The SAAB 29 Tunnan

v1.0.1 / 01 may 02 / greg goebel / public domain

* Svenska Aeroplan AB (SAAB) of Sweden became well-known in the postwar period for the design of a series of excellent fighters that had long and distinguished service careers. One of the earliest of these fighters was the SAAB J-29 "Tunnan (Barrel)", a portly aircraft that was surprisingly fast and agile. This document provides a short history of the Tunnan.

[1] ORIGINS

* The Swedes were thoroughly intimidated by the fall of Norway and Denmark to Hitler in the spring of 1940, as they knew their country could not withstand a German assault. This led to a high-priority effort to improve Sweden's defenses, with a strong emphasis on the development of modern combat aircraft.

By the end of the war, it was obvious to the engineers of the primary Swedish aviation company, Svenska Aeroplan AB (SAAB), that jet power was the way of the future for combat aircraft. However, Axis and Allied jet development efforts were largely secret, and the Swedes had little knowledge of the technology.

They worked hard to catch up. By the fall of 1945, they were able to get their hands on the British de Havilland "Goblin" centrifugal-flow turbojet engine, presently arranging to manufacture it under license. SAAB used the Goblin engine to provide the Flygvapnet (Swedish Air Force) with the first indigenous Swedish jet fighter by fitting the engine to the J-21 pusher-prop fighter, developed during the war. The first jet-propelled "J-21R" flew in 1947.

The J-21R was a step in the right direction, but it was still well behind the times. As an interim measure, until Swedish industry could provide up-to-date combat aircraft, the Flygvapnet obtained a quantity of de Havilland Vampire F.1 jet fighters, giving them the designation "J-28A". The first J-28A Vampires reached operational service in 1947.

* In the meantime, SAAB was working on advanced design studies for jet fighter aircraft, beginning with the "RX-1", which was roughly along the lines of the Vampire, and then the "R-101" or "Cigar", which was more along the lines of the Lockheed P-80 Shooting Star. SAAB engineers had no knowledge of the P-80 when they drew up the R-101 design, and when they found out about the Shooting Star, they realized they were several years behind the times and went back to the drawing board.

By October 1945, they had come up with a fighter design study built around the Goblin, featuring the engine stuffed into a fuselage with a straight-in intake in the nose and a straight-out exhaust in the rear, and the pilot perched above the engine under a sliding bubble canopy. The laminar-flow wing was to be very thin, and so the tricycle landing gear had to retract into the fuselage. The resulting fuselage had a fat appearance. The fuselage extended above the exhaust to support the tail assembly, this configuration giving the tail adequate clearance on steep take-offs despite short landing gear.

The Flygvapnet was interested in the design, but then SAAB learned that de Havilland had developed a new centrifugal-flow turbojet named the "Ghost" that was substantially more powerful than the Goblin. SAAB engineers worked with their de Havilland counterparts and determined that the Ghost could be fit into the new fighter design.

Through the assistance of the Swiss, SAAB engineers were also able to get their hands on German aerodynamic research data from the war that demonstrated the effectiveness of a swept wing for high-speed flight, and so modified the original straight wing to a wing with a sweepback of 25 degrees. The design study of the revised jet fighter concept, with the Ghost engine and swept wing, was complete by early 1946.

The new fighter was expected to have a top speed of 1,000 KPH (620 MPH), and the Flygvapnet became very keen on it. A formal development program was begun in February 1946 under the project designation of "R-1001". Wind tunnel tests were performed, and a SAAB 91A "Safir" light piston aircraft was fitted with a half-scale version of the 25-degree swept wing for flight tests that began in the spring of 1946. This odd experimental aircraft was designated "Aircraft 201".

* In the fall of 1946, the Flygvapnet ordered three prototypes of the fighter, which was given the designation "J-29". The initial prototype made its first flight on 1 September 1948, with test pilot Robert Moore at the controls.

The prototype was powered by a de Havilland Ghost 45 engine, with 2,000 kilograms (4,400 pounds) thrust. It had power-boosted ailerons, and leading-edge slats fitted to the outer part of the wings to reduce landing speed. The slats were extended automatically when the flaps were lowered.

Performance exceeded expectations, and despite the aircraft's tubby looks, the J-29 proved surprising agile. The first two prototypes were unarmed, but the third was fitted with four 20 millimeter cannon, presumably the Hispano Mark V, built under license in Sweden. The cannon were fitted under the nose intake and had 180 rounds per gun. A fourth prototype was also ordered, flying in 1950.

