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Saab 37 Viggen

From Alfawiki
Saab AB
IndustryAerospace and defense
FoundedJune 2, 1937; 89 years ago (1937-06-02) in Sweden
FounderSven Wingquist, Anders Johan Andersson, Lars Magnus Ericsson, Harald S. Persson
Headquarters
Linköping
,
Sweden
ProductsAircraft, including Saab 37 Viggen
Websitewww.saab.com

Saab 37 Viggen Overview

The Saab 37 Viggen (translated as The Tufted Duck, also ambiguously referred to as The Thunderbolt) is a single-seat, single-engine multirole combat aircraft developed and manufactured by the Swedish company Saab. It holds the distinction of being the first mass-produced aircraft featuring a canard design. Additionally, it was pioneering in incorporating an airborne digital central computer based on integrated circuit technology for its avionics systems. This innovation arguably positioned it as one of Europe's most advanced combat aircraft at the time it was introduced. The digital central computer was groundbreaking worldwide, automating functions that previously required a navigator or copilot. This capability enhanced operational effectiveness in tactical scenarios demanding rapid decisions and high-speed maneuvers, a technological edge maintained until the Panavia Tornado entered service in 1981.

Development of the Viggen commenced in the early 1950s with the goal of replacing both the Saab 32 Lansen in the attack role and the Saab 35 Draken as a fighter. Saab's engineering team selected a relatively unconventional delta wing layout and designed the aircraft to function as an integrated weapons system connected to Sweden’s national electronic air defense network, STRIL-60. The Viggen was also engineered for operation from short runways, requiring only about 500 meters for takeoff and landing. Progress was supported by the so-called "37-annex," an agreement allowing Sweden access to advanced aeronautical technologies from the United States, accelerating both design and production phases. The final aerodynamic configuration was completed in 1963, with the prototype’s maiden flight occurring on 8 February 1967. The Swedish government subsequently placed an initial order for 175 units in 1968, with the first entering active service on 21 June 1971.

While the AJ 37 fighter-bomber variant was entering service, Saab simultaneously developed additional versions of the Viggen tailored to various roles. These included the SF 37 for aerial reconnaissance, SH 37 designed for maritime patrol and anti-surface warfare, and SK 37 configured as a two-seat trainer. In the late 1970s, Saab introduced the JA 37 model, an all-weather interceptor and strike fighter variant. Although there were efforts to market the Viggen internationally, these attempts did not result in export sales. The Swedish Air Force remained its sole operator until November 2005 when the last Viggens were retired, having been succeeded by the more modern Saab JAS 39 Gripen.

Name

Viggen represents the definite form of the Swedish term vigg, which carries dual meanings. Saab has indicated that the aircraft's designation references both interpretations.

The first interpretation is the Swedish name for the tufted duck, a small diving duck species commonly found in Sweden. This meaning relates to the aircraft's canard layout, as "canard" translates to "duck" in French.

Additionally, vigg is connected to åskvigg, meaning "thunderbolt" or "thunder wedge," derived from the thunderstones in Nordic mythology called "åskviggar". These are believed to originate from lightning bolts wielded by the Norse god Thor during his battles against giants using his war hammer, Mjölnir.

Origins

The Viggen was initially conceived to succeed the Saab 32 Lansen in its attack capacity and subsequently replace the Saab 35 Draken as a fighter aircraft. In 1955, as Saab's prototype Draken—then considered one of the most aerodynamically advanced fighters globally—completed its maiden flight, the Swedish Air Force was already outlining specifications for a new generation of combat aircraft. Given the complexity of these requirements, an extended development period was expected, with first flight projections set no earlier than the mid-1960s. Between 1952 and 1957, preliminary studies towards what would evolve into the Viggen were undertaken, involving Finnish aircraft designer Aarne Lakomaa. Over a hundred distinct concepts were evaluated during this phase, encompassing both single- and twin-engine designs, traditional and double delta wing configurations, as well as canard wings. Even vertical takeoff and landing (VTOL) concepts with dedicated lift engines were explored but quickly dismissed as impractical.

From its inception, the Viggen was intended as a comprehensive weapon platform integrated with Sweden's latest electronic air defense system, STRIL-60. It was designed to serve as a versatile national standard aircraft capable of fulfilling all tactical roles efficiently. Additional specifications included supersonic capabilities at low altitudes, Mach 2 performance at higher altitudes, and short landing distances at low angles of attack to protect makeshift runways from damage. The design also prioritized ease of maintenance and repair by personnel with limited technical training.

A particularly ambitious requirement was for the aircraft to operate from short runways measuring approximately 500 meters. This aligned with the Swedish Air Force's late-1950s Bas 60 air base strategy, which emphasized dispersing aircraft across numerous wartime bases, including utilizing roadways as auxiliary runways. The need to operate from partially damaged runways further underscored the necessity for short takeoff and landing (STOL) capabilities. The Bas 60 system later evolved into Bas 90 during the 1970s and 1980s, featuring even shorter runways of around 800 meters. Meeting these operational demands required several critical design features: low landing speeds without flaring during touchdown, strong braking after landing, precise ground handling in crosswind conditions on icy surfaces, and rapid acceleration during takeoff.

In 1960, under President Dwight D. Eisenhower’s leadership, the U.S. National Security Council extended a security assurance to Sweden promising military assistance if Sweden faced a Soviet attack. This agreement included a military-technology exchange known as the "37-annex," granting Sweden access to advanced American aeronautical technologies that significantly accelerated and reduced costs in developing the Viggen. Research by Nils Bruzelius at the Swedish National Defence College posits that this U.S. support aimed to safeguard Polaris submarines stationed near Sweden’s east coast against Soviet anti-submarine threats. However, this hypothesis has been challenged by Simon Moores and Jerker Widén and appears questionable given that the Viggen’s strike version became operational only in 1971 and its fighter variant in 1978—by which time Polaris submarines had been decommissioned.

