The Saab 21R was a Swedish fighter/ attack aircraft developed and produced by

Svenska Aeroplan AB Saab AB (originally , later just SAAB and Saab Group) is a Swedish aerospace and defence company, founded in 1937. Headquartered in Stockholm, the development and the manufacturing is undertaken in Linköping. Saab produced automobiles from 194 ...

(SAAB). It was a

jet Jet, Jets, or The Jet(s) may refer to: Aerospace * Jet aircraft, an aircraft propelled by jet engines ** Jet airliner ** Jet engine ** Jet fuel * Jet Airways, an Indian airline * Wind Jet (ICAO: JET), an Italian airline * Journey to Enceladus a ...

-powered development of the

piston-engine A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common feat ...

d SAAB 21 and was the first jet aircraft to be produced by Saab. The R-suffix stands for ''reaktion'' (reaction), referencing ''reaktionsdrift'' (jet power) or ''reaktionsmotor'' (jet engine). Along with the Soviet Yakovlev Yak-15, the 21R was one of only two jet fighters to have been successfully converted from piston-powered aircraft. Sweden was under threat during the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

, and ordered SAAB to develop an advanced fighter. The result was an unorthodox twin-boom pusher, with a low wing,

tricycle landing gear Tricycle gear is a type of aircraft undercarriage, or ''landing gear'', arranged in a tricycle fashion. The tricycle arrangement has a single nose wheel in the front, and two or more main wheels slightly aft of the center of gravity. Tricycle ...

, and a heavy forward-firing armament. Several options were then explored to improve its performance, leading to a jet-powered version. During 1947, SAAB began converting the piston-engined J 21s to jet propulsion, which required extensive modifications. 124 aircraft were planned, however this was reduced to 64 and they were instead mainly used as fighter-bombers. It saw service in the late 1940s and early 1950s before it was replaced by a new generation of fighters designed from the onset with jet propulsion, such as the

de Havilland Vampire The de Havilland Vampire is a British jet fighter which was developed and manufactured by the de Havilland, de Havilland Aircraft Company. It was the second jet fighter to be operated by the Royal Air Force, RAF, after the Gloster Meteor, and ...

and the

Saab 29 Tunnan The Saab 29 ''Tunnan'', colloquially ''Flygande tunnan'' or just ''Tunnan'' ( en, "The flying barrel", "The barrel"),. is a Swedish fighter that was designed and manufactured by Saab in the late 1940s. It was the second turbojet-powered comb ...

Design and development

Background

During the early stages of the

, Sweden was concerned that its neutrality and its independence could be threatened by one of the

belligerent A belligerent is an individual, group, country, or other entity that acts in a hostile manner, such as engaging in combat. The term comes from the Latin ''bellum gerere'' ("to wage war"). Unlike the use of ''belligerent'' as an adjective meaning ...

powers, and so enacted a series of emergency measures to increase its military's preparedness and deterrence value against potential aggressors. Between 1939 and 1941, the Swedish Air Force committed itself to a major expansion programme, which included the procurement of large numbers of foreign and locally developed fighters. As a consequence of the conflict, few nations possessed available production capacity or a willingness to supply modern fighters to Sweden, being a relatively small neutral country. While Sweden's own domestic production capability would be insufficient until at least 1943, Sweden would have to develop its own first-rate designs to meet its needs.Cattaneo 1967, pp. 10-12. In 1941, in response to Swedish Air Force requirements, the Swedish aviation company SAAB commenced work on a radical new fighter.Widfeldt 1966, p. 3. The company envisioned an unorthodox twin-boom

pusher configuration In an aircraft with a pusher configuration (as opposed to a tractor configuration), the propeller(s) are mounted behind their respective engine(s). Since a pusher propeller is mounted behind the engine, the drive shaft is in compression in no ...

fighter aircraft, featuring a low wing, a

, and with a heavy forward-firing armament.Widfeldt 1966, p. 4. It was powered by a licensed version of the new German

Daimler-Benz DB 605 The Daimler-Benz DB 605 is a German aircraft engine built during World War II. Developed from the DB 601, the DB 605 was used from 1942 to 1945 in the Messerschmitt Bf 109 fighter, and the Bf 110 and Me 210C heavy fighters. The DB 610, a p ...

