General Electric J85

The General Electric J85 is a small single-shaft turbojet engine. Military versions produce up to 2,950 lbf (13.1 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). 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.[1] 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.

J85
A General Electric J85-5
Type Turbojet
National origin United States
Manufacturer General Electric
First run 1950s
Major applications Cessna A-37 Dragonfly
Canadair CT-114 Tutor
Northrop F-5
Northrop T-38 Talon
Variants General Electric CJ610
Developed into General Electric CF700

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 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 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 inches (45 cm) in diameter, and 45.4 inches (115 cm) long. It features an eight-stage axial-flow compressor powered by two turbine stages, and is capable of generating up to 2,100 lbf (9.3 kN) of dry thrust, or more with an afterburner. At full throttle at sea level, this engine, without afterburner, consumes approximately 400 US gallons (1,500 L) of fuel per hour. At cruise altitude and power, it consumes approximately 100 US gal (380 L) 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.[2]

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 (45 cm) to 20.8 in (53 cm), 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 lbf (16 kN) and wet thrust to 5,000 lbf (22 kN) while reducing mechanical complexity along with the weight gain of the J85-21 model.[2]

More than 12,000 J85 engines had been built by the time production ended in 1988.[3]

Iranian reverse engineering
See also: Iran Aviation Industries Organization

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.[4][5][6][7]

The Owj engine has been used in several Iranian products like Kowsar, Saeghe and Azarakhsh fighter jets or Yasin training jet.[8][9]

Variants
J85 out of a T-38C
J85-GE-1
1,900–2,100 lbf (8.5–9.3 kN) thrust[2]
J85-GE-2
2,850 lbf (12.7 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 (11 kN) thrust, 3,600 lbf (16 kN) afterburning thrust
J85-GE-5A
3,850 lbf (17.1 kN) afterburning thrust
J85-GE-7
2,450 lbf (10.9 kN) thrust
J85-GE-12
J85-GE-13
2,720 lbf (12.1 kN), 4,080 lbf (18.1 kN) thrust[10]
J85-GE-15
4,300 lbf (19 kN) afterburning thrust[2]
J85-CAN-15
Orenda manufactured J85-GE-15 for the Canadair CF-116 4,300 lbf (19 kN) thrust
J85-GE-17A
2,850 lbf (12.7 kN) thrust[11]
J85-GE-19
J85-GE-21A
3,500 lbf (16 kN) military thrust; 5,000 lbf (22 kN) afterburning thrust.[10]
J85-GE-J1A
5,000 lbf (22 kN) thrust
J85-GE-J2
2,850 lbf (12.7 kN) thrust.
J85-GE-J4
J85-CAN-40
Manufactured by Orenda for the Canadair CT-114 Tutor, 2,650 lbf (11.8 kN) thrust

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

Other

Specifications (J85-GE-21)
A J85-GE-17A engine sectioned for display

Data from [16][17][18][19]

General characteristics
  • Type: afterburning turbojet engine
  • Length: 112.5 in (286 cm)
  • Diameter: 20.8 in (53 cm) inlet
  • Dry weight: 684 lb (310 kg)

Components

Performance
  • Maximum thrust: 3,600 lbf (16 kN) dry thrust / 5,000 lbf (22 kN) afterburner thrust
  • Overall pressure ratio: 8.3:1 (J85-21 A~C model)
  • Air mass flow: 53 lb (24 kg) per second
  • Turbine inlet temperature: 1,790 °F (980 °C)
  • Specific fuel consumption: 1.24 lb/(lbf⋅h) or 35 g/(kN⋅s) dry thrust / 2.13 lb/(lbf⋅h) or 60 g/(kN⋅s) afterburner thrust
  • Thrust-to-weight ratio: 5.25 dry / 7.3 afterburner

See also

Related development

Comparable engines

Related lists

References
  1. 2001-04-17T00:00:00+01:00. "T-38 engine upgrades set to extend trainer's life to 2040". Flight Global. Retrieved 2020-05-20.
  2. Defense Technical Information Center Compilation Part Notice dtic.mil
  3. "General Electric J85-GE-17A Turbojet Engine, Cutaway". Archived from the original on 2014-02-03. Retrieved 2014-01-28.
  4. "موتورهای هوایی مورد نیاز ایران، ایا راهی برای برون رفت از بحران هست؟". April 3, 2018.
  5. "Iran Upgrades".
  6. "Iran's U.S.-Made F-5 Jets Could Fly Until the 2040s". 11 February 2019.
  7. "Military Knowledge: Kowsar Fighter Jet + Images – Islamic World News". 30 June 2020.
  8. "Kowsar; fighter with distinctive features". iranpress.com. Retrieved 2023-04-26.
  9. Network, Frontier India News (2023-03-11). "Iran launches production of HESA Yasin Light jet powered trainer aircraft". World News briefs. Retrieved 2023-04-26.
  10. Roskam, Jan (November 28, 1985). Airplane Design. DARcorporation. ISBN 9781884885563 – via Google Books.
  11. "Turbojet Engine, Cutaway, General Electric J85-GE-17A | National Air and Space Museum". airandspace.si.edu.
  12. Guy Norris (Jul 10, 2018). "Boom Focuses On Derivative Engines For Supersonic Airliner Plan". Aviation Week & Space Technology.
  13. "OV10B". www.germanwing.de.
  14. "400 Mph On Water". Popular Mechanics. Archived from the original on September 30, 2007.
  15. "CHIMERA". Hermeus. Retrieved 2023-03-10.
  16. "Turbofan and Turbojet Engines Database Handbook" (PDF). ptabdata. Retrieved 31 July 2023.
  17. Engine Data Tables Springer
  18. Roskam, Jan (1985). Airplane Design - Jan Roskam - Google Knjige. ISBN 9781884885563.
  19. "Taiwan Plans Re-engineering J85 Turbojet Engines for Long-range Missiles". 3 January 2019.
  • Gunston, Bill (2006). World Encyclopedia of Aero Engines, 5th Edition. Phoenix Mill, Gloucestershire, England, UK: Sutton Publishing Limited. ISBN 0-7509-4479-X.
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