In this paper, we study the parametric variations on whirl flutter on a tiltrotor equipped with wing extensions and winglets. An aeroelastic model which takes into account the rotor blade torsion degree of freedom is developed. The parameters that are investigated are stiffness, structural taper, composite couplings, winglet toe cant and sweep angles. It is found that when the wing has a structural taper, and the aircraft is equipped with wing extensions and winglets, 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 to maximize whirl flutter speed. Genetic algorithms are used for the optimiza- tion process. Upper and lower bounds are placed as constraints on the design variables. The optimized design has a flutter speed of 65 (22%) knots more than that of the baseline design.