The Saab 35 Draken (; The Kite, ambiguous with The Dragon) is a Swedish fighter-interceptor developed and manufactured by Svenska Aeroplan Aktiebolaget (SAAB) between 1955 and 1974. Development of the Saab 35 Draken started in 1948 as the Swedish Air Force future replacement for the then also in development Saab 29 Tunnan day fighter and Saab 32B Lansen all-weather fighter. It featured an innovative but unproven double delta wing, leading to the creation of a sub-scale test aircraft, the Saab 210, which was produced and flown to test this previously unexplored aerodynamic feature. The full-scale production version entered service with frontline squadrons of the Swedish Air Force on 8 March 1960. It was produced in several variants and types, most commonly as a fighter-interceptor.
The Draken functioned as an effective supersonic fighter aircraft of the Cold War period, although it was never used in conflict. Even though the type was designed and intended as an interceptor, it was considered to be a very capable dogfighter for the era. In Swedish service, it underwent several upgrades, the ultimate of these being the J 35J model. By the mid-1980s, the SAF's Drakens had largely been replaced by the more advanced JA 37 Viggen fighter, while the introduction of the more capable Saab JAS 39 Gripen fighter was expected in service within a decade, although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 the air forces of Austria, Denmark and Finland. Danish aircraft have been exported, post-service, to the United States where they have seen use as training aircraft for test pilots.
Naming The Swedish word "Draken" has a double meaning, translating either as "The Dragon" or "The Kite". It is said that the name was derived from the appearance of the prototype, like a paper kite, when seen from above.Saab HjartaFlygvapnet, Forsvarsmakten. "Hösten 1955 flög den första prototypen av Saab 35 "Draken" (den såg ut som en pappersdrake ovanifrån" ("In the autumn of 1955, the first prototype of the Saab 35 Draken flew (it looked like a paper kite from above").
The number "35" comes from the aircraft's Swedish Air Force-designation: "flygplan 35" (fpl 35), meaning "aeroplane 35". Depending on the given role, the aircraft received a prefix to indicate its type, the most common being "J 35" to indicate "jaktflygplan" (pursuit-aircraft), the Swedish term for fighter aircraft.
Development
As jet fighter technology developed after World War II, Sweden foresaw a need for a supersonic fighter that could intercept bombers at high altitude as well as engage other 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.Flight International 30 December 1960, p. 1017. The original requirement specified a top speed of Mach 1.4 to 1.5, but this was revised upwards in 1956 to Mach 1.7 to 1.8 and then again in 1959 to Mach 2.0.
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 from relatively austere airstrips, carrying all equipment needed to neutralize modern jet bombers. Although other interceptors like the US Air Force's 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 SAAB's 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 (formally flygplan 210, "aircraft 210"), unofficially nicknamed "Lilldraken" (the little dragon), 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 type's exceptional speed, range, and complicated systems. The second prototype, equipped with an afterburner, unintentionally broke the sound barrier during its first flight while climbing.Erichs et al. 1988
During 1956, the first operational version of the Draken, designated as the J 35A, was ordered into quantity production and the first production aircraft flew for the first time on 15 February 1958.Flight International 30 December 1960, pp. 1017–1018. Mach 2 was reached on 14 January 1960 with test pilot Erik Dahlström at the controls of the J 35B prototype. The engine used was a slightly modified British made Rolls-Royce Avon Mk.48A (Swedish designation RM6BE), engine number 3459.
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 aircraft's 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/cm2 (20.6 MPa), 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 (also known as Avon Mk.48A and Mk.60).Flight International 30 December 1960, p. 1018. A ram turbine, positioned under the aircraft's nose, provided emergency power, while the engine also featured a built-in emergency starter unit. 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.Flight International 30 December 1960, p. 1020.
Instability
Due to a lack of knowledge regarding the then historically unproven design of the J 35's tailless double delta wing configuration, the plane encountered problems at the start of its service life. The unstable design of the double delta wing 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 a "super stall"; which can be described as an uncontrollable stall affecting aircraft with specific wing configurations when experiencing high alpha numbers. Due to this, J 35 pilots were trained to prevent super stalls, and this training led to the development of the cobra maneuver. The cobra is performed by entering into a controlled super stall state, gaining high alpha and then quickly negating the angle of attack to counter the stall. This forces the airframe to act as an air brake for a few seconds, which rapidly reduces the speed.
The Swedish Air Force is the first air force to have discovered and developed the cobra maneuver. The Swedish named it (short parry) after the fencing maneuver of the same name, in English known as ‘beat parry’. Initially it was used during training to teach pilots how to counter super stalls, however it also saw secondary use as a combat maneuver which would cause a pursuing enemy fighter overshoot, allowing the pilot to riposte.
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 Norrköping. 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.