Saab 37 Viggen – Nordic Thunder

An AJS 37 Viggen seen preserved at Madrid-Cuatro Vientos, Spain in 2018.

Hammer of the Gods 

First flown in February of 1967 and entering service with the Swedish air force in 1971, the Saab 37 Viggen cut such a distinctive shape in the sky with its delta wing and canard fore-plane arrangement that for nearly four decades it was an unmistakable symbol of Saab’s skill as an aircraft manufacturer and Sweden’s ability to protect its sovereignty in a visible and credible manner.

Saab’s model 35 Draken, which had preceded the Viggen, caught the aviation world’s attention and left no doubt that Saab were capable of competing with larger players in the field and were certainly not afraid of pushing boundaries. The Viggen further underlined these facts and showed that Saab were not about to rest on their laurels.

The name Viggen, generally translated simply as “Thunderbolt”, was taken from Norse mythology and is quite specifically connected to the thunder created by the god Thor’s hammer. A fitting name for a truly thunderous and imposing machine.

Let’s spend some time with one of Saab’s most recognizable products:

An AJS 37 Viggen seen preserved at Madrid-Cuatro Vientos, Spain in 2018.

A Revolutionary Replacement 

The catalyst for creating the Viggen was the need for a multi role aircraft which could replace Saab’s model 32 Lansen in the attack role and, eventually, the model 35 Draken in the fighter role. Studies to determine the form of what would become the Viggen started in the early 1950s with the final design approved in 1962 and construction of the prototype started in 1964.

The service specifications for the new aircraft were very demanding ones specific to Sweden’s unique defensive doctrines at the time. This included the ability to operate from remote locations, away from established bases, using sections of highway as airstrips. Additionally, the aircraft had to be easily serviced by a minimal ground crew team that could be largely composed of conscripts and reservists with minimal training.

The Viggen also had to function as part of Sweden’s unique Stril 60 defensive network, be able to be refueled and rearmed in a maximum of ten minutes between missions, have mach 1 performance at low altitude and Mach 2 performance at high altitude.

A closer view of the Viggen’s canard fore-plane.

Saab settled on the distinctive delta wing and canard design to best address the flying performance stipulated by the air force. The canards made high speed flight at low altitudes smoother as well as guiding the airflow over the main wings in such a way as to increase lift, improve low speed stability and shorten take off and landing distances. The Viggen was the worlds first serial produced aircraft to feature canards as a standard design aspect.

Another first associated with the Viggen was to be found internally; it was the first European aircraft to feature a computer with integrated circuits as standard equipment. It was decided very early on to make the Viggen a single seat aircraft; The computer Saab developed to do away with a human navigator and weapons operator in the Viggen, known as the CK37, was a much more capable and maintainable system than the bulky analog flight computers of the day and proved that complex fast jets could be operated by a pilot alone.

Other distinctive aspects of the Viggen’s design included a hinge at the base of the tail fin to allow it to be folded down for storage in the many hangars the Swedish military had carved into mountainsides around the country and a thrust deflection system which could redirect the engine exhaust forward to significantly shorten landing length.

An AJSF 37 variant preserved at the Kbely Air Museum in Prague, Czech Republic in 2014.

Foreign Flavours

Many sources state that Saab benefited from access to American data and resources when developing the Viggen; however, many of those same sources are not particularly clear on exactly what Saab was provided with from America.

What is for certain is that there was some exchange of information between Saab and American companies, Texas Instruments and Fairchild, while developing the CK37 computer. Both American companies were developing integrated circuit computers in the late 50s for the same goal as Saab had; a computer that would allow a single pilot to operate a complex jet aircraft.

As with their previous aircraft, Saab looked abroad for an engine to power the Viggen. They favoured the emerging turbofan engine technology to existing turbojets as it balanced the power of the turbojet with better fuel economy.

At first, Saab planned for the Pratt & Whitney TF30 as the Viggen’s power source but it would not be ready in time. Saab then looked to the Rolls Royce Medway from Great Britain; the Medway, however, was cancelled when the British aircraft it was intended to power was also cancelled.

The Pratt & Whitney JT8D engine, an airliner engine used in the Boeing 727 and Douglas DC-9 among others, was ultimately chosen for the Viggen and license built in Sweden as the RM8A and RM8B. The engine was married to a Swedish designed afterburner section and easily pushed the aircraft to the Mach 2 speeds required.

AJSF 37 preserved at Prague in 2014.

Worthy of note in regards to the RM8 engine is that many sources cite American imposed export restrictions on it as the reason the Viggen was not successful on the export market. However, this is something of an overstatement and oversimplification.