B inline piston engine, which was refined and built by Svenska Flygmotor AB. The Swedish Air Force designated it the J 21, and a prototype was flown on 30 July 1943. By 1945, options were being explored to improve its performance.Widfeldt 1966, p. 7. Many of these involved the substitution of the 605B engine with a more powerful powerplant. During the first half of the year, a variant was planned with a

Rolls-Royce Griffon The Rolls-Royce Griffon is a British 37-litre (2,240 cubic inch, cu in) Engine displacement, capacity, 60-degree V12 engine, V-12, liquid-cooled Aircraft engine, aero engine designed and built by Rolls-Royce Limited. In keeping with compan ...

engine which would have raised the top speed to . Other projects, such as the ''SAAB 27'', were intended to use the Griffon as well, but the end of the year, all work on piston-engine design was abandoned. In parallel with the piston-engine studies, SAAB and other Swedish companies had been evaluating a new type of engine - the

jet engine A jet engine is a type of reaction engine discharging a fast-moving jet (fluid), jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include Rocket engine, rocket, Pump-jet, water jet, and ...

. Two early studies, ''RX 1'' and ''RX 2'', had been studied, both of which being twin-boom aircraft similar to the 21.Widfeldt 1966, pp. 7-8. Recognising the Swedish Air Force's enthusiasm for a jet-powered aircraft for late 1945, SAAB decided to produce a version of the 21 harnessing

jet propulsion Jet propulsion is the propulsion of an object in one direction, produced by ejecting a jet of fluid in the opposite direction. By Newton's third law, the moving body is propelled in the opposite direction to the jet. Reaction engines operating on ...

.Widfeldt 1966, p. 8. A design study was initiated for converting the J 21A to jet power. It was recognized that Sweden would otherwise be left behind while nations such as the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

already had the

Gloster Meteor The Gloster Meteor was the first British jet fighter and the Allies' only jet aircraft to engage in combat operations during the Second World War. The Meteor's development was heavily reliant on its ground-breaking turbojet engines, pioneere ...

and

in production. The design study was proceeding in late 1945 despite no specific engine having been chosen, but the opportunity came up to purchase a license to manufacture the " Goblin 2"

turbojet The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, ...

engine in Sweden. This was the first jet engine to be used by the Swedish Air Force, who designated it as the RM1. The first flight of Saab's first jet aircraft, a converted J 21, was on 10 March 1947, powered with a single Goblin 2 engine. The results of the flight test programme were largely satisfactory.

Conversion programme

During 1947, SAAB began to receive piston-engined J 21s to convert them to jet propulsion. This requiring each aircraft to be extensively modified. In all, in over 50 per cent of the airframe, tailplane and wing was changed and, each of them was equipped with a single British-sourced

de Havilland Goblin The de Havilland Goblin, originally designated as the Halford H-1, is an early turbojet engine designed by Frank Halford and built by de Havilland. The Goblin was the second British jet engine to fly, after Whittle's Power Jets W.1, and the ...

engine, which replaced the DB 605B and propeller unit. It became the Swedish Air Force's first jet aircraft. In light of the extensive changes, rebuilt 21s were redesignated J 21R.Erichs et al. 1988, p. 23. Many changes were made to accommodate the Goblin engine, which had considerably different properties and requirements than the DB 605B engine. The horizontal stabilizer had to be raised to clear the jet engine's exhaust, which required that the tail section be redesigned. Additionally, to feed the thirsty turbojet, the fuel capacity was increased significantly with additional tanks in the wing centre section and wingtip tanks. The fighter's aerodynamics were improved during the rebuild, with a curved

windscreen The windshield (North American English) or windscreen (Commonwealth English) of an aircraft, car, bus, motorbike, truck, train, boat or streetcar is the front window, which provides visibility while protecting occupants from the elements. ...

, and a modified wing

leading edge The leading edge of an airfoil surface such as a wing is its foremost edge and is therefore the part which first meets the oncoming air.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 305. Aviation Supplies & Academics, ...