Project initiation

In December 1961, the Swedish authorities granted approval for the creation of Aircraft System 37, which would later be known as the Viggen. By 1962, nearly all components required for the program were either completed or nearing completion; these encompassed the aircraft itself, its engine, ejection seat, weaponry, reconnaissance equipment, ground support tools, and training devices such as simulators. In February 1962, the overall design configuration received formal approval, followed by a development contract issued in October of the same year. Aviation experts Bill Gunston and Peter Gilchrist described the initiative as "by far the largest industrial development task ever attempted in Sweden." Throughout the 1960s, the Viggen project represented approximately 10 percent of Sweden's total research and development expenditure.

By 1963, Saab had finalized the aircraft's aerodynamic layout, which was considered highly innovative. The design integrated a rear-positioned double delta wing with a small, elevated canard foreplane fitted with powered trailing flaps located ahead of and slightly above the main wing. This configuration was deemed optimal for balancing conflicting requirements such as short takeoff and landing (STOL) capability, supersonic speed, low sensitivity to turbulence at low altitudes, and efficient lift during subsonic flight. Although canard configurations have since become widespread among fighter jets—seen in aircraft like the Eurofighter Typhoon, Dassault Rafale, Saab JAS 39 Gripen, and IAI Kfir—the primary motivation in those cases has been enhanced maneuverability rather than STOL performance. Later aerodynamic improvements included adding dog-tooth extensions on the main wing to generate vortices, which allowed removal of blown flaps from the canard. Additionally, a thrust reverser was incorporated to achieve the desired short landing distances.

File:AJ37 Viggen Aircraft.jpg
AJS 37 Viggen exhibited at the Swedish Air Force Museum, Linköping

For propulsion, Saab opted to equip the aircraft with a single large turbofan engine. Initially, the British Rolls-Royce Medway engine was chosen as it was considered a suitable foundation for a supersonic powerplant with a fully variable afterburner. However, development of the Medway ceased after its intended application—the de Havilland Trident airliner—was scaled down during its design phase. Consequently, Saab selected a licensed-produced version of the American Pratt & Whitney JT8D engine, designated Volvo RM8. This engine underwent significant redesigns including new materials capable of withstanding Mach-2 flight conditions, incorporation of a domestically produced afterburner, and installation of a fully variable exhaust nozzle.

Construction of the first prototype began in 1964; on 8 February 1967, the initial prototype among seven completed its maiden flight as scheduled. The test pilot Erik Dahlström reported that handling characteristics were straightforward throughout the 43-minute flight. Contemporary aerospace publication Flight International praised this event as marking "Sweden's astonishing unilateral stand in the front rank of advanced aircraft-building nations."

Each prototype was assigned distinct developmental roles; however, early models primarily supported progress toward producing the AJ37 variant. In 1967, Swedish officials determined that the AJ37 would be more cost-effective and superior in performance compared to the McDonnell Douglas F-4 Phantom II. The following year, official authorization was granted for production to commence with an initial order for 175 units. Concurrently in 1968, Saab initiated development on maritime reconnaissance and photo reconnaissance versions of the Viggen. The aircraft made its international debut at the Paris Air Show in May 1969. The first production AJ37 flew on 23 February 1971 and was delivered to the Swedish Air Force by July of that year.

Further development

File:Saab SF 37 Viggen 37951 F 13 Bråvalla 001.jpg
An SF 37 Viggen in flight, 1977

While the AJ 37 Viggen was being introduced into operational service, additional variants of the Viggen were finalized and began production.[1] The first SK 37, a trainer model featuring a staggered rear cockpit canopy to accommodate an instructor, was delivered to the Swedish Air Force in 1972.[2][3] On 21 May 1973, the prototype SF 37 Viggen, designed for tactical reconnaissance with a redesigned nose housing seven sensors, completed its inaugural flight.[4]

Although other versions entered production during the late 1960s, Saab continued refining the JA 37, an all-weather interceptor variant with enhanced capabilities. A thorough review of Sweden’s air defense in 1970 concluded that the upcoming JA 37 was particularly well-suited for this role.[5] The Swedish government approved further development of this fighter-interceptor variant in 1972, followed by several significant contracts to advance its design.[6] Five prototypes were built in total—four adapted from AJ 37 airframes and one pre-production JA 37—to evaluate control systems, engine performance, avionics, and weapons integration.[5] The first prototype took flight in June 1974, with an initial order for 30 JA 37 units placed later that year.[5]

The JA 37 Viggen incorporated multiple upgrades over earlier models, including structural modifications to the airframe, installation of the more powerful RM8B engine, adoption of advanced electronics, and a revised weapons layout. Externally, it was distinguished by a taller vertical stabilizer and a gunpack mounted beneath the fuselage.[2][7][8] Besides its primary role as an air superiority fighter, the JA 37 retained secondary ground-attack capabilities and was optimized for low-altitude missions.[5][9] The first production JA 37 flew in November 1977.[10] Operational testing occurred from January through December of 1979, culminating in its entry into active service that same year.[10][11] At the time of its deployment, Flight International recognized the JA 37 as Europe’s most advanced fighter aircraft.[7]

File:Saab JA37C Viggen, Sweden - Air Force AN1117367.jpg
JA 37 Viggen at the Royal International Air Tattoo 1993

In April 1964, Sweden’s government unveiled a budget plan for the Air Force envisioning production exceeding 800 Viggens. This ambitious target aimed to replace all existing combat aircraft with this single platform.[12] Nevertheless, factors such as inflation led to a reduction in total production numbers to just under 330 units.[13] By the year 1980, projections estimated up to149 JA37s would be manufactured before production ceased within that decade as focus shifted toward developing the Saab JAS39 Gripen—the Viggen’s successor.[7] Technological advancements like the microprocessor allowed greater system flexibility beyond what physical modifications to the Viggen could provide; consequently, further upgrades were deemed economically unjustifiable.[14] Production ended in1990 with delivery of the final aircraft.[15][16]

