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SAAB JA-37 Viggen

saab37


Studies aimed at developing a successor to the Draken were carried out between 1952 and 1957. The Saab 37 Viggen (Thunderbolt) multi-role combat aircraft configuration and engine were specified in 1960 from the requirement for STOL performance to permit operation from short roadway dispersal airfields, and the naviga-tion system was selected the next year.

Prolonged research led to adoption of a then-unique canard configuration for the interceptor that was to form the airborne component of the weapon system. The configuration comprises a large rear-mounted delta wing combined with a delta foreplane incorporating trailing-edge flaps. This was adopted to provide improved STOL performance so that the Saab-37 would be able to operate from short runways and sections of roadway about 500m in length, greatly increasing the flexibility of dispersed operations. This configuration, in combination with a high-power turbofan engine, has provided the essential short take-off capability. The engine also complements short landing capability by introducing thrust reversal, its first use in a combat aircraft. The Saab-37 has been designed for a 'no-flare' approach to landing with a rate of sink of 5m per second, and this has meant the design of special landing gear able to absorb such a high rate of descent. Once on the ground, thrust reversal plus anti-skid brakes ensure the achievement of a minimum landing run. The pilot is accommodated on a zero-zero ejection seat in an air-conditioned, heated and pressurised cockpit, protected by a bird-proof windscreen. Much of the capability of this aircraft results from the incorporation of the latest avionics, including for attack a head-up display linked via an air-data computer to a digital fire-control system; for its own protection ECM (electronic countermeasures) and radar warning equipment; for navigating Doppler radar and radar altimeter; and for landing in all weathers a tactical instrument landing system plus a blind-landing guidance system.

The first JA37 Viggen was delivered to the Swedish airforce in 1979. This aircraft was made especially in mind for Swedish air force specifications about STOL. The Swedish airforce needed a high quality all weather fighter, able to take off and land on short strips. The system builds on using regular roads as landing/take off strips spread out around the country, making it harder for an enemy to defeat the fighters on the ground during reloading, service and refuelling. The first delivery to the Swedish airforce was the year 1979 and the last one 1990. JA37 is the fifth member of the Viggen family. Viggen is built out of aluminium, honeycomb-elements and titanium-reinforcements. JA37 Viggen is the only aircraft in the Viggen family equipped with a head-down display from Smiths Industries. It makes it possible for the pilot to fly in any kind of weather. Totally 329 Viggen were built, 149 of then are JA37´s.

Many of the functions in Viggen are automated. Examples of this are the automatic cannon. Once the pilot has his target locked on radar, the aircraft will steer itself so that every round will hit its target. The cockpit in Viggen is a relaxed environment; automatic throttle helps the pilot to keep an optimum speed, altitude and angel at short and steep landings. It can land at speeds between 195-249km/h (121-154 mph) with an aoa (Angel of attack) 16, 5 degrees.

Once the landing gear hits the ground and presses together, the reversing function sets in. This is optional, the pilot may choose to use the reversing system manually is he so wishes. The Viggen has a unique reversing system built in, which helps it to keep the landings under 500 meters. It also results in that the pilot can go backwards with his aircraft without any external help.

Construction commenced in 1964, the first of seven prototypes making its maiden flight on February 8, 1967.

Saab received the initial order for 149 production aircraft in 1968 and first production Saab JA37 Vig-gen (301) made its initial flight on 4 November 1977. The first of them were delivered during 1979 to a squadron of F13 Wing based at Norrkfiping. It is powered by a US-designed JT8D turbofan engine which has a Swedish-produced afterburner. Short-field ability is enhanced by an automatic speed control and a thrust reverser, so that with its numerous aerodynamic aids the Viggen can take off in 400 m (1,310 ft) and land in 500 m (1,640 ft), coming 'over the fence' at a remarkably docile 220km/h (137mph) for such a high-performance aircraft.

The first operational squadron was established at F7 Wing in Sâtenäs from June 1971 onwards. Equipped with uprated turbofan, cannon, BAe Sky Flash missiles and I/J-band pulse-Doppler radar.

Production of the AJ37 totalled 110 aircraft, but three basically similar models were produced in parallel, conforming to the Swedish practice of producing a single airframe capable of adaptation to specialist roles.

