The SAAB 21 is a Swedish single-seat low-wing monoplane fighter and attack aircraft designed and manufactured by SAAB. Its twin boom fuselage with a pusher engine gave the aircraft an unusual appearance.

Work began at SAAB following a Swedish Air Force decision to embark on a major expansion programme 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 at the rear of the fuselage nacelle, driving a pusher propeller. This arrangement allowed guns to be carried in the aircraft's nose while providing the pilot with good visibility. An ejection seat was adopted to enable the pilot to bail out without hitting the propeller.

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 heavier armament, and the A 21A-3 fighter-bomber.

With jet-powered aircraft rapidly overtaking piston-powered aircraft, in 1947 SAAB produced a conversion of the 21 using the British de Havilland Goblin jet engine, the resulting airframe being designated the SAAB 21R. Along with the Soviet Yakovlev Yak-15, the SAAB 21 was one of only two jet fighters to be successfully converted from piston power to jet power.
Design and development
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 defense 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 rebarreled to fire American 12.7 mm (0.50 in) ammunition due to economics. These 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 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 takeoff, 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.
Operational history
The first example from the first batch of 54 of the first production variant, the J 21A-1 was delivered to the Swedish Air Force on 1 December 1945. Construction was at SAAB's main plant in Trollhättan and deliveries of this model ran until 5 December 1946, when deliveries of two batches totalling 124 of the J 21A-2 began. A third order, in two batches totalling 119 of the A21A-3 fighter-bomber completed production of the piston-engine variants.A total of 298 J 21As were constructed prior to the production line ending in 1948.

During December 1945, the Svea Wing F8 became the first fighter unit to receive the J 21. During the following year, other units of the Swedish Air Force, such as Göta Wing F9, also began to receive the type. However, within less than four years, some squadrons were already being re-equipped with a new generation of jet fighters capable of far greater speed, such as the de Havilland Vampire.Despite the original intention for the type to be principally used in air defence roles, in service, the J 21 was utilized mainly in the light bomber role. The type was used only by the Swedish Air Force.

Officials doubted its effectiveness due to its unconventional design. In response, the Swedish Air Board requested that SAAB study a development with the engine in the nose as the J 23. This aircraft used the J 21's DB 605B engine and had a more traditional appearance, similar to the North American P-51 Mustang, but its projected performance was reduced, which became a key factor in improving the J 21 instead. The Swedish Air Force became interested in jet propulsion and from 1945, SAAB began studying modifications of the airframe to accommodate a jet engine in place of its piston engine. Production of the piston-engine version continued until 1948 while examples of the new jet engine version began being converted on the line. As a result of the conversions, the piston-engine powered J 21A began being retired in 1954.
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 (66 aircraft each built between 1947 and 1949). 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.
J 21B
Planned version armed with three 20 mm (0.79 in) nose guns, radar in the starboard boom, improved aerodynamics, P-51 style bubble canopy and a stronger engine. Suggested engines were at first the Daimler-Benz DB 605E or the Rolls-Royce Griffon engine[7] but due to the end of the war Germany could not deliver the DB-605E and the British had not yet finished the development of the Griffon engine. It was then decided to use the Swedish DB-605B engine modified to 1700 hp. A full scale mockup was built but due to the jet age the project was scrapped at the end of 1945 due to the Saab 29 project. None built.







Specifications (J 21A)
General characteristics
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 takeoff 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 V-12 inverted liquid-cooled piston engine, 1,085 kW (1,455 hp) built by SFA
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

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)
Landing speed: 145 km/h (90 mph; 78 kn)
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
4x 15 cm (5.9 in) sprängraket m/46 High-explosive semi-armour-piercing (SAP) RP-3 rocket

Outer wing mount

8x 8 cm (3.1 in) pansarraket m/46 Armour-piercing RP-3 rocket
8x 14.5 cm (5.7 in) Bofors pansarsprängraket m/49A & B High explosive anti-tank (HEAT) rocket
8x 15 cm (5.9 in) sprängraket m/46 High-explosive semi-armour-piercing RP-3 rocket or Bofors sprängraket m/51A & B high-explosive rocket
2x 18 cm (7.1 in) Bofors halvpansarraket m/49A & B Armour-piercing high-explosive anti-ship rocket (later used against general targets.)

Belly

1x 250 kg (550 lb) minbomb m/37 general-purpose bomb
1x 250 kg (550 lb) minbomb m/40 general-purpose bomb
1x 250 kg (550 lb) minbomb m/50 general-purpose bomb
1x 500 kg (1,100 lb) minbomb m/41 general-purpose bomb
1x 600 kg (1,300 lb) minbomb m/50 general-purpose bomb

Wingtips

2x vingspetstank drop tanks which could be armed in flight as incendiary bombs, and were tested with napalm.

Saab 21R
During 1947, SAAB began converting the piston-engined J 21s to jet propulsion, which required extensive modifications. One hundred twenty-four aircraft were planned, however this number 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 and the Saab 29 Tunnan.
Background
During the early stages of the Second World War, Sweden was concerned that its neutrality and its independence could be threatened by one of the belligerent 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.

