Design of a Variable Stiffness Spar
Final rept. 22 Sep 95-25 Oct 96
CSA ENGINEERING INC PALO ALTO CA
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Several studies have indicated that the performance of an aircraft can be considerably improved by adaptively varying the geometry of the wing to optimally suit the various flight conditions. The objective of this study was to seek a design concept for adaptively varying the torsional stiffness of an aircraft wing structure. Contemporary aircraft wing design consists of heavy cantilever beams spars which take the span-wise bending and shear loads. Metal ribs are spaced along the span in a chord-wise direction to maintain the airfoil shape. Metal skins are attached to this framework to stabilize the structure in torsion and provide stiffness. Recent studies showed that performance of an aircraft could be considerably improved by adaptively varying the torsional load carrying capacity of the wing spar. Hence, design concepts for adaptively varying the torsional stiffness of an aircraft wing spar were studied. Three different concepts were considered 1 Variable torsional constant by varying the member cross-section. 2 Variable axial shear stress by activatinginactivating some member elements. 3 Preventing one of more cross-sections along the length of the member from warping. The first two concepts are discussed in this report. A comparison of the effectiveness of these two concepts through a finite element analysis are also presented.