Saab 21R

Svenska Aeroplan AB (SAAB)

Company type	Aircraft manufacturer
Industry	Aerospace
Founded	1937
Headquarters	Linköping , Sweden
Products	Aircraft, including Saab 21R fighter and attack aircraft

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The Saab 21R represents a jet-powered iteration of the Swedish fighter and attack platform originally developed by Svenska Aeroplan AB (SAAB). As a successor to the piston-driven SAAB 21, it marked Saab's initial venture into jet propulsion. The suffix "R" derives from the Swedish term reaktion, which relates to reaktionsdrift (jet propulsion) or reaktionsmotor (jet engine). Together with the Soviet Yakovlev Yak-15, the 21R stands out as one of the rare jet fighters successfully adapted from a piston-engine design.

During the Second World War, Sweden faced potential threats that prompted SAAB to design an advanced combat aircraft. The outcome was a distinctive twin-boom pusher configuration featuring low-mounted wings, tricycle undercarriage, and substantial forward-firing weaponry. To enhance its capabilities, various modifications were examined, ultimately leading to a jet-powered variant.

In 1947, SAAB initiated the conversion of piston-engine J 21s into jet-powered versions, necessitating significant structural changes. Although plans initially called for 124 units, production was scaled back to 64 aircraft primarily fulfilling fighter-bomber roles. The Saab 21R served through the late 1940s into the early 1950s before being superseded by purpose-built jet fighters such as the de Havilland Vampire and the Saab 29 Tunnan.

Background

At the onset of the Second World War, Sweden's leadership was apprehensive about maintaining neutrality and sovereignty amid escalating global conflict. Consequently, comprehensive measures were implemented to bolster military readiness and serve as a deterrent against possible invasions. Between 1939 and 1941, the Swedish Air Force embarked on an extensive expansion program that involved acquiring numerous foreign and domestically produced fighter aircraft. Due to limited international production capacity and reluctance from other countries to supply advanced fighters to a small neutral nation, Sweden recognized that its indigenous manufacturing capabilities would not meet demands until approximately 1943. This reality compelled Sweden to develop competitive homegrown designs.

In response to these requirements in 1941, SAAB began designing a groundbreaking new fighter tailored for Swedish needs. The concept featured an unconventional twin-boom layout with a pusher propeller arrangement, low wings, tricycle landing gear, and heavy forward armament. Propulsion came from a licensed version of the German Daimler-Benz DB 605B inline piston engine, produced domestically by Svenska Flygmotor AB (Volvo Aero). The Swedish Air Force assigned this model the designation J 21, with its prototype taking flight on 30 July 1943.

By 1945, efforts were underway to enhance performance further. Various proposals included replacing the DB 605B engine with more powerful alternatives; one such plan involved fitting a 2,000 hp (1,500 kW) Rolls-Royce Griffon engine capable of pushing speeds up to 416 mph (669 km/h). Other projects like the SAAB 27 also intended to utilize this engine. However, by year’s end, development of new piston-engine variants was discontinued.

Alongside these piston-engine developments, SAAB and other Swedish firms explored emerging jet propulsion technology. Early studies named RX 1 and RX 2 examined twin-boom configurations akin to the J 21. Recognizing growing interest within the Swedish Air Force for jet-powered fighters by late 1945, SAAB initiated efforts to convert the J 21A model to incorporate jet engines. This move was partly motivated by awareness that other countries such as the United Kingdom already fielded operational jets like the Gloster Meteor and de Havilland Vampire.

Though no specific engine had been selected during late 1945 design phases, an opportunity arose to license-produce the "Goblin 2" turbojet in Sweden. This powerplant became Sweden’s first operational jet engine under the designation RM1 within their air force. On 10 March 1947, Saab’s inaugural jet aircraft—a modified J 21 equipped with a single Goblin 2 engine—completed its maiden flight. Test results from this program were predominantly positive.

Conversion programme

In 1947, SAAB commenced the process of transforming piston-engine J 21 aircraft into jet-powered models, which involved substantial modifications to each plane. More than half of the original structure, including the tailplane and wings, underwent alterations. Each aircraft was fitted with a single British-made de Havilland Goblin turbojet engine, replacing the DB 605B piston engine and propeller assembly. This adaptation marked the Swedish Air Force's initial adoption of jet technology. Due to the extensive nature of these modifications, the updated aircraft were reclassified as J 21R.

