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A unique twin-boom pusher design, the futuristic-looking Saab J21 first flew in 1943.

The Saab J21

By E.R. Johnson
2/12/2018 • Aviation History Magazine

Saab’s J21 was among the few aircraft produced in both piston engine and turbojet versions.

To most Americans, the name SAAB brings to mind a line of modish and distinctively Swedish auto­mobiles. It might come as a surprise that Saab is actually an acronym for Svenska Aeroplan Aktie Bolaget, or “Swedish Airplane Company.” Although the company has been in the car business since 1947, it got its start in aviation 10 years earlier and remains one of Europe’s leading manufacturers of military and commercial aircraft and related systems. Saab also began as a state-owned industry but is now a publicly held corporation with about 40 percent of its ownership outside of Sweden.

The circumstances that led to the development of the unorthodox J21 (J for Jakt, or fighter), the first fighter designed by Saab to be built and flown, are connected to the origins of the company itself. Despite being traditionally neutral, the Swedish government by the mid-1930s was becoming increasingly alarmed by the rising political and military tensions in Europe, and in particular, the growing power of nearby Nazi Germany. Though Sweden was a rela­tively advanced industrial power at the time, it possessed practically no domestic industrial base for manufacturing aircraft. In fact, its small air force, the Flygvapnet, was entirely equipped with aircraft imported from Great Britain, Germany, the United States and Italy. In the event of a general European war between Germany and the Allied nations, Sweden was understandably concerned that it would be cut off from its traditional trading partners. Against that backdrop, in April 1937 Svenska Aeroplan Aktie Bolaget came to be.

Saab’s earliest aircraft manufacturing experience was gained by license-producing foreign aircraft designs (e.g., Junkers Ju-86K bombers [B3s], Northrop 8A-1/A-17 attack/ dive-bombers [B5s] and North American NA16/BT-9 trainers [Sk14s]). With the help of American consultants, the Saab engineering team led by Frid Wanstrom was by 1939 already developing completely original designs for a dive bomber, the B17, a twin-engine light bomber, the B18, and two fighters, the J19 and J21. The J19 was a conventional all-metal monoplane designed for a radial engine, but the J21 had an unusual twin-boom pusher configuration. After the outbreak of hostilities between Germany and the Allies in September 1939, however, the hoped-for supply of aircraft engines from the United States and Britain dried up, and Saab was forced to place both of its fighter projects on hold.

In 1940 Svenska Flygmotor (Swedish Aero Motors) began tooling up to produce a copy of the Pratt & Whitney R-1830 (a nonlicensed-built example also known as the STW, or “Swedish Twin Wasp”), but initial production was already earmarked for Saab’s B17 dive bomber, which was in the final design stages, and possibly after that, the J22 fighter, which was being designed and planned by FFVS (an aircraft factory run by the Flygvapnet). The STW-powered J22 had been conceived as a conventional monoplane design, but unlike Saab’s earlier J19, was designed to be constructed primarily of wood, since it was feared that strategic metals would be in short supply. In 1941 the company was advised that an arrangement was being reached with the German government to procure and eventually license-build Daimler-Benz in-line engines (i.e., the DB 601, 603 and 605), and that future aircraft should incorporate those power plants. Saab at that point revived the idea of the twin-boom J21, but added a second proposal for a more conventional fighter designated the J23, both to be powered by Daimler-Benz in-line engines. The so-called trading relationship with the Nazis was essentially a one-way proposition under which the Swedes were expected to supply steel and allow troop movements across their soil in return for not being absorbed into the Reich. Only a small number of German-made engines actually made it to Sweden, the bulk coming later as license-built versions produced by Svenska Flygmotor.

The exact chain of events that led to the decision to develop the J21 isn’t entirely clear, but sometime in the fall of 1941 the Swedish government apparently told the company to discontinue work on the twin-boom J21 and to proceed with the J23. Then, in December 1941, the government completely reversed itself. A possible explanation might be that the J23 and the FFVS’s J22 were too similar to be placed in production at the same time. In any case, detailed design work began in earnest on the J21 and continued throughout 1942 and into 1943. Frid Wanstrom had originally proposed the unusual twin-boom pusher layout because he believed it would offer a better gun platform. Planned armament would consist of a 20mm cannon and two 13.2mm (51.97-caliber) machine guns mounted in the nose, plus a 13.2mm machine gun mounted in each boom (comparable firepower to the Lockheed P-38). On the other hand, the centerline pusher arrangement would obviously present a grave hazard in the event the pilot was forced to bail out. A parallel proj­ect at Saab was already testing the ejection seat, meaning to make it a standard feature on all of its combat aircraft. A compressed-air system was tried first but was later replaced by two Bofors gunpowder cartridges, which, in ground testing, propelled a specially designed seat straight upward.

The final design of the J21, as it emerged in 1943, was an all-metal, low-wing monoplane featuring tricycle landing gear and a laminar flow wing with approximately 15 degrees sweepback in the panels outboard the booms, and vertical fins located at the end of each boom, connected by the horizontal tailplane. The plane’s general dimensions included a wingspan of 38 feet and a length of 24 feet 2 inches, and loaded weight totaled 11,466 pounds. Three landing gear legs of unusual length gave the pusher propeller adequate ground clearance. The J21 was powered by a German-made DB 605B engine rated at 1,475 hp, driving a fully controllable-pitch, three-bladed pusher propeller. The coolant radiators were buried in the wing roots, giving the J21 a fairly clean overall appearance.

