The aerodynamic effect where a force applied to a rotating body results in a response 90 degrees ahead in the direction of rotation is called:

• A. Torque reaction
• B. Spiral slipstream
• C. P-factor
• D. Gyroscopic precession

Answer: (D)

Gyroscopic precession is the effect where a spinning rotor responds to a torque by moving its axis in a direction that is at right angles to both the spin axis and the applied torque, effectively advancing in the direction of rotation by 90 degrees. When a force tries to tilt a spinning object, the change in its angular momentum causes the reaction to occur perpendicular to the original torque, producing a precession motion about a different axis. In aviation, this means a spinning propeller or gyroscope will exhibit a motion that appears to “precess” in the sense that the response comes about in a direction 90 degrees ahead of the applied force, following the rotation sense of the rotor. The other terms describe different phenomena: torque reaction is simply the equal and opposite torque, spiral slipstream is the helical flow behind a propeller, and P-factor is the asymmetric thrust due to differing blade angles of attack.