A tailwheel airplane with a clockwise-rotating propeller (as viewed from the cockpit) is accelerating during the takeoff roll. As the pilot raises the tail to a level attitude, gyroscopic precession causes a yawing tendency. Which best describes this effect?
- AThe airplane yaws left solely due to increased torque reaction from higher engine power
- BThe airplane yaws right, because a force applied to the top of the propeller disc is felt 90° later at the bottom
- CThe airplane yaws right because P-factor becomes the dominant force at this pitch attitude
- DThe airplane yaws left, because a force applied to the top of the propeller disc is felt 90° later at the right side of the disc, in the direction of rotation
Show answer & explanationAnswer & explanation
Correct answer: D. The airplane yaws left, because a force applied to the top of the propeller disc is felt 90° later at the right side of the disc, in the direction of rotation
Gyroscopic precession causes an applied force on a rotating body to be felt 90° later in the direction of rotation. Raising the tail applies a forward-pitching force to the top of the propeller disc; for a clockwise-rotating prop (viewed from the cockpit), this force is felt 90° later at the right side of the disc, yawing the nose to the left.
Why the other options are wrong
- A. Torque reaction is a separate left-turning tendency caused by Newton's third law reaction to propeller rotation, not precession.
- B. Precession displaces the force 90° in the direction of rotation, not 180° to the bottom.
- C. P-factor results from asymmetric propeller blade AOA at high pitch attitudes and is not the cause of this specific tail-raising yaw.
Gyroscopic Precession
A property of rotating bodies where an applied force results in a deflection felt 90° later in the direction of rotation; on takeoff, raising the tail causes a left-yawing tendency in airplanes with clockwise-rotating propellers.
- One of the four left-turning tendencies
- Force applied 90° ahead in direction of rotation is where the effect appears
- Most noticeable in tailwheel airplanes when raising/lowering the tail
Memory trick: Push the top, feel it 90° later at the side — precession slides the force around