The SNCASO SO.9000 Trident is a French jet and rocket powered interceptor aircraft built by aircraft manufacturer SNCASO during the 1950s. As part of a wider effort to re-build French military power during the late 1940s and to furnish France with advanced, new domestically produced designs, a request for a supersonic-capable point-defence interceptor aircraft to equip the French Air Force was issued to SNCASO. In response, the firm designed the mixed-propulsion Trident, powered by a single SEPR rocket engine, which was augmented by wingtip-mounted turbojet engines, and the Air Force ordered two prototypes. The two SO.9000 Trident Is demonstrated the feasibility of the design concept despite the loss of one aircraft during flight testing and the Air Force ordered a batch of three prototype SO.9050 Trident II fighters in 1954, and a batch of six pre-production aircraft in 1956 to further develop the aircraft so it could serve as a short-range interceptor. Only six of these nine aircraft were ultimately completed, of which all three prototypes were damaged or destroyed in accidents before the programme was cancelled in 1958 despite their record-setting performance.
Background and description During the late 1940s, following the end of the Second World War, France quickly set about its recovery and the rebuilding of its military, particularly the French Air Force with the indigenous development of advanced military aircraft. In this respect, one area of high interest was the relatively new field of rocket-powered aircraft. According to aviation historian Michel van Pelt, French Air Force officials were against a pure rocket-powered fighter, akin to the wartime-era Messerschmitt Me 163 Komet, but instead favoured a mixed-propulsion approach, using a combination of rocket and turbojet engines. During 1944, a new company, Société d'Etudes pour la Propulsion par Réaction (SEPR), had been founded for the purpose of developing France's own domestic rocket engines. Accordingly, SNCASO received a request from the Air Staff to begin studies for rocket-powered point-defence interceptors with auxiliary turbojets in 1948. During October, SNCASO commenced work upon a series of design studies in response. One particular design by aircraft designer Lucien Servanty was favoured by the company. This was a shoulder-wing monoplane capable of supersonic speeds using a single SEPR-built rocket engine in the fuselage augmented with a set of wingtip-mounted turbojets; operationally, both types of engines were to be used to perform a rapid climb and interception at high altitudes, while the jet engines alone would be used to return to base. Servanty persuaded the Air Force to fund a design study and a mockup on 7 July 1950. The rocket engine selected was based that used by the Matra M.04 missile. It was powered by a mixture of Furaline (C13H12N2O) and nitric acid (HNO3); according to Pelt, the decision to use nitric acid as the oxidizing agent posed some challenges as it was corrosive to both the airframe and engine. The combination of Furaline, which was relatively difficult to manufacture in comparison to conventional kerosene, and nitric acid functioned as a hypergolic propellant, not requiring any igniting agent. However, as manned rocket aircraft were an entirely unknown commodity within France, the Air Force decided to modify an existing aircraft, the Sud-Ouest Espadon, to serve as an aerial test bed to prove the propulsion arrangement. During March 1951, the first ground tests of the rocket engine were performed; on 10 June 1952, the modified Espadon test bed performed its maiden flight. During its test programme, improved rocket engines were trialed and the aircraft became the first European aircraft to attain Mach 1 during level flight. Encouraged by the success of the Espadon, the Air Force issued a request to French aircraft companies for a high-speed, lightweight interceptor aircraft that harnessed either turbojet or rocket propulsion, or some combination thereof. Amongst the specified requirements given were the ability to attain Mach 1.3, a relatively high climb rate, and the possibility of deploying the aircraft from austere airstrips. Amongst the various responses from French industry was SNCASO with their own proposal, which was based upon their earlier design studies; their design was later designated as the SO.9000 Trident. The Trident was a fast-looking bullet-shaped aircraft, furnished with an aerodynamically clean fuselage and thin, straight wings in order to minimise drag. It was equipped with a narrow-track tricycle landing gear with the main wheels retracting into the fuselage. The design was unusual for more than just its mixed-propulsion arrangement. Instead of a conventional ejection seat, the entire nose section could be jettisoned. Particular attention had been dedicated to the control system to ensure it would be suitable throughout the transonic and supersonic stages of flight; while conventional ailerons were used when flown at slow speeds, these would be locked out of use at higher speeds to prevent the formation of shock waves; instead, the tailplane controlled roll by moving in opposite directions. All three tail surfaces were all-moving, eliminating the requirement for separate elevators and rudders while preventing control lock-ups during high speeds. Suitably impressed with the design and its projected performance, SNCASO received a contract for two prototypes on 8 April 1951.
SO.9000 Trident I
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