Saab 37 Viggen

Viggen is the definite form of the Swedish word vigg, which has two meanings. According to Saab, the aircraft's name alluded to both. The first meaning refers to the Swedish name for the tufted duck, a small diving duck common in Sweden. In this sense, it serves as a reference to the aircraft's canard configuration, as "canard" is French for duck. Vigg is also åskvigg, or "thunderbolt" (thunder wedge), stemming from the thunderstones of Nordic folklore, called "åskviggar", said to come from the lightning strikes of Norse god Thor when he hunted giants with his war hammer, Mjölnir. == Development ==

Origins The Viggen was initially developed as an intended replacement for the Saab 32 Lansen in the attack role and later the Saab 35 Draken as a fighter. Between 1952 and 1957, the first studies towards what would become the Viggen were carried out, involving the Finnish aircraft designer Aarne Lakomaa. Over 100 different concepts were examined in these studies, involving both single- and twin engine configurations, both traditional and double delta wings, and canard wings. Even VTOL designs were considered, with separate lift engines, but were soon identified as being unacceptable. One radical requirement of the proposed aircraft was the ability for it to be operated from relatively short runways only 500 meters long; this was part of the Bas 60 air base system that had been introduced by the Swedish Air Force in the late 1950s. Bas 60 revolved around force dispersal of aircraft across many wartime air bases, including road runways acting as backup runways. Utilizing partially destroyed runways was another factor that motivated STOL capability. Bas 60 was developed into Bas 90 in the 1970s and 1980s, and included short runways only 800 meters in length. Enabling such operations imposed several critical demands upon the design, including a modest landing speed, no-flare touchdown, powerful post-landing deceleration, accurate steering even in crosswinds on icy surfaces, and high acceleration on take-off. According to research by Nils Bruzelius at the Swedish National Defence College, the reason for this officially unexplained U.S. support was to protect U.S. Polaris submarines deployed just outside the Swedish east coast against the threat of Soviet anti-submarine aircraft. The connection also appears doubtful due to the time scale – the Viggen's strike version only became operational in 1971, and the fighter version in 1978, by which time Polaris had already been retired. Project launch In December 1961, the Swedish government gave its approval for the development of Aircraft System 37, which would ultimately become the Viggen. By 1962, all elements for the project either existed or were close to fully developed; these included the aircraft itself, the powerplant, ejector seat, armaments, reconnaissance systems, ground servicing equipment, and training equipment such as simulators. During the 1960s, the Viggen accounted for 10 percent of all Swedish R&D funding. In 1963, Saab finalized the aerodynamic design of the aircraft; the aerodynamic configuration was radical: it combined an aft-mounted double delta wing with a small, high-set canard foreplane, equipped with powered trailing flaps mounted ahead of and slightly above the main wing; this would be judged to be the best means to satisfy the conflicting demands for STOL performance, supersonic speed, low turbulence sensitivity at low level flight, and efficient lift for subsonic flight. Canard aircraft have since become common in fighter aircraft, notably with the Eurofighter Typhoon, Dassault Rafale, Saab JAS 39 Gripen and the IAI Kfir, but principally for the purposes of providing agility during flight rather than for its STOL capabilities. Further aerodynamic refinements during the later stage of development included the addition of dog-tooth patterns upon the main wing to generate vortices, allowing for the elimination of blown flaps from the canard. The use of a thrust reverser enabled the sought short landing performance. , Linköping During development, Saab had opted to power the type using a single large turbofan engine. Originally, the British Rolls-Royce Medway engine had been selected to power the Viggen, which was then considered to be ideal for the basis for a supersonic engine equipped with a fully modulated afterburner; however, development of the Medway engine was cancelled due to the intended launch aircraft, the de Havilland Trident, being downsized during development. This first flight, which lasted for 43 minutes, was flown by Erik Dahlström, Saab's chief test pilot, who reported the prototype to have been easy to handle throughout. Writing at the time, aerospace publication Flight International described the flight as having been "Sweden's astonishing unilateral stand in the front rank of advanced