Simultaneous Optimisation of Composite Wing Structures and Control Systems for Active and Passive Load Alleviation

Abstract

Future composite aircraft wing designs will exploit anisotropic material properties by aeroelastic tailoring and include active control methods for manoeuvre and gust load alleviation. The research focuses on the simultaneous optimisation of aeroelastically tailored wing structures with active manoeuvre and gust load alleviation as well as the analysis of their interaction.
The development of the framework allowing the rapid integrated preliminary design of aeroservoelastically tailored wing structures includes the formulation of a suitable model order reduction method for the aerodynamic models. The approach establishes reduced-order models that have high robustness against structural modifications and thereby can be used throughout the entire optimisation process. Besides passive structural tailoring facilitated by exploiting the anisotropic properties of composite materials, active aeroelastic control is implemented by scheduled control surface deflections redistributing the aerodynamic loads during manoeuvres to achieve manoeuvre load alleviation and a feed-forward control law for gust load alleviation. The panel-based aerodynamic modelling of spoiler deflections is improved by a correction of the spatial distribution of the boundary condition derived from higher fidelity simulation data. Rate and deflection saturation is considered in a nonlinear manner. Various structural weight optimisations are performed, with the individual technologies being activated or deactivated. Besides the use of different material allowables, alternative approaches such as simultaneous, separate and iterative optimisation are investigated. Also, the influence of configurational changes on the optimisation results is analysed, considering the addition of winglets and a modification of the control surface layout.
The results of the individual and combined optimisations reveal significant design differences. A substantial shift of effectiveness from active aeroelastic control to passive structural tailoring is observed with increased allowables resulting in more flexible and hence less stiff wing designs. While the results confirm that simultaneous optimisation is the only way to find the optimal solution, separate and iterative approaches offer the possibility to separate certain subspaces of the optimisation and still reach results close to the optimum. The investigated configurational changes influence the prevailing load hierarchy and active constraints. As a result, the optimiser reacts to these changes by adapting the mechanism of structural tailoring to optimally fulfil the respective active constraints.