What does the angle of incidence refer to?

The angle of incidence specifically refers to the angle that the wing's chord line makes with the aircraft's longitudinal axis. This angle is critical because it directly influences the aerodynamic properties of the wing and the overall performance of the aircraft.

When the wing is set at a particular angle of incidence, it determines how the airflow interacts with the wing during flight. A properly configured angle of incidence allows for optimal lift generation while minimizing drag. This angle is typically fixed on a wing design, as it plays a fundamental role in the aircraft's stability and control characteristics in various flight conditions. Effective management of this angle is essential for ensuring that the aircraft can maintain level flight, ascend, or descend safely and efficiently.

Other options do not accurately describe the angle of incidence. The angle between the wing and the vertical, the angle of the aircraft to the ground, and the angle in level flight refer to different aerodynamic aspects or attitudes of an aircraft, but they do not define the specific relationship that the angle of incidence represents.