Advancing Blade Concept (ABC)™ High Speed Development

Development of the Advancing Blade Concept at Sikorsky Aircraft began in 1964. Major program milestones have included: full scale wind tunnel tests completed in 1970 and flight test of the demonstrator aircraft in the helicopter mode which was completed in 1977. Subsequent to the helicopter tests, the aircraft was reconfigured to the auxiliary propulsion mode. The primary changes in this reconfiguration were reduction of horizontal tail incidence from +10 degrees to -5 degrees and installation of two J60-P3A turbojet engines for auxiliary thrust. Flight testing of the auxiliary propulsion configuration was initiated in 1978. Two different rotor indexings have been investigated with the flight envelope being expanded to over 235 knots. The results of this flight program to date are presented in this paper. Included are envelope expansion, handling qualities, performance and flight loads. Each speed increment has included full expansion of the maneuver, turn and sideslip envelopes, further expanding on the excellent envelopes developed during the helicopter tests. Performance results have agreed well with predictions, and comparisons with theory are included. As with the helicopter mode, rotor blade stresses have been fully controllable and control loads have remained low. It has been determined that with no vibration treatment installed (absorbers or isolators) the vibration levels are the same magnitude as untreated current generation helicopters. Test results show the performance, stability and control power characteristics of the ABC rotor system provide the XH-59A with excellent agility characteristics.