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The SAAB 37 Viggen

v1.0.0 / 01 mar 04 / greg goebel / public domain

* During the Cold War, Sweden pursued a policy of neutrality between East and West, and went to considerable lengths to build up a defense force to back up their neutrality. One of the major components of this force was a series of combat aircraft built by SAAB, and one of the most impressive of this series was the "SAAB 37 Viggen (Thunderbolt)", a multirole combat aircraft that was the backbone of Swedish air power from the 1970s to the end of the century. This document provides a history and description of the Viggen.



* In the early 1960s, Sweden was looking for a multirole fighter that could replace the SAAB 32 Lansen in the strike role and the SAAB 35 Draken in the air defense and reconnaissance roles. The specifications for the new aircraft were ambitious:

SAAB had been considering various designs to follow the Draken since 1952. The company was able to submit a proposal to meet the specification, the "SAAB System 37", in February 1962. The design featured a canard configuration that offered better short-field operation than a traditional delta wing, and a powerful RM8 afterburning bypass turbojet engine with a thrust reverser to cut down landing roll. The SAAB 37 would feature an automated microwave instrument landing system (ILS) to help perform short landings, and would also be equipped with state-of-the-art avionics and combat systems. In addition, since Sweden was and remains strongly reliant on large numbers of reservists who would be called up in time of war, the SAAB 37 was designed to be easily maintained by ground crews with relatively limited training.

The Svenska Flygvapnet (Swedish Air Force) liked the proposal and gave the go-ahead on 28 September 1962 for full development of the "Viggen (Thunderbolt)", as the type was named, with details released to the public in December 1962. Incidentally, "Viggen" actually has a somewhat more specific meaning, being the clap of thunder produced by the thunder god Thor's hammer Mjoelnir, but "Thunderbolt" gives the desired impression in any case.

Several different lines of Viggen development were envisioned:

Six single-seat AJ 37 Viggen prototypes and one two-seat Sk 37 Viggen prototype were ordered in 1965, at about the same time a mockup of the aircraft was displayed to the media. The first single-seat prototype was rolled out on 24 November 1966 and performed its its initial flight on 8 February 1967, with Erik Dahlstrom, SAAB's chief test pilot, at the controls. Dahlstrom stated that the Viggen handled as pleasantly as a sportsplane. Pilots would always like the Viggen's handling, particularly in comparison to that of the more challenging Draken, but the steep landings were tricky to master, and even Dahlstrom scraped the tail at least once.

The second prototype followed on 21 September 1967, and the third on 29 March 1968. The last of the six single-seat prototypes was in the air by April 1969, with this machine being very close to production AJ 37 specification. The initial prototype had been involved in a fatal freak accident on 31 May 1968, when Lennart Fryoe dropped a flight checklist while preparing to take off and accidentally triggered the ejection seat. Fryoe's parachute didn't open fully and he was killed. The aircraft kept on rolling until it hit a drainage ditch and hangar. It was repaired and returned to service. The fourth prototype was lost in an accident on 7 May 1969, with another prototype built to take its place. It is unclear if this prototype was an additional aircraft or part of the seven originally ordered.

A production order for 175 AJ 37 / SF 37 / SH 37 machines had already been placed on 5 April 1968. Initial flight of the first production AJ 37 was on 23 February 1971, with initial service deliveries to the Flygvapnet in June 1971.



* The AJ 37 attack variant of the Viggen, where "AJ" stands for "Attack Jagt / Strike Fighter", was the first of the series to go into service, and makes a useful baseline for further discussion.

The AJ 37 has a spikelike fuselage, with: fixed oval-shaped engine inlets alongside the canopy, the inlets set off from the fuselage to avoid ingesting stagnant "boundary layer" air; a large rear-mounted delta wing; canards alongside the engine inlets; and a tall tailfin. Overall construction is of aircraft aluminum honeycomb, with titanium where required, such as engine firewalls. The Viggen is arguably less elegant in appearance than its predecessor, the SAAB 35 Draken, or its successor, the SAAB 39 Gripen, but it has a certain solid, businesslike, and combatative style of its own. However, the extensive use of aluminum honeycomb makes it a surprisingly light aircraft for its size.

