10.1.3 Precession

The tilting or turning of the gyro axis as a result of applied forces. When a deflective force is applied to the rim of a stationary gyro rotor the rotor moves in the direction of the force. However when the rotor is spinning, the same force causes the rotor to move in a different direction, as though the force had been applied to a point 900 around the rim in the direction of rotation.

A gyro will resist any force that attempts to change the direction of its spin axis. However, it will move (precess) in response to such force; NOT in the direction of the applied force, but at right angles to it, as illustrated below. The figure shows the application of a force which gives rise to a couple about the torque axis. The resulting turning movement about the axis of precession causes the rotor to move to a new plane of rotation, as the spin axis attempts to align itself with the axis about which the torque is applied.

These rules apply to all spinning gyros:

1. A gyro rotor will always precess about an axis at right angles to both the torque axis and the spin axis.
2. A gyro rotor always precesses in a direction so as to align itself in the same direction as the axis about which the torque is applied.
3. Only those forces tending to rotate the gyro rotor itself will cause precession.
4. Precession continues while torque is applied and remains constant under constant torque.
5. Precession ceases when the torque is removed or when the spin axis is in line with the torque axis (the axis about which the force is applied).