Aero-Structural Optimization of Non-Planar Lifting Surface Configurations

Abstract

Non-planar lifting surface aircraft configurations offer potentially significant gains in aerodynamic efficiency by lowering the total induced drag. There are many options for non–planar wing configurations, from winglets and multiwings to box and joined wings. Non–aerodynamic considerations such as structures, weight and stability and control can significantly impact the overall improvements in efficiency.Here, a medium fidelity panel method and equivalent beam finite element model are used to explore the possibilities of non–planar lifting surface configurations taking into account the coupling between aerodynamics and structures. Two main cases, a single discipline aerodynamic optimization and a multidisciplinary aero–structural optimization are investigated. To demonstrate the effect of non–planar configurations, the main lifting surface of a typical commercial aircraft at cruise is optimized. The optimization of the wing configurations is geometrically constrained by a maximum projected span and height. The effect of incorporating parasitic drag in the aerodynamic model is also explored. Due to the complexity of the design space and the presence of multiple local minima, an augmented Lagrange multiplier particle swarm global optimizer is used. The particle swarm algorithm is a global optimization algorithm based on a simplified social model and is closely tied to swarming theory. The aerodynamic optimum solution found for rectangular lifting surfaces is a box wing, as predicted by theory. Allowing for sweep and taper as design variables yields a joined wing as the aerodynamic optimum result. The addition of parasitic drag in the aerodynamic model reduces the size of the non–planar elements in the topology of the aerodynamic optimum solutions. Including structures and the coupling between structures and aerodynamics in the optimization has a profound impact due to the additional weight of non–planar segments. The aero–structural optimal solution found is the C–wing configuration when parasitic drag is neglected and the addition of a winglet to the planar wing when parasitic drag is included.