If the vertical fin of a single-engine, propeller-driven airplane is rigged properly, it will generally be parallel to?

When the vertical fin of a single-engine, propeller-driven airplane is rigged properly, it is oriented to be parallel to the vertical axis of the aircraft. The vertical fin is designed to provide stability and control around the vertical axis, which is the axis that runs vertically through the aircraft from top to bottom. Ensuring that the vertical fin is parallel to this axis helps maintain directional stability and effective yaw control, which is particularly important in ensuring the airplane tracks straight during flight and does not experience excessive yawing tendencies.

In contrast, the longitudinal axis runs from the nose to the tail of the airplane, the lateral axis runs from wingtip to wingtip, and the thrust line pertains to the angle and direction of thrust produced by the propeller. While these aspects are critical in overall aircraft design and performance, the alignment of the vertical fin is specifically concerned with the vertical axis for optimum stability and control during flight. This makes parallel alignment to the vertical axis the correct and crucial aspect of proper rigging for the vertical fin.