Aerofoils

An aerofoil, or airfoil, is a streamlined cross-section of a wing, blade, or foil designed to generate lift when impinging air flows over it. The shape is optimized to produce a favorable pressure distribution, with a typically curved upper surface and a flatter lower surface.

Key design features include camber (the curvature of the mean camber line), thickness distribution, and the chord line (the straight line from leading to trailing edge). An aerofoil can be symmetric (same shape on both sides) or cambered (asymmetric), with camber increasing lift at a given angle of attack. The degree of curvature and thickness are chosen for the intended Reynolds number and operating regime.

Aerodynamically, lift arises from the air’s deflection around the foil, generating a higher pressure on one side and a lower pressure on the other. The lift coefficient and drag coefficient quantify performance and depend on angle of attack, Reynolds number, and flow conditions. At a critical angle, flow separates, causing stall, which markedly reduces lift and increases drag.

Aerofoils are used in aircraft wings, rotor blades, propellers, wind turbines, and hydrofoils. They are studied with theoretical (potential flow, Kutta–Joukowski theorem) and empirical approaches. Airfoil shapes include symmetric and cambered families such as NACA designs, which specify thickness and camber distributions to achieve target lift at given speeds.

Historical development began in the 19th century with early experiments and theoretical work, leading to modern standardized airfoil sections and computational tools for design and optimization.