North American XF-108 Rapier - Development

Development

During the early 1950s, the USAF proposed a very high-performance, long-range interceptor. On 20 July 1955, formal development of what became known as the Long-Range Interceptor, Experimental (LRI-X) was approved, planned as a F-102 Delta Dagger/F-106 Delta Dart replacement. The specification was laid down on 6 October 1955, calling for an interceptor that could fly at 60,000 ft (18,000 m) at a speed of Mach 1.7 (1,122 mph (1,806 km/h), with a range of 1,000 miles (1,600 km). It was to have a two-man crew and at least two engines. A further consideration was that an integrated fire-control system would be fitted, allowing interception of a bomber at 60 nmi (110 km) and three targets to be destroyed during a single mission.

Of the eight interested companies, contracts for preliminary studies were issued to North American Aviation, Lockheed and Northrop on 11 October 1955, five days after the specification's release. Of the paper designs, the North American proposal, dubbed "NA-236", seemed the most promising. The NA-236 shared some similarities with the XF-108, although the most obvious differences were the additions of two finlets at the midspan of the horizontal stabilizers, and canards. Political and budgetary difficulties led to the cancellation of the program on 9 May 1956. After considerable confusion, the program was reinstated on 11 April 1957 with North American awarded a contract for two prototypes. The designation F-108 was issued, also known as "Weapon System 202A". North American's company designation was "NA-257", although it was basically identical to the NA-236. At the time, Air Defense Command anticipated an order for 480 aircraft.

The resulting design went through considerable evolution, owing to both its cutting-edge technology and continual redefinition of the USAF requirements. Early revisions prominently featured canards, with a span of 19 ft 10 in (6.04 m), and a wing of 53.5° sweep. The aircraft in this configuration would have a maximum take-off weight of 99,400 lb (45,088 kg) with a 72,550 feet (22,113 m) operational ceiling. In addition to the F-108's interceptor role, North American proposed it as an escort fighter for its own B-70 Valkyrie supersonic bomber prototype. Commonality between the B-70 bomber and the F-108 included the escape capsule and General Electric YJ93 engines. Another role considered was for the F-108 to be "gap-fillers" for the Distant Early Warning (DEW) system; because of its great speed, the F-108 could have scanned up to 278,000 square miles (720,000 km2) per hour.

From September 1958, substantial engineering and design changes were implemented; however, SAC had lost interest in the escort fighter concept. To accompany the B-70 all the way to its target and back, the F-108 in its initial concept would have, at best, marginal range. On 30 December 1958, YF-108A pre-production aircraft on order were reduced from 31 to 20 test aircraft and the first test flight was delayed from February to April 1961. The eventual design, which was built as a full-sized XF-108 mock-up, was displayed to Air Force officials on 17–20 January 1959. The project was given the name "Rapier" on 15 May 1959, following a contest by the Air Defense Command asking airmen for suggestions.