Wing spars and box beams

This chapter analyzes actual aircraft components, including, wing spars and box beams. Aircraft structural components are complex, consisting usually of thin sheets of metal stiffened by arrangements of stringers. These structures are highly redundant and require some degree of simplification or idealization before they can be analyzed. The analysis presented in the chapter is, therefore, approximate and the degree of accuracy obtained depends on the number of simplifying assumptions made. A further complication arises in that factors, such as warping restraint, structural and loading discontinuities, and shear lag significantly affect the analysis. Generally, a high degree of accuracy can be obtained only by using computer-based techniques such as the finite element method. However, the simpler, quicker, and cheaper approximate methods can be used to advantage in the preliminary stages of design, when several possible structural alternatives are being investigated; they also provide an insight into the physical behavior of structures that computer-based techniques do not. Major aircraft structural components, such as wings and fuselages, are usually tapered along their lengths for greater structural efficiency. Thus, wing sections are reduced both chordwise and in depth along the wing span toward the tip, and fuselage sections aft of the passenger cabin taper to provide a more efficient aerodynamic and structural shape.