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ⓘ Saab 35 Draken




Saab 35 Draken
                                     

ⓘ Saab 35 Draken

The Saab 35 Draken is a Swedish fighter aircraft developed and manufactured by Saab between 1955 and 1974. It was the first fully supersonic aircraft to be deployed in Western Europe and the first aircraft to do something resembling a true Cobra maneuver.

The Draken was developed during the 1940s and 1950s to replace Swedens first generation of jet-powered fighter aircraft, the Saab J 29 Tunnan and, later, the fighter variant J 32B of the Saab 32 Lansen. It featured an innovative double delta wing; in order to test this previously-unexplored aerodynamic feature, a sub-scale test aircraft, the Saab 210, was produced and flown. Developed in Sweden, the Draken was introduced into service with the Swedish Air Force SAF on 8 March 1960 under the designation J 35, the prefix J standing for Jakt which translates to "Hunter" or "pursuit". Early models were intended purely to perform air defence missions, the type being considered to be a capable dogfighter for the era.

The Draken functioned as an effective supersonic fighter aircraft of the Cold War period. In Swedish service, it underwent several upgrades, the ultimate of these being the J 35J model. By the 1980s, the SAFs Drakens had largely been replaced by the more advanced Saab 37 Viggen fighter, while the introduction of the more capable Saab JAS 39 Gripen fighter was expected in service within a decade, although delayed. As a consequence of cutbacks and high maintenance costs, the SAF opted to retire the Draken during December 1999. The type was also exported to Austria, Denmark, Finland, and the United States; the last operated the type as a training aircraft for test pilots.

                                     

1. Development

At the dawn of the Jet Age, Sweden foresaw a need for a jet fighter that could intercept bombers at high altitude as well as engage fighters. During September 1949, the Swedish Air Force, via the Swedish Defence Materiel Administration, released its recently formulated requirement for a cutting-edge interceptor aircraft that was envisioned to be capable of attacking hostile bomber aircraft in the transonic speed range. The original requirement specified a top speed of Mach speed 1.4 to 1.5, but in 1956, this was revised upwards to Mach 1.7-1.8.

It had to be flown by a single pilot, yet be capable of conducting combat operations under all weather conditions, night or day, while operating out of relatively austere airstrips, carrying all equipment needed to neutralize modern jet bombers. Although other interceptors like the US Air Forces F-104 Starfighter were being conceived at the time, this fighter would have to undertake a role unique to Sweden; the ability to operate from reinforced public roads, which were to be used as part of wartime airbases. The aircraft also needed to be refueled and rearmed in no more than ten minutes by conscripts with minimal training.

SAAB commenced work on producing an aircraft to meet these requirements. Preliminary studies found that the majority of critical issues posed by these requirements could be met with a delta wing configuration. However, to obtain an aerodynamically desirable location, the forward fuselage needed to be extended, making the aircraft too heavy. The optimum solution was thought to be a double delta wing. However, this wing configuration was new and untested, so SAABs design staff, headed by aircraft engineer Erik Bratt, and a team of more than 500 technicians, constructed a small test aircraft to explore the behaviour of the new wing.

A sub-scale test aircraft constructed in Sweden, the Saab 210, unofficially nicknamed "Lilldraken" the little kite, comprised a test of the double delta wing, and performed its first flight on 21 January 1952. Results produced by these test flights led to an order for three full-size Draken prototypes. On 25 October 1955, the first of these prototypes, not fitted with an afterburner, conducted its maiden flight. According to aircraft publication Flight International, an atypically intensive flight test program was conducted to define and test the types exceptional speed, range, and complicated systems. The second prototype, equipped with an afterburner, unintentionally broke the sound barrier during its first flight while climbing.

During 1956, the first operational version of the Draken, designated as the J 35A, was ordered into quantity production. During February 1958, the first production aircraft performed its first flight.

                                     

2. Design

The Saab 35 Draken is a fighter aircraft, equipped with a distinctive double delta wing. According to Flight International, it is difficult to differentiate between the fuselage and the wing. The design anticipates what would later be known as a blended wing-body’. The fuselage has a circular section, and the inboard portion of the wing is a large-chord surface which extended almost to the engine intakes. It was possible to dispense with a tailplane, resulting in a clean, simple overall design. The leading edge of the inner wing was swept back 80° for high-speed performance, and the outer wing 60° for good performance at low speeds.

