Define gyroscopic precession

• A. Occurs when precession is caused by gravity
• B. Occurs in rotating blades that manifest an applied force 90 degrees after application in the direction of rotation
• C. Rotation causes blade flapping
• D. The lag between pitch and RPM

Answer: (B)

Gyroscopic precession is the effect where a spinning rotor responds to an applied torque with a deflection that occurs 90 degrees away from the direction of the applied force, in the direction of rotation. When you push to change the blade pitch, the rotor’s angular momentum resists that change. The resulting change in angular momentum is perpendicular to both the spin axis and the applied torque, so the blade moves in the direction of rotation, but a quarter turn later. That 90-degree phase shift in the response is what we call gyroscopic precession.

This matches the description of the correct choice: the effect appears 90 degrees after the applied force, in the direction of rotation. The other ideas don’t describe this gyroscopic response: gravity isn’t the defining cause here, blade flapping is a different aerodynamic/inertial phenomenon, and a lag between pitch and RPM isn’t about gyroscopic precession.