aircraft-building nations…" Each of the seven prototypes were assigned different roles, although the initial aircraft were focused on supporting the development of the initial production variant, the AJ37. In 1967, the Swedish Government concluded that the in-development AJ 37 Viggen would be both cheaper than and superior to the McDonnell Douglas F-4 Phantom II. Also in 1968, Saab began work on the Viggen's maritime reconnaissance and photo reconnaissance variants. On 23 February 1971, the first production aircraft, an AJ37 model, conducted its first flight. Further development As the initial AJ 37 Viggen was being introduced to service, further variants of the Viggen proceeded to complete development and enter production. In 1972, the first SK 37, an operational trainer variant with a staggered second canopy for an instructor, was delivered to the Swedish Air Force. On 21 May 1973, the first prototype of SF 37 Viggen, a tactical reconnaissance variant featuring a modified nose to accommodate seven sensors, conducted its first flight. While other variants entered production during the 1960s, Saab continued the development of the more capable all-weather interceptor version of the aircraft, the JA 37. In 1970, Sweden's air defenses had been closely inspected and it was determined that the prospective JA 37 Viggen was highly suited to the role. The JA 37, in addition to its principal aerial combat mission, also retained a secondary ground-attack capability, and was better suited to low-level operations. However, a combination of inflation and other factors eventually reduced the total number of aircraft manufactured to 329. In 1990, production of the Viggen ceased and the final aircraft was delivered. In May 1991, a SEK 300-million program to upgrade 11 AJ37, SF37 and SH37 Viggens to a common multirole variant, designated AJS37, was announced. Amongst the changes involved, interchangeable armaments and sensor payloads were implemented in addition to the adoption of new mission planning and threat analysis computer systems. The onboard ECM systems were also improved. == Design ==

Propulsion The Viggen was powered by a single Volvo RM8 turbofan. This was essentially a heavily modified licence-built variant of the Pratt & Whitney JT8D engine that powered commercial airliners of the 1960s, with an afterburner added for the Viggen. The airframe also incorporated a thrust reverser to use during landings and land manoeuvres, which, combined with the aircraft having flight capabilities approaching a limited STOL-like performance, enabled operations from 500 m airstrips with minimal support. The requirements from the Swedish Air Force dictated Mach 2 capability at high altitude and Mach 1 at low altitude. At the same time, short-field take-off and landing performance was also required. Since the Viggen was developed initially as an attack aircraft instead of an interceptor (the Saab 35 Draken fulfilled this role), some emphasis was given to low fuel consumption at high subsonic speeds at low level for good range. With turbofan engines just emerging and indicating better fuel economy for cruise than turbojet engines, the former was favoured, since the latter were mainly limited by metallurgy development resulting from limitations in turbine temperature. Mechanical simplicity was also favoured, so the air intakes were simple D-section types with boundary layer splitter plates, while the fixed inlet had no adjustable geometry for improved pressure recovery. The disadvantage was that the required engine would be very large. It had a bypass ratio of around 1.07:1 in the RM8A, which reduced to 0.97:1 in the RM8B. The RM8A was the most powerful fighter engine in the late 1960s. Thrust is 72.1 kN dry and 125.0 kN with afterburner. Owing to the increased length and weight of the RM8B engine over its predecessor, the airframe of the JA 37 was stretched in order to accommodate it. In practice, the CK 37 proved to be more reliable than predicted. The computing techniques and concepts, such as distributed computing, went beyond use of the Viggen, in addition to civil-orientated derivatives, it directly contributed to the computers used on board the Viggen's replacement, the Saab JAS 39 Gripen. Various electronic countermeasures (ECM) were installed upon the Viggen, these were typically provided by Satt Elektronik. an optional Ericsson Erijammer pod and BOZ-100 chaff/flare pod. Infrared warning receivers were also later installed. In total, the electronics weighed 600 kg, a substantial amount for a single-engine fighter of the era. In order to effectively enforce Sweden's air space, the Viggen was integrated with STRIL 60 national defence system. In 1985, the "fighter link" entered service, permitting encrypted data communication between up to four fighters; this enabled one fighter to "paint" an airborne enemy with