The cockpit of the Draken featured mostly Swedish-sourced instrumentation. Successive models introduced various improvements to the cockpit fittings, such as the revised canopy and new avionics. For export customers, the Draken was outfitted with a Ferranti-built Airpass II fire-control radar, which was effective for acquiring various air-to-air or air-to-surface targets, along with a ground-mapping mode working in conjunction with the aircrafts navigation systems. Typically, two separate radio units would be installed, along with a high-speed data link and two navigation systems. As there is no natural feedback placed upon the stick, artificial forces were generated by a q-feel system. The Draken was also fitted with a three-axis autopilot.

The fuselage of the Draken consisted of two sections, front and rear, joined by bolts. The forward section, which was integral with the intake ducts and neighbouring wing structure, accommodates the fire-control radar, cockpit, nose undercarriage, integral fuel tanks and various systems. The rear portion, which was manufactured as a single piece alongside the rest of the inner wing, contained the engine and afterburner, bag-type fuel tanks, armament, main landing gear, and other systems. The flight control surfaces consisted of a rudder, along with inboard and outboard elevons, the outer sections being fitted with mass-balance weights. Each surface was operated by a tandem hydraulic jack, which was connected to separate circuits. As a weight-saving measure, the hydraulic systems would operate at a line pressure of 210 kp/cm 2 20.590 kPa, which would be greater than double the pressure used in the earlier Saab 29 Tunnan.

Propulsion was provided by a single Svenska Flygmotor RM6B/C turbojet engine, a licence-built model of the Rolls-Royce Avon 200/300 engine. A ram turbine, positioned under the aircrafts nose, provided emergency power, while the engine also featured a built-in emergency starter unit. In order to reduce its landing distance when required, the Draken was equipped with a drogue parachute. The principal armament was carried externally, up to four AIM-9 Sidewinder air-to-air missiles were carried on hard points beneath the wings and fuselage; alternative payloads include a variety of bombs and rockets, along with provisions for the installation of a pair of 30 mm cannons, located within each of the inboard wing panels. In place of the cannons, additional fuel tanks could be fitted in the same space. For aerial reconnaissance missions, a variety of camera pods could be carried underneath the fuselage.

                                     

3. Operational history

At the end of 1959, deliveries of the J 35A Draken commenced to the SAF, the first unit to receive the type being fighter wing F13, stationed at Norrkoping. During March 1960, the Drakens of unit F13 participated in a three-day long exercise, flying by night and day while operating under a state of "highest readiness" throughout. According to Flight International, the introduction to service of the J 35A was "very smooth", and that the scramble and turn-round times had been found to be "most satisfactory". By the end of 1960, multiple wings had been equipped with the Draken and had attained operational status.

Although the J 35 Draken was designed as a high altitude interceptor and not as a dog fighter, it proved to have a good quick-turn capability and high speed at all altitudes, making it a very capable fighter plane. The early models were intended purely to perform the air defense mission. However, in order to assist pilots in converting to the type, Saab produced a small number of twin-seat J 35C trainer aircraft, the first of which having been completed during December 1959. During 1959, an improved air defence fighter model, designated as the J 35B, was developed, which featured improved performance and equipment over the J 35A. Amongst other things, it was powered by an improved engine fitted with an enlarged afterburner, a redesigned rear fuselage, a new Saab-built S.7 collision-course gunsight and fire-control radar, and integration with Swedens STRIL.60 air defence control network.

Due to a lack of knowledge on the then historically unproven design of the J 35s double delta wing, the plane had a lot of problems at the start of its service life. The unstable design of double delta wings made it difficult to land early versions of the J 35 as they had to be manually stabilized during landing. The design also allowed the plane to enter what the Swedish called "super stalls", which simplified can be described as an uncontrollable stall which appears on planes with specific wing configurations when pulling high alpha numbers. Due to this pilots on the J 35 were trained to prevent super stalls from happening. But out of this training came what is today known as the Cobra maneuver, which starts with an entry into a controlled super stall by pulling high alpha and then quickly pulling negative alpha. This basically makes the plane a full body air brake for a few seconds, which heavily drops the speed. The maneuver, which the Swedish named "kort parad", was used by the J 35 pilots as a combat maneuver to make a pursuing enemy fighter overshoot.

A total of 651 Drakens were manufactured by Saab. Swedens fleet of Drakens comprised a total of six different versions, while two additional models of the Draken were offered to prospective export customers. The final model of the Draken to be produced was the J 35F, which was also the final version to remain in Swedish service. Its export customers included Denmark and Finland. In May 1985, the Austrian Air Force purchased 24 J 35Ds, which had been refurbished by Saab.