In 1941, in response to Swedish Air Force requirements, the Swedish aviation company SAAB commenced work on a radical new fighter. The company envisioned an unorthodox twin-boom pusher configuration fighter aircraft, featuring a low wing, a tricycle landing gear, and with a heavy forward-firing armament. It was powered by a licensed version of the new German Daimler-Benz DB 605B 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. 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 2,000 hp (1,500 kW) Rolls-Royce Griffon engine which would have raised the top speed to 416 mph (669 km/h). Other projects, such as the SAAB 27, were intended to use the Griffon as well, but by the end of the year, all work on the 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. Two early studies, RX 1 and RX 2, had been studied, both of which being twin-boom aircraft similar to the 21. 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. 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 already had the Gloster Meteor and de Havilland Vampire 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 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 turbojet 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.

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, and a modified wing leading edge. Air brakes were added as an additional flap on the outer wing's trailing edge. The ejection seat, which was a relatively new innovation, received various improvements that enabled it to eject at higher speeds.

The A 21R attack version could now carry 14.5 and 18 cm (5.7 and 7.1 in) ground attack rockets installed underneath the wing centre section. An alternative external paddan ("the toad") gunpod could be mounted under the wing centre section instead of the rockets. The gunpod contained eight 8 mm (0.31 in) ksp m/22 machine guns with 800 rounds of ammunition per two magazines (400 per magazine) feeding each gun with 100 rounds. 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 1,360 kg (3,000 lb) 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 1,500 kg (3,300 lb) Goblin 3 or RM1A engine.
Operational history
The first prototype Saab 21R first flew on 10 March 1947, almost 2 years after the Second World War. 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 – First production series, intended as fighters, powered by British-built de Havilland Goblin II engines, 34 built in 1950 (including four prototypes)
A 21RA – J 21RA redesignated as attackers in 1951 and modified to carry external attack ordnance, retired in 1953
J 21RB – Second production series, intended as fighters, powered by Swedish-built de Havilland Goblin III engines, 30 built between 1950 and 1952
A 21RB – J 21RB redesignated as attackers in 1951 and modified to carry external attack ordnance, retired in 1956




Specifications (Saab 21RA)
General characteristics
Crew: 1
Length: 10.55 m (34 ft 7 in) including 20mm cannon
Wingspan: 11.37 m (37 ft 4 in)
Height: 2.9 m (9 ft 6 in)
Wing area: 22.1 m2 (238 sq ft)
Airfoil: Saab laminar airfoil
Empty weight: 3,090 kg (6,812 lb)
Gross weight: 4,340 kg (9,568 lb)
Max takeoff weight: 5,615 kg (12,379 lb)
Fuel capacity: 1,690 L (450 US gal; 370 imp gal) total maximum; 590 L (160 US gal; 130 imp gal) in fuselage tank, 300 L (79 US gal; 66 imp gal) in wing tanks and 800 L (210 US gal; 180 imp gal) in optional tip tanks
Powerplant: 1 × de Havilland Goblin II (Svenska Flygmotor RM1) centrifugal-flow turbojet engine, 13.24 kN (2,980 lbf) thrust J 21RA / A 21RA
Performance
Maximum speed: 800 km/h (500 mph, 430 kn)
Cruise speed: 610 km/h (380 mph, 330 kn)
Minimum control speed: 155 km/h (96 mph, 84 kn)
Range: 450 km (280 mi, 240 nmi) internal tanks only
Ferry range: 900 km (560 mi, 490 nmi) with drop tanks
Service ceiling: 12,000 m (39,000 ft)
Rate of climb: 17 m/s (3,300 ft/min)
Take-off run: 650 m (2,133 ft)
Armament
Guns
1 × 20 mm automatkanon m/45 [sv] (20 mm akan m/45) – 20 mm (0.79 in) gun in the nose with 140 rounds
4 × 13,2 mm automatkanon m/45A (13,2 mm akan m/39A) – 13.2 mm (0.52 in) guns, two in the nose with 350 rounds per gun and two in the wings with 325 rounds per gun (early on retrofitted with 12,7 mm barrels for 12.7×99 ammunition)
Belly maximum 700 kg (1,543 lb); loadouts:
1 × gunpod – tillsatslavett "paddan" (add-on mount "the toad") – with 8 × 8 mm kulspruta m/22 (8 mm ksp m/22) – 8 mm (0.31 in) machine guns with 100 rounds per gun
1 × rocket mount for 10 × "light" rockets or 5 × "heavy" rockets:
10 × 8 cm pansarraket m/46C (8 cm prak m/46C) – 8 cm (3.1 in) 25 lb AP Mk II RP-3 Armour Piercing rockets
10 × 14,5 cm pansarsprängraket m/49B (14,5 cm psrak m/49B) – 14.5 cm (5.7 in) high-explosive anti-tank rockets
10 × 15 cm sprängraket m/51 (15 cm srak m/51), m/51A, m/51B – 15 cm (5.9 in) high explosive rockets
5 × 18 cm halvpansarraket m/49B (18 cm hprak m/49B) – 18 cm (7.1 in) semi armour-piercing rockets
Wingtips
2 × vingspetstank (drop tanks) which could be used as incendiary bombs and were tested with napalm
(Text from Wikki)