Abstract
This paper presents an analysis of the interaction and trade-off between active aeroelastic control and passive structural tailoring on a free-flying fully flexible aircraft model. Both technologies are included in the preliminary design of a typical transport aircraft configuration with a conventional control surface layout containing trailing edge control surfaces and spoilers. The passive structural tailoring is facilitated by exploiting the anisotropic properties of composite materials to steer the static and dynamic aeroelastic behaviour. 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. The optimisation of active control laws requires the consideration of constraints of the actuation system, namely rate and deflection saturation, in a nonlinear manner. The interaction of manoeuvre load alleviation, gust load alleviation and passive structural tailoring is investigated on the basis of results of different aeroservoelastic optimisations. Therefore the primary wing structure is simultaneously optimised with the individual technologies being activated or deactivated, resulting in eight different wing structures. The results of the individual and combined optimisations reveal significant design differences. The potentials of the different technologies can only be optimally exploited by simultaneous optimisation. The paper concludes with a study of the sensitivity of the major findings with respect to the knockdown factor for failure applied to the material properties. 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.
Highlights
The introduction of composite materials was an important milestone in the development of lightweight wing structures
The interaction between active gust load alleviation and structural tailoring in the integrated optimisation of composite wings has not been studied on the example of transport aircraft configurations
The unsteady aerodynamic model is based on a continuous-time state-space formulation of the Unsteady Vortex Lattice Method (UVLM) that has been first described by Mohammadi et al [32] for two-dimensional airfoils, formulated for three-dimensional lifting surfaces by Werter et al [33], and extended for arbitrary motion and control surface deflections by the authors [34]
Summary
The introduction of composite materials was an important milestone in the development of lightweight wing structures. The interaction of structural tailoring and active control was studied by Handojo et al [25] using the example of optimisation of a composite wing in the presence and absence of a fixed control law for manoeuvre and gust load alleviation. Integrated design of subsonic transport aircraft composite wings employing structural tailoring and active trailing edge morphing for manoeuvre load alleviation has been presented by Werter [26] finding that design difference occur both in the stiffness distribution as well as the morphing induced camber distribution whether or not the other technology is accounted for. The interaction between active gust load alleviation and structural tailoring in the integrated optimisation of composite wings has not been studied on the example of transport aircraft configurations. The paper concludes by answering the remaining question whether the observed interactions are robust to variations in the selected material by a sensitivity analysis of the major findings with respect to the knockdown factor applied to the material properties
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