 Aircraft wing

An aircraft wing is an aerodynamic lifting structure of an aircraft. Its three-dimensional shape combines airfoil sections with a spanwise arrangement described by the wing planform. The airfoil specifies a local profile; the wing planform specifies the shape seen from above. Wingspan, wing area, wing taper ratio and wing sweep describe different aspects of that geometry.^[ref]

The surrounding fluid flow exerts pressure and viscous stress on the wing's surface. Integrating these surface forces gives a resultant whose component perpendicular to the incoming flow is lift and whose parallel component is drag. A useful whole-wing relation iswhere $\rho$ is air density, $V$ is flight speed relative to the air, $S$ is wing area and $C_L$ is lift coefficient. The lift coefficient packages the effects of shape and operating conditions, including angle of attack; it is not determined by wing area alone.

For a stipulated example, $\rho =1.2kg/{\mathrm{m}}^3$, $V=30m/s$, $S=10{\mathrm{m}}^2$ and $C_L=0.8$ give dynamic pressure $540\mathrm{Pa}$ and lift $4320\mathrm{N}$. Halving the speed at unchanged lift coefficient reduces lift to one quarter. Maintaining the original lift would require $C_L=3.2$, which the actual wing might be unable to achieve before aerodynamic stall.

A wind tunnel makes the shape–force connection measurable: hold a model at controlled angle of attack, measure its lift and drag with a balance, and vary the model or flow conditions. Such measurements distinguish a geometrical description from an aerodynamic prediction. Two wings with equal wingspan and wing area can still have different lift coefficients, drag and stall behavior.