guidance radar for the Skyflash missiles of the three other fighters in a group while they had their own search and guidance radars switched off. This system was operational ten years before any other country's. The autopilot was also slaved to the radar control to obtain better precision firing the cannon. Once in service, the Viggen's software was regularly updated every 18 months. In 1983, the mean time between failures (MTBF) was reported as 100 hours, a very high reliability level for the generation of avionics systems involved. Cockpit The displays in the original cockpit were all of the traditional analogue/mechanical type with the exception of an electronic head-up display (HUD), which Saab has claimed makes the Viggen easier to fly, especially at low altitudes during air-to-ground strike missions. Unusually for a 1970s fighter, the JA 37 variant of the Viggen featured three multi-purpose cathode-ray tube (CRT) display screens fitted within the cockpit, in a system called AP-12, developed by Saab and Ericsson. On the twin-seat SK 37 trainer, the rear cockpit used by the instructor is only fitted with conventional instrumentation and lacks a HUD, computer controls and other features. The ejection seat was the Raketstol 37 (literally; Rocket chair 37) and was the last Saab designed seat in service. A derivative of the Saab 105 trainer seat, the seat was optimized for low altitude, high speed ejections. As per then-standard practice within the Swedish Air Force, all cockpit instrumentation and labeling were in Swedish. Wings and airframe With the performance requirements to a large extent dictating the choice of the engine, the airframe turned out to be quite bulky compared to contemporary slimmer designs with turbojet engines. The first prototypes had a straight midsection fuselage that was later improved with a "hump" on the dorsal spine for reduced drag according to the area rule. The wing had the shape of a double delta with a dogtooth added to improve longitudinal stability at high incidence angles. A consequence of a tailless delta design, such as in the Viggen, is that the elevons, which replace more conventional control surfaces, operate with a small effective moment arm; their use adds substantial weight to the aircraft at takeoff and landing. Hinged leading edge surfaces can help counteract this, but an even more effective tool is the canard. The canard surfaces were positioned behind the inlets and placed slightly higher than the main wing, with a higher stall angle than the wing, and were equipped with flaps. The lifting canard surfaces act as a vortex generator for the main wing and therefore provide more lift. An added benefit was that they also improved roll stability in the transonic region. The canard flaps were deployed in conjunction with the landing gear to provide even more lift for takeoff and landing. To withstand the stresses of no-flare landings, Saab made extensive use of aluminium in the airframe of the Viggen, which was constructed using a bonded metal honeycomb structure; the entire rear section of the fuselage, downstream of the engine nozzle, formed a heat-resistant ring composed of titanium. The main landing gear, manufactured by Motala Verkstad, was highly strengthened as well; each leg held two small wheels fitted with anti-skid brakes placed in a tandem arrangement. The design requirements imposed by the large anti-ship missiles employed upon the Viggen necessitated that both the undercarriage and vertical stabilizer be quite tall. The pylons behind the landing gear were not used until the JA 37D modification when BOL countermeasure dispensers were fitted to them. Ground crew would enter the munitions fitted into the aircraft's central computer using a load-selector panel, which would automatically choose the correct values for fire control, fuel consumption, and other calculations. The RB-04 was a relatively simple cruise missile that was further developed to become the more capable RBS-15, also integrated on the Viggen. An optional load consisted of two Rb 05 air-to-surface missiles on the fuselage pylons. The RB 05 was later replaced by AGM-65 Maverick (Swedish designation "RB 75") television-guided missiles. In a ground-attack role, a combination of unguided 135 mm rockets in sextuple pods and 120 kg fragmentation bombs on quadruple-mounts could be used. Other armaments include explosive mines, and 30 mm ADEN cannon pods with 150 rounds of ammunition on the inboard wing pylons. Self-defence measures included various ECM systems, as well as either the AIM-4 Falcon (Swedish designation "RB 28") or AIM-9 Sidewinder (Swedish designation "RB 24") air-to-air missiles. At one point, the AJ 37 Viggen was under consideration as a carrier of both a Swedish nuclear weapon and chemical weapons, although no nuclear or chemical weapons were ultimately adopted