SAAB 21

SAAB

Industry	Aerospace, defense
Founded	1937 in Trollhättan, Sweden
Headquarters	Trollhättan , Sweden
Products	Aircraft, including the SAAB 21 fighter and attack aircraft

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The SAAB 21 represents a Swedish single-seat low-wing monoplane developed by SAAB as both a fighter and an attack aircraft. Its distinctive design features a twin-boom fuselage combined with a pusher engine configuration, which gives it a unique silhouette.

Development commenced at SAAB following the Swedish Air Force's decision to significantly expand its capabilities in anticipation of possible involvement in the Second World War. The design featured a monoplane with twin booms, powered by a solitary Daimler-Benz DB 605B engine mounted at the rear of the central fuselage pod, driving a pusher propeller. This layout enabled armament to be concentrated in the nose while offering the pilot enhanced forward visibility. To ensure pilot safety during ejection, an ejection seat was incorporated to allow escape without risk of striking the propeller.

The SAAB 21 took to the skies for its inaugural flight on 30 July 1943, and by 1 December 1945, the initial J 21A-1 models entered operational service. This was soon succeeded by the upgraded J 21A-2, which carried heavier weaponry, as well as the A 21A-3 variant designed for fighter-bomber roles.

With jet propulsion rapidly surpassing piston engines in performance, SAAB adapted the existing model in 1947 by installing a British de Havilland Goblin jet engine, resulting in the SAAB 21R variant. Alongside the Soviet Yakovlev Yak-15, this aircraft was among the very few jet fighters converted successfully from piston-engine designs.

After less than a decade in service, the SAAB 21 was phased out during the mid-1950s, replaced by advanced aircraft such as the similarly configured de Havilland Vampire and the Saab 29 Tunnan.

Background

During the late 1930s, SAAB conducted various design explorations for a new fighter aircraft. Many concepts incorporated the British Bristol Taurus radial engine and included several unconventional features for that era. One notable design involved a monoplane with a twin-boom structure and a pusher engine located behind the pilot within a central nacelle. This innovative configuration offered multiple benefits: it allowed most of the armament to be placed in the nose, enhanced pilot visibility, and simplified maintenance procedures. Although this promising concept was finalized, it remained inactive until renewed defense priorities in 1941 increased its urgency.

At the onset of the Second World War, Sweden's leadership grew concerned about preserving their neutrality amid threats from European powers. As an emergency response, between 1939 and 1941, the Swedish Air Force undertook significant rearmament efforts that included acquiring foreign aircraft and developing indigenous modern designs. However, due to wartime restrictions, few belligerent nations were willing to supply fighters to neutral Sweden, and domestic production capacity was insufficient until approximately 1943. Consequently, Sweden procured outdated Italian Fiat CR.42 biplanes as an interim solution—aircraft that were largely ineffective against contemporary monoplane fighters. In response to these challenges, SAAB began addressing potential production issues related to their proposed fighter design.

Design

File:SAABA21A-3Soderhamn.jpg

SAAB A21A-3 exhibited at Söderhamn /F15 Aviation Museum, Söderhamn, Sweden

To achieve a minimum top speed of 480 km/h (300 mph), the SAAB J 21 required a robust powerplant. Initially, the American Pratt & Whitney R-1830 Twin Wasp radial engine was chosen to replace the Taurus engine. Nevertheless, Svenska Flygmotor (Volvo Aero) was also tasked with developing an alternative to the Twin Wasp. Due to pressing time constraints, options were confined to engines already licensed for production. Consequently, a domestically manufactured variant of Germany’s new 1,100 kW (1,500 hp) Daimler-Benz DB 605B inline engine was selected. However, extensive refinement and modifications by Swedish engineers were necessary to prepare the DB 605B for operational deployment owing to its developmental immaturity.

