A body moving relative to a fluid can experience a force perpendicular to the relative motion. For an airfoil this force is called lift.

Lift is commonly summarized by

$$L=\frac12\rho v^2 C_L A,$$

where $C_L$ depends on airfoil shape, angle of attack and flow conditions.

Pressure distribution

An airfoil changes the surrounding flow and develops an unequal pressure distribution over its surfaces. Integrating pressure and viscous stresses over the body produces the net aerodynamic force, whose perpendicular component is lift.

Bernoulli's relation helps connect local velocity and pressure where its assumptions apply, while momentum conservation provides the complementary global statement that the airfoil deflects the surrounding flow.

Angle of attack

The angle of attack is the angle between the airfoil reference line and the incoming flow. Increasing it generally increases lift over an initial range.

Stall

At sufficiently large angle of attack, the boundary layer can separate over a substantial part of the upper surface. The lift coefficient then drops and drag rises sharply: the airfoil has stalled.