Northrop N-156F

Last revised January 4, 2014

The Northrop F-5 was one of the most successful export products of the US aircraft industry. Although it did not have the performance of some of its more-costly contemporaries, it was reliable, easy to maintain, and relatively inexpensive. It served only in relatively small numbers with the United States armed forces, first as a trial with the USAF in Vietnam and then later as an adversary aircraft with the USAF, Navy, and Marine Corps. It was widely exported, sometimes funded under the terms of the Military Assistance Program (MAP) and sometimes sold commercially under the terms of Foreign Military Sales (FMS). A total of 1871 F-5s were built by Northrop, and a further 776 were built under license in Canada, Spain, Switzerland, Korea, and Taiwan. The F-5 is still an important part of many foreign air forces.

The development of the Northrop F-5 began as far back as 1954, when a Northrop team toured Europe and Asia to examine the defense needs of NATO and SEATO countries. The result of the tour was a 1955 company design study for a lightweight supersonic fighter that would be relatively inexpensive, easy to maintain, and capable of operating out of short runways and secondary airstrips as well as from small aircraft carriers.

The powerplant was to be the General Electric J85 turbojet, which had originally been intended as the engine for the GAM-72 Green Quail decoy drone. The availability of the General Electric J85 engine made it possible to build a lighter aircraft than heretofore thought possible. The original YJ85-1 engine was a non-afterburning engine rated at 2100 lb.s.t. General Electric promised an afterburning version rated at 3850 lb.s.t., and Northrop began work on a fighter aircraft based on this engine.

The design of the lightweight fighter began in 1955 under the company designation N-156. The N-156 went through several different configurations before the final design was decided. The N-156TX proposal had the engines mounted in two underwing pods and had a crew of two seated in tandem underneath a shallow canopy. The N-156NN was a proposal for a naval version that had a configuration similar to that of the Grumman F9F and was intended for use from US Navy escort carriers and similar-sized ships such as those operated by the Royal Navy. The mothballing of the Navy's fleet of escort carriers effectively killed off the N-156NN. In 1965, some studies were made of an aircraft with a folding ventral fin and a booster rocket.

The final configuration was given the company designation N-156F. At the same time, a two-seat advanced trainer version was also proposed under the designation N-156T. Both versions were to be powered by a pair of General Electric J85 turbojets grouped closely together in the rear fuselage and fed by a pair of lateral air intakes on the sides of the lower fuselage.

The proposal was submitted to both the Air Force and the Navy. The Navy turned down the Northrop proposal, since it had already decided to take its small aircraft carriers out of service. The Air Force did not initially look favorably upon the proposal either, since it perceived no need for a lightweight fighter. However, it did need a new trainer to replace the Lockheed T-33, and Northrop decided to press forward with the two-seater to meet this requirement, which was formalized in the USAF's 1955 General Operational Requirement SS-240L. In June of 1956 the Air Force announced that it was going to acquire the N-156T trainer version under the designation T-38. The name Talon was chosen. The construction of three prototypes was authorized.

Undaunted, the Northrop company decided on February 25, 1958 to proceed with the development of the N-156F as a private venture. The N-156F drew heavily on the design of the N-156T (T-38). Like the T-38, the low-mounted thin wings had almost equal taper on the leading and trailing edges, and featured no dihedral or anhedral and no incidence. The N-156F wing differed from that of the T-38 in having a forward-angled fillet or leading-edge extension (LEX) at each root, which had a sweep of 60 degrees. In contrast to the N-156T, the wing of the N-156F featured continuous-hinge flaps on the leading edges of full-depth honeycomb construction. Hydraulically-powered sealed-gap ailerons were provided at approximately mid-span, with light alloy single-slotted flaps inboard. The electrically-operated leading edge slats and trailing edge flaps had three positions. For takeoff and landing, both leading and trailing edge flaps were fully extended, while droop alone was used for maneuvering st speeds below 300 mph. The leading edge droop was locked slightly extended whenever the landing gear was extended.

The N-156F had larger intakes than those of the N-165T in anticipation of the use of larger engines with greater air mass flow. It also featured a square-shaped air intake splitter plate, with a perforated section just inside the intake to bleed away any remaining boundary layer airflow.

There was an all-flying horizontal tail mounted low on the fuselage underneath the engines. The rudder was limited to 6 degrees of travel except when the landing gear was down, when the full 30-degrees of travel were allowed. There was a drag chute fairing installed at the base of the rudder.

The fuselage was designed according to the Area Rule, with the cross section of the fuselage being narrowed in the region of the wing to present a nearly constant total cross-section area to the airflow passing over the aircraft. In profile, the aircraft was bent slightly to maximize the view from the cockpit, with a pronounced cambering of the forward fuselage giving what was referred to as a "lady's slipper" profile, with a slightly concave underside.

The cockpit was fairly roomy and provided an excellent all-round view. The pilot was provided with a Northrop-built rocket-assisted ejector seat. The seat was provided with a canopy-breaker in case the automatic canopy ejection mechanism failed.

Armament was to have consisted of two 20-mm M39 cannon in the upper nose plus a AIM-9 Sidewinder missile at each wingtip. Additional offensive loads could be carried underneath a centerline pylon and on two underwing stores stations.

