Wing Weight Prediction Using Multidisciplinary Design Optimization

Weight prediction plays a crucial role in aircraft design,and has a large impact on the success or failure of aircraft design.In order to calculate wing structure weight with high fidelity,not only the detailed structural information but also the information for other disciplinaries are needed,such as accurate outer-shape of 3D wing after aerodynamic optimization,accurate pressure distribution on wing surface,fuel distribution in the wingbox,and dynamic characteristic of wing and applied materials.Since some information from different disciplinaries is coupling,iterations and optimizations are need for obtaining the weight.Taking a civil-jet wing as a case study,a wing structural weight calculation method using multi-disciplinary design optimization(MDO)is developed for the preliminary design,which provides an effective tool for determining weight index in the preliminary design of civil-jet.The primary contributions are summarized as follows:1)A new method for wing structural weight prediction is proposed using multi-disciplinary design optimization(MDO)and finite element method(FEM),after analyzing the pros and cons of wingbox weight calculaton based on beam theory.Not only the problems in each disciplinary such as aerodynamics and structure are studied,but also the problems in interdisciplinary are studied.The maximum lift-to-drag ratio and minimum structural weight of the wing are taken as the objectives,and the coupling between aerodynamic and structure(loads and aeroelastics)and the application of different materials are considered.2)The parameterization methods for wing geometry and structure are studied,which are suitable for conventional back-swept wing,as well as for unconventional forward-swept wing.Also,a parameterization method for the stiffened skin is presented,which is beneficial for the structural layout optimization.3)An equivalent method including stiffness equivalent and strength equivalent is proposed.Combining equivalent method with finite element(FE)model,the parameterization of wing FE model is enhanced.The shortcomings of conventional FE method,such as complicacy of the detailed FE modeling and expensive computation are avoided,and the FE model for static,buckling and dynamic analyses is unified.4)A ‘three-step’ strategy for the wing structural optimization is proposed.The wing structural optimization is decomposed into three levels of the structural optimization.The first is composite laminate propotion optimization;the second is structural weight and efficiency optimization;and thethird is wing stiffness and aeroelastic optimization.5)The wingbox weight calculation using FE method and secondary structures and miscellaneous items weight calculation based on empirical equation are integrated,which can predict the whole wing structure weight.Compared to the wing weight calculation based beam theory,this method has higher accuracy.6)A wing weight calculation environment(platform)based on MDO is created.The weight analysis for a conventional backswept wing and an unconventional forward-swept wing using this environment are performed.The results show that the method proposed in the paper is able to enhance accuracy and extend application for the wing weight prediction.