THE 456th FIGHTER INTERCEPTOR SQUADRON

THE PROTECTORS OF  S. A. C.

 

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North American The F-108 Rapier

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First known as the LRIX (long-range interceptor, experimental), development of the XF-108 followed USAF GOR 114, dated 6 October 1955. The North American letter contract of 6 June 1957 called for an all-weather, two-man, two-engine, long-range interceptor, with a combat speed of at least Mach 3 and swift maneuver at 70,000 feet. The aircraft would carry two or more air-to-air missiles with nuclear or conventional warheads. The armament bay was to house a number of weapon combinations.

The Air Force expected a lot from the complex new plane. Many subcontractors were involved. Hughes Aircraft Corporation would provide the aircraft's fire-control system and GAR-9 missiles; Convair, the wing, Marquardt, the air induction control system; Hamilton Standard, the air conditioning and pressurization; Federal Division of the International Telephone & Telegraph Co., the mission and traffic control system; and Electronic Specialty Co., the antenna system. The Air Force would take care of the engine, the General Electric J-93 turbojet (first developed as the X-279E). It wanted an early 1963 operational date, 1,000-nm cruise speed with 5 minutes of combat at Mach 3, and a cruise speed of Mach 3 for 350-nm and 10 minutes of combat time (also at Mach 3). Finally, the F-108 should be able to fly to a specified point at supersonic speed, loiter for about an hour, and speed on to the target.

A mockup inspection on 26 January 1959 disclosed few needed changes. Nonetheless, the XF-108 (nicknamed the Rapier on 15 May 1959) never flew. The Air Force in 1957 had programmed for more than 480 F-108s, but the pinch in funds wiped out the whole project on 23 September 1959. The Air Force believed the F-108 would have been a good mobile missile launcher to intercept enemy aircraft far away from their intended targets. This was a role the B-70 bomber (being also built by North American and later consigned to the XF-108's fate) could not perform. Total RDT&E expenditures then stood at $141.9 million.

 

 

North American F-108A "Rapier"

 

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The North American F-108 was designed as a very high speed (mach 3) interceptor and escort fighter for the B-70 "Valkyrie" bomber under development at the same time. The delta wing Rapier, in its pre-mockup phase, was to have a canard (forward-mounted pitch-control surface), and three vertical stabilizers: one on the fuselage centerline a a pair at the halfway point on the wing trailing edge for high speed stabilization at speeds above mach 2.

The aircraft design was changed during the mockup phase. The canard was removed and the upper portions of the wing-mounted vertical stabilizers were removed. The wing was changed from a standard delta to a double-delta; the winglet incorporated a droop and 45 degree sweep (the main wing had about a 65 degree sweep).

The F-108 program was canceled on 23 September, 1959 never getting past the mockup phase.

 

TYPE Number built/Converted Remarks
F-108A  0 Reached mock-up stage only

 

SPECIFICATIONS (Mockup configuration)
Span: 57.4 ft.
Length: 89.2 ft. (not including nose boom)
Height: 22.1 ft.
Tread: 11 ft.
Weight: 102,000 lbs. maximum design gross weight
Armament: Four 20mm cannons, 108 2.75 in. rockets and up to 4,000 lbs. of bombs
Engines: Two General Electric J93-GE-3 turbojets of 30,000 lbs. thrust each with afterburner.
Crew: Two

PERFORMANCE
Maximum speed: approximately Mach 3
Range: 1,150 miles

COURTESY OF THE AIR FORCE MUSEUM

 

The General Electric J93-GE-3 turbojet

The 1950s and 1960s saw the J93, the first engine to operate at Mach 3, power the experimental XB-70 bomber; a nuclear-powered turbojet; and the addition of a fan to the rear of the CJ805 to create the first turbofan engine for commercial service for the Convair 990. In August 1965, the Air Force picked GE's TF39 to power its C-5 Galaxy cargo plane. This was the world's first high bypass turbofan to enter service. Another success of the period was the J85 turbojet engine that powered the Northrop F-5 Freedom Fighter, which was used by more than 30 nations.

 

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General Electric J93-GE-3 turbojet

The General Electric J93 turbojet engine was designed as the powerplant for both the North American XB-70A Valkyrie bomber and the North American XF-108 Rapier interceptor. The J93 was a single-shaft axial-flow turbojet with a variable-stator compressor and a fully-variable convergent/divergent exhaust nozzle. The maximum sea-level thrust was 31,500 pounds.

