A two-phase analytical investigation was conducted to continue the development and evaluation of the variable-diameter telescoping rotor aircraft (TRAC) rotor system. The first phase was a preliminary design of a full-scale, flightworthy rotor system suitable for subsequent wind tunnel testing in the NASA-Ames 40-by 80-foot wind tunnel and for flight testing on an H-3 helicopter or the NASA/Army Rotor Systems Research Aircraft (RSRA). The second phase of the investigation was a comparative parametric analysis to evaluate TRAC rotor compound helicopter and stowed rotor aircraft concepts relative to conventional-rotor pure and compound helicopters.