In this paper, we study multi-objective optimization methodologies for tiltrotor aircraft with wing extensions and winglets. The objective is to maximize aircraft cruise performance while minimizing wing weight, subject to whirl flutter, buckling, strength, and wing loading constraints. A wing structural model for strength and wing weight predictions, an aerodynamic model for performance predictions, and an aeroelastic model for whirl flutter predictions are developed for the optimization. Parametric studies on whirl flutter speed, cruise efficiency (lift-to-drag ratio, L/D), and wing weight are conducted; and the parameters include key variables such as wing thickness, and extension and winglet planform variables. The parametric studies predict that structural taper can increase the whirl flutter speed by 35 knots (12.5% increase), while reducing the wing weight. The optimization studies reveal that the L/D of the optimum design is 12% more than the baseline, while the optimum wing weight is 0.3% less than the baseline.