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A change in pitch causes the aircraft to rotate around which axis?

  • A

    Lateral axis, which passes through the centre of pressure.

  • B

    Lateral axis, which passes through the centre of gravity.

  • C

    Longitudinal axis, which passes through the centre of gravity.

  • D

    Longitudinal axis, which passes through the centre of pressure.

Refer to figure.
When in flight, the aircraft is controlled about one point - The centre of gravity (CG). All three axes of rotation therefore pass through the CG: the lateral, longitudinal and normal (directional) axis. When aerodynamic forces are created using any controls, or from any stabilising forces, they create rotation about the CG.

  • The longitudinal axis runs forward - aft. The aircraft rolls about this axis. "longitudinal stability" refers to stability in pitch.
  • The lateral axis runs through the wingspan. The aircraft pitches about this axis. “lateral stability” refers to stability in roll.
  • The normal (directional) axis is perpendicular to the plane made by the other two axes. The aircraft yaws about this axis, and directional stability refers to stability in yaw. 

When changing the pitch angle, the aeroplane rotates around the lateral axis which passes through the CG.

The Centre of Pressure (CP) is the point through which aerodynamic force (lift and drag) seems to act. The CP is usually behind the CG.

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