The North American XF-108 Rapier was a proposed long-range, high-speed interceptor aircraft designed by North American Aviation intended to defend the United States from supersonic Soviet strategic bombers. The aircraft would have cruised at speeds around Mach 3 (3,200 km/h; 2,000 mph) with an unrefueled combat radius over 1,000 nautical miles (1,900 km; 1,200 mi), and was equipped with radar and missiles offering engagement ranges up to 100 miles (160 km) against bomber-sized targets.
To limit development costs, the program shared engine development with the North American XB-70 Valkyrie strategic bomber program, and used a number of elements of earlier interceptor projects. The program had progressed only as far as the construction of a single wooden mockup when it was cancelled in 1959, due to a shortage of funds and the Soviets' adoption of ballistic missiles as their primary means of nuclear attack. Had it flown, the F-108 would have been the heaviest fighter of its era.
Prior to the project's cancellation, the President of the United States Gen. Dwight D. Eisenhower noted that raising the F-108 interceptor force would have cost the U.S. taxpayer $4 billion (equivalent to $34 billion today).
|Artist's impression of two F-108s attached to Elmendorf AFB, Alaska. Note: Top aircraft's weapons bay opening.|
|Manufacturer||North American Aviation|
|Primary user||United States Air Force (intended)|
|Number built||One mockup|
|Program cost||US$141.9 million (R&D only) (equivalent to $1.22 billion today)|
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 the 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" (WS-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 feet 10 inches (6.05 m), and a wing of 53.5° sweep. The aircraft in this configuration would have had a maximum takeoff weight of 99,400 pounds (45,100 kg) with a 72,550-foot (22,110 m) operational ceiling. In addition to the F-108's interceptor role, North American proposed it as a penetration fighter to aid 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 preproduction 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 mockup, 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.
Even as the XF-108 program was progressing well, there were signs that would ultimately lead to its eventual cancellation. Unconfirmed Soviet bomber threats, the overwhelming trend toward offensive and defensive nuclear missiles in the late 1950s and early 1960s, as well as rising costs, contributed to the termination of the XF-108. The cancellation was announced on 23 September 1959. North American continued refining the design through 1960 in hopes that the program might be revived. Despite the extra money and time spent on the Rapier, it was not wholly in vain; the North American A-5 Vigilante supersonic carrier-based nuclear strike bomber developed for the U.S. Navy, which was later modified into a carrier-based reconnaissance aircraft, retained the fuselage/weapon package and systems design of the Rapier. In many ways the Vigilante could be seen as the successful application of the Rapier design principles in a Mach 2 supersonic design.
Hughes Aircraft would continue the development of the advanced fire control system and the GAR-9 missile.[N 1] 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 AN/ASG-18 fire control system.
The initial F-108 configuration featured a very large "cranked" delta wing. 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 separate tailplanes or forward canards, both were abandoned in the final design. The large fuselage and wing had two and five fuel tanks, respectively, giving an estimated combat radius of some 1,100 nautical miles (2,000 km). Top speed was estimated at 1,980 miles per hour (3,190 km/h), about Mach 3, at 81,800 feet (24,900 m). The aircraft was powered by two General Electric J93 turbojet engines, also used in North American's XB-70 Valkyrie bomber, in the fuselage.
The F-108 was intended to carry the Hughes AN/ASG-18 radar, the U.S.'s first pulse-Doppler radar set. It was to have look-down/shoot-down capability, but could track only one target at a time. The radar was paired with an infra-red search and tracking (IRST) 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 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 112 miles (180 km).
As part of WS-202A, a design for a high-speed (Mach 3+) aerial target for use in testing the F-108's weapons system was proposed. The Wright Air Development Center requested the designation XQ-11 for the target design; the request was denied due to the early stage of development, and the F-108 program was cancelled before further work was undertaken.
Aircraft of comparable role, configuration and era
The Hughes AIM-47 Falcon, originally GAR-9, was a very long-range high-performance air-to-air missile that shared the basic design of the earlier AIM-4 Falcon. It was developed in 1958 along with the new Hughes AN/ASG-18 radar fire-control system intended to arm the Mach 3 XF-108 Rapier interceptor aircraft and, after its cancellation, the YF-12A. It was never used operationally, but was a direct predecessor of the AIM-54 Phoenix.AIM-4 Falcon
The Hughes AIM-4 Falcon was the first operational guided air-to-air missile of the United States Air Force. Development began in 1946; the weapon was first tested in 1949. The missile entered service with the USAF in 1956.
Produced in both heat-seeking and radar-guided versions, the missile served during the Vietnam War with USAF McDonnell Douglas F-4 Phantom II units. Designed to shoot down slow bombers with limited maneuverability, it was ineffective against maneuverable fighters over Vietnam. Lacking proximity fusing, the missile would only detonate if a direct hit was scored. Only five kills were recorded.
