Saab J 21R
The Saab J 21R was Sweden's first jet aircraft: a jet-powered development of the piston-engined Saab 21, created by rebuilding the twin-boom pusher fighter around a de Havilland Goblin turbojet. First flown on 10 March 1947, it was, with the Soviet Yakovlev Yak-15, one of only two fighters successfully converted from piston to jet power. Sixty-four were built, but the type disappointed as a fighter and served mainly as the A 21R attack aircraft before retirement in the 1950s; no original example survives.
Why It Mattered
The Saab J 21R was Sweden's first jet aircraft, and the first jet type produced by Saab. It was not a new design: Saab rebuilt its wartime twin-boom pusher fighter, the J 21, around a British jet engine. The Swedish Air Force had decided in the autumn of 1945 to gain experience of jet propulsion by converting some of its J 21s. Wikipedia counts the 21R, along with the Soviet Yakovlev Yak-15, as one of only two jet fighters successfully converted from a piston-powered aircraft. The R in the name stood for reaktion, the Swedish term of the day for jet propulsion.
Design Notes
The conversion kept the J 21's central nacelle and twin booms, but a single de Havilland Goblin turbojet, British-sourced, replaced the piston engine and propeller. It was no simple engine swap: over 50 per cent of the airframe, including the tailplane and wing, was changed. The tailplane was raised to clear the jet exhaust, and the wing-root intakes were moved to the sides of the rear fuselage. Fuel capacity grew significantly, with added tanks in the wing centre section and at the wingtips. Air brakes were fitted as an extra flap on the outer wing, and the ejection seat inherited from the J 21 was improved for use at higher speeds. The nose kept its concentrated armament of one 20 mm cannon and four 13.2 mm guns; the attack version, the A 21R, could carry rockets under the centre section or a belly gun pod, nicknamed paddan — "the toad" — holding eight 8 mm machine guns.
Operational History
The first prototype, a converted J 21, made its first flight on 10 March 1947, with Åke Sundén as pilot. The flight test programme's results were largely satisfactory, and a production run of 124 aircraft, including four prototypes, was planned. The first aircraft were delivered to F 10, the Scania Wing at Ängelholm, in August 1949. As a fighter the type disappointed: at altitude on interception work it could exceed its wing's Mach limit and become nose-heavy, vibrating and hard to control. Production was therefore cut back to 64 aircraft, and it was concluded that all of them would be attack aircraft instead. The first series, the J 21RA, numbered 34 aircraft including the four prototypes, with British-built Goblin II engines; the second, the J 21RB, numbered 30, with Swedish-built Goblin III engines. After about a year, F 10 replaced its jets with J 28B Vampires, and the 21Rs moved to F 7, where they flew as A 21R attack aircraft until they were scrapped in the autumn of 1954. The first series, redesignated A 21RA in 1951, was retired in 1953. Ten aircraft ended their service at F 17 as trainers for future Saab 32 pilots, remaining in use until the spring of 1957.
Afterlife
No original 21R survived after the type was taken out of service, and none had been set aside for museum display. In the late 1990s, volunteer aviation historians rebuilt one of the three surviving piston-engined J 21s into a 21R. The airframe they used had stood on display for many years at Tekniska museet in Stockholm. The rebuilt aircraft now stands at Flygvapenmuseum, the Swedish Air Force Museum in Linköping. The only 21R a visitor can see is therefore this rebuild: an original jet airframe does not exist, so the display aircraft is a piston-engined J 21 in jet form.