Aircraft Principal Axes

Since aircraft live in a three-dimensional world, it is necessary to control the attitude or orientation of a flying aircraft in all three dimensions. In-flight, any aircraft will rotate about its center of gravity, a point which is the average location of the mass of the aircraft. We can define a three-dimensional coordinate system through the center of gravity with each axis of this coordinate system perpendicular to the other two axes. We can then define the orientation of the aircraft by the amount of rotation of the parts of the aircraft along these principal axes. The position of all three axes, with the right-hand rule for its rotations

The vertical axis (yaw)

• The yaw 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. The motion about this axis is called yaw. A positive yawing motion moves the nose of the aircraft to the right. The rudder is the primary control of yaw.

Transverse axis (pitch)

• The pitch axis : (also called transverse or lateral axis) has its origin at the center of gravity and is directed to the right, parallel to a line drawn from wingtip to wingtip. The motion about this axis is called pitch. A positive pitching motion raises the nose of the aircraft and lowers the tail. The elevators are the primary control of pitch.

Longitudinal axis (roll)

• The roll axis : (or longitudinal axis) has its origin at the center of gravity and is directed forward, parallel to the fuselage reference line. The motion about this axis is called roll. An angular displacement about this axis is called a bank. 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. The ailerons are the primary control of the bank. The rudder also has a secondary effect on the bank.

References :

• FAA (2004). Airplane Flying Handbook.
• https://www.grc.nasa.gov/

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