Nonlinear Aeroelastic Behaviour of Compliant Airfoils

Since begin of the aviation and up to the present times, airfoils have always been built as rigid structures. They are designed to fly under their divergence speed in order to avoid static aeroelastic instabilities and the resulting large deformations which are not compatible with the typically low compliance of such airfoils. In recent years, research on airfoil morphing has generated interest in innovative ideas like the use of compliant systems, i.e. systems built to allow for large deformations without failure, in airfoil construction. Such systems can operate in the neighbourhood of divergence and take advantage of large aeroelastic servo-effects. This, in turn, could allow compact, advanced actuators to control the airfoil’s deformation and loads, and hence complement or even replace conventional flaps. In order to analyze and design such compliant, active aeroelastic structures a non-linear approach to static aeroelastic is needed, which takes into account the effect of large deformations on aerodynamics and structure. Such an analytical approach is presented in this paper and applied to a compliant passive airfoil as the preliminary step to the realisation of a piezoelectrically driven, active aeroelastic airfoil. Wind-tunnel test results are also presented and compared with the analytic prediction. The good agreement and the observed behaviour in the wind tunnel give confidence in the potential of this innovative idea.