What is defined as the angle of attack of an aerofoil?

The correct answer is defined as the angle between the chord line of an aerofoil and the relative airflow. This is a fundamental concept in aerodynamics, critical for understanding how lift is generated by an aerofoil or wing.

The angle of attack is a key parameter because it directly affects the airflow around the aerofoil. When the angle of attack increases, up to a certain point, the lift produced by the aerofoil increases due to the change in airflow over its surface. Understanding this relationship is vital for pilots and engineers alike as it influences the aircraft's performance, stability, and control.

While other choices touch on related concepts, they do not accurately define the angle of attack. The angle between the wing and the horizon refers to the aircraft's pitch attitude rather than the aerodynamic properties of the wing itself. The maximum angle at which an aircraft can stall is more related to the limits of angle of attack rather than the definition itself. Finally, the angle between the aircraft and the ground describes terrain or reference positioning, which is not pertinent to the aerodynamic characteristics of the wing or aerofoil.