In May1991,a SEK300-million program was launched to upgrade eleven AJ37,SF37,and SH37 Viggens into a unified multirole version designated AJS37. This modernization included interchangeable armament and sensor configurations along with new mission planning and threat analysis computers. Electronic countermeasure systems were also enhanced.[17] Notably,the integration of a new stores management system and a MIL-STD-1553 serial data bus—similar to that employed on the JAS39 Gripen—enabled compatibility with AIM-120 AMRAAM missiles; additionally,the radar was upgraded to an Ericsson PS-46A model,and a new tactical radio was installed. The first upgraded JA37 prototype flew on4 June1996.[18]

According to General Steffan Nasstrom,the Swedish Air Force’s chief of material in1996,the cumulative upgrades since introduction had effectively doubled the overall combat effectiveness of the Viggen fleet.[18]

Propulsion

File:Viggen cockpit.jpg
Detailed view of the JA 37 Viggen's cockpit and air intake

The Viggen was equipped with a single Volvo RM8 turbofan engine, which was essentially a significantly modified licence-built version of the Pratt & Whitney JT8D engine that powered 1960s commercial airliners, enhanced with an afterburner specifically for the Viggen. The aircraft's structure included a thrust reverser utilized during landing and ground operations. This feature, combined with flight capabilities nearing limited STOL performance, allowed the Viggen to operate from airstrips as short as 500 m with minimal infrastructure.[19] The thrust reverser could be armed while airborne and activated upon compression of the nose-wheel strut after touchdown via a pneumatic mechanism.[5][20]

The Swedish Air Force specified requirements for the Viggen to achieve Mach 2 speeds at high altitude and Mach 1 at low altitude, alongside short take-off and landing capabilities. Since the Viggen was initially conceived as an attack aircraft rather than an interceptor (a role filled by the Saab 35 Draken), priority was placed on efficient fuel consumption during high subsonic low-level cruise for extended range. With turbofan engines emerging as more fuel-efficient than turbojet engines at cruise speeds — the latter limited by metallurgical constraints affecting turbine temperature — turbofans were preferred.Template:Fix/category[citation needed] Simplicity in design was also important; thus, the air intakes were straightforward D-section types with boundary layer splitter plates, featuring fixed geometry without adjustable components to optimize pressure recovery. This choice resulted in a notably large engine.[19] Upon its introduction, it ranked as the second-largest fighter engine globally, measuring 6.1 m in length and 1.35 m in diameter; only the Tumansky R-15 surpassed it in size.Template:Fix/category[citation needed]

File:Goteborg Volvo Museum 09 RM8.jpg
Volvo RM8 engine exhibited in 2014

Initially, Saab intended to use the Rolls-Royce Medway engine for the Viggen.[19] However, following the Medway's cancellation, they adapted the JT8D as their base for modification. The RM8 became the world’s second operational afterburning turbofan and was pioneering as the first to incorporate a thrust reverser. Aviation expert Christopher Chant notes that the RM8 was unique for being the first engine fitted with both an afterburner and a thrust reverser.[9] The RM8A variant had a bypass ratio near 1.07:1, which decreased to approximately 0.97:1 in the RM8B model.[21]Template:Page needed During the late 1960s, the RM8A stood out as the most powerful fighter engine available.[7]

The AJ, SF, SH, and SK versions of the Viggen were powered by the initial RM8A engine variant featuring upgraded internal components derived from the JT8D. This configuration delivered thrust of 65.6 kN without afterburner and up to 115.6 kN with afterburner engaged.[22] For the JA 37 model, development led to the RM8B variant by adding a third low-pressure compressor stage compared to its predecessor, raising turbine inlet temperatures and improving fuel diffusion within the combustion chamber.[23] This version produced thrust levels of 72.1 kN dry and reached 125.0 kN when using afterburner.[22] Due to increased dimensions and weight of the RM8B compared to earlier models, the JA 37’s airframe was extended to accommodate it.[23] Electrical power onboard was supplied by a generator rated at 60 kVA. In case of an engine failure during flight, emergency power could be maintained via an automatically deployed ram air turbine (RAT) capable of producing up to 6 kVA.[24]

Avionics

File:LA2-Datasaab-CK37-full.jpg
The CK 37 computer

During the early 1960s, Saab concluded that the Viggen would be designed as a single-seat fighter, recognizing that cutting-edge avionics such as a digital central computer combined with a head-up display could handle navigation duties and eliminate the necessity for a second crew member.[19] Employing a digital computer was intended to replace or significantly reduce reliance on analogue systems, which had proven costly to maintain and modify, as evidenced by earlier aircraft like the Draken, while also addressing accuracy shortcomings.[25] This central processing unit, known as the CK 37 [sv] (meaning "central calculator 37"), was the first airborne computer globally to utilize integrated circuit technology. Developed by Datasaab, the CK 37 served as the core integration hub for all electronic systems supporting the pilot, managing tasks such as navigation, flight control, and weapons targeting computations.[24][25][26] In operational use, the CK 37 demonstrated greater reliability than initially anticipated.[25]

From the JA37 variant onward, a newer and more robust digital central processor, the Singer-Kearfott SKC-2037, was selected and produced under license by Saab as the CD 107.[25][27][28] The computing concepts implemented—including distributed computing—extended beyond the Viggen platform, influencing civil adaptations and directly impacting the onboard computers of its successor, the Saab JAS 39 Gripen.[25][29] The Viggen was equipped with several electronic countermeasure (ECM) systems typically supplied by Satt Elektronik.[24] These ECM components included radar warning receivers developed by Satt Elektronik installed in both wings and tail,[30] an optional Ericsson Erijammer jamming pod, and a BOZ-100 pod for deploying chaff and flares. Later additions included infrared warning sensors. Collectively, these electronic systems added approximately 600 kg to the airframe—a significant weight for a single-engine fighter of that period.[24]

