SNCASO Trident

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. During this time, the French Air Staff sought both to become a strong military force once again and to foster the indigenous development of advanced military aircraft. In this respect, one area of high interest for prospective development was the relatively new field of rocket-powered aircraft.[1] According to author Michel van Pelt, French Air Force officials were against a pure rocket-powered fight, 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), was founded for the purpose of developing France's own domestic rocket engines.[1]

Accordingly, French aircraft company SNCASO received a request from the Air Staff to conduct activities upon the development of a capable and advanced point defence interceptor aircraft.[1] During October 1948, SNCASO commenced work upon a series of design studies with the formal request in mind.[2] Out of these studies, one particular design, led by aircraft engineer Lucien Servanty, emerged of a shoulder-wing monoplane which was capable of supersonic speeds. The envisioned aircraft made use of a mixed-propulsion configuration, being primarily powered by a single SEPR-built rocket engine and augmented with a set of wing-tip mounted turbojet engines; operationally, both rocket and turbojet 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.[1]

The rocket engine selected was based upon the unit used upon the Matra M.04 missile.[1] It was powered by a mixture of Furaline and nitric acid; 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.[1] However, as manned rocket aircraft were an entirely unknown commodity within France, it was decided to modify a single 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 was performed; on 10 June 1952, the adapted Espadon test bed performed its maiden flight.[3] During its test programme, improved rocket engines were trialed and the aircraft became the first European aircraft to attain Mach 1 during level flight.[4]

Encouraged by the performance of the Espadon, the French 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.[4] 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.[4] The Trident was a fast-looking bullet-shaped aircraft, furnished with an aerodynamically clean fuselage and thin, straight wings in order to minimise drag.[4]

The design of the Trident was unusual for more than just its mixed-propulsion arrangement. Instead of a conventional ejection seat, the entire nose section in which the pilot was accommodated could be jettisoned.[5] 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 be used when flown at slow speeds, these would be locked out of use at higher speeds to prevent the formation of shock waves; instead, differential application of the flight control surfaces upon the horizontal surfaces of the tail unit controlled roll instead.[5] 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 to proceed with development. Accordingly, work on the production of a pair of prototypes commenced shortly thereafter.[6]

On 2 March 1953, the first prototype Trident I conducted the type's maiden flight; flown by test pilot Jacques Guignard, the aircraft used the entire length of the runway to get airborne, being powered only by its turbojet engines.[2] It was initially flown without any rocket engine installed, relying solely upon its turbojet engines instead.[7] According to aviation author Bill Gunston, the early test flights of the SO.9000 were 'hairy' prior to the installation of the rocket motor, which first occurred during September 1954. On 1 September 1953, during the first flight of the second Trident I prototype, flown by Guignard, the aircraft crashed after struggling to gain altitude after takeoff and colliding with an electricity pylon, resulting in its loss and Guignard sustaining severe injuries.[8]

On 16 January 1954, test flights using the remaining Trident I prototype were resumed, flown by test pilot Charles Goujon.[8] Partially in response to the loss of the second Trident I due to a lack of engine power, it was decided to adopt new turbojet engines in the form of the more powerful Dassault MD.30 Viper, a license-produced version of the British Armstrong Siddeley Viper engine, which were capable of producing 7.34 kN (1,654 lbf) thrust each, nearly double the thrust of the original engines. During March 1955, the first Trident I prototype performed its first flight following its refitting with the Viper engines. Powered by these engines, the aircraft soon proved its ability to exceed Mach 1 during a shallow dive even without the added thrust of the rocket motor.[9][8]

In April 1956, it was decided to end flight testing with the sole remaining Trident I.[8] During the 18-month-long flight test programme, the Trident I had completed over 100 flights, having eventually reached a maximum recorded speed of Mach 1.8 and a peak altitude of 20,000 metres (65,000 ft).[2] A total of 24 of these flights had been flown using the rocket engine.[8] According to Pelt, the French Air Force were impressed by the performance of the Trident, and were keen to adopt an improved operationally-capable model into service.[10] By May 1957, an initial order for a batch of 10 pre-production Tridents had been issued.[11]

On 21 May 1957, the first Trident II, 001, was destroyed during a test flight out of Centre d'Essais en Vol (Flight Test Center); caused when highly volatile rocket fuel and oxidiser, Furaline ( C₁₃H₁₂N₂O) and Nitric acid (HNO₃) respectively, accidentally mixed and exploded, resulting in the death of test pilot Charles Goujon.[12][11] During 1958, the Trident II established new time-to-height and altitude records; its officially-observed record-breaking altitude of 24,300 metres (79,700 ft) was achieved during a flight in May, flown by test pilot Roger Carpentier.[13]

During July 1957, a decision was taken to terminate all work upon the programme. According to Gunston, the cancellation had been heavily influenced by political developments in the neighbouring United Kingdom, specifically the announcement of the 1957 Defence White Paper by the British Defence Minister, Duncan Sandys, in which a large number of advanced aircraft development programmes, including their own mixed-power interceptor programme, had been abruptly aborted in favour of concentrating upon the development of missiles instead.[2]