The Saab 35 Draken

v2.0.0 / 01 apr 02 / greg goebel / public domain

* Following World War II, aircraft sophistication and performance evolved at a rapid rate, with new designs becoming obsolete in a matter of years. Although the Swedes lacked the resources of the larger powers, they were able to compete effectively in this race, producing a series of straightforward, capable, and highly flexible fighter designs.

One of the best and most long-lived of these designs was the Mach 2 "Saab 35 Draken (Dragon)". This document outlines the history of the Draken.

[1] DRAKEN ORIGINS
[3] J35A
[3] J35B / J35C / J35D / J35E / J35F / J35J
[4] DRAKENS IN FOREIGN SERVICE
[5] COMMENTS, SOURCES, & REVISION HISTORY

[1] DRAKEN ORIGINS

* In 1949, the Royal Swedish Air Board issued a request with the designation "Project 1200" for a new fighter that would follow the Saab 29 "Tunnan", then about to go into service with the Flygvapnet (Swedish Air Force). This new aircraft was to have a speed of at least Mach 1.4 and be capable of operating from existing airbases, as well as stretches of road that had been specially reinforced to allow use as dispersed airfields. The machine was to be rugged, easily maintained, and cheap to operate.

Saab's engineering team, under Erik Bratt, focused on a delta-wing design, with a radical sweepback of 70 degrees. Further design studies led to a "double delta" scheme, with the thick inner delta (with a sweep of 80 degrees) allowing accommodation of fuel and landing gear, and the thin outer delta (with a sweep of 57 degrees) providing additional lift for low-speed performance and short-field operation while retaining low-drag characteristics for high-speed flight.

Nobody had ever flown a double delta aircraft before. After some wind tunnel experiments in the USA, the wing scheme was validated using a 70% scale demonstrator aircraft, the "Saab 210", originally named the "Draken" but renamed the "Lill Draken (Little Dragon)" after the production type acquired the Draken name itself.

The Saab 210 was powered by an Armstrong Siddeley "Adder" turbojet with 450 kilograms (1,000 pounds) thrust. This left the machine seriously underpowered, and in fact in warm weather, it was often flown in the dark hours of the morning. Despite this limitation, the Lill Draken performed about a thousand test flights before being donated to the Flygvapnet museum.

In its original configuration, the engine intakes of the Saab 210 were on the nose of the aircraft, separated by a small nosecose in the shape of a pyramid. The nose cone was later modified to a chisel shape, but as the intake scheme did not provide enough airflow, the the entire forward fuselage was finally redesigned, giving it a long nose and moving the intakes back to the front of the cockpit.

* In August 1953, the Swedish government ordered three prototype and three pre-production "Saab 35" fighters. The British "Avon 200" turbojet was selected as the powerplant for the production machine. A license was obtained by Svenska Flygmotor (later Volvo Flygmotor) to manufacture the Avon under the designation "RM6B". The RM6B provided 4,800 kilograms (10,600 pounds) dry thrust and 6,800 kilograms (15,000 pounds) afterburning thrust.

The initial Saab 35 prototype flew on 15 October 1955, powered by an imported Avon 200 engine, as used on the Supermarine Swift fighter. There were three flight prototypes, plus a static test item. The type was approved for full production in 1956. By this time, the specifications had been raised, dictating a fighter with a top speed of Mach 1.8.

The first production "J35A (Adam)" fighter, fitted with the Swedish-built RM6B engine with a Swedish-designed "Model 65" afterburner, performed its first flight on 15 February 1958. The J35A went into initial operational service with the Flygvapnet in March 1960.

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[3] J35A

* The Draken proved to have excellent performance and was a "pilot's aircraft", easy to fly and with few or no vices. The only major limitation of the type, common to jet aircraft of that era, was that it had limited range and endurance, and as a delta it had a relatively long takeoff run, since flaps could not be used with the such a configuration. It was easy to maintain, with the fuselage bolted together at midsection to make it straightforward to pull apart for engine access. The outer wing sections could be easily removed for shipping or storing the aircraft.

Flight control was provided by rudder, along with "elevons" running the width of the rear of the wing. The elevons were split, with one on the inboard section of the wing and the other on the outboard section of the wing. The elevons on each side of the wing operated in unison for pitch control and in opposition for roll control. The flight surfaces were driven by a dual redundant hydraulic system. There was a small airbrake on either side of the fuselage, near the end of the wing.

The pilot sat in a simple Saab-designed ejection seat, reclined 30 degrees to help deal with gee forces, under a clamshell-style canopy. The cockpit was pressurized and air-conditioned. The Draken had tricycle landing gear, with single wheels on each assembly. The nose gear had a mudguard for rough field operation and retracted backward, while the main gear hinged from the wing root to retract outward into the wing. The main gear legs contracted during retraction. A drag chute was fitted at the base of the vertical tailplane to reduce landing roll. A pop-up ram-air turbine was provided for emergency power.

