Certified Flight Instructor - Flight Instructor Airplane Practice Exam

Lift produced by an airfoil is the net force developed perpendicular to which reference?

1. Chord of the airfoil.

2. Relative wind.

3. Longitudinal axis of the aircraft.

4. Vertical axis of the aircraft.

The correct answer is: Relative wind.

The correct choice indicates that lift is the net force developed perpendicular to the relative wind. This perspective is essential for understanding how lift is generated in flight. The relative wind is the airflow that is relative to the wing, and it is a crucial factor in determining the pressure differences above and below the airfoil. When the wing moves through the air, it creates an angle of attack with respect to the relative wind. This angle is significant, as it influences the flow of air around the airfoil, leading to differing air pressures above and below the wing. The resulting pressure difference generates lift, which acts perpendicular to the direction of the relative wind. Understanding this relationship between lift and relative wind is fundamental for flight instructors teaching students about aerodynamics and aircraft performance. It clarifies why a pilot must manage speed and angle of attack to optimize lift during various phases of flight.