The Northrop F-20 Tigershark (initially F-5G) is a prototype light fighter, designed and built by Northrop. Its development began in 1975 as a further evolution of Northrop's F-5E Tiger II, featuring a new engine that greatly improved overall performance, and a modern avionics suite including a powerful and flexible radar. Compared with the F-5E, the F-20 was much faster, gained beyond-visual-range air-to-air capability, and had a full suite of air-to-ground modes capable of utilizing most U.S. weapons. With these improved capabilities, the F-20 was claimed to become competitive with contemporary fighter designs such as the General Dynamics F-16 Fighting Falcon, but was said to be much less expensive to purchase and operate.
Much of the F-20's development was carried out under a US Department of Defense (DoD) project called "FX". FX sought to develop fighters that would be capable in combat with the latest Soviet aircraft, but excluding sensitive front-line technologies used by the United States Air Force's own aircraft. FX was a product of the Carter administration's military export policies, which aimed to provide foreign nations with high quality equipment without the risk of US front-line technology falling into Soviet hands. Northrop had high hopes for the F-20 in the international market, but policy changes following Ronald Reagan's election meant the F-20 had to compete for sales against aircraft like the F-16, the USAF's latest fighter design. The development program was abandoned in 1986 after three prototypes had been built and a fourth partially completed.
Development
F-5 When John F. Kennedy entered office in 1961, the U.S. Department of Defense was instructed to find an inexpensive fighter aircraft that the United States could offer to its allies through the Mutual Defense Assistance Act. A number of designs were studied, including stripped-down versions of the Lockheed F-104 Starfighter and Vought F-8 Crusader, and the newly designed Northrop N-156F. On 23 April 1962, the United States Air Force (USAF) informed the United States Secretary of Defense that the N-156F had been selected, under the designation F-5 and given the name "Freedom Fighter."Donald 1997, p. 708. 847 F-5s of various early marks would be produced."Factsheet: Northrop F-5 Freedom Fighter" , National Museum of the United States Air Force. Retrieved: 28 October 2012.
As the Mikoyan-Gurevich MiG-21 became more common, the USAF initiated the International Fighter Aircraft (IFA) program to provide an equivalent to allies. The USAF desired a lightweight fighter with competitive performance to the MiG, inexpensive when purchased in large numbers, and with reasonable operating costs for prospective customer nations. Although numerous companies entered designs, Northrop's existing F-5 put them in a leading position. They submitted an upgrade, the F-5E Tiger II, with the AN/APQ-153 radar and other changes to allow the AIM-9 Sidewinder missile to be fired from wing-tip rails. On 20 November 1970, Northrop's entry was announced as the IFA winner.Eden, Paul, ed. "Northrop F-5 family." Encyclopedia of Modern Military Aircraft. London: Amber Books, 2004. . Northrop produced a total of 1,399 F-5E/F Tiger IIs by the time manufacturing ended in 1986.
F-5G and export limitations In the late 1970s, the Taiwanese Republic of China Air Force started looking for a fighter aircraft to match improvements made in the Chinese People's Liberation Army Air Force. In particular, they wanted a platform capable of firing the AIM-7 Sparrow long-range missile. At the time, the US was in the process of opening up ties with the People's Republic of China after President Nixon's famous visit in 1972. China considered US support of Taiwan against their interests, and the US State Department wanted to tread carefully. They blocked export of all of the AIM-7 capable aircraft, even otherwise outdated early models of the McDonnell Douglas F-4 Phantom II. The State Department suggested the Israeli IAI Kfir instead; however, it was rejected. Taiwan was already producing the F-5E under license, so the Department of Defense asked Northrop to study adding an AIM-7 capable radar to the Tiger II as an alternative. This effort became the first of several F-5G studies.Fink, Donald. "Taiwan Offered F-5G with Sparrow." Aviation Week and Space Technology, 21 August 1978, p. 12.
In the spring of 1977, Jimmy Carter's administration had announced a new military export policy that limited sales of front line designs to NATO, Australia, and Japan.Frey, Lieutenant Colonel William. "The F-20, Saga of an FX." Air University Review, May–June 1986. Carter stated at the time that the U.S. could not be "both the world's champion of peace and the world's leading supplier of the weapons of war." Previously, there was no coherent export policy, fueling concerns that the US's latest technologies might quickly end up in Soviet hands.
Numerous exceptions were made; Israel and Egypt could buy advanced designs under the Camp David Agreements, Israel was even allowed to buy McDonnell Douglas F-15 Eagles, a key component in U.S. air-defense technology. Iran was already receiving the Grumman F-14 Tomcat, and this demonstrated the problem with advanced exports in February 1979 when reports emerged that Iran had sold an AIM-54 Phoenix missile to the Soviets."Iran Arms Concern." Aviation Week & Space Technology, 19 February 1979. South Korea's F-16 order was initially blocked under this policy, but later allowed in the context of strengthening relations. Despite exceptions, the export policy was implemented, covering many potential and current customers. As the F-5G was a relatively modest upgrade to the F-5E, the F-5G appeared to be in a strong position for sales given the limitations placed on rival designs; nonetheless, President Carter personally blocked the sales of the F-5G to Taiwan.