by Sweden. JA 37 The JA 37 fighter interceptor, introduced in 1979, featured the Ericsson PS 46/A radar which was capable of guiding the medium-range semi-active radar homing RB 71 Skyflash air-to-air missiles. Both the RB 71 and the PS 46/A radar were designed to provide the Viggen with a look-down/shoot-down capability and to engage targets at beyond visual range distances. This, in conjunction with the fire control system, allowed air-to-air engagements at longer range than other fighters. Perhaps the most important improvement was the expanded STRIL datalink which entered service in 1982–85. It allowed not only ground control-aircraft communication, but also between up to four aircraft simultaneously regardless if airborne or on the ground. Datalink information was displayed on the Horizontal Situation Display and a tactical display, the latter using link symbology that could be overlaid with an electronic map on a multifunction display. == Operational history ==

In July 1971, the first production AJ 37 Viggen was delivered to the Swedish Air Force. In October 1973, Skaraborg Wing was reportedly close to achieving full operational effectiveness; In practice, one of the most significant issues encountered with the Viggen during low-level flight, as extensively performed during a typical attack mission profile, was the threat posed by birds; thus, the Swedish Air Force paid close attention to their migratory patterns. During the later half of the 1970s and into the 1980s, the introduction of various variants of the Viggen proceeded; these included the SK 37, a two-seat operational-conversion trainer, introduced in 1972, the SF 37, an overland reconnaissance model, introduced in 1977, and the SH 37, a maritime reconnaissance version, introduced in 1975. The Viggen went on to become Sweden's primary air defense platform for many years. The Viggen was designed to be simple to maintain, even by conscripted flight line mechanics with limited technical training. A single Viggen could be maintained by a team of five conscripts under the supervision of a single chief mechanic. Standard turnaround, including refueling and rearming, took less than ten minutes to perform; while an engine replacement took four hours. Over the long term, the Viggen required 22-man hours per flight hour of maintenance work at the depot level, and nine-man hours per flight hour at the front line. The Viggen is the only aircraft to get an acknowledged radar lock on the SR-71. Retirement By 1994, the replacement of the Viggen by the later and more advanced Saab JAS 39 Gripen was in progress, the type being progressively phased out as greater numbers of Gripen aircraft were delivered. On 25 November 2005, the last front line Viggen was formally retired by the Swedish Air Force. Overseas sales efforts Although Saab offered the Viggen for sale worldwide, and was the subject of a heavy marketing campaign in both European and developing countries during the 1970s, ultimately no export sales were made. During the 1970s, Saab proposed a new variant of the Viggen, designated the Saab 37E Eurofighter (unrelated to the later Eurofighter Typhoon), for the United States Air Force Air Combat Fighter competition to find a replacement for the Lockheed F-104 Starfighter. The 37E Eurofighter competed against Dassault-Breguet's proposed Mirage F1M-53, the SEPECAT Jaguar, Northrop's P-530 Cobra (on which the YF-17 was based), and General Dynamics's YF-16; on 13 January 1975, United States Secretary of the Air Force John L. McLucas announced the YF-16 had been selected as the winner of the ACF competition. In 1978, the United States blocked a major prospective sale to India, which would have involved selling a number of Swedish-built Viggens in addition to a licensed production agreement under which the Viggen would also have been built in India, by not issuing an export license for the RM8/JT8D engine and other American technologies used. India later opted to procure the SEPECAT Jaguar in its place. According to leaked United States diplomatic cables, India's interest in the Viggen was reported to be entirely due to Rajiv Gandhi's influence, and had alleged have been without any input from the Indian Air Force. According to author Chris Smith, the Viggen had been the favoured candidate for the Indian Air Force prior to the deal being blocked by the US. == Variants ==

;AJ 37: Primarily a single-seat ground-attack fighter aircraft (AJ: Attack-Jakt), with a secondary fighter role. RM8A powerplant. PS 37A radar. First delivery in mid-1971, 108 built, with serial numbers 37001–108. 48 airframes upgraded to AJS 37. Partially decommissioned in 1998. ;SK 37: Two-seat trainer aircraft (Sk: Skol) with no radar and reduced fuel. First flight on 2 July 1970. 17 built, with delivery from June 1972, serial numbers 37801–817. It made its first flight on 21 May 1973. 28 built, with deliveries from April 1977, serial numbers 37950–977. 27 built, with delivery from June 1975, serial numbers 37901–927. ;Saab 37X: Proposed export version offered to Norway in 1967–68, none built. ;JA 37: Primarily a single-seat all-weather interceptor fighter, with a secondary attack role. Its first flight was on 27 September 1974 with the first deliveries starting in 1979, Cancelled in favour of F/A-18 Hornet. ==Operators==