The wing has a somewhat complicated form, featuring a double delta with something of a "hoop skirt" appearance in planform and a dogtooth on each outer span. The dogtooth was added to improve logitudinal stability when carrying external stores. Each dogtooth is further marked by a bullet fairing for a radar warning receiver (RWR) antenna. There are two-section hydraulically actuated elevons on the trailing edge of each wing.

The canards direct turbulent airflow over the main wing at low speeds, reducing the stall speed on landings. They have no dihedral and are fixed at a few degrees of incidence, but have trailing-edge flaps to improve takeoff performance. The canards on the first prototype had a noticeable dihedral when the machine was rolled out, but the dihedral was eliminated before the initial flight. The tailfin is fixed, with a one-piece rudder. It folds to the left to allow the aircraft to be stowed in hardened shelters at field bases. There is a fixed ventral fin under the tail.

The AJ 37 features tricycle landing gear, with all gear featuring two wheels. The nose gear retracts forward. Each main gear assembly unusually features its two wheels in tandem to reduce its depth for storage in the wing, and retracts inward from the wing towards the fuselage, with the main gear struts telescoping during retraction for a tighter fit. The landing gear is heavily shock-absorbed to permit steep approaches for short landings. Landings are said to be "firm" and apparently are much along the lines of carrier landings, except that the landing strip isn't moving.

The RM8A afterburning turbofan is actually at the core a Pratt & Whitney JT8D-22 commercial turbofan used on the Boeing 727 and Douglas DC-9 airliners, built under license by Svenska Flygmotor (later Volvo Flygmotor) and fitted with a Swedish-designed afterburner and thrust reverser. It is said to be the first production engine to ever have such a combination of features. The engine provides 115.7 kN (11,800 kgp / 26,015 lbf) afterburning thrust. The thrust reverser features three "jaws" that snap shut when the nose gear touches down and blast the exhaust forward through three slots around the fuselage under the tail.

It is unclear how the engine is started; cutaways of the machine do not show anything that resembles an auxiliary power unit. The Viggen does have a ram-air turbine for emergency flight power, fitted to a door under the trailing edge of the left canard that pops out when hydraulic power is lost and (for some puzzling reason) when the landing gear is extended.

There is a fuel tank in each wing, a saddle tank over the engine, a tank on each side of the engine, and a tank behind the cockpit, for a total of six tanks. There is no provision for inflight refueling, as that would imply a "force projection" capability not in line with Sweden's defensive posture.

The pilot sits under a rear-opening clamshell canopy behind a one-piece windshield hardened against birdstrikes. There is a prominent humped dorsal spine running back from the canopy; most of the prototypes had a less prominent straight spine, but the enlarged spine improved transonic handling and was adopted for production.

The Viggen was originally fitted with a SAAB "Mark 2" rocket-boosted ejection seat with zero-altitude capability, but as demonstrated by the accident that killed Lennart Fryoe, the aircraft had to be moving 75 KPH (47 MPH) or more for the seat to work reliably. The "Mark 1" seat, incidentally, was the development version and was apparently never operationally fielded on any aircraft. It is an indication of the Swedish "do it ourselves" mentality that SAAB actually developed their own ejection seat, when a all-but-standard British Martin Baker seat would have probably been as good or better in technical and economic respects.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                10.60 meters        34 feet 9 inches
   wing area               46.0 sq_meters      495.16 sq_feet   
   canard span             5.45 meters         17 feet 10 inches
   canard area             6.20 sq_meters      66.74 sq_feet   
   length                  16.30 meters        53 feet 6 inches
   height                  5.80 meters         19 feet

   empty weight            11,800 kilograms    26,015 pounds
   normal weight           15,000 kilograms    33,070 pounds
   MTO weight              20,500 kilograms    45,195 pounds

   max speed at altitude   2,125 KPH           1,320 MPH / 1,145 KT
   service ceiling         18,300 meters       60,000 feet
   takeoff run             400 meters          1,310 feet
   landing run             500 meters          1,640 feet
   combat radius           1,000 kilometers    620 MI / 540 NMI
   _____________________   _________________   _______________________

