An airfoil is defined as any surface that provides aerodynamic force when interacting with moving air. Which term best fits this definition?

• A. Airfoil
• B. Lift device
• C. Drag surface
• D. Stall plane

Answer: (A)

Airfoils are surfaces that generate aerodynamic forces when air flows over them, thanks to their shape and angle of attack. That makes airfoil the best-fitting term for a surface that produces lift, drag, and other forces as it interacts with moving air. Lift device isn’t a standard name for the surface itself, and drag surface implies only one component of force. Stall plane isn’t a general term for a surface and doesn’t describe the surface type. So the term that matches the definition is airfoil.