The J93 engine was ready before either the XB-70A or the XF-108 were, so the Air Force concluded that the engine should be initially flight tested in an existing aircraft. B-58A serial number 55-662 was selected for the project, and on July 1, 1959, Convair began the modification of the aircraft so that it could accept the installation of a J93 engine in a specially-modified underfuselage pod. Following the completion of the Convair modifications, the aircraft was delivered to General Electric's Edwards AFB operation as a NB-58A. While there, a J93-GE-3 engine was installed in a special underfuselage pod.

Unfortunately, the F-108 interceptor was cancelled outright and the B-70 project was reoriented to a research project only. A few NB-58A ground runs were made with the J93 engine in place, but the day before the first flight was scheduled to take place, the funding for the NB-58A project was cancelled. Consequently, the NB-58A/J93 combination never took to the air. The special pod was removed from the NB-58 testbed, and the NB-58A itself was converted to a TB-58A and later flew chase missions for the XB-70A at Edwards AFB. It was consigned to storage at MASDC in 1970, and eventually scrapped in 1977.

Joe Baugher

Sources:

  1. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.
     
  2. Post World War II Bombers, Marcelle Size Knaack, Office of Air Force History, 1988.
     
  3. United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian, 1989.
     
  4. Convair B-58 Hustler: The World's First Supersonic Bomber, Jay Miller, Aerofax, 1997.
     
  5. E-mail from Jennifer Raabe, with information and confirmation that NB-58A flight tests with J93 engine never actually took place.

 

 

An Interceptor ahead of its time

By Erik Simonsen

 

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During the early 1950s, as strategic planners at North American Aviation were surveying requirements for the next decade, two significant advanced concepts began to emerge.

One was a Mach 3+ intercontinental bomber, later designated the XB-70 Valkyrie, the other a long-range Mach 3+ interceptor that could protect the entire North American continent from intruders carrying nuclear arms.

In November 1955, the U.S. Air Force awarded study contracts to NAA, Lockheed and Northrop after the completion of a Phase I advanced interceptor competition initiated during September of that year.

NAA was awarded the development contract on June 1, 1957, for what was officially known as Weapons System 202A. Designated the F-108, a full-scale mockup was completed and on January 20, 1959, presented to the Air Force. Named Rapier in May 1959, and slightly preceding the development of the XB-70, the Department of Defense and NAA considered the F-108 a significant technological leap.

Ambitious as the project was, NAA felt the development of the advanced interceptor was well within its capabilities. With unmatched mass production credentials, NAA had developed the first operational supersonic fighter, the F-100, and was concurrently developing the Mach 2 A-3J Vigilante (later RA-5C) for the Navy.

As a cost-saving measure while developing the F-108, NAA instituted a program of shared technologies with the proposed XB-70. The interceptor would incorporate the same basic 30,000-pound-thrust YJ-93 engine, honeycomb stainless steel materials and clamshell escape systems as the XB-70. The F-108 also could be utilized as an escort for the B-70.

Operating at Mach 3 at 75,000 feet (and zoom climbing to 100,000 feet), the Rapier would have provided U.S. air defenses an effective look-down-shoot-down capability, intercepting potential adversaries with nuclear arms well away from U.S. borders.

While air defense was considered top priority within some circles, U.S. defense budgets began to flow in favor of intercontinental ballistic missile development.

As a result, NAA's fighter legacy would come to an end on September 23, 1959, with a statement from the Air Force announcing that the F-108 program was being canceled. This decision resulted in a domino effect by immediately negating the shared technology program and dramatically increasing the cost of the embryonic XB-70—a factor leading to its eventual cancellation.

No Rapiers would be built, and its advanced AN/ASG-18 radar system and funding soon would be transferred to the classified Lockheed YF-12A/F-12B. Yet, surprisingly, in 1968 the promised F-12B Mach 3+ interceptor also was canceled, twice leaving the United States without a high-technology air defense fighter.

The U.S. strategy of nuclear intercontinental ballistic missile parity with the Soviet Union was reflected in the eventual selection of the F-106 Delta Dart as the nation's top air defense fighter. Though it was an excellent aircraft, its Mach 2.3 supersonic performance in afterburner was limited to about 12 minutes. The rationale for a Mach 3+ interceptor had been to meet threatening nuclear-armed bombers quickly, keeping any fallout from jettisoned ordnance or premature detonations far from the United States. The F-108 would have intercepted targets a thousand miles from its base.

