Southern California's lost long-range interceptors, part 1: North American F-108 Rapier

For many US aircraft manufacturers, the 1950s would see quantum leaps in combat aircraft technology when it came to supersonic speed, punctuated by the USAF's introduction of its first supersonic jet fighter, the North American F-100 Super Sabre, but also the Douglas D-558-2 Skyrocket becoming the first plane to reach Mach 2 in November 1953. The Convair F-102 Delta Dagger and F-106 Delta Dart, first flown in 1953 and 1956 respectively, constituted quantum leaps in the development of US supersonic fighter planes because they gave America the first-ever purpose-built supersonic interceptors to take down Soviet long-range bombers intruding into North American airspace. With development of the North American XB-70 Valkyrie Mach 3 supersonic bomber underway, however, the US Air Force began shopping for an all-new long-range interceptor capable of traveling at Mach 3 and countering the USSR's upcoming supersonic bombers like the Myasishchev M-50, Tsybin RSR, and Tupolev Tu-22. In response, the aircraft industry in southern California unveiled a spree of Mach 3 long-range interceptor designs, some conceived from scratch and others derived from existing aircraft designs. Due to the prolonged quest by the USAF for a Mach 3 interceptor, I am writing a two-post series on Mach 3 interceptor design in the Los Angeles basin; the first post will focus on the North American F-108 Rapier.

Top: Northrop N-144 interceptor design submission for the 1954 LRI competition
Bottom left: Desktop model of the North American submission to the 1954 LRI competition
Bottom right: An artist's conception of the North American NA-236, the winner of the LRI-X competition and the final step towards the F-108 Rapier  

In late April 1954, the USAF announced the Long-Range Interceptor (LRI) program for an advanced long-range interceptor with an operating altitude of 60,000 feet (18,000 meters) at Mach 1.7 (1,122 mph (1,806 km/h) with a maximum range of 1,151 miles (1,852 km), and the ability to detect enemy targets over a distance of 115 miles (185 km). The parameters for the LRI requirement were covered under the designation WS-202A, and ten companies undertook design studies for the LRI requirement, of which seven submitted bids. Northrop submitted a revised design for its earlier N-126 'Delta Scorpion' design for the WS-202A specification with a long, slim fuselage, turbojets below the wings, and low-mounted horizontal stabilizers, and it also worked out two additional designs, the N-144 (a scaled-up version of the N-126) and the lightweight N-149. North American's WS-202 submission had twin upper and lower vertical stabilizers, a cropped delta wing, a long, slim fuselage, and delta wing canards, and Lockheed's submission, the CL-288, looked like an F-104 Starfighter with mid-wing mounted turbojets. None of the seven designs offered for the LRI competition fully met the performance requirements in the LRI specification, but the N-144 was judged by Wright Field to come closest to meeting the parameters of the LRI requirement. As the submissions for the LRI requirement did not meet the required operational altitude, the evaluators at Wright Field asked for a relaxation of the original requirements, and on July 20, 1955, the US Air Force initiated the LRI-X (Long-Range Interceptor - Experimental) program, which like the earlier LRI program stipulated that a new-generation long-range interceptor should fly at 60,000 feet (18,000 meters) at a speed of Mach 1.7 (1,122 mph (1,806 km/h), but called for the new interceptor to utilize an integrated fire-control system to allow for interception of a bomber over a range of 69 miles (111 km), with the ability to make three kills. The GOR-114 requirement was initiated on October 6 to cover the LRI-X operational parameters, and by October 11, the USAF awarded study contracts to three companies (Lockheed, Northrop, and North American). The Lockheed CL-320 was similar to the CL-288 but was much larger and heavier, and it was powered by four General Electric J79 turbojets housed in two mid-wing nacelles, along with outrigger landing gear below the nacelles. North American proposed the NA-236, which resembled the 1954 North American interceptor proposal in having delta canards but differed in utilizing a delta wing, the canards atop the forward fuselage, and two side-by-side General Electric J93 turbojets. A large central vertical stabilizer was situated between the turbojets, and two smaller vertical stabilizers were mounted in mid-wing position along the wing's trailing edge. Northrop's LRI-X design, the N-167, had four General Electric J79 turbojets housed inside the fuselage, fed by air flowing through intakes in the wing roots, and two designs were investigated, the baseline N-167 with a tail empennage similar to that of the F-104 and wings with pronounced anhedral, and the N-167A design of April 1956 with the horizontal stabilizer on the rear side of the fuselage and of the same span as the wings. By January 1956, the NA-236 was declared the winner of the LRI-X contest, but budgetary constraints forced the Pentagon to cancel the LRI-X program on May 9. At the behest of the Air Defense Command, however, the Pentagon revived the long-range interceptor program on April 11, 1957, and in June of that year North American won a contract for the aircraft, which eventually was designated F-108.The Air Defense Command at the time was hoping to procure 480 F-108s.

