Even though the low-level performance of the XF-84F was good, the USAF felt that more power was badly needed to improve a relatively sluggish takeoff, climb, and high-altitude performance. For this purpose, the British-designed Armstrong-Siddeley Sapphire axial-flow turbojet of 7200 lb.st. was selected, and arrangements were made to have the Sapphire engine produced under license in the USA by Curtiss-Wright as the J65.
The Sapphire engine was considerably larger than the J35, which required that the fuselage of the XF-84F be extensively redesigned in order to accommodate it. The depth of the fuselage was increased by seven inches, and the nose intake was enlarged to an elliptical shape. The first prototype XF-84F (49-2430) was reengined with an imported Sapphire, and flew for the first time with this engine on February 14, 1951.
Two pre-production YF-84F aircraft (51-1344 and 51-1345) with Sapphire engines were built by Republic in 1951. The second example (51-1345) was completed with wing root air intakes, leaving the nose with a solid cover. The wing root intakes resulted in thrust losses as compared to the nose intake version, and were not adopted for production fighters.
Sources:
-
Fighters of the United States Air Force, Robert F. Dorr and David Donald,
Temple Press Aerospace, 1990.
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The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.
-
American Combat Planes, Third Enlarged Edition, Ray Wagner,
Doubleday, 1982.
-
United States Military Aircraft Since 1909, Gordon Swanborough and
Peter M. Bowers, Smithsonian, 1989.
- The Republic F-84F Thunderstreak, Ray Wagner, Profile Publications, 1966.