The primary sensor aboard was an Ericsson PS 37 X-band monopulse radar, featuring a mechanically steered parabolic reflector enclosed within a radome.[24] This radar fulfilled multiple roles such as air-to-ground and air-to-air telemetry, target searching and tracking, terrain avoidance via terrain-following radar capability, and cartographic functions.[6] On the JA 37 interceptor variant, this radar was superseded by the Ericsson PS 46 X-band pulse-doppler radar, which enabled all-weather look-down/shoot-down operations reportedly exceeding a range of fifty kilometers. It also provided continuous-wave illumination for guiding Skyflash missiles and could simultaneously track two targets while scanning.[5] Ericsson claimed this radar had a fifty percent probability of detecting low-flying McDonnell Douglas F-4 Phantom II aircraft within one scan and exhibited strong resistance to ECM interference.[5]

Saab collaborated with Honeywell to develop an automatic digital flight control system for the JA 37 Viggen—purportedly among the first of its kind implemented in production aircraft.[5] For enhanced low-level flight capabilities, a Honeywell radar altimeter with transmitters and receivers integrated into the canard wings was utilized.[24] The aircraft also incorporated a Decca Type 72 Doppler navigation radar. Additionally, TILS (Tactical Instrument Landing System), manufactured by Cutler-Hammer AIL, improved landing precision to within thirty meters on short highway airstrips.[31] To enforce Swedish airspace effectively, integration with the national defence network STRIL (STRIL 60) was established.[32] The JA 37 variant also featured a digital Central Air Data Computer from Garrett AiResearch, adapted from technology used in the Grumman F-14 Tomcat.[5]

Initially planned as solely a reconnaissance (S) model, attempts to equip cameras alongside radar proved unfeasible. The SH 37 maritime strike/reconnaissance version closely resembled the AJ 37 but incorporated a maritime-optimized PS 371/A radar with extended range capabilities, an air-data camera in the cockpit, and tape recorders for mission data analysis. Typically mounted on fuselage pylons were “Red Baron” pods and SKa 24D long-range optical (LOROP) cameras measuring six hundred millimeters in focal length.[9] For a brief interval, the centerline fuel tank was converted into a camera pod housing two Recon/Optical CA-200 cameras with focal lengths of sixteen hundred seventy-six millimeters each. Besides reconnaissance gear, this variant retained full compatibility with AJ 37 weaponry.Template:Fix/category[citation needed] The photographic SF version omitted nose radar in favor of four SKa 24C cameras (120 mm), two SKa31 cameras (570 mm), one VKa702 infrared linescan camera (57 mm), plus an air-data camera—all integrated with and controlled by the central computer.[9] Additional equipment options such as extra camera pods, auxiliary fuel tanks, ECM pods, and self-defense air-to-air missiles could also be mounted on fuselage pylons.[9]

The JA 37 fighter-interceptor featured numerous avionics enhancements that combined extensive digital electronics with traditional mechanical systems.[33] Introduced in service in 1985 was the “fighter link,” an encrypted data communication system linking up to four fighters simultaneously; this allowed one aircraft to designate an airborne target using its guidance radar while three others engaged their Skyflash missiles with their search radars turned off. This capability became operational roughly ten years ahead of similar systems elsewhere.[34] The autopilot system was integrated with radar controls to enhance cannon firing precision.[35] Throughout its operational life, software updates for the Viggen were routinely applied approximately every eighteen months.[36] By1983,the reported mean time between failures (MTBF) reached one hundred hours—an exceptional reliability figure for avionics technology of that generation.[37]

Cockpit

File:Viggen 2008-03-01-35.jpg
Cockpit of an AJSF 37 Viggen

The original cockpit featured predominantly analogue and mechanical instruments, with the notable exception of an electronic head-up display (HUD). Saab has stated that this HUD enhances the aircraft's handling, particularly during low-level air-to-ground attack operations.[38] In a distinctive feature for a fighter from the 1970s, the JA 37 version of the Viggen incorporated three multifunctional cathode-ray tube (CRT) screens within the cockpit, part of the AP-12 system developed jointly by Saab and Ericsson.[21] These displays provided processed radar imagery, computer-generated maps, flight and weapons information, as well as guidance cues for precise landings.[11]

File:Viggen skolversion.jpg
A two-seat SK 37 Viggen on display

From 1989 to 1992, the AP-12 system underwent a major modernization. By 1999, the CRT-based AP-12 was superseded by a new tactical liquid-crystal display (LCD) system derived from the Saab JAS 39 Gripen, which entered flight testing with the Swedish Air Force.[39] The rear cockpit of the twin-seat SK 37 trainer, intended for instructors, retained traditional instruments and did not include a HUD, computer interface, or other advanced features.[40]

The ejection seat installed was known as the Raketstol 37 (meaning Rocket chair 37), representing Saab's final in-house seat design. Derived from the Saab 105 trainer’s ejection seat, it was specifically engineered for high-speed ejections at low altitudes.[24] Activation occurred via triggers embedded in the armrests; in dual-seat configurations, the pilot in front could initiate ejection for both seats simultaneously. The ejection process was fully automated including canopy jettisoning, with a backup trigger available in case of failure.[41] The seat incorporated an integrated parachute and harness system featuring a barometric interlock to ensure proper release timing during ejection; a manual release handle was also provided.[41]

Warning caption panels were positioned on each side of the pilot’s legs. The right console housed numerous dedicated controls and indicators such as those for weapons and missile systems, navigation panel, oxygen supply toggle, windshield defogger, IFF controls, and lighting switches. On the left console were radar controls, canopy release handle, landing gear lever, radio systems controls, and cabin pressure gauge.[42][43] Consistent with Swedish Air Force standards at that time, all cockpit instrumentation and markings were presented in Swedish.[41][44][45]

Wings and airframe

The engine selection, largely driven by performance demands, resulted in an airframe that was notably bulkier than the sleeker turbojet-powered aircraft of the same era. Early prototypes featured a straight mid-fuselage section, which was subsequently refined by adding a dorsal "hump" to minimize drag in accordance with the area rule. The wing design adopted a double delta configuration, enhanced with a dogtooth leading edge to boost longitudinal stability at high angles of attack.

