a stiff in - plane gimbaled rotor head for a rotorcraft , such as a helicopter , includes a vertically extending rotor shaft , a center hub disposed on the rotor shaft for conjoint rotation therewith , and an outer hub surrounding the center hub and coupled thereto through a spherical gimbal bearing for conjoint rotation therewith , and such that the outer hub is also capable of an angular range of gimbaling movement relative to the center hub . a plurality of rotor blades , which may include three or more blades , is coupled to the rotor shaft through the inner and outer hubs by a constant velocity joint that enables the blades to be rotated in a common plane about the axis of the rotor shaft while controlling the respective pitches of the blades and such that any other relative in - plane and out - of - plane movements of the blades during rotation is prevented .