The first prototype J21 flew on July 30, 1943. Flight trials demonstrated a maximum speed of 403 mph, a cruising speed of 304 mph, a service ceiling of 33,450 feet and a range of 1,920 miles. Though 45 mph faster than the FFVS J22, the J21 was still 30 to 50 mph slower than the Focke Wulf Fw-190D, Supermarine Spitfire Mk.XIV and North American P-51B, which all flew about the same time, and was not nearly as maneuverable. Nonetheless, the Flygvapnet—no doubt hard pressed for new fighters—ordered 484 of the type into production as the J21A-1, with deliveries starting in June 1945.

Even as J21A-1s began reaching operational units, the Flygvapnet expressed disappointment with the plane’s performance as an air-to-air fighter, and began replacing it in the immediate postwar period with North American P-51Ds. By the end of 1949, the type had been completely withdrawn from frontline fighter units. Yet, as early as 1945, Saab had started developing a follow-on version designed for an air-to-ground attack role. The resulting J21A-2s and A21A-3s retained the fighter’s gun armament but were specifically modified to carry bombs and rockets and use RATO (rocket-assisted takeoff) to improve takeoff performance. In 1945 Saab proposed an improved J21B with heavier armament, radar and a more powerful DB 605E engine, but the project never went beyond the proposal stage. Later still, Saab suggested yet another version with a 2,050-hp Rolls-Royce Griffon engine, but by this time the Flygvapnet was seeking new designs with jet propulsion. When the last A21A-3 was delivered in 1949, a total of 298 of all versions had been built. J21A-2s and A21A-3s continued to serve with Flygvapnet attack units until 1954.

Saab brought the J21 into the jet age by replacing its piston engine with a de Havilland turbojet. While the fighter gave Saab design experience, the J21 continued to come up short. (©Saab AG)
Saab brought the J21 into the jet age by replacing its piston engine with a de Havilland turbojet. While the fighter gave Saab design experience, the J21 continued to come up short. (©Saab AG)

As World War II drew to a close, Sweden found itself years behind Britain and the United States in the development of jet propulsion. In an effort to gain experience quickly, Saab investigated the feasibility of wedding turbojet power to a J21 airframe and purchased British-made de Havilland Goblin engines, rated at 3,100 pounds static thrust. Three incomplete J21A-1s were taken from Saab’s assembly lines to undergo the conversion, which turned out to be more complex than originally expected: The entire fuselage section aft of the cockpit was replaced in order to house the larger diameter turbojet; the empennage was redesigned to move the horizontal stabilizer above the thrust line; and the stance of the landing gear was modified to compensate for the change in thrust angle.

The first Goblin II-powered prototype, designated the J21R, flew on March 10, 1947. Flight testing revealed a maximum speed of 496 mph, a cruising speed of 378 mph, a service ceiling of 39,350 feet and a range of 558 miles. It was ordered into production as the A21RA, to be used in a ground attack role, with the last examples delivered to the Flygvapnet in 1952. Production versions were adapted to carry a belly-mounted pod containing an additional eight 13.2mm machine guns. The last 30 produced as the A21RB were powered by the Swedish-built Goblin III, which boosted them to 3,300 pounds static thrust and a top speed of 520 mph. The greatest drawback of the aircraft was range: When fully loaded, the A21R’s combat radius was only 118 miles. All A21Rs were withdrawn from service by the end of 1956.

If the A21R had fallen short of success, it gave Saab’s engineers a wealth of experience. Even before the last A 21R was retired, Saab was rapidly moving up the ladder as one of the world’s leading designers of military jet aircraft. The sweptwing J29 Tunnan, which flew in 1948, began equipping Flygvapnet fighter units in 1951; the two-seat, all-weather J32 Lansen flew in 1952 and served in fighter-interceptor units until the mid-1970s; and the strikingly innovative double-delta J35 Draken, when it flew in 1955, was perhaps the most advanced second-genera­tion super­sonic fighter aircraft in the world.

Saab was developing a controversially large, expensive multirole fighter when it began partially privatizing and merged with Aktie Bolaget Scania-Vabis in 1970. In 1972 the JA37 Viggen (Thunderbolt) fighter entered service, subsequently joined by attack, conversion trainer and other variants. The 1980s saw the development of a single-engine multirole successor to the Viggen, the JAS 39 Gripen (Griffin), a close-coupled delta canard designed to satisfy a Swedish military that, as one parliamentarian put it, “wants a Mercedes, but can only afford a Volkswagen.” Passing its flight tests in December 1996, the Gripen offers a fourth-generation jet fighter that can change directly to the attack and reconnaissance role by means of its upgradable computer software. What is now called the Saab Aircraft Division of Saab-Scania has gone a long way since its failed direct transi­tion from the piston to the jet age, the J21. 

This feature appeared in the November 2004 issue of Aviation History. Subscribe here!

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