An improved aeroelastic formulation for the advanced geometry blades, involving variable sweep, droop, pretwist, and planform, is presented. The blade is modeled as a series of arbitrarily-oriented elastic segments with each segment divided into finite elements. Inter-element compatibility relations governing non-Eulerian moderate rotations of the finite elements are also presented. Fuselage dynamic interaction with the advanced geometry blades is included in the formulation. The nonlinear partial differential equations of motion are discretized in space and time using Hamilton's principle. Selective results are presented in hover and forward flight. Results indicate that sweep, and droop in particular, can have a strong influence on both the rotor aeroelastic stability and the rotorcraft aeromechanical stability. Droop can be considerably stabilizing. Sweep increases the blade torsional loads, but is not detrimental to flap and lag vibratory loads. 1 1 Copyright © by American Institute of Aeronautics and Astronautics, Inc., 1993. All rights reserved.