NACA-TN-2232

Abstract

Experimental investigations of swept box beams (references 1 and 2) have shown that the stresses and distortions in a swept wing can be appreciably different in character from those that would exist if the root were normal to the wing axis. The principal effect of sweepback on the stresses occurs under bending loads .and consists in a concentration of bending stress and vertical shear in the rear spar near the fuselage. With regard to distortions, the effect of sweep is to produce some twist under loads that would produce only bending under loads that would produce only twist of an unswept wing. <br>A relatively small amount of theoretical work has thus far been published on the analysis of swept wings of the shell type. Reference 3 presents an energy method for determining influence coefficients of a swept box beam with bulkheads parallel to the flight path, and references 1 and 2 contain a semiempirical method for the deflection analysis of a swept box beam with bulkheads perpendicular to the spars. No publications are known to be available on the stress analysis of a swept box beam with either type of bulkhead arrangement. <br>The purpose of this paper is to present a method for the calculation of both stresses and distortions of a swept box beam-representing the main structural component of a swept wing with a carry-through section and with bulkheads perpendicular to the spars. The analysis is based on the four-flange idealized structure illustrated in figure 1. In a four-flange box beam of this type the carry-through and outer sections can be analyzed by existing methods for unswept four-flange box, beams if some means is provided for analyzing the triangular section which connects them. <br>A method is presented for analyzing an idealized representation of the triangular section end for establishing continuity between the parts of the box beam; consideration is also given to the relationships between the idealized and actual structures and a comparison between the stresses and distortions calculated by this method and the experimental data of references 1 and 2. In the discussion, the effects of shear lag, which the method cannot give, are considered and an extension of the basic approach to permit their inclusion is indicated; also, the importance to the analysis of including the shear and bending flexibility of the bulkheads bordering the triangular region is demonstrated. A complete numerical example is worked out in an appendix.