What defines the longitudinal axis of an aircraft?

The longitudinal axis of an aircraft is defined as the axis that runs from the nose to the tail. This axis is essential for understanding how the aircraft navigates and maneuvers in three-dimensional space. Movement around this axis is referred to as roll, which is controlled by the aircraft's ailerons.

This axis plays a significant role in stability and control during flight, as it allows the aircraft to bank left or right in response to control inputs. Understanding the longitudinal axis is critical for pilots and aerospace engineers alike, as it directly relates to the aircraft's performance characteristics in flight.

The other options refer to different axes or specific parts of the aircraft: the wingtip-to-wingtip measurement describes the lateral axis, the vertical axis pertains to yaw and is associated with movements around a vertical centerline, and while the center of gravity is a critical point for balance, it does not itself define an axis but rather relates to the overall aerodynamics and stability of the aircraft.