When rigged properly, the vertical fin of a single-engine airplane will generally be parallel to which axis?

When the vertical fin of a single-engine airplane is rigged properly, it is designed to be parallel to the vertical axis of the aircraft. The vertical axis is an imaginary line that runs vertically through the center of the aircraft, allowing the airplane to define its yaw motion, which is the rotation around this vertical axis. This alignment ensures that the fin can effectively provide directional stability and control, allowing the aircraft to maintain straight flight and respond appropriately to control inputs from the rudder.

In this context, if the vertical fin is misaligned with the vertical axis, the aircraft may experience issues with directional control, leading to difficulty in maintaining a straight flight path or creating unwanted yaw movements. Therefore, proper rigging of the vertical fin is essential for optimal performance and safety in flight operations.