File:J-21-Intro.jpg

Artist’s rendering of a J 21 in flight

The SAAB 21 featured an unconventional design as a twin-boom, low-wing fighter with a pusher configuration, equipped with tricycle landing gear and substantial forward-firing weaponry. Its design integrated several contemporary innovations, including an ejection seat for pilot safety. The pusher layout later facilitated straightforward conversion to jet propulsion. Advantages of this configuration included an unobstructed forward pilot view and concentration of armament in the nose section. However, a significant challenge was ensuring safe emergency egress, as the pilot risked being drawn into the propeller blades during bailout attempts. Various solutions were considered, such as using explosive charges to jettison either the propeller or engine before escape. Ultimately, an ejection seat developed by Swedish defense company Bofors was adopted concurrently with the fighter’s development. The J 21 became one of the world’s earliest operational aircraft equipped with an ejection seat.

The wing structure utilized a SAAB-designed laminar airfoil. Since the main landing gear could not be housed within the wings when retracted, dedicated wells were incorporated into the tail booms behind the rear wing spar. To minimize aerodynamic drag, engine coolers and air ducts were positioned within the wing section between the fuselage and tail booms, and integral fuel tanks were installed.

Initially, armament comprised one nose-mounted 20 mm (0.79 in) Hispano-Suiza Akan m/41A cannon alongside four 13.2 mm (0.52 in) Akan m/39A autocannons—two mounted in each wing and two in the nose. On the A-2 variant, the 20 mm (0.79 in) guns were replaced by belt-fed 20 mm (0.79 in) Bofors Akan m/45 cannons. The J 21A-3 (later redesignated A 21A) was capable of carrying rockets and bombs for ground attack roles. Later in its service life, the 13.2 mm (0.52 in) autocannons were re-barreled to fire American 12.7 mm (0.50 in) ammunition for economic reasons. While this enhanced firing performance, it relegated the Saab 21 primarily to ground attack missions due to rapid advancements in fighter aircraft design.

Three prototypes were constructed; only two were intended for flight testing while the third served as a static test airframe for stress analysis. The maiden flight took place on 30 July 1943 when SAAB test pilot Claes Smith flew the first J 21 prototype. During takeoff, excessive flap deployment hampered acceleration and climb rate, causing the aircraft to collide with a fence and sustain undercarriage damage; nonetheless, Smith managed to land safely.

Further development

Main article: Saab 21R

Throughout 1945, multiple avenues were investigated to enhance the performance of the 21. Early in the year, efforts focused on developing a variant equipped with a 1,500 kW (2,000 hp) Rolls-Royce Griffon engine, aiming for a top speed of approximately 669 km/h (416 mph). Concurrently, projects like the Saab 27, also intended to utilize the Griffon powerplant, were underway; however, all piston-engine upgrade initiatives were discontinued by year’s end. Alongside these endeavors, SAAB and various Swedish firms explored the potential of jet propulsion. Initial concepts, labeled RX 1 and RX 2, featured twin-boom configurations reminiscent of the 21. The Swedish Air Force’s growing interest in jet fighters by late 1945 prompted SAAB to adapt the J 21 for jet propulsion.

In response to a request from the Swedish Air Force, existing J 21 airframes were converted to jet power in 1947 and reclassified as J 21R. This conversion necessitated alterations to more than half of the airframe, including modifications to the tailplane and wings. The piston-powered DB 605B engine was replaced with a single British de Havilland Goblin turbojet engine. This marked the aircraft’s entry into service as Sweden’s inaugural jet fighter.

Operational history

The initial delivery of the first production series, consisting of 54 units of the J 21A-1, took place on 1 December 1945. These aircraft were manufactured at SAAB’s primary facility in Trollhättan, with deliveries continuing until 5 December 1946. Subsequently, two production batches totaling 124 units of the J 21A-2 were supplied. A third contract produced two batches amounting to 119 units of the A21A-3 fighter-bomber model, finalizing production of all piston-engine variants. In total, SAAB constructed 298 J 21As before ceasing production in 1948.

