Which control surfaces cause the aircraft to move about the longitudinal axis?

The ailerons are the control surfaces responsible for causing the aircraft to roll about the longitudinal axis. The longitudinal axis runs from the nose of the aircraft to the tail, and rolling is the motion that occurs around this axis. Ailerons are typically located on the outer trailing edges of the wings and operate by changing the lift produced by each wing. When one aileron is deflected upward, the lift on that wing decreases, causing it to drop, while the opposite aileron is deflected downward, increasing the lift on that wing and causing it to rise. This differential lift results in a rolling motion, which allows the pilot to control the aircraft's orientation in flight.

In contrast, the elevators control motion about the lateral axis, the rudder affects movement around the vertical axis, and flaps are primarily used to increase lift during takeoff and landing rather than directly influencing roll.