The J35A was armed with twin 30 millimeter British Aden revolver-type cannon, with one cannon in each inner wing section, outboard of the engine intake. There were 90 rounds per gun.

One confusing issue about the J35A is the number of stores pylons. The configuration seen in most images of the Draken is two pylons arranged side-by-side under the fuselage, and a single pylon on each wing, for a total of four pylons. All four pylons were "wet" and could carry external tanks, but the two fuselage pylons usually carried the tanks, which had a capacity of 530 liters (140 US gallons) each.

To complicate matters, apparently a single centerline pylon could be fitted, likely as an alternative to the two fuselage pylons rather than in addition to them, and instead of the single wing pylon, three stub pylons for carrying unguided air-to-surface rockets could be installed. It appears that these alternative pylon configurations were rarely fitted, and so as a rule the J35A had four stores pylons.

In 1961, J35As were fitted for carriage of four "RB24" air-to-air missiles (AAMs), which were US AIM-9B Sidewinder heat-seekers built in Sweden under license. The Adam could also be used in a secondary ground attack role, carrying Bofors 135 millimeter (5.3 inch) unguided rockets, 100 kilogram (220 pound) bombs, and 250 kilogram (550 pound) bombs.

The Draken was essentially a day interceptor, intended for tail chase pursuit, though it did have Saab "S6" fire-control system (FCS), featuring Ericsson-built Thomson-CSF "Cyrano" radar, to give it some all-weather capability. A few J35As were later modified with the "SB6" FCS, which included an "infrared search and track (IRST)" sensor under the nose. The Adam was fitted with a simple autopilot, a Swedish built copy of a US Lear design.

90 J35As were built in all. The first three were pre-series aircraft, while the next seventeen were operational evaluation machines, and so it wasn't until the 21st J35A that the type reached a stable standard.

The last 28 were fitted with an improved "Model 66" afterburner, resulting in a longer rear fuselage with revised contours. This demanded fit of a pair of small retractable "roller skate" tailwheels to keep the rear of the aircraft from scraping the runway during high angle of attack takeoffs or landings. Earlier J35As had a small solid bumper for this purpose, which was said to have left quite a trail of sparks when it struck the tarmac.

The J35A wasn't compatible with the Swedish "STRIL 60" semi-automatic ground control system, limiting its usefulness, and so the J35A mostly served as an operational trainer and evaluation aircraft.

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[3] J35B / J35C / J35D / J35E / J35F / J35J

* The J35A led to the next model, the "J35B (Bertil)", which performed its initial flight on 29 November 1959, and reached operational status in late 1961. The Bertil looked almost identical to the late-build Adam, with the longer rear fuselage and twin tailwheels, but featured a "Saab S7" FCS, which was compatible with the STRIL 60 system and supported "collision course" intercepts, rather than the tail chase intercept required by the J35A.

As the RB24 Sidewinder had to be boresighted on a target's exhaust, it was useless for collision course intercepts, and so J35Bs fitted for the interceptor role generally carried two 19-round Bofors 75 millimeter (3 inch) unguided rocket pods. The Bertil could also be used in a secondary ground-attack role, carrying unguided rockets and bombs. 73 J35Bs were built in all.

* The J35 was a fairly hot aircraft, and so a tandem two-seat trainer version, the "J35C (Caesar)" was developed, first flying on 30 December 1959. The instructor sat in the rear seat in a raised position behind the cadet pilot, and had a stereoscopic periscope to improve his forward visibility. The periscope apparently left something to be desired, the view being described as something like "staring through two rolls of toilet paper", but was better than nothing.

There was a blast barrier between the student and instructor seats to protect the instructor in case of a bird strike or other accident that broke the canopy. The canopy opened to the side. A small fin was added under each wing to improve yaw stability, which was affected by the new big canopy.

The second seat was fitted by reducing the size of the fuselage fuel tanks, but in compensation the two Aden cannon were deleted, allowing larger fuel tanks in the wings. Radar was deleted as well, but the Caesar retained stores pylons, and Sidewinders or other AAMs could be carried for training.

The only new-build Caesar was the prototype. 25 more were rebuilt from early production J35As, and retained the Model 65 afterburner and short fuselage of the original aircraft.

* Following production of the RM6B engine, a successor designated the "RM6C" was developed, based on the "Avon 300" engine. The Avon 300 was capable of 5,750 kilograms (12,700 pounds) dry thrust and 7,830 kilograms (17,260 pounds) thrust with the initial Model 66 afterburner.

