This method provides a fast but relatively simple method to predict the weight of aluminum wing and tail structural boxes which are simultaneously loaded in bending and torsion. The basic data were derived from the extensive compression testing of stiffened aluminum panels conducted by the NACA. The tests used 24S-T and 75S-T aluminum, which are practically identical to 2024-T3 and 7075-T6 in current use.

The bending load is the typical maximum vertical load on a wing or tail, and the torsion load is about the span axis of the box. The typical aircraft wing or tail cambered box is represented by an equivalent rectangular box. The upper and lower covers are determined from the bending and torsion moments, and the front and rear faces are determined from the combination of vertical shear and torsion.

The cross-sectional area of the box is calculated at each rib or other panel end restraint. One equation is used for each material. There are two aluminum equations: one for Z-stiffened 24S-T (2024-T3), and one for 75S-T (7075-T6). A graphite composite material was estimated for one structural configuration using the ratios of the modulus of elasticity for aluminum and graphite and the aluminum stiffened sheet curves.