The Rockwell International XFV-12A, a thrust-augmented wing prototype supersonic fighter/attack aircraft, was designed to operate from small ships. The single engine, single seat prototype aircraft used parts from the A-4 and F-4; the fuselage was 44 ft long with a 28.5 ft wingspan and a 12 ft canard span. Operational vertical take-off weight was expected to be 19,500 lb, with a maximum speed of over Mach 2 anticipated by Rockwell.
In March 1961 NATO requested proposals for a new V/STOL close-support fighter with supersonic speed capability. The Hawker design team responded with the P.1154, a configuration with twice the thrust, twice the speed, twice the weight, and twice the performance of the P.1127. While pursuing the P.1154, Hawker continued demonstrations of the subsonic P.1127 and kept the program alive. The Labour government in the United Kingdom cancelled the P.1154 program and instructed the frustrated Royal Air Force to accept an upgraded version of the subsonic P.1127-the Harrier.
In the fall of 1972, the US Navy issued a request for proposals of the next generation V/STOL aircraft. Unfortunately, the list of candidates did not include any further development of the Harrier. Instead, the Navy favored the North American Rockwell XFV-12A supersonic fighter design. The XFV-12A used a thrust augmentation scheme that diverted the total exhaust flow of the main engine and ejected it through a venetian blind arrangement in the wings to give vertical-lift capability. The concept was considered by many to be very risky when compared with the proven Harrier approach, but the Navy was prepared to fully fund the development of the aircraft and close out further development of the Harrier.
The XFV-12A was a "Thrust Augmenter Wing" concept using a modified 30,000 lb thrust (in afterburner) Pratt & Whitney F401 engine. A diverter valve in the engine exhaust system blocked the nozzle and directed the gases through ducts to ejector nozzles in the wings and canards for vertical lift. The thrust of the spanwise ejectors was modulated by varying the diffuser angle. Pitch and roll were controlled by differential variation of the four ejectors from fore to aft and left to right, while yaw was controlled by differential ejector vectoring. An auxiliary engine inlet for use in vertical flight was located immediately behind the cockpit.
Engine rig testing began testing in 1974. The results of the free-flight model tests in 1974 in the NASA Langley Full-Scale Tunnel indicated that the projected thrust augmentation for the XFV-12A was considerably less than expected, and the thrust available for vertical flight was insufficient to permit powered-lift flights. Although the configuration flew well in conventional wing-borne flight, the NASA Langley team expressed grave concern over the deficient V/STOL capability of the free-flight model.
The Navy unveiled its new XFV-12A vertical/short takeoff and landing research aircraft at the Rockwell International facility in Columbus, Ohio on 26 August 1977. Aircraft ground testing in July 1977, and suspended tether trials conducted in 1978. Only one of two contracted aircraft were completed in order to curtail increasing costs.
In early 1978, tethered hover tests of the full-scale XFV-12A were carried out by a joint team of NASA, Navy, and Rockwell personnel. During 6 months of tests, it became apparent that major deficiencies existed in the XFV-12A for hovering flight, including marginal vertical thrust. Lab tests were interpreted to show that 55% augmentation could be anticipated, but differences from the lab models to the full scale system caused the actual augmentation to be onlu 19% for the wing and 6% for the canard. Although the augmentation of flow at the wing augmentors was as predicted, large losses in the internal ducting and corners of the propulsion system seriously degraded the net thrust to the extent that only 75 percent of the weight of the vehicle could be supported in attempts to hover.
The results of the tests at Langley influenced the Navy's decision to cancel the XFV-12A Program. Lift improvement testing and plans to modify the ejector/augmentor system were discontinued in 1981 due to cost overruns and waning Navy V/STOL interest.
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