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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.^{[citation needed]} 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.

[edit] 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).^{[citation needed]} 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.

[edit] 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

[edit] Applications

Scaled Composites White Knight sporting two General Electric J85 afterburning engines

[edit] Other

American Challenge water speed record jet-powered boat - Two J85-GE-21^[1]
Messerschmitt Me-262A-1c and B-1c. The "c" suffix stands for the flyable reproductions equipped with the J85 engine instead of the original Junkers Jumo 004 jet engine.

[edit] 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

Compressor: 8 stages (9 in J85-21)
Combustors: annular
Turbine: 2 stages

Performance

Maximum Thrust: 2850 – 3100 lbf thrust (dry)
Specific fuel consumption: 0.96 – 0.97
Thrust-to-weight ratio: 7.5 (-21), 6.6 (-5), 6.8 (-13), 7 (-15)

[edit] See also

Related development

Comparable engines

Related lists

List of aircraft engines

[edit] References

^ 400 Mph On Water - Popular Mechanics

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

[edit] External links

[0] 400 Mph On Water - Popular Mechanics

[1]

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