With the AIM-4's poor kill record rendering the F-4 ineffective at air-to-air combat, the fighters were modified to carry the USN-designed AIM-9 Sidewinder missile instead, which was already carried on USN and USMC F-4 Phantom II and F-8 Crusader jet fighters. The Sidewinder was much more effective and continues to serve the armed forces of the United States and numerous allied nations to this day.AIM-54 Phoenix
The AIM-54 Phoenix is a radar-guided, long-range air-to-air missile (AAM), carried in clusters of up to six missiles on the Grumman F-14 Tomcat, its only operational launch platform. The Phoenix was the United States' only long-range air-to-air missile. The combination of Phoenix missile and the AN/AWG-9 guidance radar was the first aerial weapons system that could simultaneously engage multiple targets. Due to its active radar tracking, the brevity code "Fox Three" was used when firing the AIM-54.
Both the missile and the aircraft were used by Iran and the United States Navy. In US service both are now retired, the AIM-54 Phoenix in 2004 and the F-14 in 2006. They were replaced by the shorter-range AIM-120 AMRAAM, employed on the F/A-18 Hornet and F/A-18E/F Super Hornet—in its AIM-120D version, the latest version of the AMRAAM just matches the Phoenix's maximum range.The AIM-54 is credited with 62 air-to-air kills, all scored by Iran during the long Iran–Iraq War. Following the retirement of the F-14 by the U.S. Navy, the weapon's only current operator is the Islamic Republic of Iran Air Force.AN/ASG-18
The Hughes AN/ASG-18 Fire Control System was a prototype airborne fire control radar system for the planned North American XF-108 Rapier interceptor aircraft for the United States Air Force. It was the US's first Pulse-Doppler radar, giving it look-down/shoot-down capability, and was also the first track while scan radar (could track one target at a time). This was paired with an infrared search and track (IRST) system. Range of the radar was estimated at between 200 and 300 miles (322 to 482 km), with reliable detection of bomber-sized targets at 100 miles. The installation itself was massive, weighing 2,100 lb (953 kg), and taking up most of the nose of the aircraft. The system was to be used with the Hughes AIM-47 Falcon missile, which also had a range of about 100 miles.
While development work was done with the XF-108, the AN/ASG-18 and Falcon missiles were first tested on a highly modified Convair B-58 Hustler bomber. To fit the radar, the nose was lengthened nearly 7 feet (2.13 m), and the infrared sensors were mounted on either side of the forward fuselage. The resulting nose shape led to it being nicknamed "Snoopy". A single missile was housed in a specially built pod underneath the fuselage.
Before the test "Snoopy" could fly, the XF-108 program was cancelled, and the proposed Lockheed YF-12 interceptor was to instead receive the radar/missile system pair. Tests of the system were conducted first in 1960 and until 1963 only on the modified B-58, after which the YF-12 took over until the cancellation of the whole program in 1966.Avro Canada
Avro Canada was a Canadian aircraft manufacturing company. It started in 1945 as an aircraft plant and within thirteen years became the third-largest company in Canada, one of the largest 100 companies in the world, and directly employing over 50,000. Avro Canada was best known for the highly advanced CF-105 Arrow, but through growth and acquisition, it rapidly became a major, integrated company that had diverse holdings.
Following the cancellation of the CF-105 Arrow the company ceased operations in 1962.Century Series
The Century Series is a popular name for a group of US fighter aircraft representing models designated between F-100 and F-106 which went into full production. They included the first successful supersonic aircraft designs in the United States Air Force's service, which remained in active service well into the 1970s and 1980s with the Air Force Reserve and Air National Guard. Three later variants, the QF-100, QF-102 and QF-106, also continued in service, primarily as aerial target drones, until the late 1990s.Convair F-106 Delta Dart
The Convair F-106 Delta Dart was the primary all-weather interceptor aircraft of the United States Air Force from the 1960s through to the 1980s. Designed as the so-called "Ultimate Interceptor", it proved to be the last dedicated interceptor in U.S. Air Force service to date. It was gradually retired during the 1980s, with the QF-106 drone conversions of the aircraft being used until 1998 under the Pacer Six Program.General Electric YJ93
The General Electric YJ93 turbojet engine was designed as the powerplant for both the North American XB-70 Valkyrie bomber and the North American XF-108 Rapier interceptor. The YJ93 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 28,800 lbf (128 kN).Lockheed YF-12
The Lockheed YF-12 is an American prototype interceptor aircraft evaluated by the United States Air Force in the 1960s. The YF-12 was a twin-seat version of the secret single-seat Lockheed A-12 reconnaissance aircraft, which led to the U.S. Air Force's Lockheed SR-71 Blackbird twin-seat reconnaissance variant. The YF-12 set and held speed and altitude world records of over 2,000 miles per hour (3,200 km/h) and over 80,000 feet (24,000 m) (later surpassed by the SR-71), and is the world's largest, heaviest and fastest manned interceptor to date. After retirement it served as a research aircraft for NASA, which used it to develop several significant improvements in control for supersonic aircraft, including the SR-71.Look-down/shoot-down
A radar system has look-down/shoot-down capability if it can detect, track and guide a weapon to an air target moving below the horizon as seen by the radar.North American A-5 Vigilante
The North American A-5 Vigilante is an American carrier-based supersonic bomber designed and built by North American Aviation for the United States Navy. It set several world records including long distance speed and altitude records. Its service in the nuclear strike role to replace the Douglas A-3 Skywarrior was very short; however, as the RA-5C, it saw extensive service during the Vietnam War in the tactical strike reconnaissance role. Prior to the unification of the Navy designation sequence with the Air Force sequence in 1962, it was designated the A3J Vigilante.North American Aviation
North American Aviation (NAA) was a major American aerospace manufacturer, responsible for a number of historic aircraft, including the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F-86 Sabre jet fighter, the X-15 rocket plane, and the XB-70, as well as Apollo command and service module, the second stage of the Saturn V rocket, the Space Shuttle orbiter and the B-1 Lancer.