In December 1945, the Svea Wing (F 8) became the first operational unit to receive the J 21. Over the following year, additional Swedish Air Force squadrons such as Göta Wing (F 9) also began integrating this type. Nevertheless, within less than four years, several squadrons transitioned to newer jet fighters offering significantly higher speeds, including models like the de Havilland Vampire. Although initially intended primarily for air defence missions, the J 21 was predominantly employed in a light bomber capacity during its service life and remained exclusively operated by the Swedish Air Force.

Concerns regarding its unconventional design led officials to question its combat effectiveness. Consequently, the Swedish Air Board commissioned SAAB to investigate a design featuring a nose-mounted engine, resulting in the J 23. This model retained the DB 605B engine from the J 21 but adopted a more conventional layout akin to that of the North American P-51 Mustang. However, its anticipated performance was lower, which motivated further refinement of the J 21 instead. Interest in jet propulsion grew within the Swedish Air Force from mid-1945 onward, prompting SAAB to explore modifications allowing installation of a jet engine in place of the piston unit. While production of piston-powered variants continued through to 1948, conversion to jet-powered models commenced on existing airframes. Following these upgrades, retirement of piston-driven J 21A aircraft began in earnest by 1954.

Variants

File:Saab J 21A.jpg

Saab A 21A-3

J 21A-1

The initial production batch of the fighter model. A total of 54 units were manufactured between 1945 and 1946, with retirement occurring by 1949.

J 21A-2

The second and third production runs of the fighter variant, each consisting of 62 aircraft built from 1946 to 1947. These planes featured enhanced avionics and were equipped with a Swedish 20 mm (0.79 in) cannon. They were phased out between 1953 and 1954.

J 21A-3 (later renamed A 21A)

This attack variant encompassed the first and second production series, with 66 aircraft produced between 1947 and 1949. It was essentially a J 21A-2 fitted with a bomb sight and mounting points for bombs and rockets. Subsequently, it was upgraded to utilize two RATO boosters.

J 21B

A proposed model featuring three 20 mm (0.79 in) guns in the nose, radar installed in the starboard boom, refined aerodynamics, a bubble canopy akin to the P-51 Mustang, and a more powerful engine. Initial engine candidates included the Daimler-Benz DB 605E or the Rolls-Royce Griffon. However, due to post-war limitations—Germany's inability to supply the DB-605E and Britain's incomplete Griffon development—the decision was made to adapt the Swedish DB-605B engine to deliver 1700 hp. Although a full-scale mockup was constructed, the project was cancelled by late 1945 as jet technology advanced and focus shifted to the Saab 29 program. No units were produced.

Operators

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• Swedish Air Force

Surviving aircraft

Three examples remain preserved for permanent exhibition:

• J 21A-3, serial number 21286, restored as an A 21R, displayed at the Swedish Air Force Museum.
• J 21A-3, serial number 21311, exhibited at F 15 Söderhamn Flygmuseum.
• J 21A-3, serial number 21364, also held at the Swedish Air Force Museum.

Specifications (J 21A)

File:Saab J-21.svg

Saab J 21 three-view illustration

References

Bibliography

• Billing, Peter. "A Fork-Tailed Swede." Air Enthusiast No. 22, August–November 1983.
• Cattaneo, Gianni. The Fiat CR.42 (Aircraft in Profile number 170). Leatherhead, Surrey, UK: Profile Publications Ltd., 1967. No ISBN.
• Erichs, Rolph, Kai Hammerich, Gudmund Rapp et al. The Saab-Scania Story. Stockholm: Streiffert & Co., 1988. ISBN 91-7886-014-8.
• This Happens in the Swedish Air Force (brochure). Stockholm: Information Department of the Air Staff, Flygstabens informationsavdelning, Swedish Air Force, 1983. No ISBN.
• Widfeldt, Bo. The Saab 21 A & R (Aircraft in Profile number 138). Leatherhead, Surrey, UK: Profile Publications, 1966. No ISBN.
• Wilson, Stewart. Combat Aircraft since 1945. Fyshwick, AU: Aerospace Publications, 2000. ISBN 1-875671-50-1.