Fortunately, during the Cold War the Soviet bomber force did not evolve into an overwhelming threat—and the delayed supersonic Tupolev Tu-160 Blackjack achieved limited production.
 

Courtesy Of The Boeing Company

 

 

The F-108A Rapier

By Greg Goebel / Public Domain

 

One of the interesting footnotes to the XB-70 program was that technology developed for the XB-70 was to also be applied to a huge long-range interceptor / escort fighter named the "F-108A Rapier". The F-108 had the sole distinction of being the last fighter project worked on by North American.

The Rapier project was initiated by the USAF in October 1955, originally under the designation of "Long Range Interceptor / Experimental (LIRX)", leading to the award of a contract to North American in June 1957 for two F-108A prototypes. The F-108A would have Mach 3 performance and range adequate to intercept Soviet bombers flying over the North Pole to attack North America, and was also considered as an escort for the B-70. The Air Force hoped to have the F-108A in service by 1963, and contemplated buying hundreds of them.

The F-108A was to be a two-seat aircraft, powered by twin J93 engines and armed with advanced Falcon missiles. It evolved through a number of configurations, converging on a design implemented in a mock-up unveiled in January 1959. The type received the name "Rapier" in May of that year.

As the F-108A was conceived at that time, it looked something like the fuselage of the North American "Vigilante" carrier-based bomber, then in flight test, mated to a high-mounted delta wing with drooping wingtip panels, featuring a single tall vertical tailplane on the end of the fuselage and a smaller vertical tailplane under the middle of each wing.

The crew were to set in tandem seats fitted with ejection capsules for high-speed escape. The Rapier was to be armed with three GAR-9 advanced Falcon long-range air-to-air missiles, directed by the aircraft's powerful AN/ASG-18 radar.

   NORTH AMERICAN F-108A RAPIER (ESTIMATED SPECIFICATIONS):
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                17.5 meters         57 feet 5 inches
   length                  27.2 meters         89 feet 2 inches
   height                  6.73 meters         22 feet 1 inch

   empty weight            23,000 kilograms    51,000 pounds
   max loaded weight       46,700 kilograms    103,000 pounds

   maximum speed           3,200 KPH           2,000 MPH / 1,740 KT
   service ceiling         23,000 meters       75,000 feet
   ferry range             4,000 kilometers    2,500 MI / 2,175 NMI
   _____________________   _________________   _______________________

Initial flight of the first prototype was scheduled for the spring of 1961, but the USAF was already having second thoughts. The Soviet nuclear force was moving towards ICBMs, and an expensive dedicated long-range interceptor didn't seem like it was worth the money any more.

The Rapier program was cancelled in September 1959. The GAR-9 (later AIM-47A) missile and the AN/ASG-18 were later used with the Lockheed YF-12A, which was essentially an experimental interceptor version of the famed Lockheed "SR-71 Blackbird" reconnaissance aircraft. The YF-12A never got out of the prototype stage.

 

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North American XF-108 Rapier

By Joe Bauger

 

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The F-108A Rapier was destined to be the last fighter project carried out by North American Aviation, builders of such immortals as the P-51 Mustang and the F-86 Sabre.

The F-108 project was originally known as the LRIX (Long-Range Interceptor, Experimental) and was initiated by the Air Force on October 6, 1955. On June 6, 1957, North American was issued a letter contract for two prototypes of a long-range, high-performance interceptor to be designated F-108A. The company designation for the aircraft was NA-257. It was to be capable of Mach 3 performance and was intended to serve as a long-range interceptor that could destroy attacking Soviet bombers over the poles before they could get near US territory. It was also to serve as the escort fighter for the XB-70 Valkyrie Mach-3 strategic bomber, also to be built by North American. The Air Force expected that the first F-108A would be ready for service by early 1963. An order for no less than 480 F-108s was anticipated.

The F-108A design that North American ultimately produced called for a large delta-winged aircraft powered by a pair of afterburning General Electric J93-GE-3AR turbojets fed by variable inlets mounted underneath the wing roots. The F-108 aircraft was designed for a maximum speed of 1980 mph at 75,550 feet and for a 1020-mile combat radius. The pilot and radar operator sat in tandem individual ejector capsules in the forward cockpit. The aircraft was to be equipped with an extremely sophisticated avionics system, directed by the Hughes AN/ASG-18 search and tracking radar which was to have a range of over 100 miles.