File:JA 37D tail.jpg
Vertical stabilizer

Due to the tailless delta planform characteristic of the Viggen, elevons replaced traditional control surfaces but operated with a relatively short moment arm, contributing significantly to the aircraft’s weight during takeoff and landing phases. While leading-edge slats offered some compensation, the incorporation of canard surfaces proved even more effective. Positioned just aft of the air intakes and slightly above the main wing, these canards featured a higher stall angle and were equipped with flaps. Serving as vortex generators, they enhanced lift on the main wing and also improved roll stability in transonic flight regimes. The canard flaps were synchronized with landing gear deployment to further augment lift during takeoff and landing.

To endure the rigors of no-flare landings, Saab extensively utilized aluminium within the Viggen’s airframe, which was built using bonded metal honeycomb construction. The rear fuselage section behind the engine nozzle consisted of a heat-resistant titanium ring. The main landing gear, produced by Motala Verkstad, was heavily reinforced; each gear leg incorporated two small wheels arranged in tandem and fitted with anti-skid braking systems. The substantial size of the anti-ship missiles carried by the Viggen dictated that both the undercarriage and vertical stabilizer be relatively tall. To accommodate this, the landing gear legs shortened during retraction, allowing them to be housed outside the wing root area. Additionally, the vertical stabilizer could be folded via an actuator mechanism to enable storage within compact hangars, hardened shelters, or underground facilities—measures employed by Swedish forces to mitigate damage from potential preemptive strikes.

Fuel capacity consisted of six internal tanks across the fuselage and wings holding about 5,000 litres, supplemented by an external drop tank containing 1,500 litres. The specific fuel consumption at cruising speed was approximately 0.63 (measured as 18 mg/Ns dry and 71 mg/Ns with afterburner). At full afterburner power, fuel flow reached roughly 15 kg/s. Air for the engine was supplied through two fixed-geometry inlets located beside the cockpit; these were larger than those on the Draken and stood clear of the fuselage contours.

Armament

File:Saab viggen underside.jpg
View of a Viggen's underside, 1985, showing empty weapon pylons.

The Viggen could carry a maximum ordnance weight of 7,000 kg distributed across nine hardpoints. These included a single centreline pylon, two pylons on the fuselage, two inner wing pylons, two outer wing pylons, and two additional pylons located behind the wing landing gear. Typically, the centreline pylon was dedicated to an external fuel tank, as it was the only pylon equipped for this purpose. The outboard wing pylons, being lighter in construction, were primarily intended for mounting a pair of air-to-air missiles. The pylons situated behind the landing gear were initially unused until the JA 37D upgrade introduced BOL countermeasure dispensers on them. Ground personnel would input the installed munitions into the aircraft’s central computer through a load-selector panel, which then automatically adjusted parameters for fire control, fuel usage, and other operational computations.

AJ 37

The AJ 37 generally featured seven hardpoints: three beneath the fuselage and two under each wing. While an option existed to add two more wing-mounted hardpoints, this was infrequently utilized. The aircraft was capable of carrying various rocket types, including the 135 mm M56GP armour-piercing rocket weighing 4 kg, the M56B equipped with 6.9 kg of high explosives, and the M70 armed with a 4.7 kg HEAT warhead.

For anti-ship missions, the AJ 37 was designed to carry two RB 04E missiles on the inboard wing pylons with an optional third missile mounted on the centreline pylon. The RB 04 was a relatively basic cruise missile that later evolved into the more advanced RBS-15 system, also compatible with the Viggen platform. Additionally, two RB 05 air-to-surface missiles could be carried on the fuselage pylons as an optional loadout; these were eventually superseded by television-guided AGM-65 Maverick missiles (designated RB 75 in Swedish service). In ground-attack roles, combinations of unguided 135 mm rockets housed in six-round pods and 120 kg fragmentation bombs mounted on quadruple racks were employed. Other armament options included explosive mines and 30 mm ADEN cannon pods loaded with 150 rounds each on the inboard wing pylons.

Defensive systems encompassed various electronic countermeasures alongside air-to-air missiles such as the AIM-4 Falcon (designated RB 28) or AIM-9 Sidewinder (designated RB 24). At one stage, there was consideration for equipping the AJ 37 Viggen with Swedish nuclear or chemical weapons; however, Sweden ultimately did not adopt either nuclear or chemical armaments for this aircraft.

JA 37

The JA 37 interceptor, which entered service in 1979, was equipped with the Ericsson PS 46/A radar system capable of directing the medium-range semi-active radar homing RB 71 Skyflash air-to-air missiles. Both the RB 71 missile and the PS 46/A radar were engineered to grant the Viggen look-down/shoot-down functionality and to engage adversaries at beyond visual range distances. Typically, the JA 37 could carry a maximum of two RB 71 missiles mounted on the inner wing pylons; these were usually paired with four RB 24J air-to-air missiles—a more advanced and modern iteration of the Sidewinder missile compared to those used on earlier Viggen models.

