Abstract: A rotor system (4) having odd and even blade assemblies (O.sub.b, E.sub.b) mounting to and rotating with a rotor hub assembly (6) wherein the odd blade assemblies (O.sub.b) define a radial length R.sub.O, and the even blade assemblies (E.sub.b) define a radial length R.sub.E and wherein the radial length R.sub.E is between about 70% to about 95% of the radial length R.sub.O. Other embodiments of the invention are directed to a Variable Diameter Rotor system (4) which may be configured for operating in various operating modes for optimizing aerodynamic and acoustic performance. The Variable Diameter Rotor system (4) includes odd and even blade assemblies (O.sub.b, E.sub.b) having inboard and outboard blade sections (10, 12) wherein the outboard blade sections (12) telescopically mount to the inboard blade sections (10). The outboard blade sections (12) are positioned with respect to the inboard blade sections (10 such that the radial length R.sub.E of the even blade assemblies (E.sub.

Abstract: A variable diameter rotor for a tilt rotor aircraft has an inboard section having a linear twist from a root end to an outboard end thereof, and an outboard section telescoped over the inboard section which additionally has a linear twist from a root end to an outboard end thereof. The outboard section is disposed at an offset of about 4.degree. to 15.degree. relative to the inboard section to provide a step wise change in twist angle when in the extended condition, such that the rotor when operated in the helicopter mode, can be operated at high blade pitch angles without premature stalling along the inboard airfoil surfaces This allows efficient operation at high thrust coefficient/solidarity ratios. Optionally, the trailing edge of the outboard section is rotated along the aft 30% of chord of the airfoil section to provide an equivalent twist increase in the offset at the transition between the blade sections.