An aeroelastic stability model with coupled rotor, pylon, and wing degrees of freedom has been developed and analyzed. The research is focused on understanding the effect of a wing extension and winglet on whirl flutter stability. Composite tailoring of wings, as well as wing extensions, is investigated for potential benefits to wing mode stability. The results indicate that wing extensions can significantly increase both wing beam mode and torsion mode damping, and the flutter speeds of beam mode and torsion mode are increased by 60 knots and 80 knots, respectively; and their influence on wing chord mode is minimal. Tuning the beam-bending stiffness of the wing extensions can increase the whirl flutter speed by 80 knots through damping exchanges between the wing beam and torsion modes. The composite tailoring of wing and wing extension box beams has the potential to increase both wing beam and chord mode stability margins with only slight decrease of damping of wing torsion mode. Parametric studies of winglets show that damping of wing modes is sensitive to winglet geometry such as cant, sweep and toe.