After assessing various cannon options including the British ADEN cannon, American M61 Vulcan, and French DEFA cannon, the choice fell on the Oerlikon KCA 30mm cannon for the JA 37. This weapon was housed in a conformal pod beneath the fuselage, carrying 126 rounds of ammunition. The cannon’s firing rate could be selected between 22 and 11 rounds per second. It utilized the same cartridge as the GAU-8, reportedly firing shells that were approximately 50% heavier and at a higher velocity than those of the ADEN cannon, delivering roughly six and a half times more kinetic energy upon impact. Its effective range extended up to 2,000 meters. Coupled with the aircraft’s fire control system, this enabled air-to-air combat engagements at distances greater than those achievable by many contemporary fighters.

Arguably, the most significant advancement was the enhanced STRIL datalink introduced between 1982 and 1985. This system facilitated communication not only between ground control and aircraft but also allowed simultaneous data exchange among up to four aircraft, whether airborne or on the ground. Information transmitted via this datalink was presented on both the Horizontal Situation Display and a tactical display; the latter featured link symbology that could be superimposed on an electronic map displayed on a multifunction screen.

Operational history

File:Saab 37 Viggen flygvapenmusèum.JPG
The initial production JA 37 Viggen displayed at the Swedish Air Force Museum
File:SAAB J-37 Viggen special red version.jpg
In 1999, this AJS 37 was painted red during the final operational years of Viggen flights at F 10 Ängelholm.

The Swedish Air Force received its first production AJ 37 Viggen in July 1971.[46] The Skaraborg Wing (F 7) was the pioneer wing to be equipped with both the single-seat AJ 37 attack variant and the twin-seat SK 37 trainer version of the Viggen, initiating the phase-out of their older Lansen aircraft.[47] Pilot conversion training for the Viggen required a minimum of 450 flight hours, starting with the Saab 105, then progressing to the Lansen, and finally transitioning to the Viggen itself; specialized Viggen simulators played a crucial role in facilitating this transition.[48][49]

By October 1973, Skaraborg Wing was reportedly nearing full operational capability;[3] and by May 1974, two squadrons were actively operating the Viggen, with a third squadron close to achieving full readiness.[48] Despite the aircraft's complexity and relative novelty, by 1974, its safety and reliability had surpassed initial expectations.[50] One notable challenge during low-altitude flight—common in attack missions—was bird strikes; consequently, the Swedish Air Force closely monitored migratory bird routes.[51]

Throughout the late 1970s and into the 1980s, several Viggen variants were introduced: the SK 37 two-seat operational-conversion trainer in 1972, the SF 37 overland reconnaissance variant in 1977, and the SH 37 maritime reconnaissance model in 1975.[2][9] The JA 37 fighter-interceptor version was brought into service by September 1980, with Bråvalla Wing (F 13) being the first to transition to this model.[7] The Viggen subsequently became Sweden’s main air defense aircraft for an extended period.[52]

Designed for straightforward maintenance, even conscripted ground crew with limited technical expertise could service the Viggen.[53] Typically, a single five-person conscript team under one chief mechanic could maintain one aircraft.[11][54] Routine servicing—including refueling and rearming—required less than ten minutes; replacing an engine took approximately four hours. Over time, maintenance demands averaged twenty-two man-hours per flight hour at depot level and nine man-hours per flight hour at front-line units.[11]

By the mid-1980s, Swedish pilots flying Viggens had successfully locked their radar onto Lockheed SR-71 Blackbird reconnaissance flights over the Baltic Sea on multiple occasions. Despite intense electronic jamming from the SR-71, target tracking was maintained by integrating ground radar data into the Viggen’s fire-control system. This radar lock-on most frequently occurred within a narrow corridor of international airspace between Öland and Gotland used by SR-71 return flights.[55][56][57] Notably, the Viggen remains the only known aircraft to have achieved an officially recognized radar lock on the SR-71.[58]

Retirement

By the year 1994, the transition from the Viggen to the more modern Saab JAS 39 Gripen was underway, with the Viggen gradually withdrawn as increasing numbers of Gripen jets were introduced. On 25 November 2005, the Swedish Air Force officially retired the last operational frontline Viggen. A limited number of these aircraft were retained in flying condition to support electronic warfare training exercises against the Gripen at F 17M in Linköping; these final Viggen sorties occurred in June 2007.

Overseas sales efforts

Despite Saab's global marketing initiatives during the 1970s aimed at promoting the Viggen across Europe and developing nations, no export contracts were secured.

In the same decade, Saab developed a new version of the Viggen called the Saab 37E Eurofighter (distinct from the later Eurofighter Typhoon) to compete in the United States Air Force's Air Combat Fighter competition, which sought a successor to the Lockheed F-104 Starfighter. The 37E Eurofighter contended with several competitors including Dassault-Breguet's Mirage F1M-53, the SEPECAT Jaguar, Northrop’s P-530 Cobra (the foundation for the YF-17), and General Dynamics’ YF-16. On 13 January 1975, United States Secretary of the Air Force John L. McLucas declared the YF-16 as the winner of this contest.

In 1978, a significant potential sale to India was thwarted by U.S. authorities who withheld export licenses for the RM8/JT8D engines and other American components integral to the Viggen’s systems, effectively blocking both direct sales and a licensed production agreement for manufacturing Viggens in India. Subsequently, India chose to acquire the SEPECAT Jaguar instead. According to leaked U.S. diplomatic cables, India's interest in acquiring the Viggen was largely driven by then-Prime Minister Rajiv Gandhi, reportedly without consultation from Indian Air Force officials. Author Chris Smith notes that prior to U.S. intervention, the Viggen was considered India’s preferred option for their air force requirements.

