Since the Navier-Stokes equations only allow for an analytical treatment in very simple special cases, there was an early need to search for suitable simplifications. A major problem in modelling aerodynamic lift was to find the suitable approach within a wide range. This was first achieved by Kutta and Joukowski. The lift-specific curvature behaviour of the streamlines on wings can be formulated in the streamline curvature theorem. Subsequently, the lift on wing profiles is calculated using the Kutta-Joukowski theory. As the paradox of d’Alembert illustrates, vortex formation plays a crucial role in lift.