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No. 14333
ID: a2431f
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In February of 1977, in a well-meaning but ultimately futile gesture, President Jimmy Carter announced a new arms transfer policy in an attempt to reduce arms proliferation throughout the world. Under this policy, American manufacturers could no longer sell to foreign air forces any combat aircraft that were the equal of those in the US inventory.
There were significant exceptions to this rule, e.g. the four NATO users of the F-16 and, as a special exception, the nation of Israel. Exceptions were also made for arms deliveries to Iran so that the Shah could continue to act as a bulwark against Soviet expansion in the Persian Gulf region.
At first, South Korea's request for F-16s was turned down under this new rule, but was later approved as a quid pro quo for pending US troop withdrawals from Korea. However, nations such as Jordan, Taiwan, and Venezuela were denied access to the F-16. To cater for the 'embargoed' air forces, the FX Export Fighter Program was proposed, calling for an aircraft satisfying the following criteria:
-Performance, cost & capabilities should be between those of the F-5E and F-16A
-Multirole design (but optimized for the air-to-air role) and deliberately limited strike capabilities
-Payload/range performance had to be substantially inferior to that of contemporary fighters in the US inventory
-Deployment and maintenance had to be easier.
Finally, the design was to be such tat it was not easily upgradable without US help or permission. The DOD had no intent to sponsor the program, so the development of the FX Export Fighter depended entirely on the will of companies to take the financial risk.
Because of the high financial risk involved with the FX program, only two proposals were ultimately submitted: Northrop entered the F-5G/F-20, while General Dynamics teamed with General Electric to produce a less-capable export version of the Fighting Falcon, powered by a derivative of the J79 single-shaft turbojet. This project was announced by General Dynamics in November of 1979.
Although the J79 production in the states came to an end in 1979 (13,686 engines built) and the license production in Japan ceased the following year (while production in Israel still continued for use in the Kfir), the GE engine was the obvious choice to power a low-cost, easy-to-maintain export fighter. Used to power the B-58 Hustler, the F-104 Starfighter and the F-4 Phantom, the latter two were already in widespread service with large numbers of foreign air arms.
GE made some changes to the original design for use in the F-16/79 and designated it the J79-GE-17X. Obviously, the shape of the engine had to be altered to fit in the F-16s engine bay, furthermore a new feature was added to the engine, called Combat Plus (originally intended to boost the F-4 performance). When engaged by the pilot , Combat+ increases momentarily the fuel flow to the engine, in the mean time closing the engine nozzle slightly. This results in a net increase of the exhaust gas temperature by 100°F (56°C), producing a useful amount of extra thrust.
Even with Combat Plus, performance of this new version of the J79 was significantly inferior to the F100, and Combat Plus could only be used for short periods of time when specific operating conditions were met: the engine had to be running in full AB, compressor inlet temperature should not exceed 15°F (-9°C) and certain combinations of high speed / low altitude would result in excessive internal pressure build-up (due to high airflow involved) and would place extremely high strain on the engine casing. Combat Plus was eventually fitted to Israeli Kfir C-7 aircraft, which were powered by a J79 variant.
The main drawback of the uprated J79-GE-17X, however, is its military power fuel consumption, which is far higher than that of the F100. This was not considered to be a mission-critical factor, as the FX requirement restrained the range of the export fighter (limited strike capability). Another modification was the mating of the engine to the fuselage-mounted gearbox in the F-16, driving generators and hydraulically pumps. This problem was solved by adding a transfer gearbox to the powerplant.
A total of 3 development engines were built, the first being used for 60 hours of Preliminary Flight Rating Tests, running for 5 hours under simulated Mach 2.0 conditions. The two others were supplied to GD, where one of them was installed as the J79-GE-119 in F-16B serial number #75-0752 (acquired form the USAF in June 1980), one of the two original FSD F-16B aircraft.
Since the J79 engine required a lower airflow than did the F100 turbofan used on all production F-16A/B's, the shape of the air intake was altered. Only external difference between the original, modular designed (and thus easily replaceable) intake section and the new one is the lengthened upper surface of the intake, which extends much further forward, making it an obvious recognition feature. As the J79 engine was also 18 inches (46 cm) longer than the F100, the rear fuselage had to be extended.
In order to limit the required changes to a minimum, the front face of the engine compressor was located at almost the exact same position as with the F100 resulting in a lengthening of the fuselage by 18 inches aft of the stabilator pivot point.
Internally, the new intake incorporated a fixed compression ramp in its roof, and, because the J79 turbojet ran a lot hotter than the F100, a bypass valve was added to supply the engine bay with a cold air flow. As an additional protection measure against the extra heat, a steel shield weighing almost 2,000lbs (900kg) had to be installed around most of the length of the new engine. The aircraft came to be known as the F-16/79.
It was projected that the F-16/79 would have a unit cost of a million dollars less than that of a standard F-16A, the unit flyaway cost being about $8 million in 1980 prices. The total program cost (development, construction & flight testing) was split between GD and GE, and amounted to an estimated $18 million.
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