The SAAB 21 is a Swedish single-seat low-wing monoplane fighter and attack aircraft designed and manufactured by SAAB.
It used a relatively unorthodox twin boom fuselage with a pusher engine, giving the aircraft an unusual appearance.
Work began at SAAB following a Swedish Air Force decision to embark on a major expansion program in preparation for the possibility of being drawn into the Second World War.
The company designed a monoplane twin-boom aircraft, powered by a single Daimler-Benz DB 605B engine that was positioned to the rear of the fuselage nacelle, directly behind the pilot, that drove a pusher propeller.
This arrangement allowed guns to be carried in the aircraft’s nose while providing the pilot with good visibility.
To enable the pilot to bail out without hitting the propeller behind him, they adopted an ejection seat.
On 30 July 1943, the 21 performed its maiden flight and on 1 December 1945, the first examples of the J 21A-1 were introduced to service.
It was quickly followed by the improved J 21A-2, which featured a heavier armament, and the A 21A-3 fighter-bomber.
Due to Swedish Air Force interest in jet fighters, SAAB produced a conversion using the British de Havilland Goblin as the Saab 21R.
The 21 was replaced in the mid-1950s after less than 10 years of service by the similarly configured de Havilland Vampire and the Saab 29 Tunnan.
The SAAB J 21 needed a top speed of at least 480 km/h (300 mph), which required a powerful engine.
It was decided to substitute the Taurus engine for the American Pratt & Whitney R-1830 Twin Wasp radial engine.
However, Svenska Flygmotor was also asked to provide an alternative to the Twin Wasp.
Options were limited by the urgency involved, leaving a license-produced engine as the only option.
Accordingly, a locally built version of Germany’s new 1,100 kW (1,500 hp) Daimler-Benz DB 605B inline engine was selected, however, due to the DB 605B’s lack of maturity, a great deal of refinement and modification by Swedish engineers was required to ready it for operational use.
The SAAB 21 was an unorthodox twin-boom low wing pusher configuration fighter aircraft with a tricycle landing gear, and a heavy forward-firing armament.
Several recent innovations were incorporated into its design, including an ejection seat for the pilot while the pusher layout later allowed the type to be readily re-engined with a turbojet.
The advantages of a pusher design include an unobstructed forward view for the pilot, and the armament can be concentrated in the nose, however, a major drawback is difficulty in making an emergency exit as the pilot could get drawn into the propeller blades.
Many solutions were examined, such as jettisoning either the propeller or the engine via explosive charges prior to bailing out, before it was decided to adopt an ejection seat developed by Swedish defence firm Bofors, in parallel with the fighter.
The J 21 was one of the first operational aircraft in the world with an ejection seat.
The wing of the 21 was built around a SAAB-designed laminar airfoil.
As the wings could not readily accommodate the main landing gear when retracted, wells were provided in the tail booms, aft of the rear wing spar.
To reduce drag, coolers and ducts for the engine were located in the wing section between the fuselage and tail booms, and integral fuel tanks were fitted.
The armament initially consisted of one nose mounted 20 mm (0.79 in) Hispano-Suiza Akan m/41A and four 13.2 mm (0.52 in) Akan m/39AA autocannons, two in the wings, and two in the nose.
On the A-2 the 20 mm (0.79 in) guns were replaced with belt fed 20 mm (0.79 in) Bofors Akan m/45.
The J 21A-3 (later designated A 21A) could carry rockets and bombs.
Later in the Saab 21’s service life the 13.2 mm (0.52 in) autocannons were re-barreled to fire American 12.7 mm (0.50 in) ammunition due to economics.
This improved firing performance, but the Saab 21 was now only viable as a ground attack aircraft due to the rate of change in fighter design.
Three prototypes were completed of which only two of these were to be flyable, while the third was a static airframe for stress testing purposes.
On 30 July 1943, the first J 21 prototype conducted its maiden flight, flown by SAAB test pilot Claes Smith.
During the take-off, he used too much flap, impairing acceleration and climb.
This resulted in it hitting a fence and damaging the undercarriage, although he was able to land successfully afterwards.
Variants
J 21A-1
First production series of fighter version.
54 built between 1945 and 1946, retired in 1949.
J 21A-2
Second and third production series of fighter version (62 aircraft each built between 1946 and 1947).
Aircraft had better avionics and was armed with a Swedish 20 mm (0.79 in) gun.
Retired between 1953 and 1954.
J 21A-3 (later designated A 21A)
First and second production series of attack version.
Aircraft was a J 21A-2 equipped with a bomb aiming sight and had pylons for bombs and rockets.
It was later upgraded to be able to use two RATO rockets.
Specifications
Crew
1
Length
10.45 m (34 ft 3 in)
Wingspan
11.6 m (38 ft 1 in)
Height
3.97 m (13 ft 0 in)
Wing area
22.2 m2 (239 sq ft)
Airfoil
Saab laminar airfoil
Empty weight
3,250 kg (7,165 lb)
Gross weight
4,150 kg (9,149 lb)
Max take-off weight
5,200 kg (11,464 lb)
Fuel capacity
510 l (130 US gal; 110 imp gal) internal
2x 160 l (42 US gal; 35 imp gal) drop tanks J 21A-1 & J 21A-2
2x 400 l (110 US gal; 88 imp gal) drop tanks J(A) 21A-3
Powerplant
1 × Daimler-Benz DB 605B, built by SFA. V-12 inverted liquid-cooled piston engine, 1,085 kW (1,455 hp)
Propellers
3-bladed constant-speed pusher propeller
Performance
Maximum speed
650 km/h (400 mph, 350 kn) J 21A-1 / J 21A-2
560 km/h (350 mph; 300 kn) J(A) 21A-3
Cruise speed
495 km/h (308 mph, 267 kn) J 21A-1 / J 21A-2
425 km/h (264 mph; 229 kn) J(A) 21A-3
Landing speed
145 km/h (90 mph; 78 kn)
Range
750 km (470 mi, 400 nmi)
Ferry range
1,190 km (740 mi, 640 nmi) J 21A-1 / J 21A-2
1,650 km (1,030 mi; 890 nmi) J(A) 21A-3
Service ceiling
10,200 m (33,500 ft) J 21A-1 / J 21A-2
7,500 m (24,606 ft) J(A) 21A-3
Rate of climb
15 m/s (3,000 ft/min)
Armament
Guns
J 21A-1
1× 20 mm (0.79 in) akan m/41A with 60 rounds in the nose
2x 13.2 mm (0.52 in) akan m/39A with 350 rpg in the nose
2x 13.2 mm (0.52 in) akan m/39A with 325 rpg in the wings
J 21A-2 & A-3
1× 20 mm (0.79 in) akan m/45 with 140 rounds in the nose
2x 13.2 mm (0.52 in) akan m/39A with 350 rpg in the nose
2x 13.2 mm (0.52 in) akan m/39A with 325 rpg in the wings
J(A) 21A-3 700 kg (1,543 lb) maximum
Inner wing mount
(the inner wing mount was only used for rockets until the outer racks were developed)
4x 50 kg (110 lb) minbomb m/37 general-purpose bombs, or sprängbomb m/42 or m/47 fragmentation bombs or bombkapsel m/43 cluster bombs
4x 8 cm (3.1 in) pansarraket m/46 Armour-piercing RP-3 rocket
