What is an airfoil?

• A. The straight line along the wing
• B. A surfaced body or structure designed to produce a lift or thrust force when subjected to airflow
• C. The wing tip
• D. The center of gravity

Answer: (B)

An airfoil is the cross‑sectional shape of a surface (like a wing or blade) that is designed to generate lift (and, in some cases, thrust) as it moves through air. The curved upper surface and flatter lower surface cause air to move faster over the top, creating lower pressure there and producing an upward lifting force, while pressure is higher beneath. This aerodynamic interaction is what makes flight possible. The other options describe parts or properties of the wing or aircraft that aren’t the airfoil itself: a straight line along the wing isn’t the surface shape, the wing tip is just a edge of the wing, and the center of gravity is a mass property.