The choice of the wing section and area which will give the desired performance in steady motion is the first step to be made in the aerodynamical design of an airplane. The determination of the best combination of section and area is a complicated calculation, for it is impossible to select the section independently of the area in securing the limit performance for a given type of airplane. Certain criteria can be applied, however, which allow the elimination of the poor sections and the selection of a few predominantly good profiles for certain types of airplanes. These criteria, while not sufficiently fine to differentiate aerofoils of nearly the same quality, constitute an accurate method
of choosing the most valuable.