What does the angle of incidence refer to?

The angle of incidence is defined as the angle between the longitudinal axis of the aircraft and the wing's chord line, which is the imaginary line from the leading edge to the trailing edge of the wing. This angle is a critical factor in determining how the wing interacts with the airflow during flight, influencing lift and overall aerodynamic performance.

Setting the angle of incidence affects the entire flight characteristics of the aircraft. A fixed angle of incidence is designed into the aircraft's structure, which helps to optimize lift and drag at various speeds and conditions. The relationship of the wing to the fuselage at this angle is crucial for stability and control during flight.

In contrast, the other options refer to different aspects of flight. The angle of attack is a separate measurement that describes the angle between the wing's chord line and the oncoming air. The angle formed by the fuselage and vertical stabilizers involves directional stability but is not directly related to the wing's performance. The angle of descent pertains to landing procedures, which is unrelated to the fixed aerodynamic configuration of the aircraft. Thus, the choice regarding the angle between the longitudinal axis and the wing’s chord is the most appropriate definition of angle of incidence.