Which primary flight control surface controls movement about the vertical axis?

• A. Aileron
• B. Flap
• C. Rudder
• D. Elevator

Answer: (C)

Movement about the vertical axis is yaw, and the surface that controls that motion is the rudder. The rudder, located on the trailing edge of the vertical stabilizer at the tail, deflects left or right. This deflection creates a side force on the vertical stabilizer, producing a yawing moment that turns the nose of the aircraft in the desired direction. This is essential for coordinating turns and counteracting crosswinds.

The other primary flight surfaces govern other axes: ailerons control roll about the longitudinal axis (banking the wings to tilt the aircraft), the elevator controls pitch about the lateral axis (raising or lowering the nose), and flaps primarily adjust lift and drag on takeoff and landing rather than controlling yaw.