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3.7.  GYROSCOPIC PRECESSION

The result of applying force against a rotating body occurs 90° in the direction of rotation from where the force is applied. This effect is called gyroscopic precession and it is illustrated in figure 3.5. For example, if a downward force is applied at 9 o'clock, as in the figure, the result appears at 6 o'clock as shown. This will make the 12 o'clock position in the figure tilt up an equal amount in the opposite direction.

Figure 3.5. Gyroscopic Precession.

Figure 3.6 illustrates the offset control linkage needed in a helicopter to enable the pilot to tilt the main rotor disc in the direction he wants to go. If such linkage were not used the pilot would have to move the cyclic stick 90° out of phase or to the right of the direction desired. The offset control linkage is attached to a lever extending 90° in the direction of rotation from the main rotor blade.

Figure 3.6. Offset Control Linkage.

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