In NACA Report 492, the four and five digit airfoils were subjected to systematic variation of the thickness distribution to allow the airfoil designer to choose the position of maximum thickness and leading edge radius. These modifications are indicated by a suffix consisting of a dash and two digits, such as 0012-34 or 23015-64. These modifications change the leading edge radius and the position of maximum thickness. The first integer following the dash indicates the relative magnitude of the leading edge radius. The nominal leading edge radius is denoted 6 and a sharp leading edge would be zero. The leading edge radius varies as the square of this index number. The second integer indicates the position of the maximum thickness in tenths of chord.
For example, a 23015-64 airfoil would have a maximum thickness of 15 per cent, a 230 mean line, a leading edge radius corresponding to an index of 6, and the position of maximum thickness would be at 40 per cent chord.
The thickness distribution is given by the following equation ahead of the maximum thickness:
y = A0 sqrt(x) + A1 x + A2 x**2 + A3 x**3
where ** denotes exponentiation, (t/c) is the maximum thickness to chord ratio of the airfoil, x is the position as fraction of chord, and y is the half-thickness as fraction of chord.
and by the following equation from maximum thickness to trailing edge:
y = D0 + D1(1-x) + D2 (1-x)**2 + D3 (1-x)**3
There is a special page that describes the details of the calculation of A0, A1, A2, A3, D0, D1, D2, D3 from the values of thickness, position of maximum thickness, and leading edge radius that are specified by the user.