[Antennaware] Cylindrical Model for Triangular Tower

[btippett@alum.mit.edu (Bill Tippett)]

        Somewhere I got the following formula for a cylindrical
equivalent to triangular tower like Rohn 45.  

Equivalent Cylindrical Diameter = 2 * CUBEROOT [(D * F^2)/2]
 
where D = tube diameter and F = Face width.  For Rohn 45, D = 1.25" 
and F = 18", so cylindrical diameter equivalent = 11.7446"

        Does anyone know where this came from or if it is valid? 

                                                73,  Bill  W4ZV