The F-108A was to be armed with three advanced Hughes GAR-9 Falcon missiles housed in an internal weapons bay. The GAR-9 missile was powered by a Lockheed storable liquid-propellant rocket motor which was capable of driving the missile to hypersonic speeds of up to Mach 6 and achieving ranges of up to 115 miles. The GAR-9 missile used semi-active radar homing for midcourse guidance, with passive infrared homing being used for the final run-in to the target.

A mockup was inspected in January 1959, with the initial flight being planned for March 1961. The popular name *Rapier* was assigned on May 15, 1959.

However, by mid 1959, the Air Force was already beginning to experience some doubts about the high cost of the Rapier program. The primary strategic threat from the Soviet Union was now perceived to be its battery of intercontinental ballistic missiles instead of its force of long-range bombers. Against intercontinental ballistic missiles, the F-108A interceptor would be completely useless. In addition, the Air Force was increasingly of the opinion that unmanned intercontinental ballistic missiles could accomplish the mission of the B-70 Valkyrie/F-108 Rapier combination much more effectively and at far lower cost. Consequently, the F-108A project was cancelled in its entirety on September 23, 1959, before any prototypes could be built. The XB-70 project was also halted, and on December 3, 1959 was cut back to only one prototype.

The work on the Rapier did not entirely go to waste. The work that Hughes did on the AN/ASG-18 radar was later transferred over to the Lockheed YF-12A interceptor project, and the GAR-9 Falcon (redesignated AIM-47A in 1962) missile originally developed for the F-108A was used to arm the YF-12A.

 

Specification of F-108A Rapier (estimated):

Two General Electric J93-GE-3AR turbojets, 20,900 lb.s.t. dry, 30,000 lb.s.t. with afterburner. Maximum speed: 1980 mph at 76,550 feet. Service ceiling 80,100 feet, combat ceiling 76,550 feet. Initial climb rate 18,000 feet per minute. Climb to 50,000 feet in 5.4 minutes. Combat radius 1020 miles with three missiles. 2488 miles ferry range. Dimensions: wingspan 57 feet 5 inches, length 89 feet 2 inches, height 22 feet 1 inches, wing area 1865 square feet. Weights: 50,907 pounds empty, 76,118 pounds combat, 102,533 pounds gross. Armed with three Hughes GAR-9 Falcon air-to-air missiles.

Sources:

  1. The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.
     
  2. Fighters of the United States Air Force, Robert F. Dorr and David Donald, Temple Press Aerospace, 1990.
     
  3. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.
     
  4. Post-World War II Fighters, 1945-1973, Marcelle Size Knaack, Office of Air Force History, 1986.

By Joe Bauger

 

 

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The F-108 Rapier was North American Aviation's answer to DOD cutting edge interceptor criteria issued in the mid-Fifties and envisaged as countering all airborne threats in the post 1962 world. A complete weapons system, as were other members of the "Century Series", the F-108 was to eventually supplant the F-106 by operating independently, well beyond the limits of the then standard SAGE (Semi-Automatic Ground Environment) air intercept system. The Rapier was designed to "run with the big dogs," at Mach 3 and to zoom climb altitudes in excess of 100,000 feet. Manned by two aircrew members in a tandem cockpit, powered by two brutish J93 General Electric engines (six of which powered the XB-70), the cranked delta-winged Rapier was some fifteen feet longer and slightly heavier than the F-111. Missiles only were the order of the day, and the F-108 carried three AIM 47 Falcons on a rotary launcher in the weapons bay.

The project moved along smartly, with a full scale mockup finished, the first flight scheduled for 1961 and Initial Operating Capability (IOC) estimated in 1963. Although the project was on schedule with few, if any, developmental glitches, the USAF suddenly announced in September 1959 that the F-108 was canceled "because of a shortage of funds and priorities....." "Priorities" seems to be the operative word, since an apparently unknowing North American design team was running against a parallel "Black World" ultra project which was to become the YF-12. Interestingly, the Hughes radar and AIM 47s appeared on the Lockheed Blackbird!

 

 

 XF-108 Rapier Photo Gallery

 

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