airfoil

An airfoil is a curved shape designed to generate lift when air flows around it. It is typically the cross-sectional profile of a wing, blade, or turbine rotor. The airfoil's shape is described by camber, thickness, and leading-edge geometry. When air moves over the surface, the flow is deflected downward or forward, creating a pressure difference between the upper and lower surfaces that produces lift. The design balances aerodynamics, structural weight, and operating conditions.

Lift is influenced by angle of attack, speed, air density, and surface smoothness. A cambered airfoil has asymmetry that can produce lift at zero angle of attack, while a symmetrical airfoil requires a positive angle. As the angle increases, lift increases until the flow separates, causing stall and rapid drag rise. The lift-to-drag ratio is a key performance measure for aircraft and rotor blades. At small Reynolds numbers, such as in model aircraft or micro-air vehicles, viscous effects become more important.

Airfoils are designed to meet mission requirements; common classifications include symmetric and cambered profiles and those with various thickness distributions. Many airfoils used in aviation come from standardized families, such as NACA or other standardized airfoil series. The choice depends on desired lift, drag, stall characteristics, and Reynolds number. Airfoils can be optimized for cruise, maneuverability, or high-speed performance.

In practice, airfoils are studied with computational fluid dynamics and wind tunnel testing. They are used in airplanes, rotorcraft, wind turbines, and propellers. The historical development of airfoil theory began in the early 20th century with the work of Prandtl and the lifting-line theory, and later the formulation of standardized airfoil shapes by NACA and others.