Variants

AJ 37
Designed mainly as a single-seat ground-attack fighter (AJ stands for Attack-Jakt), with a secondary capability as a fighter.[59] Powered by the RM8A engine and equipped with the PS 37A radar system.[60] Initial deliveries began in mid-1971,[61] totaling 108 units produced, identified by serial numbers 37001 through 37108.[62] Forty-eight airframes were later upgraded to the AJS 37 standard.[63] Partial retirement occurred in 1998.
SK 37
A two-seat trainer variant (Sk meaning Skol), which lacked radar and carried less fuel.[64] Its maiden flight took place on 2 July 1970.[65] Seventeen units were constructed, delivered starting in June 1972, with serial numbers ranging from 37801 to 37817.[62] The type was retired in 2003, with ten airframes converted into SK 37E models.
SF 37
A single-seat photographic reconnaissance aircraft (SF stands for Spaning Foto), featuring a camera suite in place of radar at the nose and provisions for additional reconnaissance pods.[66] Its first flight occurred on 21 May 1973.[67] Twenty-eight units were built and delivered from April 1977, bearing serial numbers between 37950 and 37977.[62] Twenty-five airframes were upgraded to the AJSF 37 standard.[63] Partial decommissioning took place in 1998.
SH 37
Known as SH (Spaning Hav) for maritime reconnaissance and strike missions, this single-seat variant was equipped with the PS-371A radar.[67] Twenty-seven examples were produced and delivered beginning June 1975, with serial numbers from 37901 to 37927.[62] Twenty-five airframes received upgrades to AJSH 37 configuration.[63] Partial retirement occurred in 1998.
Saab 37E Eurofighter
Proposed in 1975 as a NATO replacement for the F-104 Starfighter; no units were manufactured.[68]
Saab 37X
An export model offered to Norway during the years 1967–68; no production ensued.[69]
JA 37
Primarily designed as a single-seat all-weather interceptor with a secondary attack function. Its inaugural flight was on September 27, 1974,[70] with deliveries commencing in 1979,[70] assigned serial numbers from 37301 to 37449. The fuselage featured an approximately 10 cm (4 in) wedge-shaped extension between the canard and main wing that was broader at the bottom than at the top compared to the AJ 37. It incorporated the PS-46A LD/SD radar system. Partial retirement began in 1998; some units were upgraded to JA 37D.
AJS/AJSF/AJSH 37
These designations refer to modernization programs conducted between 1993 and 1998 on selected AJ/SF/SH variants. Upgrades included avionics and software enhancements. Forty-eight AJ airframes were modified alongside twenty-five SH and twenty-five SF airframes each. The fleet was retired by 2005.
JA 37C
This upgrade of earlier JA models encompassed avionics improvements and software updates along with countermeasure integration.
JA 37D
Between 1993 and 1998, older JA aircraft received avionics and software enhancements along with integration of the Rb99 air-to-air missile (the Swedish equivalent of the AIM-120). Thirty-five airframes underwent this modification.
JA 37DI
A version of the JA 37D adapted for international operations featuring avionics and software modifications. Instruments were labeled in English using feet and knots rather than meters and kilometers per hour. Twenty units were converted.
SK 37E
An electronic warfare trainer developed through conversion of ten outdated SK trainers from the years between 1998 and 2000, identified by serial numbers ranging from 37807 to37811 and from37813 to37817. These were retired in2007.
37AU
A proposed export variant intended for Australia that would have been equipped with AIM-54 Phoenix missiles.[71][72][73][74] The project was ultimately cancelled in favor of procuring the F/A-18 Hornet.[75]

Operators

File:Saab 37 Viggen klargöring 1982 001.jpg
Saab 37 Viggen undergoing ground maintenance, April 1982
File:SE-DXN SAAB Viggen "Gustav 52" (21366952562).jpg
Viggen touching down at Prestwick, Scotland, 2015

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Units in service

  • F 4 Frösön
    • Two JA 37 squadrons from 1983 to 2003
    • One SK 37 squadron between 1999 and 2003
    • One SK 37E squadron from 1999 to 2003
  • F 6 Karlsborg
    • Two AJ 37 squadrons active from 1978 until 1993
  • F 7 Såtenäs
    • Three AJ 37 squadrons operational between 1972 and 1998
    • One SK 37 squadron from 1972 to 1974
  • F 10 Ängelholm
    • One combined AJ/SF/SH 37 squadron from 1993 to 2001
  • F 13 Norrköping
    • One combined SF/SH 37 squadron between 1977 and 1993
    • One JA 37 squadron active from 1980 to 1993
  • F 15 Söderhamn
    • Two AJ 37 squadrons from 1974 through to 1998
    • One SK 37 squadron during the same period, 1974–1998
  • F 16 Uppsala
    • Two JA 37 squadrons between the years of 1986 and 2003
  • F 17 Kallinge
    • One JA 37 squadron active from 1981 to 2002
    • One combined SF/SH 37 squadron from 1979 until 1993
    • Another JA 37 squadron serving between 1993 and 2002
  • F 21 Luleå
    • Two JA 37 squadrons operational from 1983 to 2004
    • One SF/SH 37 squadron active between 1979 and 2002
    • One combined SK 37E squadron flying from 2003 to 2007

Accidents and incidents

Information regarding Sweden's military aviation accidents is scarce. Notably, on October 16, 1996, a Saab 37 pilot tragically lost his life during a reconnaissance pass near the Russian nuclear-powered battlecruiser Pyotr Velikiy. This event represents the last recorded fatality among a total of nineteen known deaths linked to over fifty Saab 37 Viggen accidents throughout its nearly four decades of service.

