NACA airfoils developed in the 1930’s and 40’s use a consistent naming convention that is based on the airfoil thickness and shape of the camber line. In the 4-digit airfoils, the first integer indicates the maximum value ordinate of the mean line in percent of chord. The second integer indicates the location of that maximum measured from the leading edge in percent of chord and the last two integers represent the maximum thickness of the airfoil in percent. A NACA 4212 has a 4 percent camber that whose maximum value is located at 20 percent of chord and is 12 percent thick.
In the NACA 5-digit airfoils, the naming convention is based on the theoretical design characteristics of the airfoil. The first integer is the amount of camber in terms of the magnitude of the design lift coefficient. The second and third integers indicate twice the distance from the leading edge to the location of the maximum camber. The last two integers represent the thickness in percent of chord. A NACA 23015 has a design lift coefficient of 0.2, the location of the maximum chamber is at 15 percent behind the leading edge, and the airfoil is 15 percent thick.
The naming convention of NACA 6-series of airfoils is a combination of the location of maximum thickness, the type of mean line used to generate the chamber line, and the thickness ratio. A NACA 63-415 will have its maximum thickness at approximately 30 percent of chord, the design lift coefficient is 0.4, and the airfoil is 15 percent thick.