General Electric J85

Monday, September 27, 2010

The J85 was a single-shaft, axial-flow turbojet engine developed by General Electric for Northrop to power the F-5 Freedom Fighter and the T-38 Talon. It was also used on the A-37 Dragonfly attack aircraft. The GE J85 could produce up to 2,950 lbf (13 kN) of thrust dry, as afterburning variants could reach up to 5,000 lbf (22 kN).

The basic engine design was quite small, about 18 inches (0.46 m) in diameter, and 45 inches long (1.14 m). It was fitted with an eight-stage axial-flow compressor powered by two turbine stages, as it was 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, consumed approximately 400 US gallons (1,520 L) of fuel per hour. At cruise altitude and power, it consumed approximately 100 gallons (380 L) per hour. Several variants of the J85 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 of the General Electric J85

Type: Turbojet engine
Length: 45.4 inches
Diameter: 17.7 inches
Dry weight: 396 – 421 pounds (depending on accessory equipment installed)
Compressor: 8 stages (9 stages in J85-21)
Combustors: annular
Turbine: 2 stages
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)