Which part of the empennage controls yaw about the vertical axis?

The rudder is the part of the empennage specifically designed to control yaw about the vertical axis. Yaw refers to the left or right movement of the aircraft's nose. The rudder is situated on the vertical stabilizer (tail fin) of the aircraft, and when the pilot applies rudder input through the rudder pedals, it creates a differential in aerodynamic forces on either side of the aircraft's tail. This action yawns the aircraft in the desired direction, allowing the pilot to maintain coordinated flight or make turns.

Understanding the role of the rudder is critical for effective aircraft control and handling, particularly in situations where aileron input alone may not be sufficient to maintain the desired flight path.