The control layout is analog, as would be expected of aircraft of its period, but features a Svenska Radio / Ericsson (SRA) head-up display (HUD) for primary flight data, including displays generated by the instrument landing system to help guide the aircraft down. The most significant element in the AJ 37's avionics suite is its Ericsson PS-37A monopulse X-band radar, which is primarily focused on air-to-ground and navigation, though it has limited air-to-air capabilities. The rest of the avionics is impressive, or at least it was for its era, and includes:

The AJ 37 has seven stores pylons, including a centerline pylon; a pylon under each engine inlet; and two pylons on each wing outboard of the main landing gear. There is provision for a third outboard pylon under each wing. Maximum external load is 7,000 kilograms (15,400 pounds). An external fuel tank is almost always carried on the centerline pylon. It does not appear that any of the other pylons are "wet". Primary stores initially included:

As mentioned, the Viggen was designed to be easy to maintain. It has over 100 access panels, with the nose cone sliding forward to give access to the radar system, and the rear fuselage can be quickly pulled off to give access to the engine. Most of the access panels can be reached without use of a ladder or service scaffold. Systems are modular to ease servicing and upgrades. A "built-in test system" was integrated into the aircraft, with specialized servicing vehicles produced to help find and fix faults.

* A total of 109 production AJ 37s was built, with the type equipping six squadrons. Although prototypes and early production aircraft flew in natural metal finish, in service AJ 37s are painted gray on the bottom and with a "splinter" camouflage scheme on top, featuring a four-color pattern of tan, light green, dark green, and dark blue. The Flygvapnet refers to this color scheme as "fields and meadows" and it is meant to help conceal the aircraft at their dispersed bases. All Viggen variants except the JA 37 interceptor feature this color scheme.

There were a number of losses of AJ 37s in 1974 and 1975 due to wing spar failures. As it turned out, the first 27 machines had been built with lighter wing spars, and the 21 survivors were rebuilt with stronger spars. Oddly, though the Viggen is easier to fly than the Draken, the Viggen's accident rate has been higher. One interesting accident took place on 28 September 1982, when a pilot was taking off from Norrkoeping and suddenly encountered a herd of elk that had wandered onto the runway. There was a collision with one of the elk, with the aircraft suffering minor damage while the elk ended up as venison. One wonders if the pilot was at least tempted to put a "kill marking" on his machine.

In the early 1990s, a decision was made to update a number of AJ 37s and some other Viggen variants to the "AJS 37" multirole configuration, of which more is said later. The last operational flight of a true AJ 37 was in March 2000.



* A single prototype of the SF 37 dedicated reconnaissance variant of the Viggen was built, performing its first flight on 21 May 1973. The "SF" stands for "Spanings Foto / Photo Reconnaissance". Deliveries to the Flygvapnet began in early 1977, with a total of 28 machines handed over by early 1980. They replaced the Saab S35E Draken in the photo reconnaissance role.

The SF 37 is basically a modified AJ 37 Viggen attack variant. It is fitted with a distinctive camera nose and external reconnaissance pods. The nose accommodates seven vertical and oblique cameras, including an infrared linescanner, and a data recording unit. The nose camera fit can be configured for low altitude or high altitude reconnaissance missions. The pilot has a periscope that gives him a view of the ground directly below to help take vertical shots. Reconnaissance pods are carried on the pylons under the engine inlets, with options including a "Red Baron" multisensor night reconnaissance pod with an electronic strobe photoflash, or a forward-looking long-range optical (LOROP) camera pod.

Unsurprisingly, the SF 37 has no radar. It carries countermeasures pods and Sidewinders for self-defense, but it has no radar for targeting and it does not appear to have a gunsight capability.

* The SH 37 variant is a little difficult to characterize, being described as maritime reconnaissance variant, but it might also be described as a maritime patrol and strike variant. The "SH" stands for "Spanings Hasoevervakining / Coastal Surveillance & Reconnaissance."

