SNCASO Trident

The SNCASO SO.9000 Trident was a French mixed-power interceptor aircraft developed and constructed by aircraft manufacturer SNCASO. While it achieved promising results during testing, including the establishment of several world records during flight tests, the French Government chose to cancel its order for the Trident, leaving it as a development programme only.

SO.9000/SO.9050 Trident
Role Research interceptor aircraft
National origin France
Manufacturer SNCASO
First flight 2 March 1953
Number built 12

During the 1940s, as part of a wider effort to re-build French military power 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 wing-tip mounted turbojet engines.

On 2 March 1953, the first prototype Trident I conducted its maiden flight. Subsequently, refitted with Dassault-built MD 30 Viper ASV.5 wing tip engines, the prototype soon exceeded Mach 1 during a shallow dive even without the rocket motor installed. During an 18-month-long test programme, over 100 flights were conducted, during which a maximum speed of Mach 1.8 and a peak altitude of 20,000 metres (65,000 ft) were attained. On 21 May 1957, the first Trident II, 001, exploded during a test flight due an uncontrolled mixing of its fuels, Furaline and nitric acid, resulting in the loss of the aircraft and the death of its pilot, Charles Goujon.

Despite having reached a late stage of development and achieving promising performance with the addition of nearly a dozen pre-production aircraft by July 1957, it was decided to terminate all work on the Trident programme during that same month. Allegedly, the cancellation had been a result of political factors at play, including those of the neighbouring United Kingdom, who had recently announced the cancellation of dozens of aircraft programmes during the infamous 1957 Defence White Paper. Regardless of the reasons for termination, the Trident never entered production nor operational service.

Design and development

Origins

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]

Test flights

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]

Variants
SO.9000 Trident I

Two aircraft built: the first aircraft, 01, was built at Istres and was completed in late 1952, the second aircraft, 02, crashed on its first flight on 1 September 1953. Powered by two 3.924 kN (882 lbf) Turbomeca Marboré II turbojet engines with a single three-chamber SEPR 481 rocket engine, each chamber producing 12.25 kN (2,755 lbf) thrust.

SO.9050 Trident II

Three prototype and ten pre-series aircraft ordered in 1953 and first flown on 21 December 1955: Pre-series aircraft were powered by two 10.79 kN (2,430 lbf) Turbomeca Gabizo with a two-chamber (13 kN (3,000 lbf) per chamber) SEPR 631 rocket engine (each chamber now being individually ignited for finer thrust control). SO.9050 prototypes 001, 002 and 003 were powered by two 2x 7.31 kN (1,640 lbf) Dassault MD.30 Viper turbojet, and SEPR 631 rocket engines.

SO.9050 Trident III

SO.9050-07, -08 and -09, powered by two 14.71 kN (3,310 lbf) Turbomeca Gabizo turbojets with a SEPR 631 rocket engine.

Aircraft on display
on display

SO.9000-01 Trident has been on public display since 1956 at the Musée de l'Air et de l'Espace, near Paris.

Specifications (SO.9050 Trident II)

Data from Jane's All the World's Aircraft 1958-59[14], Aviafrance : Trident II[15]

General characteristics

  • Crew: 1
  • Length: 12.7 m (41 ft 8 in)
  • Wingspan: 6.9 m (22 ft 8 in)
  • Height: 3.17 m (10 ft 5 in)
  • Wing area: 14.5 m2 (156 sq ft)
  • Empty weight: 2,625 kg (5,787 lb)
  • Gross weight: 5,150 kg (11,354 lb)
  • Powerplant: 2 × Dassault MD.30 Viper turbojet engines, 7.31 kN (1,644 lbf) thrust each wing-tip mounted
alternatively 2x 6.34 kN (1,425 lbf) Turbomeca Gabizo without re-heat
alternatively 2x 14.71 kN (3,306 lbf) Turbomeca Gabizo with re-heat
  • Powerplant: 1 × SEPR 631 liquid-fuelled triple chamber rocket engine, 29.41 kN (6,612 lbf) thrust total

Performance

  • Maximum speed: 1,707 km/h (1,061 mph, 922 kn)
  • Maximum speed: Mach 1.95
  • Landing speed: 185 km/h (115 mph; 100 kn)
  • Service ceiling: 25,000 m (82,000 ft)
  • Time to altitude: 15,000 m (49,213 ft) 2 minutes 30 secs, (from brake release).
  • Take-off run: <500 m (1,640 ft)
  • Landing run: <500 m (1,640 ft)
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See also

Aircraft of comparable role, configuration and era

References
  1. Pelt 2012, p. 158.
  2. Gunston 1981, pp. 218–219.
  3. Pelt 2012, pp. 158–159.
  4. Pelt 2012, p. 159.
  5. Pelt 2012, p. 160.
  6. Pelt 2012, pp. 159–160.
  7. Pelt 2012, pp. 160–161.
  8. Pelt 2012, p. 161.
  9. Jane's All the World's Aircraft 1956/7, pp. 154–155.
  10. Pelt 2012, pp. 161–162.
  11. "The Paris Show..." Flight, 31 May 1957. p. 740. Retrieved: 15 October 2010.
  12. Jackson 1986, p. 91.
  13. "Trident's 79,720ft." Flight, 9 May 1958. p. 623.
  14. Bridgman, Leonard, ed. (1958). Jane's All the World's Aircraft 1958-59. London: Jane's All the World's Aircraft Publishing Co. Ltd.
  15. Parmentier, Bruno (23 January 1999). "S.N.C.A.S.O. SO-9050 'Trident' II". Aviafrance (in French). Retrieved 15 March 2020.

Bibliography
  • Bridgman, Leonard (1956). Jane's All the World's Aircraft 1956–57. London: Jane's All the World's Aircraft Publishing Co.CS1 maint: ref=harv (link)
  • Gunston, Bill. Fighters of the Fifties. Cambridge, England: Patrick Stephens Limited, 1981. ISBN 0-85059-463-4.
  • Jackson, Robert. "Combat Aircraft Prototypes since 1945", New York: Arco/Prentice Hall Press, 1986, LCCN 85-18725, ISBN 978-0-671-61953-4.
  • Pelt, Michel van. Rocketing into the Future: The History and Technology of Rocket Planes. Springer Science & Business Media, 2012. ISBN 1-461-43200-6.
  • Taylor, John W.R. Jane's Pocket Book of Research and Experimental Aircraft, London: Macdonald and Jane's Publishers, 1976. ISBN 0-356-08409-4.
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