General Electric J85
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General Electric J85-5

The General Electric J85 is a small single-shaft turbojet engine. Military versions produce up to 2,950 lbf (18 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 between 300 to 500 pounds, 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 US 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 CJ700 adds an uncommon rear-mounted fan for improved fuel economy.

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 operators on the ground. This mission demanded a small engine that could nevertheless provide enough power to keep up with the jet bomber. Unlike the similar Armstrong Siddeley Viper being built in England, the engine on a Quail drone did not have to last for extended periods of time, so therefore could be built of low-quality materials.

The fit was a success on the Quail, and would subsequently be used on small jet aircraft, including the T-38 Talon, F-5 Freedom Fighter, 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 was quite small, about 18 inches around and 45 long. It featured an eight-stage axial-flow compressor powered by two turbine stages. It is capable of generating up to 2,950 lbf (18 kN) of dry thrust or more, with an afterburner. At full throttle at sea level, this engine, without afterburner, consumes approximately 400 gallons of fuel per hour. At cruise altitude and power, it consumes approximately 100 gallons 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.

Specifications

Scaled Composites White Knight sporting two General Electric J85 afterburners

General characteristics

• Type: Afterburning turbojet engine
• Length: 45.4 to 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

• 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)

Versions

• J85-GE-3: 2,450 lbf (10.9 kN) thrust
• J85-GE-4: 2,950 lbf (13.1 kN) thrust
• J85-GE-5A: 3,850 lbf (17.1 kN) afterburning thrust
• J85-GE-13: 4,080 lbf
• J85-GE-15: 4,300 lbf
• J85-GE-21: 5,000 lbf

Trivia

Two J85-GE-21 engines power the American Challenge WSR jet-powered boat. [1]

References

• GE J85 product page
• GE CJ610 product page

External links

• J85 picture
• CF700 picture