The shape of an airfoil can always be thought of being composed of two parts: a camber distribution (camber line) and a thickness distribution, which is distributed along the camber line. The requirements for the three classes of tailless planes can be translated in corresponding airfoil shapes and wing twist distributions. The only way to achieve a positive moment coefficient and the required amount of lift is to use a S-shaped camber line, which is also called a reflexed camber line.
Classes of tailless airplanes and their typical airfoil shapes.
Airfoils with strongly reflexed camber lines are usually not used on conventional airplanes - they are unique to tailless airplanes. From the aerodynamicists view, airfoils with `reflex´ are quite difficult and very interesting to develop, because they are very sensitive with respect to changes in Reynolds number.
Thus the following sections will concentrate on airfoils with reflexed camber lines, as they are used in tailless planes with no or little wing sweep.