At the beginning of aviation history, aeroelastic static instabilities represented a problem in operating monoplane aircraft. After being discovered, they were systematically avoided, since they would have led to large deformations and structural failure. A new idea (active aeroelasticity) reverts this approach and utilizes static instabilities to realize wing morphing instead of avoiding them. Another innovative idea (compliant systems) deals with structures designed to achieve large deformations within the elastic range of the material. Joining those two ideas leads to a novel class of airfoil structures (active aeroelastic, compliant airfoils) which enable operation at and beyond aeroelastic instabilities. Such structures need a new modeling approach, which includes nonlinearities of structural and aerodynamic kinds. In this paper, a non linear analysis of aeroelastic bending divergence (a phenomenon which concerns forward-swept wings) is presented, initially based on so-called low-fidelity models. Such models are, to some extent, inaccurate but allow a good insight into the physical behavior of the phenomenon and are very useful in preliminary design. The results of wind-tunnel tests follow, which were performed to investigate the aeroelastic response of a compliant airfoil model near divergence. Finally, high fidelity simulation results based on state-of-the-art methods (finite element method and fluid-structure-interaction) are shown and discussed. Those tools allow the prediction of the system response more accurately and are therefore well suited to the detailed design of active aeroelastic, compliant airfoils.

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