Design and experimental validation of a morphing wing flap device

The increase of lift force required by an aircraft during take-off and landing phases is conventionally obtained through wing flap deflection. Flaps are hinged surfaces located on wing trailing edge; their rotation generates an augmentation of aerodynamic sustentation force as consequence of an induced local modification of wing airfoil camber. Such devices are usually driven by control systems made of robust actuators and control lines that significantly contribute to the weight of the whole wing structure and, whereas proper external fairings are needed, also to wing friction drag and aerodynamic noise. Moreover, the shape change locally induced by flaps to wing airfoils is clearly limited to the allowable flaps excursion; it follows that , in operative conditions, only a discrete set of few airfoil shapes can be achieved, each shape being related to a precise flap deflection angle within the allowable range. From an aerodynamic standpoint, this implies that a conventional flap can generate just a finite number of extra-lift (and extra-drag) values each one corresponding to the finite number of deflections the flap may perform within the allowable range. The naturally foreseen advantages related to an adaptive high lift device able to smoothly change its shape according to flight parameters as well as the intent of reducing high-lift devices friction drag and emitted aerodynamic noise, represent all valid motivations to search for innovative flap architectures able to replace and/or improve conventional flaps system thanks to morphing camber capability. A morphing lifting surface is generally called to perform a transition from a baseline geometry to a target shape or to a set of target shapes, under the simultaneous action of aerodynamic loads, in turn influenced by that shape variation. Such an adaptive structure must be therefore conceived under contrasting design requirements: it has to be stiff enough to withstand external aerodynamic loads without appreciable deformations while being flexible enough to dramatically change its external shape. In the framework of JTI-Clean Sky project, authors investigated a high TRL solution for a morphing flap element to be implemented on a real-scale regional transportation aircraft. On the base of specific aerodynamic requirements in terms of target shapes and related external loads, the structural layout of the device was preliminarily defined. Advanced FE analyses were then carried out in order to properly size the load- carrying structure and the actuation system. A full scale limited span prototype was finally manufactured and tested to: - demonstrate the morphing capability of the conceived structural layout; - demonstrate the capability of the morphing structure to withstand static loads representative of the limit aerodynamic pressures expected in service; - characterize the dynamic behavior of the morphing structure through the identification of the most significant normal modes. Obtained results showed high correlation levels with respect to numerical expectations thus proving the compliance of the device with the design requirements as well as the goodness of modeling approaches implemented during the design phase.