Preserved aircraft

File:Septemberleucharsviggen.jpg
Viggen serial number 37098 landing after a demonstration at Leuchars, in 2013
  • The AJS 37 Viggen bearing serial number 37098 and code F 7–52 has been preserved following an extensive restoration process restoring it to flight condition. Manufactured in 1977, it served exclusively with the F 15 Wing at Söderhamn before being registered for civilian use as SE-DXN. Its first post-restoration flight took place on March 27, 2012, departing from the F 7 Wing at Såtenäs. The aircraft remains unpainted, reflecting the appearance of the earliest Viggens delivered in the early seventies.
  • An SK 37 two-seat trainer with serial number 37809 and code F 15-61 underwent restoration to regain airworthiness. Built in 1973, it initially served with F 7 Wing at Såtenäs, later transferring to F 15 Wing at Söderhamn, and finally operated by FMV Prov in Linköping until retiring in 2007. Registered as SE-DXO for civilian operation, it completed its maiden flight after restoration on May 15, 2018, flying out of F 7 Wing at Såtenäs. This trainer features the distinctive four-color camouflage scheme adopted for all Viggens since the late seventies.
  • The Musée de l’air et de l’espace at the former Paris–Le Bourget Airport in France exhibits an SK 37E Viggen with serial number 37898.
  • A JA 37 Viggen (serial number: 37429) is displayed at the Estonian Aviation Museum near Tartu. This aircraft was acquired from the Swedish Air Force Museum and ferried from Sweden to Estonia in 2004.
  • The Polish Aviation Museum in Kraków houses an AJSF 37 Viggen with serial number 37954.
  • Near Gothenburg at the Aeroseum (formerly Göta Wing), two Viggens are exhibited along with nose sections of several JA-37s. These include an AJ-37 (serial number: 37094/57) and an AJSH-37 (serial number: 37911/55).
  • Söderhamn Aviation Museum, located at the former F 15 wing base, displays two Viggens: one AJS 37 and one SK 37 trainer.
  • Västerås Aviation Museum in Västerås exhibits an AJ 37 Viggen.
  • The Swedish Airforce Museum situated in Linköping features an AJS 37 Viggen on display.
  • An AJSH 37 Viggen (serial number: 373918) is part of the collection at Newark Air Museum in Nottinghamshire, UK.
  • The Swedish Aerial Reconnaissance Museum located at the former F 11 wing in Nyköping displays the forward fuselage section of an SF 37 Viggen.
  • Prague Aviation Museum Kbely in the Czech Republic exhibits an AJSF 37 Viggen (serial number: 37957, construction number: 56-21).
  • An AJSH 37 Viggen (serial number: 37901) is preserved at Aviodrome museum near Lelystad Airport in the Netherlands.
  • The Flugausstellung Hermeskeil museum in Hermeskeil, Germany showcases an AJSF 37 Viggen (serial number: 374974).
  • Jämtlands Flyg och Lottamuseum in Jämtland, Sweden holds five JA-37 Viggens—including one upgraded to JA37Di standard—one AJ-37, one front fuselage section of an AJS-37, and one SK-37 preserved within their collection.
  • In Luleå, Norrbotten, Sweden, one AJ-37 Viggen is on public display.
  • The Museum of Aeronautics and Astronautics in Madrid (Cuatro Vientos), Spain exhibits an AJS-37 Viggen with serial number 37074.

Specifications (JA 37 Viggen)

File:Saab J 37 Viggen 3-view.svg
Three-view illustration of the Saab JA 37 Viggen

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See also

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External links

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  2. ↑ 2.0 2.1 2.2 Cite error: Invalid <ref> tag; no text was provided for refs named fred 279
  3. ↑ 3.0 3.1 Ford 1973. p. 616.
  4. ↑ Wagner 2009, pp. 125–26.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 Warwick 1980, p. 1261.
  6. ↑ 6.0 6.1 Cite error: Invalid <ref> tag; no text was provided for refs named ford 617
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Warwick 1980, p. 1260.
  8. ↑ Chant 2014, pp. 458–59.
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 Chant 2014, p. 458.
  10. ↑ 10.0 10.1 Chant 2014, p. 459.
  11. ↑ 11.0 11.1 11.2 11.3 Cite error: Invalid <ref> tag; no text was provided for refs named warwick 1265
  12. ↑ "World News: Over 800 Viggens." Flight International, 23 April 1964, p. 630.
  13. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named bomber 247
  14. ↑ Eliasson 2010, pp. 87, 229.
  15. ↑ Forsberg1994, p.220.
  16. ↑ Eliasson2010,p.82.
  17. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named bomber247
  18. ↑ 18.0 18.1 Jeziorski, Andrzej. "Saab flies upgraded Viggen fighter." Flight International,19 June1996.
  19. ↑ 19.0 19.1 19.2 19.3 Cite error: Invalid <ref> tag; no text was provided for refs named bomber 244
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  22. ↑ 22.0 22.1 Taylor 1988, p. 702.
  23. ↑ 23.0 23.1 Warwick 1980, p. 1264.
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  31. ↑ Battle, EH et al. "Some Early Achievements in Landing Guidance using Mechanically Scanned Pulse-encoded Beams", IEEE Transactions on Aerospace and Electronic Systems, Vol. 25, no. 5, 1989, pp. 775–81.
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  33. ↑ Eliasson 2010, p. 115.
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  35. ↑ Forsling, G. and Järmark, B. "Optimal Fuselage Aiming." AIAA Paper 85-1961.
  36. ↑ Eliasson 2010, p.125.
  37. ↑ Gunston,Bill Modern Combat Aircraft: From Fighters to Battlefield Helicopters. Hong Kong: Hennerwood Publications,1983. ISBN 978-0-86273-074-1.
  38. ↑ "Head-Up Displays and Optical Systems." Archived 7 March 2016 at the Wayback Machine Saab, September 2014.
  39. ↑ "Sweden tests Viggen upgrade." Flight International, 24 March 1999.
  40. ↑ Field 1974, pp. 709–10.
  41. ↑ 41.0 41.1 41.2 Field 1974, p. 708.
  42. ↑ Field 1974, p. 709.
  43. ↑ Warwick 1980, pp. 1262–63.
  44. ↑ Detailed schematic diagram of the original cockpit layout in Coombs 2005.
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  48. ↑ 48.0 48.1 Cite error: Invalid <ref> tag; no text was provided for refs named field 707
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  50. ↑ Field 1974, p. 712.
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  52. ↑ Boyne 2002, p. 548.
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