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The North American XF-108 Rapier was a proposed Americanmarker design for a long-range, high-speed interceptor aircraft to defend the United Statesmarker and Canadamarker from supersonic Sovietmarker bombers.

Development history

A very high performance, long-range interceptor had been proposed by the USAF as early as 1952, but formal development of what became known as the Long-Range Interceptor, Experimental (LRI-X) was not approved until 20 July 1955. The specification was laid down on 6 October, calling for an interceptor that could fly at at a speed of Mach 1.7 ( at that altitude) with a range of . It was to have a two-man crew, at least two engines and a powerful radar. A further consideration was that an integrated fire control system would be fitted allowing interception of a bomber at and that three targets could be destroyed during a single mission.

Contracts for preliminary studies were issued to North American Aviation, Lockheed and Northrop. Of the paper designs, the North American proposal, dubbed NA-236, seemed most promising. 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 NA-236. At the time, Air Defense Command anticipated an order for 480 aircraft.

The resulting design went through considerable evolution, both owing to its cutting-edge technology and continual redefinition of the USAF requirements. In addition to the F-108's interceptor role, North American proposed it as an escort fighter for the NAA-proposed B-70 supersonic bomber. The "F-108 development was to 'precede' the B-70 bomber, and a portion of the "150 million dollars expended" on the F-108 through September 1959 was of direct application to the XB-70 Valkyrie. Commonality between the B-70 bomber and the F-108 included the escape capsule and General Electric YJ93 engines.

From September 1958, when 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, at best have marginal range.

The eventual design, which was built as a full-sized XF-108 mock-up shown on 17–20 January 1959 to Air Force officials. The project was given the name "Rapier" on 15 May 1959 following a contest by the Air Defense Command asking airmen for suggestions.


The initial F-108 configuration featured a very large "cranked" delta wing, with a 58° sweep angle at the leading edge and wingtip extensions of about 40°, with a 4° anhedral. There were fixed ventral stabilizers on the wings, mounted at mid-span, and a tall all-moving vertical tailfin, supplemented by two ventral stabilizers that extended when the landing gear retracted. Although some earlier versions of the design had had separate tailplanes and later forward canard, both were abandoned in the final design.

The aircraft was powered by two General Electric J93 turbojet engines, also used in North American's XB-70 Valkyrie bomber, in the fuselage; USAF requests for an alternate installation of the Pratt & Whitney J58 later used in the SR-71 came to naught. The engines were fed by side-mounted intakes with a shape very similar to the North American A-5 Vigilante.

The large fuselage and wing had nine fuel tanks for a total of of JP-6 fuel, giving an estimated combat radius of some , which could be extended by in-flight refueling. Top speed was estimated at , about Mach 3, at . It was stressed for +5.33/-3.00 g.

The aircraft had a crew of two, a pilot and a weapon systems officer (WSO), in a tandem cockpit arrangement. Each crewman had an escape capsule designed to permitting safe ejection even at extreme speeds and altitudes. The weapon systems operator in the rear seat had no flight controls.

The F-108 was intended to carry the Hughes AN/ASG-18 radar, the U.S.marker's first pulse doppler radar set. It was to have look-down/shoot-down capability, but could only track one target at a time. It was a massive installation filling most of the long nose. The radar was paired with an infrared search and track system on the wing leading edges.

The radar was used to guide the Hughes GAR-9 (later redesignated AIM-47) air-to-air missile, three of which would be carried on a rotary launcher in an internal weapons bay. The F-111B and later F-14 Tomcat would both adopt a pulse doppler radar and long range AIM-54 Phoenix missiles similar to the AIM-47. The GAR-9 was a very large, long-range weapon with its own radar set for terminal homing. It was intended to fly at Mach 6, with a range of almost . An alternative version with a heat-seeking terminal homing mode was also developed. The missiles were long with a wingspan, weighing for the radar version, for the IR version. The earlier Northrop N-126 proposal suggested various weapons combinations, including GAR-1 Falcon missiles, packs of FFAR, or two T-171 Vulcan cannon, but none were part of the North American design.

Development of the F-108 radar and missiles was continued by the USAF and the system was eventually used in the Lockheed YF-12 program.The final configuration for the rear cockpit in the YF-12A looked similar to that of the F-108 since it incorporated the same displays and controls required for the Hughes ASG-18 fire control system.


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. On 16 September 1959, after President Eisenhower identified the military financial situation as "getting quite serious", Secretary of Defense Neil H. McElroy informed him of a reduction of 27,000 USAF personnel and that the "F-108 project is expected to be cancelled within thirty days." The cancellation was announced on 23 September and identified that Hughes Aircraft would continue development of the advanced fire control system and the GAR-9 missile. North American kept refining the design through 1960 in hopes that the program might be revived.

However, the money and time spent on the Rapier was not wholly in vain – the A-5 Vigilante supersonic bomber/reconnaissance aircraft developed for the U.S. Navy retained the fuselage/weapon package and systems design of the Rapier. In many ways the Vigilante can be seen as the successful application of the Rapier design principles in a Mach 2 supersonic bomber design.

Specifications (XF-108, as designed)

See also


  1. Jenkins and Landis 2004, p. 14.
  2. Buttler 2007, p. 107.
  3. Buttler 2007, p. 108.
  4. Jenkins and Landis 2004, p. 17.
  5. O'Connor, Sean. "AIM-47: Hughes GAR-9/AIM-47 Falcon." Directory of U.S. Military Rockets and Missiles, 2004. Retrieved: 31 July 2009.
  6. Jenkins and Landis 2004, p. 20.
  7. Goodpaster, Andrew J. "Memorandum of Conference with the President: September 16, 1959." Dwight D. Eisenhower Presidential Library, White House Office, Office of the Staff Secretary: Records, 1952-61 – Subject Series, Dept. of Defense Subseries, Box 2 Vol III Folder 8, 18 September 1959. Retrieved: 18 October 2009.
  8. "DoD news release 1088-59: Air Force Terminates F-108 Development ." Dwight D. Eisenhower Presidential Library, White House Office, Office of the Staff Secretary: Records, 1952-61 – Subject Series, Dept. of Defense Subseries, Box 2 Vol III Folder 8, 23 September 1959. Retrieved: 18 October 2009.
  9. Pace 1986, p. 51.


  • Buttler, Tony. American Secret Projects, Fighters & Interceptors 1945-1978. Hinckley, UK: Midland Publishing. 2007. ISBN 1-85780-264-0.
  • Dorr, Robert F. and Jon Lake. Fighters of the United States Air Force. London: Temple Press, 1990. ISBN 0-600-55094-X.
  • Jenkins, Dennis R. and Tony R. Landis. "F-108 Rapier The Elusive Mach 3 Interceptor." Airpower, Volume 34, no. 9, September 2004.
  • Knaack, Marcelle Size. Encyclopedia of US Air Force Aircraft and Missile Systems: Volume 1 Post-World War II Fighters 1945-1973. Washington, DC: Office of Air Force History, 1978. ISBN 0-912799-59-5.
  • Pace, Steve. "Supersonic Cavaliers." Airpower, Volume 16, no. 6, November 1986.
  • Pace, Steve. X-Fighters: USAF Experimental and Prototype Fighters, XP-59 to YF-23. Osceola, Wisconsin: Motorbooks International, 1991. ISBN 0-87938-540-5.

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