To accommodate the Goblin turbojet, which differed significantly from the DB 605B engine in both design and operational demands, numerous adjustments were necessary. The horizontal stabilizer was elevated to avoid interference with the jet exhaust, necessitating a redesigned tail section. Fuel capacity was greatly expanded with additional tanks installed in the wing center section and wingtip areas to meet the turbojet's increased consumption. Aerodynamic enhancements included a reshaped curved windscreen and alterations to the wing leading edge. Furthermore, air brakes were integrated as supplementary flaps along the trailing edge of the outer wings. The ejection seat, an emerging safety feature at that time, was upgraded to function effectively at higher ejection speeds.

The attack variant, known as the A 21R, was equipped to carry 14.5 and 18 cm (5.7 and 7.1 in) ground-attack rockets mounted beneath the wing center section. Alternatively, a detachable external paddan ("the toad") gunpod could be installed in place of the rockets under the same wing section. This gunpod housed eight 8 mm (0.31 in) ksp m/22 machine guns, each supplied with 800 rounds divided into two magazines of 400 rounds apiece. Its fire control system enabled simultaneous discharge of all onboard armaments—guns and rockets or gunpod alike.

Initially, production was slated for 124 units, including four prototypes. After operational evaluation by F 10 wing personnel, it was decided that all aircraft would serve in an attack role, leading to a reduction in production numbers to 64 units. Of these, 34 fighters were designated J 21RA, powered by the 1,360 kg (3,000 lb) Goblin 2 engine—referred to domestically as RM1. These were subsequently redesignated as A 21RA. The remaining 30 aircraft carried the designation A 21RB and were equipped with Swedish-manufactured 1,500 kg (3,300 lb) Goblin 3 engines known as RM1A.

Operational history

The Saab 21R prototype took its maiden flight on 10 March 1947, nearly two years after the conclusion of World War II. Service entry occurred in August 1950 with F 10 squadron. Although originally intended for fighter duties, the emergence of the Saab J 29—which flew by October 1948—prompted a reduction in orders to 60 units. Eventually, all J 21Rs were reassigned exclusively as attack aircraft, bearing either the A 21RA or A 21RB designation depending on their engine configuration.

Variants

• J 21RA – The initial production batch designed as fighters, equipped with British-made de Havilland Goblin II engines; 34 units produced in 1950, including four prototypes
  • A 21RA – In 1951, the J 21RA was reclassified as an attacker and adapted to carry external ordnance; withdrawn from service in 1953
• J 21RB – The second production series also intended for fighter roles, powered by Swedish-manufactured de Havilland Goblin III engines; 30 built between 1950 and 1952
  • A 21RB – The J 21RB was redesignated as an attacker in 1951 and modified to accommodate external weaponry; retired in 1956

Operators

Template:SWE

• Swedish Air Force
  • F7 Såtenäs, operated A21RA/B from 1950 to 1954
  • F10 Ängelholm, flew J21RA between 1949 and 1951
  • F17 Kallinge, utilized A21RA/B from 1954 to 1956

Surviving aircraft

File:Saab 21R (J 21R) Linköping 05.08.03.jpg

J 21A-3 restored to represent an A 21R at the Swedish Air Force Museum

No original aircraft remain following their withdrawal from active duty. Nevertheless, during the 1990s, enthusiasts restored a derelict Saab 21 airframe into a 21R variant for exhibition at the Swedish Air Force Museum.

Specifications (Saab 21RA)

File:Saab J-21R.svg

Illustration of Saab J-21R

References

Bibliography

• Andersson, Hans G. Saab Aircraft since 1937, First Edition. London: Putnam, 1989. ISBN 0-85177-831-3.
• Billing, Peter. "Saab's Jet Debutant". Air Enthusiast, Issue 23, December 1983 – March 1984. Template:ISSN.
• Cattaneo, Gianni. The Fiat CR.42 (Aircraft in Profile No. 170). Leatherhead, Surrey, UK: Profile Publications, 1967. No ISBN.
• Erichs, Rolph; Kai Hammerich; Gudmund Rapp et al. The Saab-Scania Story. Stockholm: Streiffert & Co., 1988. ISBN 91-7886-014-8.
• Sharpe, Michael. Attack and Interceptor Jets. London: Friedman/Fairfax Publishers, 1999. ISBN 1-58663-301-5.
• Widfeldt, Bo. The Saab 21 A & R (Aircraft in Profile No. 138). Leatherhead, Surrey, UK: Profile Publications, 1966.

External links

• J.21R in the Air – a 1948 article from Flight covering the flight characteristics of the SAAB J.21R