The General Electric J85 is a small single-shaft turbojet engine. Military versions produce up to 3500 lb-f of thrust dry; afterburning variants can reach up to 5000 lb-f. The engine, depending upon additional equipment and specific model, weighs from 300 to 500 lb. It is one of GE's most successful and longest in service military jet engines, with the civilian versions having logged over 16.5 million hours of operation. The United States Air Force plans to continue using the J85 in aircraft through 2040. Civilian models, known as the CJ610, are similar but supplied without an afterburner and are identical to non-afterburning J85 variants, while the CF700 adds a rear-mounted fan for improved fuel economy.

Design and development

The J85 was originally designed to power a large decoy missile, the McDonnell ADM-20 Quail. The Quail was designed to be released from a B-52 Stratofortress in-flight and fly for long distances in formation with the launch aircraft, multiplying the number of targets facing the SA-2 surface-to-air missile operators on the ground. This mission demanded a small engine that could nevertheless provide enough power to keep up with the jet bomber. Like the similar Armstrong Siddeley Viper being built in the UK, the engine on a Quail drone had no need to last for extended periods of time, so therefore could be built of low-quality materials. The fit was a success on the Quail, but again like the Viper it was later built with normal grade materials and subsequently used to power small jet aircraft, including the Northrop T-38 Talon, Northrop F-5, Canadair CT-114 Tutor, and Cessna A-37 Dragonfly light attack aircraft. More recently, J85s have powered the Scaled Composites White Knight aircraft, the carrier for the Scaled Composites SpaceShipOne spacecraft, and the Me 262 Project. The basic engine design is quite small, about 17.7 in in diameter, and 45.4 in long. It features an eight-stage axial-flow compressor powered by two turbine stages, and is capable of generating up to 2,100 lb-f of dry thrust, or more with an afterburner. At full throttle at sea level, this engine, without afterburner, consumes approximately 400 USgal of fuel per hour. At cruise altitude and power, it consumes approximately 100 USgal per hour. Several variants were produced. The most advanced variant in the J85 series is the J85-21 model designed specifically for the F-5E/F during its development process. The J85-21 design replaces AM 355 chromium nickel molybdenum stainless steel alloy, used by previous J85 models for compressor rotors and blades, with a titanium alloy. Its inlet diameter was increased from 17.7 in to 20.8 in, and it included an added stage ahead of the base 8-stage compressor for a total of 9 stages. Its multiple disk rotors were replaced with a single-spool rotor, thus improving dry thrust to 3,600 lb-f and wet thrust to 5,000 lb-f while reducing mechanical complexity along with the weight gain of the J85-21 model. More than 12,000 J85 engines had been built by the time production ended in 1988.

Iranian reverse engineering

The Iranian Ministry of Defense constructed a new engine based on the General Electric J85-GE-21B named "OWJ" and presented it at a defense exhibition on 22 August 2016. The Owj engine has been used in several Iranian products like Kowsar, Saeghe and Azarakhsh fighter jets or Yasin training jet.

Variants

Applications

Other

Specifications (J85-GE-21)