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J85
A General Electric J85-5
Type Turbojet
National origin United States
Manufacturer General Electric
First run 1950s
Major applications A-37 Dragonfly
Canadair CL-41 Tutor
Northrop F-5
T-38 Talon
Variants General Electric CJ610
Developed into General Electric CF700

The General Electric J85 is a small single-shaft turbojet engine. Military versions produce up to 2,950 lbf (13 kN) of thrust dry, afterburning variants can reach up to 5,000 lbf (22 kN). The engine, depending upon additional equipment and specific model, weighs from 300 to 500 pounds (140 to 230 kg), giving it the highest thrust-to-weight ratio of any production turbojet in the world. It is one of GE's most successful and longest in service military jet engines, 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, while the CF700 adds an uncommon rear-mounted fan for improved fuel economy.

Contents

Design and development

The J85 was originally designed to power a large decoy aircraft, 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 England, 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 T-38 Talon, Northrop F-5, Canadair CT-114 Tutor, and Cessna A-37 Dragonfly light attack aircraft. More recently, J85s are used on the Scaled Composites White Knight aircraft, the carrier for the Scaled Composites SpaceShipOne spacecraft, and the aircraft in the US Me 262 Project.

The basic engine design is quite small, about 18 inches (46 cm) in diameter, and 45 inches long (114 cm). It features an eight-stage axial-flow compressor powered by two turbine stages, and is capable of generating up to 2,950 lbf (13 kN) of dry thrust, or more with an afterburner. At full throttle at sea level, this engine, without afterburner, consumes approximately 400 US gallons (1,520 L) of fuel per hour. At cruise altitude and power, it consumes approximately 100 gallons (380 L) per hour.

Several variants were produced. The J85-21 variant added a stage ahead of the base 8-stage compressor for a total of 9 stages, improving thrust.

Variants

  • J85-GE-1 - 2,600 lbf (11.6 kN) thrust
  • J85-GE-3 - 2,450 lbf (10.9 kN) thrust
  • J85-GE-4 - 2,950 lbf (13.1 kN) thrust
  • J85-GE-5 - 2,400 lbf (10.7 kN) thrust, 3,600 lbf (16 kN) afterburning thrust
  • J85-GE-5A - 3,850 lbf (17.1 kN) afterburning thrust
  • J85-GE-13 - 4,080 lbf (18.1 kN), 4,850 lbf (21.6 kN) thrust
  • J85-GE-15 - 4,300 lbf (19 kN) thrust
  • J85-GE-17A - 2,850 lbf (12.7 kN) thrust
  • J85-GE-21 - 5,000 lbf (22 kN) thrust

Applications

Scaled Composites White Knight sporting two General Electric J85 afterburning engines
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Other

Specifications

A J85 engine sectioned for display

General characteristics

  • Type: Turbojet engine (with or without afterburner)
  • Length: 45.4 – 51.1 inches (depending on accessory equipment installed)
  • Diameter: 17.7 inches
  • Dry weight: 396 – 421 pounds (depending on accessory equipment installed)

Components

Performance

See also

Related development

Comparable engines

Related lists

References

  • Gunston, Bill (2006). World Encyclopedia of Aero Engines, 5th Edition. Phoenix Mill, Gloucestershire, England, UK: Sutton Publishing Limited. ISBN 0-7509-4479-X.  

External links


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