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Rotor Systems Research Aircraft (RSRA)

The Rotor Systems Research Aircraft (RSRA) was a unique pure research aircraft developed to fill the void between design analysis, wind tunnel testing, and flight results of rotor aircraft. The aircraft was designed to investigate the concepts involved with stopping the main rotor in flight, with the large blades then providing aerodynamic lift assistance to the stubby conventional wings extending from the lower fuselage. This concept gave the aircraft the vertical flight stability of a helicopter, and the horizontal cruise capability of a conventional aircraft. The program began to investigate ways to increase the speed of rotor aircraft, as well as their performance, reliability, and safety. It also sought to reduce the noise, vibration, and maintenance costs of helicopters.

The modified RSRA was developed to provide a vehicle for in-flight investigation and verification of new helicopter rotor-system concepts and supporting technology. The RSRA could be configured to fly as an airplane with fixed wings, as a helicopter, or as a compound vehicle that could transition between the two configurations. The test aircraft had a basic helicopter fuselage with the wings and lower horizontal all-flying stabilizer installed. These aircraft were powered by two T-58-GE-5 turboshaft engines through an S-61 main transmission. The compound configuration added two TF-34-GE-400A turbofans mounted on either side of the fuselage as auxiliary engines and a large wing including fixed-wing control surfaces. These GE TF-34's were used to offset drag effects when rotor systems were being tested with the aircraft in compound configuration, and to provide thrust for the airplane configuration.

The compound aircraft was equipped with 14 load cells to measure main-rotor thrust, torque, and drag, wing lift and drag, tail-rotor thrust, and auxiliary engine thrust; the helicopter version was instrumented to measure main-rotor thrust, torque, drag, and tail-rotor thrust. Both aircraft (called Heathcliffe and Gertrude) were equipped to measure over 500 other aircraft and rotor state, structural, and acceleration parameters.

The joint NASA / Army / Defense Advanced Research Projects Agency (DARPA) project began in December of 1970, with the first of two aircraft arriving from Sikorsky on February 11, 1979. Two joint Army and National Aeronautics and Space Agency (NASA) projects were initiated during 1972 to further the advanced helicopter development effort. These were the Tilt Rotor Research Aircraft and the Rotor Systems Research Aircraft (RSRA) programs. Memoranda of Agreement were signed by the Army and NASA in November 1971 authorizing a joint development and testing effort. Preliminary design studies for the tilt rotor aircraft had been accomplished, and redesign (feasibility) study contracts for the RSRA awarded. Feasibility and predesign studies were completed in 1973 for the Rotor Systems Research Aircraft (RSRA) and a request for proposal released to industry. On 17 January 1974 the two agencies approved the plan for the RSRA of the Sikorsky Aircraft Division, United Aircraft Corporation. Completion of the project should add to basic rotorcraft technology and verify through flight experimentation a wide variety of promising rotor concepts and supporting technologies.

A Rotor Systems Research Aircraft (RSRA) underwent limited ground and flight tests at the Dryden Flight Research Center, Edwards, California, in spring of 1984. The purpose of the tests were to train pilots and to verify and develop the design flight envelope established by the Sikorsky Aircraft Company. The tests at Dryden were to familiarize pilots and researchers with the ground-handling and takeoff flight characteristics, as well as to acquire in-flight data in the aircraft configuration, with the main rotor removed. Tests were successful and lead to later rotor research conducted at NASA's Ames Research Center.

The purpose of the 1984 tests was to demonstrate the fixed-wing capability of the helicopter/airplane hybrid research vehicle and explore its flight envelope and flying qualities. These tests, flown by Ames pilot G. Warren Hall and Army Maj (soon promoted to Lt. Col.) Patrick Morris, began in May and continued until October 1984, when the RSRA vehicle returned to Ames.

The craft was rolled out 19 August 1986. Taxi tests and initial low-altitude flight tests without the main rotor attached were carried out at Dryden before the program was terminated in 1988.

The compound configuration continued in flight research and provided critical support to the X-Wing project. One contribution came in a flight test by the Ames team at Dryden, where the aircraft was flown without the rotor system. This flight mode was required for the aircraft to test high-risk rotor configurations, which might have to be separated from the aircraft as a result of system failure or instability. The pyrotechnic blade-separation system was used for both the RSRA and X-Wing. Gregory Condon led the program at the outset, followed at a later date by William (Bill) Snyder. John Burks, Ruben Erickson, and Ed Seto served as test directors for the two aircraft. Warren Hall was the project pilot throughout the program; LTC Bob Merrill also participated as a program pilot during the early stages. The RSRA compound configuration was placed in flyable storage in 1986 after an extensive internal assessment determined that the most cost-effective way to meet industry's needs for modern rotor air-load data was through tests with a UH-60 airframe.

These early tests were preparatory for a future X-Wing rotor flight test project to be sponsored by NASA, the Defense Advanced Research Projects Agency (DARPA), and Sikorsky Aircraft. A later derivative X-Wing flew in 1987. One of the two RSRA aircraft was later modified to the X-Wing and received limited testing at Dryden before the program was terminated in 1988.



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