ocr: AIRFOIL The cross-section of a bird's wing IS a cuived shape called an airfoil. This shape is ideal for flight SO much SO that engineers have based the design of aircraft wings onit. Airfoils produce an upward force that keeps a bird or airplane airborne. They also reduce friction between the wing andthe air. An airfoil only works when air is flowing overit; a bird produces this air flow when it flaps, soars, or glides through the air. SEE ALSO