The new engine led to a new Draken, the "J35D (David)", with maximum speed of Mach 2. The only really noticeable external change from the J35B was modified engine inlets, but along with the new engine, the J35D featured increased fuel capacity; a Saab "FH5" autopilot replacing the license-built Lear unit; and improved an improved Saab "S7A" FCS with Ericsson "PS-03" radar.

The pilot was provided with an improved Saab "73SE-F" rocket-boosted ejection seat, which could operate from zero altitude but required a minimum forward speed of 100 KPH (62 MPH) for safe ejection. The J35D was later updated with the Saab "RS35" ejection seat, which was a true "zero-zero" device that could get the pilot out safely even if the aircraft was sitting on the runway.

The prototype J35D, a modified J35A, performed its first flight on 27 December 1960, but deliveries to the Flygvapnet only began in 1963. 92 Davids were built.

* Saab then developed an unarmed photo-reconnaissance version of the J35D, designated the "J35E (Erik)" or "S35E", carrying a total of seven French-designed OMERA narrow-view or wide-angle cameras:

The nose cone was mounted on rails so it could be easily slid out to provide access to the cameras. Of course, the J35E had no radar, but aside from these changes and the lack of cannon, it was generally identical to a David.

The Erik had the RM6C engine and the Model 66 afterburner, though it appears that at least some J35Es were built or refitted with the improved "Model 67" afterburner that provided 8,000 kilograms (17,640) afterburning thrust. J35Es were also refitted with the "bulged" canopy introduced on the J35F, discussed below, and in the 1970s were fitted for carriage of "Blue Baron" pods with British Vinten night-photography cameras.

The J35E prototype performed its first flight on 27 June 1963 and reached operational status in August 1965. A total of 60 were built. 28 of these were originally ordered as Davids, but converted to Eriks on the production line.

* The J35D also led to the definitive J35 variant, the "J35F (Filip)", with first flight in 1961 and service introduction in 1965. Development was conducted with three modified J35As, one of which was brought up to an approximation of full J35F production specification.

The Filip was essentially a J35D with an RM6C engine and the new Model 67 afterburner; substantially increased internal fuel capacity; a bulged canopy to give better pilot visibility, along with an improved cockpit layout; improved navigation, autopilot, and communications systems; and a Saab "S7B" collision-course FCS with Ericsson "PS-01/A" radar. 

   SAAB J35F DRAKEN:
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                9.4 meters          30 feet 10 inches
   length                  15.4 meters         50 feet 4 inches
   height                  3.89 meters         12 feet 9 inches

   empty weight            8,250 kilograms     18,190 pounds
   max loaded weight       12,270 kilograms    27,050 pounds

   maximum speed (clean)   2,125 KPH           1,320 MPH / 1,150 NMI
   service ceiling         20,000 meters       65,600 feet
   range (with stores)     1,300 kilometers    800 MI / 695 NMI
   _____________________   _________________   _______________________
Along with the improved FCS, the Filip used a new armament scheme, carrying two semi-active-radar-homing (SARH) "RB27" AAMs, and a single heat-seeking "RB28" AAM or an RB24 Sidewinder under each wing. The RB27 and RB28 were US Hughes Falcon AAMs built under license in Sweden. The RB27 was too heavy to be carried on the wing pylons, which is why only two could be carried.

One of the two Aden cannon was deleted to accommodate new avionics systems. As the Falcon AAM proved entirely inadequate in US service, it is unclear how useful the J35F's armament would have been if things had come to a shooting match, but it appears the Draken never fired a shot in anger. However, the Swedish Falcons were by no means simple copies of the American models, and much was done to improve the weapon's effectiveness.

A total of 230 Filips were built. Every other J35F rolling off the production line was with a Hughes "AN/AAR-4 (S-71N)" IRST, built under license by Ericsson. Those without the IRST were designated "J35F-1 (Filip Ett)" and those with the IRST were designated "J35F-2 (Filip Tva)". Most of the J35F-1s were refitted with the IRST later.

* The Flygvapnet's Draken force provided excellent service through the 1960s and 1970s, but began to be phased out in the late 1970s and early 1980s in favor of the Saab 37 Viggen. However, budget cuts kept the J35F in frontline service well into the 1990s. To stretch out the Filip's effectiveness, in the mid-1980s an upgrade program was put in motion.

The upgraded aircraft were originally referred to "J35F Mod", but by the time the first of them were returned to service after their trip back to the factory, they were designated "J35Js". 66 were upgraded in all, with the last re-delivered in August 1991. The J35J received a comprehensive avionics upgrade, including improved radar and IRST, as well as improved cockpit displays. The only really visible change in the J35J from the J35F was the addition of a new stores pylon on the inner section of the wing, giving a total of six pylons.

The last J35J was phased out of formal service with the Flygvapnet on 8 December 1998, over 40 years after the initial flight of the first prototype. Even in its old age, the Draken was regarded as a prize mount by Flygvapnet pilots, as its performance was still impressive, and the fact that it wasn't as easy to fly as later aircraft such as the Viggen made it more of a challenge to a pilot's skill.

