Saab 37 Viggen

The Saab 37 Viggen ("Thunderbolt, ambiguous with ?"Tufted duck") is a Swedish single-seat, single-engine, short-medium range combat aircraft, manufactured between 1970 and 1990. Several distinctive variants were produced to perform the roles of strike fighter (AJ37), aerial reconnaissance (SF 37), maritime patrol aircraft (SH 37) and a two-seat trainer. In the late 1970s the all-weather fighter-interceptor aircraft JA 37 was added.


Saab 37 Viggen
Class Aircraft
Type Fighter
Manufacturer Saab Group
Production Period 1970 - 1990
Origin Sweden
Country Name Origin Year
Sweden 1967
Country Name Operational Year Retirement Year
Sweden 1971 2005 View
ManufacturerName Production From Production To Quantity
Saab Group 1970 1990 329 View

The Viggen was powered by a single Volvo RM8 turbofan. This was essentially a 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 thrust reverser could be pre-selected in the air to engage when the nose-wheel strut was compressed after touchdown. The Viggen was the first aircraft to feature both afterburners and thrust-reverser. Only the Viggen, Concorde and the Panavia Tornado featured both afterburners and thrust-reversers.

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. In fact, at the time of introduction, it was the second largest fighter engine, with a length of 6.1 m and 1.35 m diameter; only the Tumansky R-15 was bigger.

Saab had originally wanted the Pratt & Whitney TF30 as the Viggen's power-plant. Since the engine design had not been completed in 1962 when the airframe vs. engine design size needed to be frozen, the JT8D was chosen as the basis for modification instead. The RM 8 became the second operational after-burning turbofan in the world, and also the first equipped with a thrust reverser. It had a bypass ratio of around 1.07:1 in the RM 8A, which reduced to 0.97:1 in the RM 8B.

The AJ, SF, SH and SK 37 models of the Viggen had the first version of the RM 8A engine with uprated internal components from the JT8D that it was based on. Thrust was 65.6 kN dry and 115.6 kN with afterburner. For the JA 37, the RM 8A was modified to an 8B by replacing one LP compressor stage with a fan stage and improved combustor, turbine and afterburner. Thrust is 72.1 kN dry and 125.0 kN with afterburner. The engine was started via a small gas turbine, itself started by an electric motor. Standby power and cooling air for onboard avionics were supplied via an external cart. An internal battery permitted start of the starter turbine and main engine in absence of the standby power cart.

A total of 110 original, ground-attack optimized variant, AJ 37 were built, with the first operational squadron established in 1972 at F 7 Såtenäs.

A two-seat trainer was not initially planned since it was considered that new pilots could get enough experience with delta-winged aircraft on the SK 35 Draken trainer. Eventually, however, 18 SK 37 two-seat trainers were ordered and delivered in 1973. To make room for the second cockpit, one fuel tank and some avionics were removed. The radar was also omitted limiting the weapons load to gun pods and unguided rockets.

A total of 26 of the SH 37 maritime reconnaissance and strike variant were built in 1974, replacing the S 32C Lansen. Although fitted with radar and weaponry, the SH 37 Viggen could also undertake photographic missions with its single long-range camera, while external pods could carry a photographic day-set, a "Red Baron" IR set, an ELINT set, and AQ series ECM (made by SATT).

A further 26 of the SF 37 reconnaissance variant were also delivered to replace the S 35 Draken in 1975. These were recognizable by having an elongated nose, equipped with six cameras and a VKa 702 infrared linescanner for night reconnaissance. Also, the "Red Baron" pod, with three IR cameras was widely used, as well as an ELINT set.

The Viggen saw initial service in natural metal, later receiving an extremely elaborate disruptive camouflage scheme for the AJ/SF/SH/SK variants and the first 27 JA aircraft. The 28th JA was painted in a gray tone that turned out too close to white. All latter JA aircraft were painted in a darker light/dark gray, appropriate for a high altitude fighter.

The final Viggen production variant was the JA 37 interceptor entering service in 1980. The last of 149 JA 37s was delivered in 1990. Differences from the previous models included an improved and more powerful RM 8B engine, a new PS 46/A interception radar, new computers, HUD, ECM and some other subsystems.

Unusually for a 1970s fighter, three multi-purpose CRT display screens were fitted within the cockpit, in a system called AP-12, that also included a new model of HUD. The new radar was compatible with the Skyflash medium-range missiles, for the first time in a Swedish fighter. Two Skyflash missiles could be carried under the wings on hardpoints, as well as four Sidewinder J or L models. Another improvement was the addition of an Oerlikon KCA 30 mm cannon mounted internally, with 126 rounds of 360 g ammunition.

The structural strength was also improved, especially for the multi-sparred wings (initially Viggens had a high loss rate, with 21 aircraft lost in the early years). Various upgrades have been performed over the years, mainly to cockpit equipment, weapons and sensor fit. Between 1998 and 2000, 10 SK 37 trainers were converted to SK 37E electronic warfare trainers to replace the aging J 32E Lansen.

Swedish JA 37 Viggen fighter pilots, using the predictable patterns of Lockheed SR-71 Blackbird routine flights over the Baltic Sea, managed to achieve missile lock-on with radar on the SR-71 on numerous occasions. Despite heavy jamming from the SR-71, target illumination was maintained by feeding target location from ground-based radars to the fire-control computer in the Viggen. The most common site for the lock-on to occur was the thin stretch of international airspace between Öland and Gotland that the SR-71 used on the return flight. The Viggen is the only aircraft to this day to get an acknowledged radar lock on the SR-71.

Role Attack, Fighter, Reconnaissance
Manufacturer Saab
First flight 8 February 1967
Introduction 21 June 1971
Retired 25 November 2005
Primary user Swedish Air Force
Produced 1970–1990
Number built 329


General characteristics

  • Crew: One
  • Length: 16.4 m (53 ft 9 in)
  • Wingspan: 10.6 m (34 ft 9 in)
  • Height: 5.9 m (19 ft 4 in)
  • Wing area: 46 m² (500 ft²)
  • Empty weight: 9,500 kg (21,000 lb)
  • Loaded weight: AJ 16,000 kg; JA 17,000 kg (AJ 35,273 lb; JA 37,478 lb[36])
  • Max. takeoff weight: 20,000 kg (44,000 lb)
  • Powerplant: 1 × Volvo RM8B afterburning turbofan, 72.1 kN / 125.0 kN afterburning (16,200 lbf dry, 28,110 lbf afterburning)

Performance

  • Maximum speed: Mach 2.1, 2,231 km/h (1,386 mph) at 11,000 m (1,386 mph at 36,100 ft (11,003 m))
  • Range: 2,000 km internal fuel only (1242 mi)
  • Service ceiling: 18,000 m (59,100 ft)
  • Rate of climb: 203 m/s (12,200 m/min) (40,026 ft/min[36])

Armament

  • 1x 30 mm Oerlikon KCA cannon with 150 rounds
  • Six missile stations for two RB71 Skyflash (only JA37), four AIM-120 AMRAAM (JA 37D), or six AIM-9 Sidewinder or four 135 mm (5.4 in) rocket pods.
  • U95 ECM pod (JA 37D)

End notes