Parametric studies of wing extensions and winglets on whirl flutter stability

This study focuses on the influences of wing and wing tip devices (wing extension and winglets) on tiltrotor whirl flutter speed. An aeroelastic winglet model has been implemented and parametric studies of winglet geometric angles such as cant, sweep and toe have been conducted. The influences of composite tailoring of wing including wing extensions and winglets have been investigated. Approaches to enhance the wing chord mode damping have been explored. The results show that wing tip devices have significant influences on wing beam bending and torsion mode damping; however, their effect on wing chord mode is negligible. The most effective approach to increase the wing chord mode damping is through the wing, and wing extension, beam bending-chord bending coupling by twisting beam spars. With wing extensions and winglets, main wing composite tailoring with bending-twist coupling can significantly boost the wing beam mode damping. Several wing system design studies have been carried out to investigate their potential to improve the wing mode stability. These design studies are based on the structurally tailoring of main wing and wing extension, tuning wing extension flexural beam stiffness, and configuring winglet geometric angles. Significant improvement is observed, and the increases of tiltrotor whirl flutter speed are between 75 and 150 knots compared to a baseline system.