Pratt & Whitney JT4

Part of a Pratt & Whitney J75

The Pratt & Whitney JT4 (military name Pratt & Whitney J75 ) is a jet engine from the American manufacturer Pratt & Whitney . It is a twin-shaft turbojet engine with an axial design. It was manufactured in larger series between 1956 and 1967.

Development began in 1951 and lasted until 1954. The aim was to create a powerful engine for the first generation of supersonic aircraft of the US Navy and Air Force. In its basic structure and in the components for control, fuel supply and lubrication, it was similar to the smaller Pratt & Whitney J57 . The fuel was injected through six fuel nozzles each into eight individual combustion tubes arranged around the compressor housing. The military variant could be supplied with or without an afterburner . Water injection was possible to further increase performance .

The engine was initially mass-produced for the Republic F-105 , but was also used on the F-106 and the Lockheed U-2 . The first prototypes of the Lockheed A-12 Oxcart were initially also equipped with the J75, as the release of the originally planned Pratt & Whitney J58 was delayed. The first flight with a Pratt & Whitney YJ75-P-3 was in an F-105 in 1955. This pre-series sample delivered a dry thrust of 71.2 kN. The most powerful series engine, the J75-P-19W, already delivered 118 kN of thrust with an afterburner and water injection. The total length of this version with afterburner and thrust tube was 6.1 m. The engine is started with compressed air, but also has a pyrotechnic starting device that can be operated by the pilot. This means that the required starting speed can be reached within 10 s.

The civilian variant received its approval for commercial aviation by the FAA in March 1957 . It was used in the Boeing 707-220 and -320 as well as in the Douglas DC-8-20 and -30 . All civil engines were delivered without an afterburner.

Technical data (JT4A-9)

• Low pressure compressor: eight stages
• High pressure compressor: seven stages
• High pressure turbine: one stage
• Low pressure turbine: two stages
• Diameter: 1092 mm
• Length: 3680 mm
• Weight: 2291 kg
• Thrust: 74.7 kN at 8000 min-1
• 12: 1 print ratio
• Air mass flow rate: 113 kg / s

swell

• “Jane's all the World's aircraft” 1969/70

Web links

Commons : Pratt & Whitney J75  - collection of pictures, videos and audio files