Through a series of mergers and sales, North American Aviation became part of North American Rockwell, which later became Rockwell International and is now part of Boeing.Penetration fighter
The term penetration fighter was used for a short time to describe a theoretical long-range fighter aircraft designed to penetrate enemy air defences and attack defensive interceptors. The concept is similar to the escort fighter, but differs primarily in that the aircraft would not operate in close concert with bombers. The same general mission is also carried out by intruders, but these are generally night fighters or light bombers that do not have the air combat performance of this concept.
The presence of the North American P-51 Mustang above Germany allowed USAAF bombers to fly at will over the country, and is considered one of the turning points of the air war. In the post-war period, the development of jet-powered strategic bombers made this role difficult to fill; aircraft with performance to protect the bombers had very short range, and those with the range were propeller designs that could not keep up. The desire for a fighter that could penetrate enemy airspace along with the bombers led to several prototype designs in the early 1950s, including the McDonnell XF-88 Voodoo, Lockheed XF-90 and North American YF-93. In order to be competitive with existing interceptors, these had to be jet powered, and this demanded huge fuel loads. None proved able to compete with shorter range designs, and the penetration fighter concept faded.The concept re-appeared with the North American XF-108 Rapier project, a long-range interceptor intended to launch from the continental United States and intercept Soviet bombers while still in the far Arctic. This long range meant that if they were launched from forward bases in Europe, Turkey or Alaska, the F-108 would be able to travel a fair distance over the USSR and help disrupt the defences for the following North American XB-70 bombers. The F-108 was ultimately cancelled in budget cuts, and its short-lived replacement, the Lockheed YF-12, was not considered in this role.Pulse-Doppler radar
A pulse-Doppler radar is a radar system that determines the range to a target using pulse-timing techniques, and uses the Doppler effect of the returned signal to determine the target object's velocity. It combines the features of pulse radars and continuous-wave radars, which were formerly separate due to the complexity of the electronics.
Pulse-Doppler systems were first widely used on fighter aircraft starting in the 1960s. Earlier radars had used pulse-timing in order to determine range and the angle of the antenna (or similar means) to determine the bearing. However, this only worked when the radar antenna was not pointed down; in that case the reflection off the ground overwhelmed any returns from other objects. As the ground moves at the same speed but opposite direction of the aircraft, Doppler techniques allow the ground return to be filtered out, revealing aircraft and vehicles. This gives pulse-Doppler radars "look-down/shoot-down" capability. A secondary advantage in military radar is to reduce the transmitted power while achieving acceptable performance for improved safety of stealthy radar.Pulse-Doppler techniques also find widespread use in meteorological radars, allowing the radar to determine wind speed from the velocity of any precipitation in the air. Pulse-Doppler radar is also the basis of synthetic aperture radar used in radar astronomy, remote sensing and mapping. In air traffic control, they are used for discriminating aircraft from clutter. Besides the above conventional surveillance applications, pulse-Doppler radar has been successfully applied in healthcare, such as fall risk assessment and fall detection, for nursing or clinical purposes.Republic XF-103
The Republic XF-103 was an American project to develop a powerful missile-armed interceptor aircraft capable of destroying Soviet bombers while flying at speeds as high as Mach 3. Despite a prolonged development, it never progressed past the mockup stage.Third-generation jet fighter
The third-generation jet fighter was the class of fighter aircraft developed between the early 1960s to the 1970s.Tupolev Tu-28
The Tupolev Tu-28 (NATO reporting name Fiddler) was a long-range interceptor aircraft introduced by the Soviet Union in the 1960s. The official designation was Tu-128, but this designation was less commonly used in the West. It was the largest and heaviest fighter ever in service.Zero-length launch
The zero-length launch system or zero-length take-off system (ZLL, ZLTO, ZEL, ZELL) was a system whereby jet fighters and attack aircraft were intended to be placed on short-burn duration, often solid-fuel, "dropaway" rocket booster units, deployed with mobile launch platforms. Most zero length launch experiments took place in the 1950s, during the Cold War.
USAF drone aircraft designations 1948–1962
1 Not assigned