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Angle of attack is defined as the angle between the chord line of an airfoil and what?

  1. The aircraft's longitudinal axis

  2. The horizontal plane

  3. The direction of the relative wind

  4. The aircraft's tail

The correct answer is: The direction of the relative wind

The angle of attack is defined as the angle between the chord line of an airfoil and the direction of the relative wind. This definition is critical because the angle of attack directly influences the lift generated by the airfoil. The chord line is an imaginary line that extends from the leading edge to the trailing edge of the airfoil, while the relative wind is the airflow that is experienced by the airfoil as the aircraft moves through the air. Understanding this concept is vital for pilots, as the angle of attack can significantly affect the performance and safety of the aircraft. For instance, if the angle of attack becomes too high, the airflow can separate from the airfoil, leading to a stall. Therefore, maintaining an appropriate angle of attack relative to the wind direction is essential for effective flight control. In contrast, the other options do not accurately describe the angle of attack. The aircraft's longitudinal axis relates to the orientation of the aircraft itself rather than specifically to the airflow affecting the airfoil. The horizontal plane provides a reference for ground level but does not relate to the airfoil's interaction with the air. The aircraft's tail does not play a role in defining the angle of attack, which is specific to the airfoil's position relative to the incoming wind