JA 37  - SAAB 37 Viggen (1979-2004)

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System 37, ”Viggen” was developed primarily to succeed the attack aircraft A 32 Lansen, when its time as a first-line combat aircraft would be over. An interceptor and a reconnaissance version was later to be developed.

The Viggen got the at this time unusual layout with a flapped canard wing and a delta-shaped main wing. This configuration was used to combine good performance at high speed with a true STOL (Short-Take-Off-and-Landing) capability. The latter was necessary due to the base system developed by the Swedish Air Force. To reduce vulnerability, the aircraft have to able to start and land on short and narrow runways, often straight lengths of ordinary roads. In addition to the flaps fitted to the canard wing, the Viggen is equipped with a thrust-reversible engine and wheel-braking by units with an anti-skid system. This combination gives a landing run of only 500 meters.

At the end of 1961, the Swedish parliament granted economical means to develop the System 37. At the same time an agreement was made with the American aircraft engine manufacturer Pratt & Whitney concerning licence-building of  the JT8D turbo-fan engine. The engine was to be manufactured by Volvo Flygmotor at Trollhättan and got the Swedish designation RM 8 (= ”Reaktionsmotor 8”). The JT8D was basically a civil engine, but re-designed in Sweden for its military super-sonic use. Also the afterburner was to be designed in Sweden. The engine, in its first version (RM 8A) had a thrust power of 12.000 kp/117,6 kN (including reheat) and was one of the most powerful military engines at this time.

Another epoch-making feature was the digital computer system in a time dominated by analogue technique. The system relieved the pilot from many supervision tasks. He could instead concentrate on pure operational duties. To make this relatively large aircraft fit in the Swedish system of rock hangars, the tail was made foldable. 

In February 1967, the first prototype flew for the first time. Next year, the Air Force ordered the first batch of the Viggens. 108 aircraft of the attack version AJ 37 and 18 of the two-seated trainer version SK 37 were purchased. The designation ”AJ” indicates that the aircraft also is able to execute interceptor duties. Viggen was also ordered in two reconnaissance versions, the SF 37 overland reconnaissance aircraft and the SH 37 sea reconnaissance version. 28 SF 37s and 27 SH 37s were built. 

The AJ 37 was from the beginning capable to carry a considerable number of different weapons. It is possible to equip the aircraft with Air-to-Surface missiles (RBS 15F for sea- and RB 75 for ground targets, attack rockets, conventional bombs and RB 74 Sidewinder Air-to-Air missiles. Automatic cannons can be mounted externally in pods.

The Viggen was as earlier mentioned also intended for interceptor duties in the AJ-version. In order to further improve its performance as a fighter interceptor, the JA 37 Viggen was developed. Revised electronic equipment, including a much improved radar, was designed. The engine was modified, mainly to get better performance at higher altitudes. The new version, designated RM 8B, has a thrust power of 12.750 kp (125,0 kN). Without re-heath, 7.350 kp is achieved. JA 37 also houses an Oerlikon 30 automatic cannon in the fuselage. Other weapons are three different Air-to-Air missiles; RB 71 (Skyflash), (RB 74 (AIM-9L Sidewinder) and RB 99 (AIM-120B AMRAAM). Attack rockets in pods can also be carried.  The first JA 37 prototype flew in September 1974. The first serial manufactured aircraft of 149 purchased was delivered in 1979.

 Later, 100 of the earlier built aircraft have been modified to AJS-standard, a true multi-role fighter aircraft. This has been achieved by in the first place by an enhanced computer system and a certain modification of the weapon load capacity. The modified reconnaissance aircraft have got the designations AJSF 37 and AJSH 37. The trainer version has been modified for electronic warfare and is now designated SK 37E.

The name ”Viggen (Thunderbolt”) alludes to the hammer of the ancient Scandinavian god Tor. His hammer (Mjölner) was able to send away thunderbolts that could kill several enemies at the same time… 

Photos:

- Top: The JA 37 prototype (# 37301), now on display outside Flygvapenmuseum .

- Below: AJSF 37 # 37950 of Wing F 21 (Luleå) on visit to F 7 (Såtenäs) at airshow,  June 2000. Note the camera openings and the Rb 74 Sidewinder.

Bottom:

AJSF 37 # 37950 of Wing F 21 (Luleå) on visit to F 7 (Såtenäs) at airshow,  June 2000. Note the camera openings and the Rb 74 Sidewinder.

© Lars Henriksson