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J79

General Electric's answer to Pratt & Whitney's JT3 (J57) was the J79, with an innovative compressor with variable stators. General Electric's approach was to design a single spool 17 stage axial flow compressor with variable stators to prevent rotor blades from stalling. These controllable stators, or the variable geometry compressor as it came to be known, were the foundation for the J79 series of military engines. Pratt & Whitney used a successful high pressure ratio (12:1) design consisting of two separate compressors in series (one with nine stages and one with seven stages). The two compressors ran at different rotational speeds and were only aerodynamically coupled.

The development of the J79 turbojet began in 1952 as a more powerful follow-up to the General Electric J47 turbojet. The General Electric J79 engine was a high-performance single-shaft turbojet that featured variable-incidence stator blades in the later high-pressure stages of its seventeen-stage compressor. The J79 turbojet, the first high-compression variable-stator engine built in United States by GE, powered most Mach 2 U.S. aircraft, including the F-104, B-58, F11F-1F, F4H, and A3J, as well as the Regulus II missile. The production F-104 was capable of flying at Mach 1.8, while the twin-engined F-4 Phantom and the four-engined B-58 were both capable of flying at over twice the speed of sound. The engine has seen decades of faithful service and has stood the test of time.

Widely used on several types of aircraft, including the Israeli Aircraft Industries Kfir, more than 17,000 examples of the J79 were built in its thirty-year production run. In its long and successful career the dependable J79 accumulated well over 30 million flying hours and probably clocked more supersonic flying time than any other Western military aircraft engine produced during the Cold War. Civilian variants of the J79 also powered the Convair 880 and 990 airliners.

The J79 was developed as an outgrowth of the General Electric J73 engine program and was known at first as the J73-GE-X24A. The X24A was designed for reliable Mach 2 performance with minimal required maintenance. Its innovative variable stator vanes, developed by General Electric engineer Gerhard Neumann, increased compressor air pressure and helped eliminate compressor stall. Variable-incidence stators allowed the single-shaft turbojet to develop high pressures similar to those of dual-shaft engines, but at significantly lighter weight. The introduction of the variable stator vane turned out to be one of the most important developments in the history of jet aircraft engines.

The YJ79-GE-3 is the prototype version of the engine first flight-rated in 1954 for installation in the pre-production YF-104. It is just over seventeen feet long, slightly more than three feet in diameter, weighs around 3,500 pounds, and produced around 9,000 pounds of dry thrust. In full afterburner the YJ79 generated around 15,000 pounds of thrust with a fuel flow rate of ten gallons per second. Later versions of the J79 weighed anywhere from 3,500 to 3,800 pounds and produced up to 17,900 pounds of thrust in full afterburner.

On March 4, 1954, Lockheed test pilot Tony LeVier had taken the XF-104 Starfighter into the air for the first time, but subsequent flights had quickly revealed that its original engine couldn't propel the dramatic new interceptor to its required speeds. A very long fuselage contained the cockpit and fuel cells, landing gear, and a single Wright YJ65-W-6 turbojet engine. This was supported by a pair of extremely short, anhedral supersonic wings with sharp leading edges that had to be padded to protect ground crews.

This design had enormous promise, but subsequent flights soon revealed that the J65 could deliver a maximum speed of only Mach 1.79 (1,324 mph), approximately double that of the F-86 but still short of the Air Force's requirement of Mach 2.0 or better. The designers soon responded with a much-refined version of the troubled plane. They stretched the already-long fuselage by 5 feet, 6 inches in order to accommodate a new General Electric J79 axial-flow engine with 4,000 pounds greater thrust.

The first flight of a J79-powered aircraft was on 17 February 1956 when the Lockheed F-104A flew for the first time. Engine troubles cut the first flight short, but within a month the aircraft easily passed Mach 1 on the power of its single J79 engine.Built by Lockheed and dubbed the Starfighter, the F-104 is a single engine aircraft with a wing span of 21 ft., 11 in. Its engine is a General Electric J79 that delivers 15,800 lbs. of thrust with afterburner. The maximum speed of the F-104 is 1,320 mph, its cruise speed is 575 mph and its altitude limit is 58,000 ft. The F-104's big J79 engine and tiny wings led to its popular nickname, "the missile with a man in it."

The four General Electric J79-5 turbojet engines, so vital to the B-58's development, consumed fuel in prodigious quantities, particularly at supersonic velocities. Each of them produced 10,000 pounds of military thrust and 15,600 pounds of thrust with maximum afterburner at standard sea level static conditions, revolutionary figures for the mid-'50s. Each J79 featured a hydraulically actuated inlet spike that extended or retracted to match airflow velocity, keeping the conical shock wave outside the engine inlet during supersonic flight. Internally, the engine had variable position stator vanes in the first six stages of the compressor, which adjusted in pitch automatically as a function of engine speed and compressor inlet temperature, to minimize the possibility of compressor stall. An adjustable exhaust nozzle incorporated slatted vanes that opened and closed, depending on throttle, to give the most efficient thrust and specific fuel consumption.

Between fiscal years 1985 and 1994, the Air Force reduced its F-4 aircraft inventory from 1,597 to 61. Depot overhauls of the J79 engine, which powered the F-4 aircraft, also declined from over 500,000 direct labor hours in fiscal year 1986 to an estimated 0 for fiscal year 1997.




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