The next versions to be developed were dedicated reconnaissance Viggens. R&D funding was allocated for a nominal 'S-37' (Spanning, or reconnaissance) aircraft programme in 1971, resulting in the SF 37 Viggen (Spanning Foto, or photo-reconnaissance) which was intended to replace the S 35E Drakens and surviving Lansens in their overland mission. The first prototype flew on 21 May 1973. The 26 SF 37 are fitted with a varied array of cameras in a chisel nose, which dispenses with radar of any kind. An array of cameras (totalling seven in all) is provided, comprising four vertical or oblique units for low-level photography, two vertical cameras for medium to high-altitude tasks, and a solitary infra-red camera, Additional capability is provided by pod-mounted systems as and when required, such facilities enhancing both day and night reconnaissance potential and including additional specialized cameras and Red Baron infra-red linescan equipment. These systems can also be supplemented by pods, particularly night recon-naissance units, on the Viggen's shoulder pylons.

Ordered into production early in 1973, the SF37 variant flew for the first time on 21 May of the same year, with deliveries to the first operational unit, F21 at Lulea, beginning during April 1977. This model replaced the same company's S35E Draken in Swedish air force service.

 

Saab-Viggen

 

The second dedicated reconnaissance version is the SH 37 Viggen (Spanning Havsovervakning, or sea surveillance) aircraft. The third production Viggen served as the SH 37 prototype, first flying in that configuration on 10 December 1973. Fitted with a long-range Ericsson PS-371/A surveillance and attack radar, optimised for over-water operations, contained in a fairing located beneath and slightly aft of the starboard engine air inlet, the 26 SH 37 also boasts an RKA 40 camera which records radar imagery for analysis.
Outwardly, the SH 37 Viggen resembles the AJ 37 aircraft, and if any additional reconnaissance systems are carried they are externally mounted on the shoulder pylons. The usual fit is a night photography pod to port and a LOROP pod to starboard. The SH37 retains a nose-mounted radar for surveillance purposes and it can also operate with additional sensors or weaponry. Production models were delivered from June 1975.
Air-to-air missiles can be carried by both reconnaissance derivatives for self-defence purposes.

With a need for a two-seat trainer version, the Sk 37 Viggen (Skol, or school), has two separate cockpits for pilot and instructor. The 18 Sk 37s have an extended fin and retain the standard Viggen nose, but carry no radar, instead relying on Doppler equipment and DME to find their way around. Based on the AJ, the Sk 37 has reduced fuel capacity as a result of its extra cockpit, and aircraft often operate with external tanks. Deliveries of the Sk37 2-seater trainer commenced in 1972. This aircraft was also designed for a limited strike role.

The first 27 Viggens were built with weakened spars and early in its career the type gained an unfortunate reputation as a result. The basic integrity of Saab's design was never in doubt, as borne out by the long service of all its post-war military aircraft, so it came as no surprise when the decision was made to proceed with the final and perhaps most radical development of System-37. To replace the J 35 Draken in the air defence role the JA 37 Viggen (Jakt, or fighter) was conceived, externally identical to the AJ 37 but underneath a very different aircraft. Design work had been underway at a low rate since 1968, and the first contracts were awarded in 1972.

A total of five prototypes were required, the first flying on 4 June 1974. The fuselage was subtly stretched by 7cm and the fin gained a distinctive extension (a la Sk 37), and additional elevon activators. The other obvious external difference is a blade VHF aerial, behind the rudder. The JA 37 has an uprated 125kN Volvo RM8B afterburning engine, (licence-built Pratt & Whitney JT-8D-22, featuring an additional fan stage, while the on-board equipment was supplemented by an all-weather long-range Ericsson UAP 1023 pulse-Doppler radar. The JA37 also possesses strike capability. Armament includes a permanent 30mm cannon pack and Skyflash and AIM-9L Sidewinder AAMs.

An extensive test programme was undertaken to integrate the new Volvo-Flygmotor RM8B engine, Ericsson PS-46 multi-mode radar, BVR missile system, and all-new cockpit avionics and displays. While still a relatively small, single-engined aircraft, the JA 37 conforms to Sweden's exacting operational requirement for short missions but high sortie rates. Its wing has been restressed to cope with a higher load factor and the aircraft's weight has increased. The first of 149 production JA 37s flew on 4 November 1977, with deliveries commencing in 1980. The final aircraft was handed over to the Flygvapen on 29 June 1990, bringing to an end the Viggen's production run of 329 aircraft.

The JA 37 at full throttle and full afterburner will empty the fuel tanks in 9 minutes, and 0-315 km/h (take off speed) takes 7 seconds.

