The Saab 21R was a Swedish fighter/attack aircraft developed and produced by Saab.
It was a jet-powered development of the piston-engine SAAB 21 and was the first jet aircraft to be produced by Saab.
Along with the Soviet Yakovlev Yak-15, the 21R was one of only two jet fighters to have been successfully converted from piston-powered aircraft.
Sweden was under threat during the Second World War and ordered SAAB to develop an advanced fighter.
The result was an unorthodox twin-boom pusher, with a low wing, tricycle landing gear, and a heavy forward-firing armament.
Several options were then explored to improve its performance, leading to a jet-powered version.
During 1947, SAAB began converting the piston-engined J 21s to jet propulsion, which required extensive modifications.
124 aircraft were planned; however, this 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.
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 as 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 (toad) gun pod could be mounted under the wing centre section instead of the rockets.
The paddan pod contained eight 8 mm (0.31 in) ksp m/22 machine guns with 800 rounds of ammunition per gun.
The fire control system allowed all installed guns and all the rockets or the gun pod 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.
Variants
J 21RA / A 21RA
First production series, powered by British-built engines, 34 built in 1950, retired in 1953.
A 21RB
Second production series, powered by Swedish-built engines, 30 built between 1950 and 1952, retired in 1956.
Specifications
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 take-off 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
&
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 runs
650 m (2,133 ft)
Armament
Guns
1 × 20 mm (0.79 in) akan m/45 with 140 rounds in the nose
4 x 12.7 mm (0.50 in) akan m/39A, 2 in the nose with 350 rpg and two in the wings with 325 rpg
Belly maximum 700 kg (1,543 lb)
Vapenkapsel paddan (toad) gun pod with 8 x 8 mm (0.31 in) Browning M1919/ksp m/22 machine guns with 800 rounds per gun
Or
10 x 8 cm (3.1 in) Armour Piercing pansarraket RP-3 m/46 rockets
Or
14.5 cm (5.7 in) High-explosive Anti-Tank pansarsprängraket m/49A & B rockets
Or
10 x 15 cm (5.9 in) High Explosive sprängraket RP-3 m/46 rockets
Or
15 cm (5.9 in) High Explosive sprängraket Bofors m/51A & B rockets
Or
5 x 18 cm (7.1 in) Semi-Armour-Piercing halvpansarraket m/49A & B rockets
Wingtips
2 x drop tanks which could be used as incendiary bombs and were tested with napalm.