Several sources suggest that the export restrictions were the primary reason why the Viggen was not purchased by Belgium, Denmark, Norway or the Netherlands. All four countries gave consideration to the Viggen as a possible replacement for their Lockheed F-104 fleets in the early 1970s. However, the Viggen had the disadvantage of being an outsider in the competition for the new fighter in Europe as its competitors were all newer designs from NATO countries. As it was, by 1975, all four countries opted to purchase the General Dynamics F-16 from America. The trade restrictions on the RM8 engine were irrelevant to potential European buyers of the Viggen.

In the wake of the 1965 India-Pakistan War, both America and Great Britain placed arms embargoes on India. While Great Britain eventually lifted their embargo, America kept theirs in place and the RM8 was affected. When India went looking for a new strike fighter in the 1970s, the American embargo was still in force and effectively blockaded any serious considerations of India purchasing the Viggen. It is from this chapter in the Viggen’s life that the stories of trade restrictions upon it find their origins.

With or without the trade restrictions, the Viggen never stood a chance in India. Those who were promoting it were politicians and business types out for personal gain while the air force themselves were adamant that the new aircraft be of two engined design. Ultimately, the Anglo-French Sepecat Jaguar was selected as India’s new strike fighter in the late 1970s.

The Swedish Air Force Historic Flight’s AJS 37 Viggen seen at Ostrava, Czech Republic in 2014.

The Viggen in Service

Though the Viggen never served any nation other than Sweden, it was a very respected machine outside the borders of its homeland throughout its nearly 40 year service career. From standpoints of serviceability, mission readiness and deployability; the Viggen was considered one of the most capable and potent combat jets in Western Europe for many years.

Built in five major variants, the Viggen served Sweden well in a variety of roles.

The first of the Viggens into service was the AJ 37, the strike fighter variant. From the same basic airframe, Saab also created the SH 37 which was optimized for maritime strike and reconnaissance. The non radar equiped SF 37 reconnaissance version was also developed from the AJ 37.

The SH 37 retained the AJ 37’s radar and thus its ability to carry the full range of both guided and unguided weapons as well as a variety of camera and electronic gear in pods carried externally. By contrast, the SF 37 did away with the radar in favour of a camera and sensor package in the nose; consequently, the SF 37 did not possess the ability to carry and operate much of the AJ 37’s arsenal beyond infrared guided air to air missiles for self defense and unguided rocket pods.

Through the years, the AJ, SH and SF variants were subject to upgrades including a particularly extensive electronics upgrade in the early 90s. Aircraft upgraded in that program were re-designated as AJS, AJSH and AJSF versions.

The AJ 37 airframe was also used to create the two seat SK 37 training aircraft. To make room for the second seat, the SK 37 had reduced internal fuel volume, electronics simplified and the radar removed. Late in the Viggen’s service career, ten SK 37s were refitted for electronic warfare training and designated SK 37E. The SK 37E was the last Viggen variant in active service when it was retired in 2007.

The late 1970s saw the development of the JA 37, the air to air specialist of the Viggen family. Created as an interceptor first and formost, the JA 37 differed in many key ways from the earlier Viggen versions.

The JA 37 had a slightly lengthened fuselage which contained very modern avionics to replace the CK37 computer at the heart of earlier versions; it also featured the much more powerful RM8B engine. The extra power of the RM8B helped to create much different handling qualities between the JA version and earlier ones.

The JA version also featured a trio of large multi-function display screens in the cockpit; while this feature became standard in combat jets through the 80s and 90s, it was certainly not a common feature at the time the JA 37 debuted.

As with earlier versions, the JA was subject to a variety of upgrading programs over the years that created the JA 37C, 37D and 37DI sub variants.

The Swedish Air Force Historic Flight’s AJS 37 landing at Ostrava in 2014

Thunder Echoes On

Retirement has been good to the Viggen. The distinctive and imposing shape that made it stand out among other aircraft during its active years was very helpful to the aircraft in ensuring that it would be in demand by museums. In fact, several Viggens were earmarked for specific museum collections even before they were retired.

Whether in Sweden or elsewhere in Europe, your chances of being able to visit a museum which possesses one of the 330 or so Viggens which were built is quite good.

As for flying examples of the Viggen, an AJS 37 and SK 37E are kept in airworthy condition by the Swedish Air Force Historic Flight and visit airshows around Europe during the airshow season.

Learning More

This is a link to a pdf document about the development of the CK37 computer. It’s a bit dry in places, but does make clear what a breakthrough the CK37 was.

This is a quite insightful interview with a former Viggen pilot.

This long out of print book by Robert F. Door is a great resource for information about the Viggen’s early development and service to the mid 1980s.