. Air brakes were added as an additional flap on the outer wing's

trailing edge The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 199 ...

. The

ejection seat In aircraft, an ejection seat or ejector seat is a system designed to rescue the pilot or other crew of an aircraft (usually military) in an emergency. In most designs, the seat is propelled out of the aircraft by an explosive charge or rocke ...

, which was a relatively new innovation, received various improvements that enabled it to eject as higher speeds. The A 21R attack version could now carry ground attack rockets installed underneath the wing centre section. An alternative external ''paddan'' (toad) gun pod could be mounted under the wing centre section instead of the rockets. The ''paddan'' pod contained eight ksp m/22 machine guns with 800 rounds of ammunition per gun. The fire control system allowed all installed guns and all the rockets or the gunpod to be fired at once. A production run of 124 aircraft was planned, including four prototypes. When F 10 wing had gained experience with the type, it was concluded that all of the aircraft were to be attack aircraft and the production batch was reduced to 64 aircraft. Of these, 34 fighters were designated J 21RA, powered by the Goblin 2 engine, or ''RM1'' in Sweden. These were later re-designated as A 21RA. The remaining 30 were designated A 21RB. These were powered by a Swedish-built Goblin 3 or ''RM1A'' engine.

Operational history

The first prototype Saab 21R first flew on 10 March 1947,Billing 1983, p. 22. almost 2 years after the

. The aircraft first entered service with F 10 in August 1950. Although the type was intended as a fighter aircraft, the Saab J 29 was flying by October 1948, so the order was reduced to 60, and all 21Rs were eventually converted to attack aircraft as A 21RA or A 21RB depending on the engine type.

Variants

;J 21RA / A 21RA :First production series, powered by British-built engines, 34 built in 1950 (including four prototypes), retired in 1953.Widfeldt 1966, p. 9. ;A 21RB :Second production series, powered by Swedish-built engines, 30 built between 1950 and 1952, retired in 1956.

Operators

; * Swedish Air Force ** F7 Såtenäs, 1950–54: A21RA/B ** F10 Ängelholm, 1949–51: J21RA ** F17 Kallinge, 1954–56: A21RA/B

Surviving aircraft

No original examples survived after being taken out of service, however, in the 1990s a group of volunteers took a surviving derelict Saab 21 airframe and rebuilt it into a 21R for display at the

Swedish Air Force Museum The Swedish Air Force Museum ( sv, Flygvapenmuseum) is located at Malmen Airbase in Malmslätt, just outside Linköping, Sweden. Malmen is where Baron Carl Cederström, nicknamed the "Flyer Baron" founded his flying school in 1912. Malmen Airb ...

Specifications (Saab 21RA)

References

Bibliography

* Andersson, Hans G. ''Saab Aircraft since 1937'', 1st ed. London: Putnam, 1989. . * Billing, Peter. "Saab's Jet Debutant". ''

Air Enthusiast ''Air Enthusiast'' was a British, bi-monthly, aviation magazine, published by the Key Publishing group. Initially begun in 1974 as ''Air Enthusiast Quarterly'', the magazine was conceived as a historical adjunct to ''Air International ' ...

'', No. 23, December 1983 – March 1984. . * Cattaneo, Gianni. ''The Fiat CR.42 (Aircraft in Profile number 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. . * * * Sharpe, Michael. ''Attack and Interceptor Jets''. London: Friedman/Fairfax Publishers, 1999. . * Widfeldt, Bo. ''The Saab 21 A & R (Aircraft in Profile number 138)''. Leatherhead, Surrey, UK: Profile Publications, 1966.

External links

''J.21R in the Air''
- a 1948 ''

Flight Flight or flying is the process by which an object moves through a space without contacting any planetary surface, either within an atmosphere (i.e. air flight or aviation) or through the vacuum of outer space (i.e. spaceflight). This can b ...

'' article on flying the SAAB J.21R {{Swedish military aircraft designations 21R 1940s Swedish fighter aircraft Twin-boom aircraft Single-engined jet aircraft Aircraft first flown in 1947 Low-wing aircraft