Which control surface is primarily responsible for roll motion?

• A. Rudder
• B. Elevator/Stabilator
• C. Aileron
• D. Spoilers

Answer: (C)

Roll is rotation about the aircraft’s front-to-back axis, so you need surfaces that create a difference in lift between the two wings. The ailerons are designed for this. Located on the trailing edges of the wings, they move in opposite directions: one wing’s aileron goes down, the other goes up. The downward-deflected aileron increases lift on its wing while the upward-deflected one reduces lift on the opposite wing. That lift difference tilts the wings and causes the airplane to roll toward the lower wing, initiating a turn.

The rudder steers around the vertical axis (yaw), and the elevator or stabilator controls pitch (nose up or down), not roll. Spoilers can alter lift and assist roll in some designs or situations, but the primary surface for rolling motion in normal flight is the aileron.