The J 35 Draken design underwent several upgrades. The last of these was the J 35J version, which was produced during the late 1980s; by this point, the Draken had been almost entirely replaced by the Saab 37 Viggen in SAF service. The Draken J 35J was effectively a service life extension programme, which had been initiated as a result of the impending delivery of the new Saab JAS 39 Gripen having suffered several delays. The extension program was intended to keep the Draken flying into the 2000s but, as a consequence of budgetary cutbacks and high maintenance costs being incurred with the type, the Draken was phased out of Swedish service in December 1999, although the aircraft has since remained operational in limited numbers within both military and civilian roles.

All Drakens functioned as interceptors with limited air-to-ground capability; the sole exception to this rule was the Danish Drakens, which functioned as strike aircraft and were capable of carrying a mixture of AGM-12 Bullpup air-to-ground missiles, electronic countermeasures, and increased internal and external fuel storage. The Danish Drakens were the heaviest of the series to have flown. During 1993, the last of the Danish J 35 fleet were retired.

During the 1990s, Finland updated its 35XS fleet with new avionics, cockpit displays, navigational/attack systems, and electronic countermeasures; these were finally retired in 2000 to be replaced by F/A-18 Hornets.

Austria was the last country to have the Draken in active military service. The Austrian Air Force bought refurbished J 35Ds. This was the last Austrian Air Force fighter plane fitted with internal cannons to perform their lone air-to-air armament because of the restriction in the Austrian State Treaty of 1955, which had forbidden their carrying air-to-air missiles. During 1993, this restriction was dropped as a response to airspace violations made by neighbouring Yugoslavian air combat services. American AIM-9 Sidewinder missiles were purchased. In 2005, these Drakens were retired, having been replaced by former Swiss Air Force F-5 Tiger IIs, while waiting for new Eurofighter Typhoons to take their place in the long term.

In the United States, the National Test Pilot School NTPS operated six Drakens that were formerly in Danish service. They were retired in 2009.



                                     

4.1. Variants Proof of concept

Saab 210 Draken Also known as Lilldraken, a scaled-down, proof of concept experimental aircraft to evaluate the double delta wing configuration, not specifically a Draken variant but included here for sequence purposes.
                                     

4.2. Variants Full-size Drakens

J 35A Fighter version, total production 90 including prototypes. The J 35As were delivered between 1959 and 1961. The tail section was lengthened after the 66th aircraft to house a new afterburner for additional thrust, the longer tail cone unexpectedly reduced drag. This forced the installation of a retractable tail-wheel. The two versions were nicknamed Adam kort Adam short and Adam lång Adam long. The Adam was fitted with a French Cyrano Radar Swedish designation PS-02 same as on the Mirage III as the Swedish radar hadnt been developed in time. J 35B Fighter version, built and delivered between 1962 and 1963, total production 73. This variant had improved radar and gun sights, and was also fully integrated into the Swedish STRIL 60 system; a combat guidance and air surveillance system. Fitted with a Swedish built radar PS-03. SK 35C 25 J 35As with short tail sections rebuilt into a twin-seated trainer version. The minor modification meant that the aircraft could easily be converted back to a J 35A standard if necessary. The trainer version lacked armament. J 35D Fighter version, delivered between 1963 and 1964, total production 120. The aircraft had a new and more powerful Rolls-Royce Avon 300 RM6C, which could deliver 77.3 kN thrust when using its afterburner. This was also the fastest Draken version, capable of accelerating until out of fuel. It was also the last Draken to carry two cannons. Fitted with the PS-03 radar. S 35E Reconnaissance version, total production 60 with 32 built from scratch and the remainder converted from the J 35D model. The armament and radar was removed and several cameras of ortho and oblique types fitted. The aircraft was unarmed to make room for the nine cameras of Vinten design five in the nose and four in the fuselage but was fitted with a countermeasure system to increase its survivability. It also carried an active infrared reconnaissance system of EG&G design in a pod fitted to a hardpoint. J 35F Fighter version, delivered between 1965 and 1972, total production: 230. This variant had improved electronics and avionics, e.g. integrated radar, aim and missile systems. The aircrafts main armament were IR and SARH versions of the Hughes Falcon missile originally intended for the J 35D, but one of the cannon was removed to make space for more avionics. The J 35F2 was a J 35F, produced with a Hughes N71 Infrared search and track sensor. This was a change in the production line from the no. 35501 airframe. The Hawe mods I & II were carried out on the P/S-01/011 radar sets in the early 1980s to improve resistance to ECM. J 35J In 1985 the Swedish government decided to modify 54 J 35F2s to the J 35J standard. In 1987, 12 more modifications were ordered: between 1987 and 1991, the aircraft received a longer lifespan, modernized electronics and cannon, additional two Sidewinder AIM-9P pylons under the air intakes and increased external fuel capacity. The final operational J 35J flew for the last time in 1999. Saab 35H Proposed export version for the Swiss Air Force; none sold or delivered. Saab 35XD 51 Danish export versions: F-35 single-seat strike aircraft, TF-35 two-seat trainer and RF-35 reconnaissance aircraft. The type was heavily modified to make it into a strike aircraft; compared to the Swedish versions the outer wings where completely redesigned, and the radar was missing. These aircraft could carry heavy bombs as well as Bullpup missiles; during the WDNS upgrade of the 1980s they received the ALQ-162 jammer, a Marconi 900 Series HUD and a Ferranti LRMTS laser rangefinder and marked target seeker Saab 35XS 12 fighter version units for the Finnish Air Force; built by Saab and assembled under licence by Valmet in Finland. The "S" stood for "Suomi" Finland. Saab 35BS Used J 35Bs sold to Finland. Saab 35FS Used J 35F1s sold to Finland. Saab 35CS Used SK 35Cs sold to Finland. Saab 35O In the mid-1980s, Saab re-purchased 24 J 35D aircraft from the Swedish Air Force and converted them into the J 35O version also called J 35OE in English literature for export to Austria. Austria bought AIM-9P5 all aspect Sidewinders for these aircraft during the war in former Yugoslavia.
                                     

