Critical behaviour of slender wing configurations

Abstract

The next generation of slender, flexible aircraft wings requires extremely lightweight structures capable of carrying a considerable amount of non-structural weight. With the increased slenderness and flexibility, possible with the advent of advanced composites, these wings can exhibit aeroelastic instabilities quite different from their rigid counterparts. The design of highly flexible aircraft, such as high-altitude long endurance (HALE) configurations, must include phenomena that are not usually considered in traditional aircraft design, such that an alternative design philosophy has been proposed for this class of vehicles. The discussion in this article is restricted, among the various aeroelastic phenomena, to the flutter condition. Classical procedures usually refer to aero-structural systems where the undeformed state is taken as the reference point. This is not the case with slender wing configuration where, due to the high structural flexibility, a proper beam model, capable of describing the structural flight deflections, should be adopted. Consequently, the flutter analysis has to be performed considering the deflected state as a reference point. Herein, an approximate procedure is proposed and flutter is evaluated by means of Galerkin's approach applied to the perturbed small motions of the aero-structural system. The effect of typical parameters, including stiffness ratio, mass eccentricity, store pod, deflection amplitude, as well as the wing aspect ratio, are considered. For a simplified wing configuration, comparisons between analytical and experimental findings are presented along with discussions and suggestions for new design criteria.