What is used to determine the angle of attack?

The angle of attack is determined by the relationship between the relative wind and the chord line of the wing. The chord line is an imaginary straight line drawn from the leading edge to the trailing edge of the wing, while the relative wind is the direction of the airflow relative to the wing as the aircraft moves through the air.

By measuring the angle between the chord line and the direction of the relative wind, pilots can understand how much lift is being generated by the wing at any given moment. This angle is crucial for controlling the aircraft, as a proper angle of attack is necessary to maintain lift and avoid stall conditions.

Other options do not adequately describe factors that directly determine angle of attack. For instance, yaw and pitch refer to the aircraft's orientation rather than specific aerodynamic measurements. Velocity and thrust are important for flight dynamics but do not directly relate to the measurement of angle of attack. Similarly, elevation and airspeed affect flight performance but are not directly correlated with the calculation of angle of attack. Thus, the relationship between relative wind and the chord line is the correct basis for determining the angle of attack.