Flightline: 179 - SAAB J 21/21R
Development of the SAAB 21, a low-wing pusher design, began in late 1939 over fears by the Swedish Air Force over being drawn into WW2.
The Svenska flygvapnet, or Swedish Air Force, was formed on 1 July 1926 after the aircraft units of the Army and Navy were spun-off and merged. The inter-war flygvapnet fighter force was composed of a hodgepodge of WWI-era biplanes from France, the UK and Germany, and the gathering war clouds over Europe made the Swedes seek a more modern fighter plane, preferably of domestic manufacture. It was estimated that Sweden's production capacity was unable to meet the needs of the air force until 1943 at best, and the county was forced to buy a brace of obsolete Fiat Cr. 42 biplanes as an interim measure.
SAAB J 21
SAAB (Svenska Aeroplan AB), founded in 1937, had been working on design studies during the late 1930s, many of which were of unconventional configuration, and most incorporated the Bristol Taurus radial engine. SAAB's engineers hit upon the idea of mounting the engine behind the pilot, driving a pusher prop with the tail and elevator mounted on twin booms extending back from the wing. This configuration would allow the plane's weapons to be mounted in the nose and provide the pilot with an unobstructed view. It was also felt that the low wing and tricycle undercarriage would provide easy servicing of the plane. During the design phase, the Taurus engine was rejected as being underpowered and the P&W R-1830 Twin Wasp was proposed in its place. The Swedish government wanted a domestic alternative, and Svenska Flygmotor was tapped to produce a licensed version of the Daimler-Benz DB 605B inverted V-12, which produced 1,455hp.
Orthograph of the SAAB 21. | Illustration: aviastar
The new plane, designated the SAAB J 21, was 10.45m long, with a wingspan of 11.6m and was 3.97m tall. The J 21 was light, weighing just 3,250kg empty and having a max TO weight of 5,200kg. The license-built BD 605B, coupled to a three-blade constant-speed prop, gave the plane a maximum speed of 650kmh and a cruise speed of 495kmh, while the 510l internal fuel load provided a ferry range of 1,190km and a combat range of 750km. The pusher configuration allowed a heavy load of forward-firing weapons, with a 20mm akan m/41A and two 13.2mm akan m/39A cannons in the nose and two more m/39A in the wings. The 21 was fitted with tricycle landing gear, with the main gear retracting into the booms as the SAAB-designed laminar flow wings were too thin. Another innovation of the aircraft was an ejection seat for the pilot, designed in tandem with the J 21, by Bofors, which allowed the pilot to clear the prop and tail in case of an emergency. The engine's coolers and intakes were housed in the central section of the wing in order to reduce drag.
One of the J 21 prototypes, later fitted for operational service. | Photo: SAAB
Two flying prototypes and one static test airframe were built, with the maiden flight of the J 21 occurring on 20 July 1943. The test flight, with SAAB test pilot Claes Smith at the controls, got off to an inauspicious start when Smith used too much flap on takeoff, resulting in the undercarriage striking a fence at the end of the runway. The pilot was able to land without further incident, and the damage was repaired. Delivery of the production J 21A-1 aircraft began on 1 December 1945, with 54 aircraft delivered by 5 December 1946, when production shifted to the more advanced J 21A-2 model. Both the A-1 and A-2 differed from the prototypes in having provisions for two drop tanks of 160l each, and the A-2 differed in having upgraded avionics as well as the m/41A cannon replaced by a Bofors belt-fed akan m/45, also in 20mm. A third model, the J 21A-3 (later redesignated A 21A), was based on the A-2, but was configured for attack missions, and was fitted with a bomb-aiming system as well as pylons on the inner and outer wings, as well as a belly mount, which could accommodate 700kg of bombs or rockets. Drop tanks could be added to the wingtips, and incendiary bombs and napalm tanks were tested, but not used operationally. The A 21A was later fitted with mounts for two RATO bottles to improve takeoffs when carrying heavy loads. Production of the attack model ran from 1947 to 1949, and totaled 66 aircraft.
