Analysis of 2-Spar Cantilever Wings With Special Reference to Torsion and Load Transference

This paper deals with the analysis of 2-spar cantilever wings in torsion, taking cognizance of the fact that the spars are not independent, but are interconnected by ribs and other structural members. The principles of interaction are briefly explained, showing that the mutual relief action occurring depends on the "pure torsional stiffness" of the wing cross section. Various practical methods of analysis are outlined. The "Friedrichs-von Karman equations" are shown to require the least amount of labor. These equations were originally derived for wings that owe their torsional stiffness to the individual torsional stiffnesses of the spars; it is shown, however, that the equations apply .also to wings in which the torsional stiffness is due to drag bracing-wires or stressed skin-arranged in two planes.

Numerical examples by the several methods of analysis are given and the agreement between the calculation and experiment is shown. In the case of a trussed-spar structure the results are practically equivalent to the results of standard least-work calculations which treat the structure as a pin-jointed space framework, but they can be obtained with so much less labor that the analysis may be made as a routine design procedure.