A general finite‐element procedure is presented for modeling rotorcraft undergoing elastic deformations in addition to large rigid body motions with respect to inertial space. Special attention is given to the coupling of the rotor and fuselage subsystems subject to large relative rotations. Initially, the rotor and fuselage subsystems are assembled separately as small‐rotation finite‐element models in a moving coordinate system. In order to handle large rigid body rotations, the coordinate systems are tied to the structure using one of several alternate constraint methods. Finally, the equations which allow large rotations are constrained together using a rotating to nonrotating transformation which allows rotor azimuth angle as a degree of freedom. The resulting system of equations, which has not been implemented, is applicable to both helicopter trim and large angle maneuver analyses.