A J 21A-3 in flight, some time in the early 1950s. | Photo: SAAB
Two products from SAAB. | Photo: SAAB
A fourth model, the J 21B, was initially proposed in 1947, with the 605B engine replaced by either a more powerful 605E or Rolls-Royce Griffon motor. Changes also included a pressurized cockpit with a bubble canopy, improved aerodynamics, an air-intercept radar in the starboard boom, and a change to three 20mm cannon in the nose. Development of jet engines, particularly for SAAB's own J 29 fighter, saw the J 21B canceled in 1945, with only a mockup completed. The post-war shift to jet aircraft also saw the J21As having a short service life, with the A-1s being retired in 1949, and the A-2 and A-3 following in the early 1950s. By 23 July 1954, all of the J 21As were gone from the Swedish Air Force. Three examples remain as museum exhibits, all A-3s, with one having been rebuilt as an A 21R.
An A 21A ground attack version of the J 21, on display at the Flyvapenmuseum in Malmen, Sweden. | Photo: Alan Wilson
SAAB J 21R
Almost before the J 21 was accepted for service, plans were underway to increase the performance of the aircraft. Aside from the stillborn J 21B, two studies by SAAB, RX 1 and RX 2, which were twin boom aircraft resembling the J 21 but with a jet engine replacing the 605B. Neither program had a specific engine in mind, but an opportunity to acquire a license for the de Havilland Goblin 2 turbojet in 1945 provided the impetus to begin plans to convert a J 21 to accept the new jet. The modified aircraft, SAAB's first jet-powered plane, took its maiden flight on 10 March 1947, and the test program was satisfactory enough that the Swedish Air Force ordered 124 existing J 21s to be converted to jet power, with the resulting aircraft designated J 21R; 4 examples were built as prototypes.
Orthograph of the J 21R. | Illustration: Kaboldy
The process of converting the A models to R spec was rather intensive, with more than 50% of the fuselage, wing and tail being modified. In particular, the tail was modified to allow the horizontal stabilizer to be raised several feet in order to clear the jet's exhaust. The lack of a propeller meant that the aircraft was overall shorter than the As however, being just under three meters tall versus the almost four meters of the A model. The changes resulted in the R model being somewhat longer than its predecessor, but the wingspan was a third of a meter shorter. A new, curved windscreen was added, as were air brakes, an additional flap on either side, and a modified leading edge. The thirst of the Goblin engine, designated the RM1 in Swedish service, meant the addition of extra fuel tanks in the center wing as well as tip tanks as seen on the A-2 and -3 models, bringing the 21R to a max TO weight of 5,615kg. The main armament remained one 20mm m/45 and four 12.7mm m/39A, with one hard point on the belly allowing carriage of 700kg of stores, including various 10, 14.5, 15 or 18cm rockets, or a paddan ("toad") gunpod, armed with eight 8mm Browning M1919 machine guns, along with 800 rounds per gun.
A J 21R in flight, showing the modifications needed to incorporate the Goblin engine. | Photo: SAAB
Conversion of newly-retired J 21A-1s began in 1947, with the first 30 receiving British-built engines. The type entered service in 1950, but SAAB had also introduced the J 29 Tunnan two years prior, and the 21R was relegated to attack duties, being redesignated the A 21RA. With the shift to attack missions, the order of 124 was cut to just 64, with the second run of A 21RB aircraft receiving Swedish-built RM1A engines, which provided 1,500kg of thrust vs the 1,360kg of the RM1. The A 21R had a very short service life, with the RA model being retired in 1953, and the RB being withdrawn in 1956. So swiftly was the 21R withdrawn that no examples were preserved. In the 1990s a surviving, but unrestored, A 21A-3 was restored and modified by a group of volunteers to represent an A 21R, which is now on display at the Swedish Air Force Museum.
The 21R as displayed in 2005, with a load of rockets. | Photo: Wassen
And in 2019, now armed with a paddan gun pod. | Photo: BugWarp