FX In 1979, problems with the export policy were becoming apparent. The Soviets continued to sell newer aircraft designs to their clients, placing allies of the U.S. at a disadvantage. Denied by the U.S., countries were turning to other vendors for modern fighters, notably France's Dassault Mirage 2000. Barry N. Blechman, Assistant Director of the Arms Control and Disarmament Agency, testified that the US reductions in foreign arms transfers had actually encouraged other nations and increased worldwide arms sales."Statements by Barry N. Blechman in the U.S. Congress Senate Foreign Relations Committee, Fiscal Year 1980 International Security Assistance Authorization." Government Printing Office 1979, p. 41. At the same time, there was considerable pressure to provide a suitable aircraft for Taiwan.
The State Department argued that the U.S. needed a modern counterpart for the role the F-5E had occupied in the 1960s and 1970s. In light of Carter's concerns, they suggested that a new aircraft be designed for the role, based on technology that would not pose a threat to the U.S. After a lengthy study, in January 1980, Carter allowed the development of a new export fighter: the FX. The FX would have to outperform the F-5E; however, it could not use any advanced avionics systems that were also used in U.S. aircraft. Unlike the Mutual Defense Assistance Act programs that led to the F-5E, FX would be entirely privately financed. Moreover, the companies could not market the aircraft directly; all sales would be handled by the Department of Defense.
Both Northrop and General Dynamics (GD) responded to the FX requirement. GD's F-16/79 was a variant of the F-16A, replacing the Pratt & Whitney F100 turbofan engine with the J79 turbojet and equipping it with downgraded avionics; Northrop responded with the F-5G.
F-20 When Ronald Reagan's administration entered office in 1981, the export restrictions put in place by the Carter administration were slowly relaxed. At first, the FX program continued as normal, but a number of events eroded the value of the program and limited the F-5G's potential sales. The signing of the 1982 US-PRC Joint Communiqué was a major agreement on arms sales, which continued blocking sales of the F-5G to Taiwan. By this point the Taiwanese had started their own light fighter project, the AIDC F-CK-1 Ching-kuo. In signing the Communiqué, the U.S. was signaling that Taiwan would not receive modern aircraft; accordingly, the Ching-kuo became Taiwan's primary focus. As a result, the F-5G's sales potential remained unestablished.Schemmer, Benjamin. "Pressures Build for DOD to Buy and Help Sell Northrop F-5G as Its Business Prospects Look Bleaker Than Advertised." Armed Forces Journal International, September 1982, pp. 98–104.
In the summer of 1982, Deputy Secretary of Defense Frank Carlucci sent a memorandum to the USAF, encouraging it to seek out potential foreign customers to procure FX aircraft.Starsiak, M.H. "Implications of Moving Away from Formal Foreign Military Sales (FMS): Procedures for Aircraft Sales." ASD-XOR Project, U.S. Department of the Air Force, 1982, pp. 22–23. However, four months later Carlucci sent a classified memo to the same services to abandon the FX, and green-lighting the exporting of front-line fighters overseas.Barnard, Richard. "Carlucci Reverses FX Policy for Persian Gulf." Defense Week, 22 November 1982, p. 1. In December, after prompting from the White House, Carlucci reversed his position again, and directed the USAF to fund a small number of F-20s in the fiscal year 1984 budget.Barnard, Richard. "Carlucci to AF: 'Buy the F-20'." Defense Week, 20 December 1982, p. 1.
The future of the FX program seemed doubtful. Following an agreement to sell F-16s to Pakistan,Singh, Pushpindar. "F-16s for Pakistan: Reactions and Views." Asian Defence Journal, September 1981, p. 41. Northrop felt that the F-5G needed to match the performance of F-16. This would require not only better performance from the engine, but a new and comparable avionics suite as well. Northrop saw that the F-5G was still being viewed as the "FX fighter", a low-cost option for second-tier air forces. To offset this impression, Northrop requested the designation "F-20"; the USAF approved in late 1982, and of the name Tigershark in March 1983. Northrop requested to skip F-19, the next available fighter designation, for an even number in order to stand out from the Soviet odd-numbered designations.Sheffield 1995, p.72
Design
The primary design change between the earlier F-5E and the F-20 was the use of a single General Electric F404 engine, which was originally designed for the F/A-18 Hornet. The new engine provided 60% more thrust than the combined output of the F-5E's two General Electric J85s. This improved the aircraft's thrust-to-weight ratio from 1.0 to 1.13. The new engine gave a speed of over Mach 2.0, a ceiling over 55,000 ft (16,800 m), an initial climb rate of 52,800 ft per minute (16,100 m/min).
The wing profile remained the same as the F-5E, but had modified leading edge extensions (LEX), which improved the maximum lift coefficient of the wing by about 12% with an increase in wing area of only 1.6%. The original aircraft was fairly sluggish in pitch, so the horizontal stabilizer was increased in size by 30% and a new dual-channel fly-by-wire control system was added. Destabilizing the aircraft in pitch and modifying the LEX improved the instantaneous turn rate by 7% to 20°/sec. Sustained turn rate at Mach 0.8 and 15,000 ft (4,572 m) rose to 11.5°/sec, which compared well with the F-16's 12.8°/sec. Supersonic turn rates were 47% higher than those of the F-5E.
The F-20 would also make greater usage of composite materials in its construction. During its development, several areas using metal were re-designed to use fiberglass, and there were numerous upgrades to various mechanical parts.Anderson, David. "Why the F-20 isn't selling." Popular Mechanics, March 1986, p. 145.