4.3. Variants Proposed modifications

Before it was decided to develop the JAS 39 Gripen in the 1970s, studies were undertaken on modification for low flight hour J 35F airframes.

35 MOD Level 4 The most ambitious modification in the program. The proposed modifications were new outer wing, additional weapon stations, RBS 15 capability, the addition of canards by the air intakes for increased maneuverability and maximum take-off weight increased to 15 000 kg. 35 MOD Level 1b Essentially the aircraft that became the J 35J.

The total number of Drakens produced and delivered was 644.

                                     

5. Operators

The Saab 35 Draken was withdrawn from military use in 2005. Several aircraft fly in the civilian service, mainly by the National Test Pilot School.

Austria
  • Staffel 2
  • Staffel 1
  • Austrian Air Force, 24 aircraft
  • Fliegerregiment 2
Denmark
  • No. 725 Squadron
  • No. 729 Squadron
  • Royal Danish Air Force, 51 aircraft
Finland
  • Fighter Squadron 21
  • Finnish Air Force, 50 aircraft
  • Fighter Squadron 11
Sweden
  • Swedish Air Force
United States
  • National Test Pilot School 6
                                     

6. Surviving aircraft

A small number of Drakens are still with civilian owners mainly in the United States, many former-operational aircraft have been preserved in the operating nations.

                                     

7. Specifications J 35F Draken

Data from The Great Book of Fighters, Combat Aircraft since 1945, Saab 35 Draken in Finnish Air Force, SAAB Aircraft since 1937

General characteristics

  • Wingspan: 9.42 m 30 ft 11 in
  • Length: 15.35 m 50 ft 4 in
  • Height: 3.89 m 12 ft 9 in
  • Airfoil: 5%
  • Crew: 1
  • Powerplant: 1 × Svenska Flygmotor RM6C afterburning turbojet engine, 56.5 kN 12.700 lbf thrust dry, 78.4 kN 17.600 lbf with afterburner
  • Gross weight: 11.000 kg 24.251 lb
  • Max takeoff weight: 11.914 kg 26.266 lb
  • Wing area: 49.2 m 2 530 sq ft
  • Empty weight: 7.865 kg 17.339 lb

Performance

  • Ferry range: 2.750 km 1.710 mi, 1.480 nmi with external drop tanks
  • Wing loading: 231.6 kg/m 2 47.4 lb/sq ft
  • Takeoff roll: 800 m 2.625 ft
  • Maximum speed: Mach 2
  • Maximum speed: 2.450 km/h 1.520 mph, 1.320 kn at 11.000 m 36.089 ft
  • Service ceiling: 20.000 m 66.000 ft
  • Thrust/weight: 0.7
  • Rate of climb: 199 m/s 39.200 ft/min

Armament

  • Guns: 1× or 2× 30 mm AKAN M/55 ADEN cannon with 100 rounds per gun in Saab 35F one cannon was omitted to fit avionics needed for Falcon missile integration, earlier variants and export variants retained twin guns.
  • Missiles: Rb 24, Rb 27 and Rb 28 air-to-air missiles
  • Hardpoints: for fuel tanks or ordnance with a capacity of 2.900 kg 6.393 lb,with provisions to carry combinations of
  • Rockets: 2× 75 mm air-to-ground rocket pods ventrally or 12× 135 mm rockets on six underwing pylons
  • Bombs: The Danish export version, F-35, was modified according to NATO standards and was fitted with 1.000lb bomb hardpoints