Attempts were made to export the aircraft, first as a Starfighter replacement to NATO nations and Japan, a Mirage III replacement for Australia and, later, as a deep penetration strike aircraft to India. All these efforts came to nothing, partly because of restrictions imposed on Saab by the national legislature.

A proposal to fund attrition replacements for the Swedish air force was also defeated, and first-generation aircraft were withdrawn before the JAS 39 Gripen became fully operational. To bridge that gap Saab is undertaking an extensive upgrade programme to modify 115 AJ, SF and SH 37s to AJS 37 standard. This involves fitting a new digital databus giving each aircraft a true multi-role capability, a terrain-following radar system, and compatibility with some of the armaments being developed for the Saab Gripen (such as the DWS 39 stand-off dispenser weapon).

AJ37
Engine: RM8A Svenska Flygmotor/Pratt & Whitney JT8D-22 (14771-26014 lbs)
Span: 10.6 m (34’9.25”)
Length:    16.3 m (53’5.75”)
Height: 5,80 m (19 ft 0.25 in)
Wing area: 46.00 sq.m (495.1 sq ft)
Empty wt: 11800 kg (26,015 lb)
Take-off weight: 16000 kg (35273 lb)
Max take-off wt: 20500 kg (45,194 lb)
Cruise speed: Mach 0.9       
Max speed at alt: M2+
Max speed 100m/330ft: M1.2    
Landing speed: 220 kph (137 mph)
Range:    2000 km (1240 sm) +
Max. altitude: 18000 m (59060 ft)
Hardpoints: 7
Rate of Climb: < 100 sec. to 10,000m (32,810 ft)

Sk37
Engine: RM8A Svenska Flygmotor/Pratt & Whitney JT8D-22 (14771-26014 lbs)
Span: 10.6 m (34’9.25”)    
Length: 16.3 m (53’5.75”)
Take-off weight: 16000 kg (35273 lb)
Max speed: Mach 2+
Cruise speed: Mach 0.9
Landing speed: 220 kph (137 mph)
Range:    2000 km (1240 sm) +
Max. altitude: 18000 m (59060 ft)

SF37
Engine: RM8A Svenska Flygmotor/Pratt & Whitney JT8D-22 (14771-26014 lbs)
Span: 10.6 m (34’9.25”)    
Length: 16.3 m (53’5.75”)
Take-off weight: 16000 kg (35273 lb)
Max speed: 2125 kph /1,320 mph / M2+
Cruise speed: Mach 0.9
Landing speed: 220 kph (137 mph)
Range: 2000 km (1240 sm) +
Max. altitude: 18000 m (59060 ft)

SH37
Engine: RM8A Svenska Flygmotor/Pratt & Whitney JT8D-22 (14771-26014 lbs)
Span: 10.6 m (34’9.25”)
Length: 16.3 m (53’5.75”)
Height: 5.80 m (19 ft 0.25 in)
Wing area: 46.00 sq.m (495,1 sq ft)
Empty wt: 9000 kg (19,840 lb)
Max take-off wt: 20500 kg (45,195 lb)
Take-off weight: 16000 kg (35273 lb)
Max speed: 2125 kph /1,320 mph / M2+
Cruise speed: Mach 0.9
Landing speed: 220 kph (137 mph)
Range: 2000 km (1240 sm) +
Max. altitude: 18000 m (59060 ft)

JA37
Engine type/thrust: RM8B Svenska Flygmotor/Pratt & Whitney JT8D-22 (16093-28108 lbs)
Thrust without afterburner 7350 kp (1066 PSI); Thrust with afterburner 12750 kp (1849, 23 PSI)
Wing span: 10.6 m (34’9.25”)    
Length: 16.4 m (53’9.75”)
Wing area: 46 sq.m    
Height: 5,90m (19, 35 ft)
T/O - Ldg run: 400 / 500 m
Take-off weight: 17000-23000 kg (37478-50705 lb)
Weight empty: 12200kg (26896 lb)
Warload: 7000 kg    
Max speed: 2+ Mach    
Max speed low altitude: 1410 km/h (876mph)
Cruise speed: 0.9 Mach
Time to height: 1 min 40 sec / 10,000m
Landing speed: 220 kph (137 mph)
Range: 2000 km (1240 sm) +
Combat radius: 500+ km
Max. altitude: 18000 m (59060 ft)
Air refuel: No
Armament: 30mm automatic Oerlikon from (150 rounds).1340 rounds/minute, 8 x AAM / 6000kg ext. Bomb
Crew: 1

saab37-ld

Saab 37 Viggen

 

 


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