The Pratt & Whitney J75 (civilian designation: JT4A) is an axial-flow turbojet engine first flown in 1955. A two-spool design in the 17,000 lbf (76 kN) thrust class, the J75 was essentially the bigger brother of the Pratt & Whitney J57 (JT3C). It was known in civilian service as the JT4A, and in a variety of stationary roles as the GG4 and FT4.
Design and development
In military use, the J75 was used on the Convair F-106 Delta Dart, Lockheed U-2, and Republic F-105 Thunderchief. It was also utilized in the prototype and experimental Avro Canada CF-105 Arrow, Lockheed A-12, Martin P6M SeaMaster, North American YF-107, and Vought XF8U-3 Crusader III.
Before the arrival of the Pratt & Whitney JT3D turbofan engine, the JT4A was used to power certain Boeing 707 and Douglas DC-8 models, bringing improved field performance in the medium-range Boeing 707-220 and Douglas DC-8-20, and intercontinental range in the Boeing 707-320 and the Douglas DC-8-30. By late 1959, P&W had considered introducing a turbofan version of the J75, which was to have tentatively been named the TF75 or JT4D. Apparently, little interest was shown by the aircraft industry, so the variant was dropped.
Marine & power generation
After its relatively short lifetime in the aircraft role, the JT4A found more enduring use in the naval role, where the FT4 was produced in a variety of models between . Well-known uses include the first all-turbine warships, the Canadian s, as well as the United States Coast Guard's s, the 1970s-built icebreakers Polar Sea and Polar Star (each 3 engines in CODOG configuration), and it was considered for the US Navy's . The same basic powerplant saw much wider use as a peak demand power turbine running on natural gas. From its introduction in 1960 over 1,000 FT4s have been sold, with many of them still in operation for electrical generation. Outdated by modern standards, refits are available that add catalytic converters to lower their emissions.
Variants
J75-P-1
J75-P-3 thrust
J75-P-5 thrust
J75-P-9
J75-P-11
J75-P-13B thrust
J75-P-15W afterburning thrust
J75-P-17 afterburning thrust
J75-P-19 afterburning thrust
J75-P-19W afterburning thrust with water injection
JT4A-3
JT4A-4
JT4A-9
JT4A-11 thrust
JT4A-29 (J75-P-19W) afterburning thrust with water injection
Applications
J75
Avro Canada CF-105 Mk1 Arrow
Convair F-106 Delta Dart
Lockheed A-12
Lockheed U-2
Martin P6M SeaMaster
North American F-107
Republic F-105 Thunderchief
Vought XF8U-3 Crusader III
JT4A
Boeing 707 (specifically, the 707-220 and 707-320) Douglas DC-8 (specifically, the DC-8-20 and DC-8-30)
Specifications (JT4A-11)