The Northrop F-5A and F-5B Freedom Fighter and the F-5E and F-5F Tiger II are part of a supersonic light fighter family, initially designed in the late 1950s by Northrop Corporation. Being smaller and simpler than contemporaries such as the McDonnell Douglas F-4 Phantom II, the F-5 cost less to both procure and operate, making it a popular export aircraft. The F-5 started life as a privately funded light fighter program by Northrop in the 1950s. The design team wrapped a small, highly aerodynamic fighter around two compact and high-thrust General Electric J85 engines, focusing on performance and low cost of maintenance. Though primarily designed for the day air superiority role, the aircraft is also a capable ground-attack platform. The F-5A entered service in the early 1960s. During the Cold War, over 800 were produced through 1972 for U.S. allies. Though the USAF had no acknowledged need for a light fighter, it did procure roughly 1,200 Northrop T-38 Talon trainer aircraft, which were directly based on the F-5A.
After winning the International Fighter Aircraft competition in 1970, a program aimed at providing effective low-cost fighters to American allies, Northrop introduced the second-generation F-5E Tiger II in 1972. This upgrade included more powerful engines, higher fuel capacity, greater wing area and improved leading edge extensions for a better turn rate, optional air-to-air refueling, and improved avionics including air-to-air radar. Primarily used by American allies, it remains in US service to support training exercises. It has served in a wide array of roles, being able to perform both air and ground attack duties; the type was used extensively in Vietnam. A total of 1,400 Tiger IIs were built before production ended in 1987. More than 3,800 F-5 and the closely related T-38 advanced trainer aircraft were produced in Hawthorne, California. The F-5N/F variants are in service with the United States Navy and United States Marine Corps as an adversary trainer. Approximately 500 aircraft are in service as of 2014.[N 1]
The F-5 was also developed into a dedicated reconnaissance version, the RF-5 Tigereye. The F-5 also served as a starting point for a series of design studies which resulted in the Northrop YF-17 and the F/A-18 navalized fighter aircraft. The Northrop F-20 Tigershark was an advanced variant to succeed the F-5E which was ultimately canceled when export customers did not emerge.
Design and development
The design effort was led by Northrop vice president of engineering and aircraft designer Edgar Schmued, who previously at North American Aviation had been the chief designer of the successful North American P-51 Mustang and F-86 Sabre fighters. Schmued recruited a strong engineering team to Northrop and assigned them the goal of reversing the trend in fighter development towards greater size and weight in order to deliver an aircraft with high performance, enhanced maneuverability, and high reliability, while still delivering a cost advantage over contemporary fighters. Recognizing that expensive jet aircraft could not viably be replaced every few years, he also demanded "engineered growth potential" allowing service longevity in excess of 10 years. Schmued recognized that new jet engine and aerodynamic technology were crucial to these goals, such as the compact but high thrust-to-weight ratio General Electric J85 turbojet engine, and the recently discovered transonic area rule to reduce drag. The J85 engine had been developed to power McDonnell's ADM-20 Quail decoy employed upon the Boeing B-52 Stratofortress. This engine with thrust-to-weight ratios of 6.25 to 7.5 over various versions had a notable thrust per pound advantage over contemporaries, such as the 4.7 thrust-to-weight ratio of the J79 engine used in the F-4 Phantom.
The first Northrop YF-5A prototype
Another highly influential figure was chief engineer Welko Gasich, who convinced Schmued that the engines must be located within the fuselage for maximum performance. Gasich also for the first time introduced the concept of "life cycle cost" into fighter design, which provided the foundation for the F-5's low operating cost and long service life. The low costs involved has been recognized as an important element of the aircraft's effectiveness;[N 2] defense analyst and combat aircraft architect Pierre Sprey stated in a 1982 U.S. Department of Defense report that, "Increases in cost and complexity that were unnecessary to enhance air-to-air effectiveness have decreased today's effective force size per constant dollar by factors of 25 to 75, relative to the F-86's 2000 sorties/day per billion dollars.[N 3] The only exception to this strikingly adverse trend is the F-5E, which manages to produce 500 sorties/day per billion dollars." The total cost of an F-5 sortie is approximately 20% that of an F-16 sortie, even though the F-16 is a cost effective modern fighter. This low cost was also a very deliberate strategy of Northrop in following a focused light fighter plan. A Northrop design study stated "The application of advanced technology was used to provide maximum force effectiveness at minimum cost. This became the Northrop philosophy in the development of the T-38 and F-5 lightweight trainer and fighter aircraft."
The flying qualities of the F-5 are often highly rated, comparable to the North American F-86 Sabre and the General Dynamics F-16 Fighting Falcon. The safe and predictable flying qualities of the F-5, while still maintaining high agility, was a deliberate goal of the design team. The company stated "Northrop took a new approach that the initial design layout shall stress excellent flying qualities such that utilization of the complete performance envelope is available to the pilot."
According to defense analyst and prominent Pentagon fighter mafia (of F-16 fame) member Pierre Sprey, the F-5 was perhaps the most effective U.S. air-to-air fighter in the 1960s and early 1970s based on his published fighter effectiveness criteria. Sprey defines the key factors of fighter effectiveness in order of importance as 1. Ability to surprise the enemy without being surprised, 2. On a per budget basis, ability to outnumber the enemy via lower unit cost and higher sortie rates and reliability, 3. Ability to outmaneuver the enemy, and 4. Once in position to fire by either surprise or maneuver, ability to attain reliable kills (weapon system effectiveness). As a prominent example of a well implemented light fighter, the F-5 is a close match to these criteria in the time frame before Beyond Visual Range missiles became reliable. A small visual and radar cross section size and consequent detection difficulty often conferred the F-5 the advantage of surprise. The F-5 has the smallest planform area of any fighter in common usage. This is a critical practical combat advantage since historically about 80% of air to air kills do occur by surprise. The aircraft is highly cost effective and reliable, allowing superior numbers in the air on a per budget basis. The aircraft also has a high sortie rate, low accident rate, high maneuverability, and is armed with an effective combination of 20mm cannon and heat seeking missiles.