The SH 37 prototype was a rebuild of the third AJ 37 prototype, and performed its first flight in its new configuration was on 10 December 1973. Externally, the SH 37 is very difficult to distinguish from the AJ 37, the most significant difference being fit of the improved Ericsson PS-371/A radar with greater range and optimizations for maritime surveillance. The radar display is recorded on a video camera for post-mission analysis, while a second camera similarly used just to log the flight data corresponding to a target location, while the pilot uses a tape recorder to log comments. An improved data processor is also fitted.

The SH 37 can carry the Red Baron or LOROP reconnaissance pods. Initially, the plan had been to build a single reconnaissance Viggen that could perform the mission of both the SF 37 and the SH 37, but it proved impossible to cram both radar and cameras into the same nose. The SH 37 can also carry Sidewinders or countermeasures pods for defense, and can carry all offensive weapons qualified for the AJ 37. 27 SH 37s were built between 1977 and 1979. Flygvapnet reconnaissance squadrons operated a mix of SF 37s and SH 37s.



* Although a two-seat conversion trainer wasn't considered for the Viggen originally, the Flygvapnet decided that it would be a good idea after all. The result was the "Sk 37" two-seat trainer, where "Sk" stood for "Skol / School". As mentioned earlier, the seventh of the first seven Viggen prototypes was to be built as a two seater, though because of the loss of the fourth single-seat prototype it is a bit unclear if the first trainer was actually the seventh or the eighth machine. In any case, the first two-seater performed its first flight on 2 July 1970, somewhat behind the original schedule, with Pers Pellesbergs at the controls. Initial deliveries of the Sk 37 were in June 1972, and a total of 17 production Sk 37s was built.

The Sk 37 uses the AJ 37 airframe. An independent, raised, second cockpit was added behind the front cockpit, with the trainee in the front cockpit and the instructor in the rear cockpit. The instructor has twin periscopes ot improve his forward view. The second cockpit was fitted by removing some fuel tankage, and to compensate a fixed ventral tank was added. The Sk 37 also features a 10 centimeter (4 inch) tailfin extension, with the trailing edge sweep reversed from the rest of the tailfin. The tailfin extension was not initially fitted to the prototype.

The Sk 37 does not have radar, navigating using Doppler and later DME, and though it can carry external stores its combat capabilities are limited by the lack of radar targeting and its short range. Although it has the bullet fairings for the RWR, it is apparently not fitted with the RWR gear itself.



* Of the six AJ 37 prototypes, five of them were subsequently modified to act as prototypes for the JA 37 interceptor ("Jakt / Fighter") variant of the Viggen, the first of these modifications performing its initial flight on 27 September 1974. An initial production order for 30 JA 37s had been placed a few days before that. A fifth JA 37 prototype, a new-build machine, flew in 1975 and was to preproduction standard. The first production aircraft performed its initial flight on 4 November 1977. A total of 149 production JA 37s were built into the mid-1980s.

The JA 37 is very similar to the AJ 37 externally, but it is, if arguably not a "second generation" Viggen, certainly a half-step forward. The major visible distinguishing characteristic is that the AJ 37 has the 10 centimeter (4 inch) tailfin extension of the SK 37. It would take a far keener eye to notice that the JA 37 is stretched by 10 centimeters (4 inches) ahead of the wing to accommodate a more powerful RM8B powerplant, with 125 kN (12,750 kgp / 28,110 pounds) afterburning thrust. The additional power was regarded as important for the air-defense role. Each wing also has four elevon actuators instead of three, as on other Viggen subtypes, to permit improved high-speed maneuvering, and there is some structural reinforcement. Another update was fit of a SAAB "Mark 3" ejection seat, with true "zero zero (zero altitude zero speed)" capability, with this new seat retrofitted to other Viggen variants. The empty weight of a JA 37 is about 400 kilograms (880 pounds) more than that of a AJ 37.

Avionics systems are largely different. The primary sensor is the Ericsson PS-46/A medium-pulse rate, pulse-Doppler, X-band, multi-mode radar, with a range of about 48 kilometers (30 miles) and "look down / shoot down" capabilities to allow it to find and target low-altitude intruders trying to hide in ground clutter. The rest of the JA 37's avionics suite includes:

One of the few items it has in common with AJ 37 avionics is an SRA HUD. However, in contrast to the JA 37, the JaktViggen has a partial glass cockpit, with a head-down display (HDD) and a tactical display.

