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

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

• A. Relative wind
• B. Airflow over the upper surface
• C. The velocity of the airplane
• D. Chord line

Answer: (A)

Lift is the net aerodynamic force that acts perpendicular to the relative wind—the airflow direction seen by the wing, which is opposite to the aircraft’s motion through the air (including any induced downwash). Because lift is defined with respect to this relative wind, its direction is always at a right angle to that airflow, not necessarily perpendicular to the wing’s surface, the upper surface geometry, or the velocity of the airplane itself. The chord line is simply a geometric reference on the wing, so lift need not be perpendicular to it. The magnitude of lift depends on speed and angle of attack, but its direction is set by the relative wind.

Lift is the net aerodynamic force that acts perpendicular to the relative wind—the airflow direction seen by the wing, which is opposite to the aircraft’s motion through the air (including any induced downwash). Because lift is defined with respect to this relative wind, its direction is always at a right angle to that airflow, not necessarily perpendicular to the wing’s surface, the upper surface geometry, or the velocity of the airplane itself. The chord line is simply a geometric reference on the wing, so lift need not be perpendicular to it. The magnitude of lift depends on speed and angle of attack, but its direction is set by the relative wind.