What is an airfoil best described as?

• A. A surface such as a wing, propeller, rudder, or trim tab that provides aerodynamic force when it interacts with moving air.
• B. A device for measuring air temperature.
• C. An engine mounting point.
• D. A part of the landing gear.

Answer: (A)

An airfoil is any surface that interacts with moving air to generate aerodynamic force. Its job is to use the flow of air to create lift, thrust, or other aerodynamic effects depending on how it’s used in the aircraft. That’s why a wing, a propeller blade, a rudder, or a trim tab fits the description—these surfaces are designed to move through air and produce meaningful forces as a result of their shape and angle of attack.

The other options describe things that don’t themselves generate aerodynamic force from their interaction with air: a device for measuring air temperature, an engine mounting point, or a part of the landing gear. While those components have important roles, they aren’t airfoils producing lift or thrust.