Effect of wing-box structure on the optimum wing outer shape

Abstract

A new method for wing shape optimisation is presented, in which the wing shape is optimised not only for the best aerodynamic properties but also for minimum structural weight. An advanced structural sizing method for wing structural weight estimation is developed. The method is based on elementary, physics based analyses of simplified structure to determine the amount of required material to resist the applied loads. The sizing loads are determined based on the airworthiness regulations using advanced aerodynamic analysis tools. In this new weight estimation method, the effect of wing outer (aerodynamic) shape on the wing-box structural weight is taken into account. A mathematical equation is derived, which relates the wing-box structural weight to the wing outer shape. The weight estimation method is validated for several existing passenger aircraft. A series of optimisations is performed to optimise the wing shape for a general objective function, which includes both aerodynamic and structural properties of the wing. The aircraft fuel weight is used as the objective function. Different structures are tested both metal and composite ones. The latter includes different composite layups. In order to find the effect of the internal structure on the optimum wing outer shape, the design lift coefficient is assumed to be constant for all the test cases. The results of the optimisations showed that the optimum wing shape is depending on the structural concept (metal alloys versus different composite layups) for different internal structures.