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The General Electric J85 engine

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Originally ordered by the U.S. Air Force strictly for the ADM-20 Quail, the J85 quickly found applications in other light-jet applications including the supersonic Northrop F-5/T-38 family.  Over 13,500 J85s and 2,000 commercial CJ610s have been delivered.

Engine Overview

The J85 augmented turbojet is a powerplant for high performance trainers and tactical aircraft. With more than 75 million flight hours experience on military and commercial models, the J85 offers the highest thrust-to-weight ratio of any production engine in its class in the free world.

J85 engines first entered service in 1960. More than 6,000 engines flying in a number of applications remain in active service in 35 countries. Current plans for the U.S. Air Force (USAF) call for J85-powered aircraft to be in service through 2040.

 

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J85 Turbojet Engine

The General Electric J85 turbine jet engine is used on the F-5 military fighter jet and the T-38 military trainer aircraft. The F-5 is a low-wing monoplane equipped with an all-moving horizontal tall mounted in the low position; the fuselage is carefully contoured in accordance with the transonic area rule. Small side-mounted inlets supply air for the two General Electric J85 afterburning turbojet engines.

The Northrop T-38 is a small low-wing two-seat trainer airplane, with a maximum weight of 12,000 lb. It is powered by two General Electric J85 afterburning turbojet engines located close together in the aft fuselage, each with 3850 lb of thrust. The first T-38 built flew in 1959. More than 1,100 were delivered to the Air Force between 1961 and 1972 when production ended. Approximately 562 remain in service throughout the Air Force and other facilities. The T-38 needs as little as 2,300 feet of runway to take off and can climb from sea level to nearly 30,000 feet in one minute. The engine problems in the T-38 aircraft were being addressed with almost $289M in the FY2001-05 FYDP for J85 engine modernization and other propulsion upgrades. The T-38 Propulsion Modernization Program (PMP) is comprised of four contractual efforts: a J85-5 engine modification and ejector nozzle will be sole source additions to a current contract with General Electric, b) the inlet/former/bulkhead kits will be a competitive award; c) a task order will be established on the existing Contractor Field Team (CFT) contract for kit installation; and d) the T-38 software changes required by the PMP will be added to the existing Boeing contract for the AUP.

General Electric J85 turbojets engines were used in the prototype for the F-117 Stealth fighter.

The X-14 accomplished its first flight on 19 February 1957 as a vertical takeoff, hover, and vertical landing. The first successful transition from hover to forward flight on occurred on 24 May 1958. In 1959, the Viper engines were replaced by General Electric J85 engines and the aircraft was delivered to the NASA Ames Research Center as the X-14A where it was used as a test aircraft until early 1963.

The C-123 featured high-mounted wings and tail surfaces on a pod-type fuselage which made for easy rear end, unobstructed on and off loading. Because of its powerful engines, it showed superior ability to operate in short field landings and take offs. It could carry 61 fully equipped troops for assault or evacuate 50 patients on litters plus six attendants. In 1966, some models were fitted with auxiliary powerplants in a pylon-mounted 2,850 lbs. thrust GE J-85 turbojet outboard of each engine. These were for emergency use.

Vietnam era gunships included the Spectre (AC-130), Shadow (AC-119G) and Stinger (AC-119K) with increases in airspeed, armor, altitudes, and computer aided guns. The AC-119G was a gunship conversion of the C-119G with four 7.62mm miniguns installed. The AC-119K's were modified "Shadow" gunships with two J85 auxiliary jet engines installed and two 20mm cannons.

Using a combination of radar reflectors, chaff, electronic repeaters, and infrared simulators to mimic the large B-52 bomber, the diminutive ADM-20 Quail decoy could be programmed to execute at least one change in cruising speed and two turns after being released from its B-52 carrier. Powered by a single General Electric J85-GE-7 turbojet engine, the Quail could achieve a maximum speed of Mach 0.85 at 50,000 feet.

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J85 Turbojet Engine with Afterburner

The BQM-34S Aerial Target is a recoverable, remote-controlled subsonic target capable of speeds up to 0.9 MACH and altitudes from 10-50,000 feet. It is propelled during flight by a single J69-T41 or J85-GE-100 turbojet engine which produces 1,920 or 2,800 pounds static thrust (respectively) at sea level.

In all, Bell Aerosystems, Buffalo, NY built five LM trainers of this type for NASA. Two were an early version called the Lunar Landing Research Vehicle ( LLRV ). Neil Armstrong was flying LLRV-1 on May 6, 1968 when it went out of control. He ejected safely and the vehicle crashed. A later version was called the Lunar Landing Training Vehicle or LLTV and three were built. Two of these were lost in crashes on December 8, 1968 (LLTV-1 piloted by Algranti) and January 29, 1971 (piloted by Stuart M. Present). Both pilots ejected safely. The LLTV was a more accurate LM simulator. The LLTV was for training in the critical final phases of the descent, from 500 to 700 feet on down. It had a J85 jet engine which, basically, maintained a constant thrust - based upon the weight of the vehicle - and took away 5/6th of the weight. That put you in a simulated lunar one-sixth gravity environment. There were sets of RCS thrusters, just like the lunar module, to control attitude. In addition, there were two other, vertically-mounted, hydrogen-peroxide-fueled 'lift' rockets that were capable of handling the extra one-sixth of the weight above the five-sixth that the J85 removed.

Given the cost of experimental flight aircraft and the evolution of increasingly sophisticated electronic and simulator systems, it was perhaps inevitable that NASA eventually turned to smaller, pilotless radio-controlled aircraft. In the 1980s, this idea was embodied in the HiMAT, a contraction of Highly Maneuverable Aircraft Technology. The HiMAT, powered by a General Electric J85 turbojet engine, had a length of 23 feet and a wing span of 16 feet.

The J85 engine was originally designed for a maximum flight speed of Mach 2. Engine performance drops off past Mach 2, and increased compressor temperatures approach material limits. In early 1998 NASA Lewis researchers completed a series of tests inside the Center's Propulsion Systems Laboratory to evaluate the operability of a General Electric J85-21 turbojet engine that they retrofitted to run at Mach 3, 1-1/2 times faster than its maximum flight speed of Mach 2. The tests were part of an overall program, supported by NASA's Hypersonics Office, to develop a turbine-based combined-cycle propulsion concept that may one day propel aircraft and spacecraft from take-off to hypersonic speeds of more than 5 times the speed of sound. The NASA Lewis concept could revolutionize high-performance aircraft and ultimately make space exploration more affordable by using air-breathing propulsion.

 

J85-5

Manufacturer:   General Electric
 

Specs:

Military Thrust 2680 lbs
Weight -
600 lbs
Compressor -
8 Stage Axial
Turbine -
2 Stage Axial
Application -
T-38 Jet Trainer, F-5 Tiger II
A-37 (non-afterburning)

Max RPM
16,550


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The GE - J85

 

 

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 lbf13 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.

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.

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Scaled Composites White Knight sporting two General Electric J85 afterburning engines
A J85 engine sectioned for display

 

 

Specifications

 

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)

 

References

  1. ^ 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. 

Wikipedia

 

 

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Last Updated

02/10/2014

 

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