, Scotland, 2015 ; • Swedish Air Force Operational units • F 4 Frösön • 2 squadrons JA 37 1983–2003 • 1 squadron SK 37 1999–2003 • 1 squadron SK 37E 1999–2003 • F 6 Karlsborg • 2 squadrons AJ 37 1978–1993 • F 7 Såtenäs • 3 squadrons AJ 37 1972–1998 • 1 squadron SK 37 1972–1974 • F 10 Ängelholm • 1 squadron AJ/SF/SH 37 (combined) 1993–2001 • F 13 Norrköping • 1 squadron SF/SH 37 (combined) 1977–1993 • 1 squadron JA 37 1980–1993 • F 15 Söderhamn • 2 squadrons AJ 37 1974–1998 • 1 squadron SK 37 1974–1998 • F 16 Uppsala • 2 squadrons JA 37 1986–2003 • F 17 Kallinge • 1 squadron JA 37 1981–2002 • 1 squadron SF/SH 37 (combined) 1979–1993 • 1 squadron JA 37 1993–2002 • F 21 Luleå • 2 squadrons JA 37 1983–2004 • 1 squadron SF/SH 37 1979–2002 • 1 squadron SK 37E (combined) 2003–2007 == Accident and incidents ==

Very little is publicized about Sweden's military air accidents and incidents, however, an incident resulting in a fatality of a Saab 37 pilot during a reconnaissance fly-by of Russian nuclear-powered battlecruiser Pyotr Velikiy occurred on 16 October 1996, and is the last known operational fatality of 19 total known fatalities (in over 50 accidents) involving the Saab 37 Viggen in its almost 40 years of operational history. == Surviving aircraft ==

• An AJS 37 Viggen (s/n 37098) with the code F 7–52 has been retained and went through a long period of restoration and maintenance to be airworthy again. This Viggen was built in 1977 and served all its active duty in F 15 Wing at Söderhamn. It was transferred into civil registry with the registration number SE-DXN. It undertook its maiden flight after having been approved by the authorities on 27 March 2012 from the F 7 Wing at Såtenäs. The Viggen is unpainted to represent the first delivered Viggens as they looked in the early 1970s. • An SK 37 Viggen (two seat trainer) (s/n 37809) with the code F 15-61 has been retained and went through a period of restoration and maintenance to be airworthy again. This Viggen was built in 1973 and served its first activities in F 7 Wing at Såtenäs, later in F 15 Wing at Söderhamn and finally in FMV Prov at Linköping until 2007. It was transferred into civil registry with the registration number SE-DXO. It undertook its maiden flight 15 May 2018 from the F 7 Wing at Såtenäs after having been approved by the authorities on 21 March 2018 The Viggen is painted in the unique four colour camouflage as all Viggens were painted from the late 1970s. • An SK 37E Viggen (s/n 37898) is preserved at the Musée de l’air et de l’espace located at the former Paris–Le Bourget Airport in France. • A JA 37 Viggen (sn: 37429) is preserved at the Estonian Aviation Museum near Tartu, Estonia. The aircraft was obtained from Swedish Air Force Museum, and flew from Sweden to Tartu in 2004. • An AJSF 37 Viggen (s/n 37954) is on display at the Polish Aviation Museum in Kraków. • Two Viggens as well as the nose parts of some JA-37s can be found at the Aeroseum near Gothenburg. An AJ-37 (s/n 37094/57) and an AJSH-37 (s/n 37911/55). • Two Viggens can be found at Söderhamn Aviation Museum at the former F 15 wing in Söderhamn, Sweden. One is an AJS 37 and the other is an SK 37 trainer aircraft. The cockpit of the AJS 37 has been converted into a simulator that is open to the public. • An AJ 37 Viggen is on display at the Västerås Aviation Museum in Västerås, Sweden. • An AJS 37 Viggen is on display at the Swedish Airforce Museum in Linköping, Sweden. • An AJSH 37 Viggen (s/n 373918) is on display at Newark Air Museum, Newark, Nottinghamshire, UK. • The front section of an SF 37 Viggen is on display at the Swedish Aerial Reconnaissance Museum located at the old F 11 wing in Nyköping, Sweden. • An AJSF 37 Viggen is on display at Prague Aviation Museum, Kbely, Czech Republic. s/n 37957 c/n 56–21. • An AJSH 37 Viggen (s/n 37901) is on display at the Aviodrome museum at Lelystad Airport in the Netherlands. • An AJSF 37 Viggen (s/n 374974) is on display at the Flugausstellung Hermeskeil museum in Hermeskeil, Germany. • Five Ja 37 Viggens, of which one is JA37Di standard preserved at Jämtlands Flyg och Lottamuseum, Jämtland, Sweden. • One SK 37 Viggen preserved at Jämtlands Flyg och Lottamuseum, Jämtland, Sweden. • One AJS 37 Viggen (s/n 37074) is on display at the Museum of Aeronautics and Astronautics (Madrid) museum in Madrid, Cuatro Vientos, Spain. == Specifications (JA 37 Viggen) ==