JA-37 Viggen, Saab

JA-37 Viggen

The Saab Viggen is a STOL-jet fighter of canarded delta configuration. It was designed to fulfill several roles with one basic airframe, but in multiple versions: fighter-bomber, attack aircraft, tactical recce, sea surveillance, operational trainer, and pure fighter. The canards and a thrust reverser -- the combination of this with an afterburner is unique -- make the Viggen capable of operating from small, dispersed airstrips. The JA 37 is the fighter version.

Type: JA 37 Viggen
Country: Sweden
Function: fighter
Year: 1977
Crew: 1
Engines: 1 * 12750 kg Volvo RM 8B afterburning turbofan
Wing Span: 10.60 m
Length: 16.40 m
Height: 5.90 m
Wing Area: 52.20 m2
Empty weight: 12200 kg
Max.Weight: about 18000 kg
Speed: 2124 km/h
Ceiling: 18300 m
Range: 2000 km
Armament: 1*g 30 mm, 6000 kg payload

Saab 37 Viggen

Viggen is a multi-role fighter, through upgrades still modern and with some almost unique features, in service with the Swedish air force in several versions, since 1971 and until after 2006. The name Viggen means The Thunderbolt, especially those resulting from the Norse god Thor's warhammer Mjölner.

In 1952 studies were started to design a replacement for Saab Draken. "Project 1357" in 1954, was the first to have a canard layout (lots of other layouts were studied as well). In 1961, PW JT8D-22 was the chosen engine to be locally built, with a locally designed afterburner and lots of material changes in the rest. In 1962 the design was frozen, and the prototype first flew in Feb 8:th 1967. During the 1960's, it was foreseen that the Swedish air force would purchase 800+ Viggens, but the final figure ended up at 329. In order to make the airframe smaller, it was early decided to replace the navigator with a good navigational computer. It's designed to withstand 12 G, but the limit in operation is 7 G.

Emergency power is supplied by a ram air turbine just before the left wing leading edge, which extends automatically on hydraulic power failure, and just before touch down. (Earlier, it was also always deployed whenever the landing gear was down.) The canard doesn't contribute much lift in itself during normal flight, it acts more as a gigantic vortex generator for the main wing. During low speed flight, its rear edge flap can be lowered to increase lift and permit a high nose angle.

The requirement was that the aircraft would be able to operate from 500 m runways. A short take-off run is possible due to the powerful engine (then, it was the most powerful installed in a fighter). Landing distance is reduced by several means: The HUD is used as a precision landing aid, making it possible to aim just 30 m in from the threshold; The landing gear thinks a landing sink rate of 5 m/s is normal, so landings are done without any flare; The thrust reverser is interconnected with the nose gear link, so it can be selected in the air and will operate when the nose is lowered. (It is not intended to be used in the air.)

The aircraft must be servicable very quickly by concripts with relatively short training. Re-fueling and re-arming by 7 men, of which 6 are concripts, must take less than 10 min for the JA 37 Viggen. The time limits for reconnaissance and attack configured aircraft are 15 and 20 minutes. It is said that attack squadrons expect to fly 11 missions per aircraft and 24-hour period.


AJ 37 Viggen

108 delivered starting in 1971, expected to remain in service until about 1998. Serial numbers 37001-37108.
This is the strike variant. When it was designed, guns were definitely passé, so there was no provision made for an internal cannon. Dumb bombs weren't popular either, so during the preliminary design stages, the only armament considered were missiles. It wasn't until the prototypes were actually in progress of beeing built, that someone thought of incorporating wiring for iron bombs, presumably as it was realised the HUD/Weapons Aiming Computer system would enable them to be dropped with good precision.

Main armament for the anti-shipping role, a very important role, is the Saab 304 rocket-powered anti-ship missile. For ground attack, 135 mm Bofors M70 rockets in pods of six each, were together with the command controlled, smoke-less liquid fuel Saab 305 missile, the main weapons, with the 120 kg bombs and 30 mm podded guns used when appropriate. The Saab 305/Rb 05 missile is now an all round weapon, as it is rather effective against slow, large aircraft and helicopters too. A TV version was contemplated as the Rb 05B, but it was cheaper to buy Mavericks instead. It has always had a secondary fighter role, with Sidewinders and 30 mm cannon in pods. In service, it replaced the A 32A Lansen.

