Abstract: A coaxial rotor system includes a center mast non-rotatably disposed at and extending from a helicopter. A rotation axis extends along the center mast. An inner mast is disposed along the center mast and is rotatable about the rotation axis in a first direction. A portion of the inner mast extends above an end of the center mast. An outer mast circumscribes the center mast and is rotatable about the rotation axis in an opposite second direction. The center mast extends above an end of the outer mast. An upper rotor blade assembly is rotatable with the inner mast. A lower rotor blade assembly is rotatable with the outer mast. A control system disposed at the center mast between the upper and lower rotor blade assemblies is operable to adjust pitch of a plurality of upper rotor blades and to adjust pitch of a plurality of lower rotor blades.