General Electric J85
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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. 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. 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.
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 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 had to last for extended periods of time, and could not 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 jet trainer, and Cessna A-37 Dragonfly light attack fighter. More recently, J85s are used on the Scaled Composites White Knight aircraft, the carrier for the Scaled Composites SpaceShipOne spacecraft.
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. Another variant, the CF700, adds a rear-mounted "flade" connected directly to the low-pressure turbine blade. Civilian versions have powered business jets such as the Learjet 23 and the Hamburger Flugzeugbau HFB-320 Hansa Jet.
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[edit] Specifications
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 (or 9)
- Combustors: cannular
- Turbine: 2 stages
Performance
- Thrust: 2850 - 3100 lb/thrust (dry)
- Specific fuel consumption: 0.96 - 0.97
- Power-to-weight ratio:
[edit] Versions
- J85-GE-3: 2,450 lb (10.9 kN) thrust
- J85-GE-4: 2,950 lb (13.1 kN) thrust
- J85-GE-5A: 3,850 lb (17.1 kN) afterburning thrust
[edit] References
[edit] External links
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