The two engines could be accessed and removed by taking off the lower part of the rear fuselage. They were sufficiently light in weight (585 pounds each) that they could be removed and refitted using human muscle alone.

All fuel was carried in fuselage tanks, with the wing remaining completely dry. However, a fuel tank could be installed at each wingtip. The removable wingtip tanks were area-ruled, a rather unusual feature for the time.

Conventional cables and pushrods were used to operate the flight controls. Rudder trim and pitch/yaw oscillation damping was provided by a stability augmentation system that ran off the utility hydraulic system. No emergency ram air intake was not provided, the aircraft relying on duplicated hydraulic and electrical systems as backup in case of a failure.

The aircraft was designed for a maximum speed of Mach 1.5, somewhat slower than many of the threat aircraft that it would have to counter.

The mockup was inspected by the Air Force early in 1958. In the meantime, the Air Force had studied the N-156F in greater depth and had come to recognize that the fighter proposal had great promise as a low-cost fighter for many of America's allies who could not possibly hope to afford the expensive interceptors that were at that time entering USAF service. On February 25, 1958, the Air Force authorized the construction of three prototypes by Northrop under the company designation N-156F and to be called *Freedom Fighter*. The USAF serials were 59-4987/4989. In addition, one static test airframe (59-4993) was ordered.

In early 1959, Northrop management began discussions with overseas manufacturers who might be interested in license production of the N-156F. Companies approached included SABCA of Belgium, Fokker of Holland, and Fiat of Italy. Talks also took place with Australia and with Fairey Aviation of the UK. Northrop's president stated that he anticipated the potential worldwide market for the N-156F to be 4000 aircraft! As it turned out, the European companies turned down Northrop's overtures, and opted instead to build the Lockheed F-104 Starfighter.

Undaunted, Northrop pressed onward with its private venture. As it turned out, license production arrangements were later to be worked out with Canadair of Canada, with CASA of Spain, with FFA of Switzerland, with Hanjin of South Korea, and with AIDC of Taiwan.

The first N-156F (59-4987) was built in just over a year. It was initially powered by a pair of non-afterburning General Electric YJ85-GE-1 turbojets rated at 2100 lb.s.t. each. The first N-156F was rolled out on May 31, 1959 and was shipped to Edwards AFB. It took off on its first flight on July 30, 1959, test pilot Lew Nelson being at the controls. The cannon armament was not fitted at the time of the first flight. Despite the lack of afterburning engines, the aircraft went supersonic on its first flight.

The non-afterburning turbojets were soon replaced by production-type J85-GE-5s, each rated at 2500 lb.s.t. dry and 3850 lb.s.t. with afterburning. The second N-156F (59-4988) soon joined the flight test program, but the third N-156F (59-4989) was shelved before completion, pending the decision by the Defense Department on whether the N-156F merited a production contract.

In the meantime, flight testing continued unabated. The aircraft conducted in-the-field maintenance tests, rough-field operations and operations from an unprepared strip at NAS Pensacola. Test firings of Sidewinder, Sparrow III, and Falcon air-to-air missiles took place, and drops of various externally mounted ordnance such as bombs, unguided rockets, napalm tanks and Bullpup air-to surface missiles took place. There was even a test with a 2000-lb "special weapons shape" on the centerline. The aircraft could carry a heavier load than the F-100 and had a higher speed, better airfield performance, and a lower fuel consumption rate. Nevertheless, at the conclusion of the tests in August of 1960, the Air Force concluded that it had no requirement for the aircraft.

The incoming Kennedy administration brought a fresh look to many defense matters. In particular, in pursuit of its goal to "support any friend and oppose any foe in the support and defense of freedom", the new administration gave new consideration to the funding of the sales of advanced warplanes to American allies throughout the world. For this mission, the USAF supported stripped-down versions of the F-104G Starfighter which was then entering service with Japan and several NATO air forces. Another contender was an adaptation of the Navy's Vought F8U Crusader. However, the Department of Defense and its International Security Affairs Agency preferred the N-156F.

While the Air Force still remained unconvinced of the usefulness of the N-156F, in early 1962, the first prototype was tested by the US Army as a possible candidate to meet an Army requirement for a fixed-wing close support aircraft. Other contenders for the Army contract were the Fiat G-91 and the Douglas A4D Skyhawk. The prototype was painted in Army markings for the tests. Although Army pilots were impressed with the N-156F, the Air Force was extremely jealous about the Army's intrusion into what it perceived to be a strictly Air Force mission, and the Defense Department was pressured into not allowing the Army to acquire any fixed-wing close support aircraft, restricting that service to operating only helicopters for this role.

On April 25, 1962, the Department of Defense announced that it had chosen the N-156F for its Military Assistance Program (MAP). America's NATO and SEATO allies would now be able to acquire a supersonic warplane of world-class quality at a reasonable cost. The USAF was to act as the purchasing agency for the program and was put in charge of crew training. The planes were to carry USAF serial numbers for record-keeping purposes. On August 9, 1962, the Model N-156F was given the official designation of F-5A and was given the official name Freedom Fighter. At the same time, a two-seat combat trainer version was ordered under the designation F-5B. It looked a lot like the T-38A, but it was to retain the full combat capability of the F-5A.

A $20 million fixed-price contract was signed in October of 1962, calling for a mix of single-seat F-5As and two-seat F-5Bs in a ratio of 9:1.


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