Top: Model of the North American F-108 Rapier at the Lyon Air Museum, photographed by me in November 2021.
Bottom: Full-scale mockup of the F-108 at the North American plant in Inglewood, California, January 1959.

The initial XF-108 design (company designation NA-257) conceived in early May 1958 was similar to the NA-236 but had the trailing edge flaps split into two downward curving surfaces. It measured 84 feet 11 in (25.9 meters) long with a wingspan of 52 feet 11 in (16.1 meters), a wing area of 1,400 square feet (130.2 square meters), and a gross weight of 99,400 lb (45,088 kg), and it was powered by two General Electric J93s. Beginning in September, however, the F-108 design was revised whereby the canards were removed and larger underwing vertical stabilizers were provided to offer better handling and directional stability at low speeds and high angles of attack. Three months later, the wing design for the F-108 was changed to a cranked arrow shape with substantial tip extensions offering improved stability at high lift conditions, and large folding ventral stabilizers were fitted to the corners of the lower fuselage to address concerns about directional stability. In this form, the overall F-108 design was to be 89 feet 2.5 in (27.2 meters), with a wingspan of 57 feet 5 in (17.5 meters), a height of 22 feet 1 in (6.7 meters), a wing area of 1,865 square feet (173.4 square meters), an empty weight of 50,907 lb (23,098 kg) and a gross weight of 102,234 lb (46,373 kg). The F-108 was armed with three GAR-9 (later AIM-47) Falcon long-range air-to-air missiles, which had a range of 115 miles (185 km/h), and the top speed was to be Mach 3, the same speed as the company's own XB-70 Valkyrie supersonic strategic bomber. A full-scale mock-up of the F-108 was completed and inspected by US Air Force officials in January 1959, and the F-108 was officially christened Rapier in May. By this time, the first flight of the F-108 was scheduled for March 1961 with service entry planned for mid-1963, and the USAF order for 30 service test F-108s was reduced from 30 to 21 aircraft. However, the Pentagon was facing a tight budget stemming from the development of the Atlas and Titan ICBMs, the XB-70 Valkyrie supersonic bomber, the Polaris SLBM, and the Navy's fielding of its first generation of ballistic missile submarines, and given the rising cost of the F-108 program, on September 23, 1959, the USAF announced the cancellation of the Rapier. Several months before the F-108's cancellation, there was a proposal for a Mach 3 target drone for the testing the F-108's weapons systems, and in July 1959 the designation XQ-11 was requested for this vehicle, but the USAF Headquarters turned down the request, stating that a specific designation for the proposed F-108 target was unnecessary at an early stage of the F-108 program, and like the F-108, the XQ-11 did not proceed to the hardware phase.

References:

Buttler, T., 2007. American Secret Projects: Fighters and Interceptors 1945 to 1978. Hinckley, UK: Midland Publishing.

Chong, T., 2016. Flying Wings & Radical Things: Northrop's Secret Aerospace Projects & Concepts 1939-1994. Forest Lake, MN: Specialty Press.

Jenkins, D.R., and Landis, T.R., 2008. Experimental & Prototype U.S. Air Force Jet Fighters. North Branch, MN: Specialty Press.