Unsteady aeroelastic analysis of the semi aeroelastic hinge including local geometric nonlinearities

A recent consideration in aircraft design is the use of folding wing tips, with the aim of enabling higher aspect ratio wings with less induced drag but also meeting airport gate limitations. Of particular interest is the concept of using in flight free floating wing tips in order to reduce aircraft gust and maneuver loads. This study investigates the effects of local geometric nonlinearities on the static response, dynamic stability, post flutter behaviour and gust response of floating wing tips. A multibody formulation is introduced to account for finite rotations of rigid folding wing tips attached through hinges on a flexible airframe structure including also aerodynamic follower forces for the folding wing tip components. It is found that the wing tip response can vary significantly when geometric nonlinearities are accounted for; the post flutter behaviour is characterised by super-critical limit cycle oscillations and no sub-critical instability was observed for the analysed cases. Moreover, the wing tip gust response can vary significantly when geometric nonlinearities are accounted for whereas a small impact was observed on the main airframe structure.