Another visible difference from the AJ 37 is that the JA 37 has built-in armament, in the form of a Swiss Oerlikon KCA 30 millimeter cannon with 150 rounds of ammunition, fitted in a belly pack and offset to the left to clear the centerline pylon. A radar gunsight is used to aim the cannon. The Oerlikon cannon has far more range and punch than the Aden cannon carried in pods by the AJ 37.

The JA 37 retains the seven stores pylons of the AJ 37. Four Sidewinders can be carried -- on the outer wing pylons and the pylons under engine inlets -- along with two Rb 71 Skyflash semi-active radar homing medium-range AAMs, this weapon being a license-built copy of the British Aerospace (BAe) Skyflash, which in turn is an improved version of the US AIM-7 Sparrow AAM. Some sources claim that an alternate configuration of four Skyflash and two Sidewinder AAMs can be carried as well, but it appears that this is an error, sometimes shown in paintings and drawings but not in photographs. As with other Viggen variants, an external tank is almost always carried on the centerline pylon. Unguided rocket pods can be carried in a secondary strike role, the pilot using the gunsight for aiming. The JA 37 lacks the capability to perform targeting for most other attack stores, just as the the AJ 37's radar cannot provide guidance for the Skyflash AAM.

In service, JA 37s were painted in a number of air-superiority color schemes, with the Flygvapnet eventually settling on a tidy two-tone gray scheme. At its peak, the JA 37 equipped five air-defense squadrons. An export version, the "Saab 37E Eurofighter", was proposed in 1975 as a replacement for the F-104 Starfighter for a group of NATO nations, but the General Dynamics F-16 won the award. (This deal, incidentally, had nothing to do with the later multinational European Fighter Aircraft program.) In fact, although SAAB considered other possibilities for export sales, no Viggen has ever been sold to another air arm.



* Viggens in service have been given a continuous stream of mostly minor upgrades, generally in the form of improved avionics and software upgrades. One of the more important enhancements, performed in the late 1980s, was carriage on the AJ 37 of the US US-designed AGM-65A Maverick ASM, license built in Sweden as the "Rb-75". This generally replaced the less sophisticated Rb-05 ASM. A comparable upgrade, also performed in the late 1980s, provided support for the much improved AIM-9L Sidewinder "all aspect" AAM, built in Sweden as the "Rb-74".

In 1992 the Swedish government approved a program to upgrade a total of 98 AJ 37s, SF 37s, and SH 37s to a multirole "AJS 37" configuration, with "AJS" standing for "Attack / Jakt / Spaning". The rationales for the upgrade were to extend the utility of the existing fleet, as well as provide an aircraft that would familiarize Flygvapnet pilots with multirole operations before they moved on to the SAAB 39 Gripen multirole aircraft, then scheduled for introduction to service later in the decade.

The drivers for the upgrade was the development of new weapons for the Gripen, such as the the DWS 39 gliding submunitions dispenser, and in particular the Rb-15F antiship missile, a vastly improved derivative of the old Rb-04 fitted with a turbojet engine and new seeker. The Rb-15F was developed for the Gripen but was ready for service well in advance of the SAAB 39. As long as the weapon was available, there was absolutely no reason to not make use of it. It was determined that the old AJ 37 could carry the missile if the aircraft was fitted with a new Ericsson processor system and a MIL-STD 1553B digital databus. A little further thought showed that the same fit could be performed on the reconnaissance Viggens, and the result was the AJS 37.

Early press releases on the program gave the impression that the AJS 37 was to be a major upgrade, and that the 48 AJ 37; 25 SF 37; and 25 SH 37 aircraft upgraded would end up with a common configuration. This was reading too much into it, and the announced total of 115 upgrades was also something of an exaggeration. Basically this was a middling sort of avionics and software upgrade that did not change the external appearance of any of the upgraded aircraft in any significant way except to permit them to carry new stores. Changes to the cockpit control layout were modest and certainly did not involve fit of a true glass cockpit. There was no airframe service life extension program (SLEP).