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[4] DRAKENS IN FOREIGN SERVICE

* While the Swedes, with a tradition of military neutrality, are not in general aggressive arms exporters, the Draken was purchased several European nations.

In 1960, the Swiss evaluated a "J35H" Draken, where "H" for "Helvetia", the old Latin name for Switzerland, as a replacement for their old de Havilland vampires in the interceptor role. The J35H was fitted with Ferranti "AI.23 Airpass" collision-course radar system, used in the English Electric Lightning. The evaluation of the F35H went well, but the Swiss opted for the French Mirage III instead.

* In 1968 the Danish government selected a J35F derivative designated the "J35X", where "X" naturally stood for "export", for the Danish Air Force. The J35X was similar to the J35F, but had greater fuel capacity, structural reinforcement, a new outer wing, and a runway arresting hook. The J35X could carry a maximum external warload of 4,500 kilograms (10,000 pounds). It was fitted with twin Aden cannon.

The Danes ended up buying a total of 51 Drakens. Three different variants were obtained:

The Danish Drakens were expected to serve well into the 1990s, but they were out of formal service by 1993, as the end of the Cold War had led to defense cutbacks.

* In 1970, Finland decided to obtain the Draken, arranging to buy twelve "J35XS" interceptors in kit form for assembly by Valmet. These were similar to the J35F, but had twin Aden cannon; a revised avionics suite; and lacked the fire-control radar needed for the Hughes Falcon, relying instead on the Sidewinder. Initial flight was in 1974, with deliveries completed in 1975. The Finnish Drakens served in both the interceptor and fighter-bomber roles.

As an interim measure to provide training experience before the J35XS fighters were available, the Finns leased six J35Bs from Sweden, giving them the designation "J35BS". These aircraft were apparently stripped of most of their combat avionics. The first was delivered in 1972. One was grounded after being badly damaged in 1974, and the Finns leased another J35B to replace it.

In 1975, the Finns decided to buy these seven aircraft outright, as they had become enthusiastic about the type, and also bought six refurbished Swedish J35Fs with the designation of "J35FS". They bought a second batch of J35FS Drakens in 1984, again all refurbished Flygvapnet aircraft.

In addition to the refurbished fighters, in 1975 the Finns obtained three refurbished J35Cs with the designation of "J35CS", and purchased two more refurbished trainers in 1984, along with the second batch of J35FS Drakens. This somewhat complicated history gave a total Finnish Draken force of: 

   J35XS:           12   built from kits.
   J35BS:  6 + 1  =  7   leased from Sweden then bought.
   J35FS:  6 + 18 = 24   refurbished from Swedish stocks.
   J35CS:  3 + 2  =  5   refurbished from Swedish stocks.
   ___________________

   TOTAL:           48
Finnish Drakens served into the 21st century, finally being withdrawn in favor of Finland's new F/A-18 Hornet fighters.

* The final user of the Draken is Austria. After considering a number of options for a replacement for the country's Saab 29 Tunnans, which had gone out of service in 1972, the Austrians settled on used Flygvapnet J35Ds, buying 24 of them in 1985. The aircraft were refurbished and modernized to an extent, being fitted with bulged J35F-style canopies, an RWR, and chaff-flare dispensers, and delivered in the 1987:1989 timeframe.

The Austrian Drakens were given the designation of "J35O", where the "O" stood for "Oesterreich (Austria)". They did not buy any J35Cs, flight training being provided in Sweden as part of the sales package. Apparently a few J35Cs have been retained in operation in Sweden for this purpose.

The J35Os were used as primarily as interceptors, though the Austrians did obtain reconnaissance pods as well. Initially, the J35Os were solely armed with their twin Aden cannon, as Austria's neutrality agreements prevented the fighters from carrying Sidewinders or other AAMs. After the fall of the USSR, the Austrians acquired surplus Swedish Sidewinders to arm their J35Os.

The J35Os were supposed to be withdrawn from service in 1998, but finding a replacement has been time-consuming. The Drakens are expected to remain in operation until 2005.

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[5] COMMENTS, SOURCES, & REVISION HISTORY

* Sources include:

Some items were also pulled off Urbain Fredericksson's Draken page.

* Revision history: 

   v1.0   / not dated / gvg
   v1.1   / 19 jul 97 / gvg / Minor tweaks, added reader comments.
   v1.2   / 22 sep 97 / gvg / A few more tweaks.
   v1.3   / 08 jan 99 / gvg / Cosmetic cleanup, note on last Swedish Draken.
   v1.4   / 02 mar 99 / gvg / Moved revision history to end.
   v2.0.0 / 01 apr 02 / gvg / General update and enhancement.
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