Joukowski's wing

On the left, a circle through z = 1 with air flowing round it; on the right, what w = z + 1/z makes of them: the circle becomes a wing, and the flow goes round the wing. Drag the centre c and the wing grows thicker or more curved; change the angle of attack α and the air comes in at a slant. With no circulation the flow usually swings round the sharp trailing edge; with the Kutta condition just enough circulation is added for the air to leave the trailing edge smoothly. In this model the lift is proportional to that circulation.