle of its rotations

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 netaerodynamicforce about the vehicle'scenter of gravity.Elevators(moving flaps on the horizontal tail) produce pitch, arudderon 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 systemconsisting of small rocket thrusters used to apply asymmetrical thrust on the vehicle.

Principal axes

See also:Ship motions

• 
  Yaw
• 
  Pitch
• 
  Roll

• Normal axis,or yaw axis — an axis drawn from top to bottom, and perpendicular to the other two axes, parallel to thefuselage or frame station.
• Transverse axis,lateral 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 thebuttock line.
• 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, similar to a ship'swaterline.

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 possibilitiesto do it.

Vertical axis (yaw)

Theyaw axishas its origin at the center of gravity and is directed towards the bottom of the aircraft,perpendicularto 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.Therudderis the primary control of yaw.

The termyawwas originally applied in sailing, and referred to the motion of an unsteady ship rotating about its vertical axis. Itsetymologyis uncertain.

Lateral axis (pitch)

Thepitch axis(also calledtransverseorlateral axis),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). Theelevatorsare the primary control surfaces for pitch.

Longitudinal axis (roll)

Theroll axis(orlongitudinal axis) 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.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.Theaileronsare the primary control of bank. The rudder also has a secondary effect on bank.

Reference planes

The principal axes of rotation imply threereference planes,each perpendicular to an axis:

• Normal plane, or yaw plane
• Transverse plane, lateral plane, or pitch plane
• Longitudinal plane, or roll plane

The three planes define the aircraft'scenter of gravity.

Relationship with other systems of axes

Yaw/heading, pitch and rollanglesand associated vertical (down), transverse and longitudinal axes

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.

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.

History

The first aircraft to demonstrate active control about all three axes was theWright brothers'1902 glider.

See also

• Aerodynamics
• Aircraft flight control system
• Euler angles
• Fixed-wing aircraft
• Flight control surfaces
• Flight dynamics
• Moving frame
• Panning (camera)
• Six degrees of freedom
• Screw theory
• Triad method

External links

• Pitch, Roll, Yaw
• Yaw Axis Control as a Means of Improving V/STOL Aircraft Performance.
• 3D fast walking simulation of biped robot by yaw axis moment compensation
• Flight control system for a hybrid aircraft in the yaw axis
• Motion Imagery Standards Board (MISB)Archived2022-08-23 at theWayback Machine