What is gyro precession?

• A. A gyroscopic effect where the axis moves opposite to the applied force.
• B. A gyroscopic effect where the axis moves in the direction of the applied force, leading to attitude errors.
• C. A failure mode of the magnetic compass.
• D. The process of aligning gyro after caging.

Answer: (B)

When a spinning gyroscope is subjected to a torque, it doesn’t simply tilt in the direction you push. Instead, it undergoes precession, a motion of the axis that follows the applied force and then settles into a new orientation. In aircraft instruments, this deflection can show up as the gyroscopic axis moving in the same general direction as the input, which over the short term translates into an attitude indication error if the pilot doesn’t account for it. The speed of that sideways deflection is proportional to the applied torque and inversely proportional to the wheel’s angular momentum, described by the relation of precession rate to torque and angular momentum.