Aeroelastic optimization of high-speed tiltrotor wings with wing extensions and winglets

Tiltrotors can experience an aeroelastic instability called whirl flutter, which is characterized by highly coupled wing-rotor vibrations, which are catastrophic in nature and limit the maximum speed of the aircraft. In this paper, an optimization study aimed at improving the whirl flutter speed of a tiltrotor equipped with a wing extension and a winglet is presented. Parametric studies are conducted on an aeroelastic model of a rotor mounted on a cantilevered wing with an extension and a winglet. The parameters that are investigated are stiffness, structural taper, composite couplings, extension sweep, and winglet cant angle. It is found that, when the wing has a structural taper and is equipped with a wing extension and a winglet, the whirl flutter speed can be increased by 15%. The parametric study is followed by an optimization study to determine the optimal combinations of these parameters that maximize whirl flutter speed. Genetic algorithms are used for the optimization process. Upper and lower bounds are placed as constraints on the design variables. It is shown that the optimized design has a flutter speed of 22% (65 kt) more than the baseline.