Which control surface is used to control an airplane directionally about its vertical axis?

The rudder is the control surface responsible for managing an airplane's directional control about its vertical axis. When the pilot moves the rudder pedals, the rudder deflects left or right, allowing the aircraft to yaw in that direction. This is especially important for maintaining coordinated flight and making turns effectively.

While ailerons primarily control roll about the longitudinal axis and elevators adjust pitch about the lateral axis, the rudder specifically influences yaw. Flaps, on the other hand, are used mainly to increase lift during takeoff and landing and do not play a role in directional control about the vertical axis. Understanding the functions of these control surfaces is crucial for effective aircraft operation and is fundamental knowledge for pilots.