BACK_TO_TOP

[2] TUNNAN IN OPERATION

* The first production version of the "Flygande Tunnan (Flying Barrel)", as it was nicknamed, was the "J-29A". A total of 224 were built from 1951 to 1954, initially entering into Flygvapnet service in January 1952.

The J-29A was powered by the RM2 Ghost with 2,270 kilograms (5,000 pounds) thrust, built under license by Svenska Flygmotor. Trim tabs were added, as well as dive brakes. The dive brakes were mounted on the wings in early J-29A production, but were then moved to the fuselage ahead of the main landing gear doors.

* The J-29A was followed by the "J-29B", which was fitted with extra fuel tanks in the wings, increasing its fuel capacity by 50%. It also was fitted with stores pylons for bombs and rockets, allowing it to be used in the attack role. For this reason it was also referred to as the "A-29B". It is unclear if any sort of stores pylons were ever fitted to the earlier J-29A.

Possible J-29B underwing loads included:

• Up to twelve 75-millimeter (2.95 inch) unguided air-to-air rockets, with three mounted in a stack on each pylon.

• Up to fourteen 145-millimeter (5.7 inch) unguided anti-armor rockets or 150-millimeter (5.9 inch) high-explosive (HE) rockets, with eight rockets connected directly to pylons and six more mounted beneath these rockets.

• Up to four 125-kilogram (275-pound) 180-millimeter (7.1 inch) HE antiship rockets.

• Two 400-liter (106 US gallon) or 500-liter (132 US gallon) drop tanks that could also be kitted up as napalm bombs.

The initial flight of the J-29B was on 11 March 1953, and 332 were built from 1953 to 1955. The type set a world speed record of 977.35 KPH (607.05 MPH) over a 500 kilometer (310 mile) closed-circuit course in 1954.

* SAAB was also working on a reconnaissance variant of the Tunnan, the "S-29C". This version featured a modified nose, with a flat bottom and straight sides, accommodating five cameras of various sorts. The cameras replaced the four cannon. The S-29C also had tail-warning radar, originally mounted in the tailcone but later moved to the fuselage.

Initial flight of the S-29C was on 3 June 1953. 76 were built from 1954 through 1956. Two S-29Cs set an international speed record of 900.6 KPH (559.4 MPH) over a 1,000 kilometer (621 mile) closed-circuit course in 1955.

Other work proceeding in parallel focused on improving the Tunnan's performance. Svensak Flygmotor developed an afterburning version of the Ghost turbojet, with 2,800 kilograms (6,175 pounds) afterburning thrust, and this improved engine was fitted to a J-29B for tests. This single modified aircraft was designated "J-29D".

* In addition, SAAB engineers were refining the wing design to improve the aircraft "critical Mach number", resulting in a new wing with a "dogtooth" leading edge. This wing was used on a new Tunnan variant, the "J-29E", with the prototype flying on 3 December 1953. 29 J-29Es were built in 1955. The new wing was also refitted to S-29C reconnaissance aircraft, with no change in designation.

The last variant of the Tunnan was the "J-29F", which featured the afterburning Ghost engine that had been evaluated on the single J-29D and the dogtooth wing developed for the J-29E. The prototype performed its first flight on 20 March 1954, and demonstrated much improved take-off and climb characteristics.

There were no new-production J-29Fs; all J-29Fs were updates of existing Tunnan fighter variants. The aircraft updated included the single J-29D, 288 J-29Bs, and 19 J-29Es. In 1963, all J-29Fs remaining in front-line service were fitted to carry a pair of US-designed "AIM-9B Sidewinder" heat-seeking air-to-air missiles, built by SAAB under license as the "Rb-24".

   SAAB J-29F TUNNAN:
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                11 meters           36 feet 1 inch
   length                  10.13 meters        33 feet 2 inches
   height                  3.75 meters         12 feet 3 inches

   empty weight            4,845 kilograms     10,680 pounds
   max loaded weight       8,375 kilograms     18,470 pounds

   maximum speed           1,060 KPH           660 MPH / 575 KT
   service ceiling         15,500 meters       50,850 feet
   range                   1,100 kilometers    680 MI / 595 NMI
   _____________________   _________________   _______________________