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.

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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.@en

This paper introduces a new assessment method for static and dynamic aeroelastic stability of free flying flexible aircraft in which the aerodynamic model is based on a continuous time state space formulation of the unsteady vortex lattice method. By the integration with the structural and flight dynamic equations of motion, the resulting aeroelastic time domain model is obtained. With utilizing the flight velocity as scheduling variable, a parameter varying state space model is formulated making efficient stability analysis possible. In order to validate the proposed method, aeroelastic stability analyses are carried out on the example of the FLEXOP demonstrator aircraft. Comparisons are made with calculations run with the commercial software package Nastran. Advantages of the proposed method are demonstrated by the analysis of effects whose consideration is not or only partly possible with other state of the art methods. Those effects include (i) steady wing loading at the point of linearization; (ii) static deformation due to steady wing loading at the point of linearization; and (iii) twist and camber distribution.@en

This paper presents the trade-off between active loads alleviation through trailing edge flaps and passive loads alleviation through bending-twisting coupling. Both loads alleviation methods have conflicting requirements for optimal effectiveness. Therefore it is of interest to trade them off in an optimisation context. A dedicated aeroservoelastic model is developed that quickly can assess gust loads in the presence of flaps and bending-twisting coupling. This model is based on a linear Euler beam closely coupled to a Theodorsen unsteady aerodynamics model that is converted to time domain using the indicial functions method of Leishman. It is demonstrated in this paper that a combination of active and passive loads alleviation outperforms separate loads alleviation methods.@en

In this paper a continuous time state space aerodynamic model is extended for accepting arbitrary motion, control surface deflection and gust velocities as inputs. Equations for formulating the inner state equation are outlined first followed by the numerical description of the boundary condition. The force calculation is presented using an unsteady form of the Kutta-Joukowski theorem enabling the method of unsteady induced drag prediction. Methods for linearization are presented. The resulting model inputs are motion, control surface deflection and gust velocities and accelerations while the system outputs are panel forces. To validate the modeling approach, comparisons to analytical methods are carried out for various oscillatory motions. Besides integrated coefficients for vertical force, drag, pitching moment and hingemoment, comparisons for unsteady pressure distributions are carried out. The comparisons indicate good agreement for a large range of reduced frequencies. The influence of wake truncation distance and discretization is discussed. Because of its time-domain formulation, the model is especially suitable for efficient aerodynamic loads analysis within aeroelastic modeling, analysis and optimization frameworks for preliminary aircraft design.

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