CONVERTIBLE ENGINES FOR FOLD TILT ROTOR AIRCRAFT AND ABC ROTORCRAFT

Study results that Identify unique development needs for convertible engines to power Fold Tilt Rotor (FTR) aircraft and Advancing Blade Concept (ABC)™ rotorcraft are presented. The FTR aircraft requires a convertible turbofan/turboshaft engine which can provide thrust at speeds to 0.75 Mach and shaft power to proprotors deployed for vertical and low speed wing borne flight. A hydrodynamic drive (torque converter) system capable of shaft speed synchronization and mechanical lockup was identified. The torque converter system can provide smooth engagement or disengagement of the fan drive. Since the fan is disengaged in the turboshaft operating mode, the fan may be designed for use only in the turbofan mode of operation to ensure maximum efficiency at cruise. The ABC rotorcraft requires a conventional turboshaft engine that can provide high power efficiently at an output rpm of 77% at 250 KTAS cruise, and at 100% rpm at takeoff. Current state of the art permits acceptable power turbine designs for these conditions, but additional turbine blade design data at high incidence angles as applicable to two-speed power turbine operation over a wide range of speeds should be obtained.