What is the angle between the chordline and the relative wind?

The angle between the chord line of an airfoil (such as a wing) and the relative wind is known as the angle of attack. This angle is crucial in aerodynamics as it directly affects the lift generated by the wing.

When the angle of attack increases, the airflow over the wing changes, which can either increase lift up to a certain point or lead to a stall if the angle becomes too steep. The angle of attack is fundamental for understanding the performance and handling characteristics of an aircraft.

In contrast, the aspect ratio refers to the wing's span in relation to its average chord length and primarily influences the aerodynamic efficiency and maneuverability of the aircraft. Pitch attitude describes the orientation of the aircraft's nose relative to the horizon and is not the angle of the chord line. True airspeed is the actual speed of the aircraft through the air, which also does not relate directly to the angle between the chord line and the relative wind. Therefore, the correct choice reflecting the specified angle is the angle of attack.