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Longitudinal stability refers to the movement about the…

  • A

    Longitudinal axis.

  • B

    Axis of rotation.

  • C

    Lateral axis.

  • D

    Vertical axis.

Refer to figure.
The longitudinal, lateral and directional stability of a helicopter is dependent on Centre of Gravity (CG) position and the distance of the horizontal and vertical stabiliser from the CG. The CG position also affects the flight characteristics of pitching, rolling and yawing about the longitudinal, lateral and vertical axis. If the CG is aft, the shorter distance between the CG and tail rotor decreases the effectiveness of yaw input.

The helicopter axes are the following:

  • The fore/aft axis is called the Longitudinal axis. Stability about this axis is called Lateral Stability. Movement around the longitidinal axis is called rolling.
  • The side to side axis is called Lateral axis. Stability about this axis is called Longitudinal Stability. Movement around the lateral axis is called pitching.
  • The axis which runs vertically through the helicopter is called Vertical or Normal axis. Stability about this axis is called Directional Stability. Movement around the normal axis is called yawing.

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