Nonlinear aeroelastic behavior of compliant airfoils

Abstract

Since the beginning of aviation and up to the present time, airfoils have always been builtas rigid structures. They are designed to fly under their divergence speed in order to avoidstatic aeroelastic instabilities and the resulting large deformations, which are notcompatible with the typically low compliance of such airfoils. In recent years, research onairfoil morphing has generated interest in innovative ideas like the use of compliantsystems, i.e. systems built to allow for large deformations without failure, in airfoilconstruction. Such systems can operate in the neighborhood of divergence and takeadvantage of large aeroelastic servo-effects. This, in turn, allows compact, advancedactuators to control the airfoil’s deformation and loads, and hence complement oreven replace conventional flaps. In order to analyze and design such compliant,active aeroelastic structures a nonlinear approach to static aeroelasticity is needed,which takes into account the effect of large deformations on aerodynamics andstructure. Such an analytical approach is presented in this paper and applied to acompliant passive airfoil as the preliminary step in the realization of a piezoelectricallydriven, active aeroelastic airfoil. Wind tunnel test results are also presented andcompared with the analytic prediction. The good agreement and the observedbehavior in the wind tunnel give confidence in the potential of this innovative idea.