Sk 37 Viggen

17 delivered starting in 1973, will remain in service for a long time yet. Serial numbers 37801-37817.
To make room for the second cockpit, fuel and avionics was removed, so it has a shorter range and lacks a radar. The fin is taller. The rear cockpit has two periscopes to give forward vision. The trainer version wasn't planned from the outset, as it was considered enough for pilots to learn to fly delta winged aircraft on Draken trainers.

SF 37 Viggen

28 delivered between 1977 and 1980, will remain in service until about 2005. Serial numbers 37950-37977.
All fixed cameras are carried in the nose, that lacks a radar. There are three SKa 24C-120 for horizon-to-horizon coverage, an SKa 24-57 for wide angle pictures and two SKa 31-600 for high altitude or stand off photography. There is also an IR-linescan designated VKA 702. For night photography, a pod is carried on the left fuselage station, with three SKa 34-75 cameras loaded with IR sensitive film in the front. The rear of the pod houses electronic IR flashes, as does a complementary pod on the starboard fuselage station. In service it has replaced the S 35E Draken.

JA 37 Jaktviggen

149 delivered between 1979 and 1990, will remain in service until 2010-15. Serial numbers 37301-37449.
By the time this version was in final design, it was clear that guns were definitely useful, so it was given the most powerful cannon a fighter has had, a 30 mm Oerlikon KCA with 150 rounds. Rate of fire is 22.5 0.36 kg rounds/s at 1050 m/s, which gives them six times more kinetic energy than the 30 mm Adens on the attack version. A unique feature is the coupling of the radar gunsighting mode to the autopilot. When the pilot places a target in a capture window, the autopilot takes over pitch and yaw, and presents bank information on the HUD for the pilot to follow. Even if it's not followed, the pitch and yaw channels have enough authority to precision aim the cannon, reducing pilot workload letting him or her concentrate on tactics and situational awareness. The fighter version has an intertial navigation system instead of the earlier versions' doppler navigation system. It is 13 cm longer, partly because the RM8B engine, which is smokeless, more powerful and better suited to high altitude than the RM8A which powers the other Viggen versions, is 8 cm longer than the RM8A. There is a three stage fan, three stage LP compressor and a seven stage HP compressor, as compared to 2/4/7 on RM8A.

The fin is the same tall one as on Sk 37 to compensate for the longer fuselage. The external tank is the same size as on the other versions, but because there's a bulge where the gun is installed, there is no room for the abbrevited top fin of the tank, instead of three fins, this tank has four fins, in a flattened 'X'. The system has gone through numerous upgrades since service entry. The radar is able to track more targets now, than at service entry, for example. The lastest software upgrade, EDIT 33, enables the JA 37 to use AMRAAM missiles. In spite of having a strengthened wing, an engine 100 kg heavier (2200 kg) and a fixed cannon, it only has an empty weight 400 kg more than earlier versions. In service it has replaced and supplemented the J 35 Draken.

Technical data

                  AJ/SH     SF        SK        JA
Take off run:     400 m     400 m     400 m     400 m
Landing run:      450 m     450 m     450 m     450 m
Landing speed:    220 km/h  220 km/h  220 km/h  220 km/h
Length:           16.30 m   16.50 m   16.30 m   16.43 m
Span:             10.6 m    10.6 m    10.6 m    10.6 m
Height:            5.6 m     5.6 m     5.6 m     5.9 m
 w folded fin:     4.0 m     4.0 m     4.0 m     4.0 m
Engine thrust:    6690 kp   6690 kp   6690 kp   7415 kp
 w afterburner:  11790 kp  11790 kp  11790 kp  13125 kp
Range:            2000 km   2000 km             2000 km
Empty weight:     9500 kg   9500 kg             9500 kg
Max payload:      3600 kg   2500 kg             1700 kg
 (excluding external tank)
Max take off
 weight:         18000 kg  17000 kg            18600 kg
Max speed                                (at 3600 kg load?)
 low altitude:  Mach 1.1   Mach 1.1           Mach 1.2
 high altitude: Mach 2+    Mach 2+            Mach 2+
Guaranteed speed
 high altitude: Mach 1.7   Mach 1.7           Mach 1.8
Time from brake release to 10 km or Mach 1 at low altitude: 100 s
Max altitude:    18000 km   18000 m            18000 m

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