The upgraded AJ 37, SF 37, and SH 37 machines acquired the new designations of "AJS 37", "AJSF 37", and "AJSH 37" respectively. All have the new processor and the MIL-STB 1553B databus; and all support a new mission planning system in which a cartridge storing a mission plan can be plugged into the aircraft, and then yanked out after the mission storing data on the flight that can be reviewed on a mission computer. Beyond that, the capabilities of the three types of machines retain considerable differences:

Re-deliveries of upgraded aircraft began in 1993 and were completed in 1996. Dedicated reconnaissance squadrons were phased out and reconnaissance machines incorporated into regular attack squadrons. However, a special reconnaissance squadron of AJSF 37 Viggens was set up late in the decade to provide support for international peacekeeping missions, the Swedes having become a little more assertive in foreign military operations following the end of the Cold War.

* As with other Viggens, the JA 37 interceptor Viggens have been continuously upgraded, in particular by being fitted with a datalink system in the mid-1980s. The Flygvapnet had developed the sophisticated STRIC ground-based defense datalink system, and STRIC allowed Viggens to be vectored onto targets without using their own radar, giving them an element of surprise. STRIC also allowed ground controllers to read simple aircraft status, and let pilots trade simple messages through the ground network. Other useful upgrades added multiple-target tracking to the PS-46A radar, and a automatic gunsight for the Oerlikon cannon that allowed it to be used in collision-course, as opposed to simple tail-chase, attacks.

In the late 1990s, a major upgrade program was implemented to convert surviving JA 37s to the "JA 37D" standard. Updates included:

The JA 37D upgrade program was initiated in 1992, with the conversions beginning in the late 1990s. It is unclear how many JaktViggens were converted.

* The Swedes really like to get their money's worth out of their aircraft, and when the Flygvapnet's J 32E Lansen electronic warfare (EW) machines were phased out in 1997, a decision was made to update ten of the fourteen surviving Sk 37s to the "Sk 37E Stoer (Jammer) Viggen" EW configuration. This was actually a fairly substantial upgrade, including:

Work on the first of the ten "Erik" conversions began in late 1997, with an initial conversion flying in early 1998 and the last conversion performed in 2000. There was some thought to given the Sk 37Es the same two-tone gray color scheme as the JA 37, but though one Erik was painted in this scheme the decision was made that the old splinter camouflage scheme was fine.

The Stoer Viggen's primary mission is EW training, acting as an "electronic aggressor" for Swedish forces in training exercises. It can be fitted with laser reflector pods on the outer wing pylons for scoring purposes. The Sk 37E is capable of being operated as an operational platform, but as a dedicated jammer aircraft tends to be more useful for offense than defense, that aspect of the Erik is downplayed.

* In the 21st century, the SAAB 39 rapidly displaced the Viggen from front-line service, but how long it takes for the sun to go down on it completely remains to be seen. About 100 Viggens had been scrapped by 2000, and the type is currently expected to be retired by 2006, but as mentioned the Swedes really like to get their money's worth out of their aircraft, and the Viggen's predecessors had long service lives. The Viggen was an excellent machine when it first flew and it may remain useful, in one role or another, for some time to come.



* The series of combat aircraft built by SAAB seem impressive enough at first sight. What makes them even more impressive is the realization that Sweden's entire population is about that of a major metropolis, in a country about the size of Germany and Hungary combined. As one author put it, imagine the mayor of New York City or Tokyo or London announcing that the city government was going to fund development and production of a combat aircraft. It puts the ambition of the effort into proper perspective.

One of the interesting observations about the Viggen was that despite the fact that it uses as much Swedish content as possible, it still uses an American engine (at least at the core), and carries American and British designed missiles. The Swedes are clearly serious about their neutrality, but during the Cold War it was never exactly a case of sitting precisely on the fence, since in practice NATO was not the threat Swedish defense planners spent most of their time worrying about. There are rumors that there was always quite a bit of intelligence-sharing between Sweden and NATO, but it was kept a tight secret.

* Sources include:

Some comments were obtained from an online article by Swedish aviation enthusiast Urban Fredriksson.

* Revision history:

   v1.0.0 / 01 mar 04 / gvg
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