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The military designation for this engine is J-58, but that given by its constructor is JT-11. The test-bench testing conducted in 1958 was with the YJ-58 prototypes. The turbofan version envisaged in the 1960s for the American SST ("Super Sonic Transport") projects carried the designation of JT-11-F4. A JT-11-B4 variant with increased thrust was envisaged during the same era for studying Mach 3 flight. It seems that the designation J-58-P4 corresponds to the JT-11-D20B series as the J-58-P2 is the version developed for the US Navy, without bypass, with only a 4 stage compressor (eight stages in all) against five in the J-58-P4. The letter "B" at the end of a Pratt & Whitney engine designation signifies that it is modified for high-altitude flight (for example with burners adapted for JP-7 fuel).
The American system of engine designation is almost identical to that used for aircraft; a letter indicates the type of engine (for example R -"radial" ) followed by a distinguishing number. With jet motors, their designation commences with "J" (for jet engine), e.g. J-58 or J-75. double-flux engines, which appeared much later, are designated by a letter "F" (for fan), e.g. The Pratt & Whitney F-100, which equipped the F-15 and F-16 fighters. These letter-number combinations continue with one or two letters indicating the factory of manufacture, ("GE" for General Electric, "P" for Pratt & Whitney) and a "batch number" indicating a particular production batch. For example the J-79-GE15 which equipped the McDonnell F-4D Phantom II, or the J-57-P55 which equipped the McDonnell F-101 Voodoo whereas the Lockheed U-2 is fitted with the J-57-P31. The entire designation can also be preceded by a special letter, for example "X" for an experimental unit, or "Y" for a pre-series unit, or even "R" (for a ramjet).
© Aérostories 2002
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