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Delta-wining Dragon: story of the SAAB J35-Sweden's Mach 2 Delta.

Article Excerpt
SAAB Test Pilot Bengt Olow poses with one of the five Draken prototypes. The J35 had tricycle landing gear with a single wheel on each unit. Main gear was hinged at the wing root to retract outward into the wing and contracted during retraction to save space. The nose gear retracted rearwards into the fuselage and was fitted with a mudguard for rough field operation which was especially useful when Drakens took off and landed from highways and farm roads.

The Draken (Dragon) concept dates back to September 1949 when the Swedish Air Force requisitioned a new single-seat all-weather interceptor to replace the Saab J29 'Tunnan'. The program was named Project 1200 and called for a supersonic aircraft capable of achieving speeds of at least Mach 1.4 yet would be able to operate off specially-built sections of public roadway. It had to be rugged, easy to maintain. and cheap to operate as well, One of the most important requirements was that it had to have a very high rate of climb in order to catch the emerging threat of fast. high-altitude jet bombers traveling at speeds of Mach 9. Sweden was a neutral country and was determined to defend its independence against any threat, especially that of Cold War bombers flora the Soviet Union.

In November 1949. a Saab engineering team under designer Erik Bratt examined a number of different options to meet the demanding specification. A single-engine configuration was preferred by Bratt because it reduced complexity, weight and cost, However, with a single-engined aircraft ir was more difficult to pack in all the necessary equipment like the landing gear, avionics, systems, fuel and weaponry. Added to this problem was how to achieve supersonic performance.

In order to accomplish supersonic flight, the wing had to be quite thin and have a low thickness-to-chord ratio (chord is the shortest distance between the leading and trailing edges of a wing). But this would create a wing too thin to hold much. However. if the wing was made thicker, a low thickness-to-chord ratio could still be obtained by making the chord very long. This is where Bratt carne up with a unique and highly successful wing planform--it could hold large items, yet still have low drag. Saab designers initially envisaged a pare delta-winged aircraft with an incredibly large wing sweep angle of 70-degrees and a nose air intake.

As handling problems were envisaged with such a radical and advanced layout, the design was modified, gaining a cranked delta wing with an inboard sweep of 76-degrees, reduced to 57-degrees outboard. The inner wing was very thick in order to accommodate the fuel and landing gear. while the thinner outer portion provided lift for short-field and low-speed operation while still keeping drag low enough for supersonic flight. This configuration was accepted under Saab's Project 1250, follow-on to the original Project 1200.

The layout of the Saab Type 35 Draken (Dragon) was finalized in March 1953. After some hesitation by the FMV, an order for three prototype and three pre-production Drakens was placed in August 1953. The first of the three Draken prototypes made its maiden flight on 25 October 1955 with Bengt Olow at the controls. It was powered by a British Rolls Royce Avon Mk 21 without afterburner, built by Svenska Flygmotor as the RM5A. However, the prototype was later re-engined with the more...