16 February 2015

The Sud-Ouest SO 6000 Triton: France's First Jet Aircraft

Sud-Ouest SO 6000 Triton prototype. Note the nose intake.
France's first jet aircraft has its roots during the German occupation during the Second World War. Sequestered away in a small Paris apartment a group of French engineers led by Lucien Servanty began work on what would become the Sud-Ouest SO 6000 Triton. Servanty was a graduate of the prestigious engineering school Ecole des Arts et Métiers and prior to the war started out working at Breguet before moving to SNCASO (Société nationale des constructions aéronautiques du sud-ouest) which was a conglomeration formed in 1936 out of several French aircraft companies including Blériot, Bloch, and Lioré et Olivier but was better known as Sud-Ouest. Sud-Ouest was one of the precursor entities to the post war Sud Aviation that would later become Aerospatiale. It was here at Sud-Ouest that Servanty worked on the last variants of the Bloch MB.150 fighter before the fall of France in 1940 to the Nazis. Some of the French aeronautical establishment fled to the Great Britain, some went south to work with the Vichy regime, some were imprisoned for refusing to collaborate (like Marcel Bloch, who later changed his name to Marcel Dassault), and others like Lucien Servanty went into hiding. This was the sort of environment that the Triton was developed, in secret places tucked away from the Nazi occupiers. Servanty's team even built small scale models and tested them in wind tunnels they constructed in secret. 

Lucien Servanty
Uniquely for pioneering jet aircraft of the time from other nations, the Triton was to be a side-by-side two seat aircraft with dual controls and a retracting tricycle undercarriage. A two seater was quite a departure from the first jets in the United States, Great Britain, Germany and the Soviet Union which were all single seaters. The cabin of the Triton wasn't really that much different from a two-seat cabin general aviation aircraft- this was Servanty's idea that the Triton might find use as more than a research aircraft but a training aircraft to introduce pilots to jet propulsion. As designed, the all-metal Triton was to use an indigenous French engine called the Rateau (named for Auguste Rateau who had done much work in the first half of the century on industrial turbines) which was also being developed clandestinely during the occupation. The intake for the Rateau engine was under the nose with the intake duct passing between the pilots to the centrally-mounted engine abreast the wings. Furthering the impression of the Triton as a general aviation aircraft was its crew access via car door-like hatches on each side of the cockpit. In fact, one writer even suggested the Triton may well be the first VLJ-class aircraft thanks to its design!

With the end of the war and the liberation of France, the new French government immediately placed an order for five Triton aircraft plus one static airframe as part of broader effort to rebuild the nation's aeronautical industry. Construction began in somewhat humble facilities outside Paris that were once the factories for Nieuport biplane fighters before moving to a more suitable facility that was once used by Farman. Like many pioneering jet aircraft of the day, the airframe work proceeded much more quickly than the engine development effort. Engineers working on the 3250 lb-thrust Rateau engine were running into difficulties and the Triton prototype was slightly modified to accept a German Jumo 004 engine as used on the Messerschmitt Me 262. This was something of a fortuitous coincidence for Lucien Servanty's team as the Jumo plants in Germany happened to be located in the French occupation sector. The first two Triton airframes would be powered by the Jumo 004. The first flight took place on 11 November 1946 with test pilot Daniel Rastel at the controls. Prior to his first Triton flights, he acquainted himself with jet propulsion by flying captured Me 262s. With this first flight, France become the fifth nation to join the Jet Age after Germany, Great Britain, the United States and the Soviet Union. The flight lasted only 10 minutes and never got about 1000 feet and it was quite clear the Jumo 004 wasn't enough engine for the Triton. 

The third Triton. Note the new lateral intakes and reprofiled cockpit.
The first Paris Air Show after the war took place only three days after the Triton's first flight and the third Triton airframe minus its engine was displayed. Not happy with the reliability of the Jumo 004 engine, Servanty's team switched to Rolls Royce Derwent engine, the same engine that powered the Gloster Meteor fighter. They then switched again to a more powerful Rolls Royce Nene engine which was the engine of the De Havilland Vampire fighter. The French company Hispano Suiza had just gotten a license to build the Nene for the French Air Force's order of Vampire fighters. Because of the increased mass air flow of the Nene engine, the third and fourth Triton featured lateral intakes and improvements to cockpit visibility. In addition, ejection seats designed by Heinkel were installed. The fourth Triton flew first on 19 March 1948 with the third Triton flying for the first time on 4 April 1950. In fact, the fifth Triton flew before the third Triton on 23 May 1949. The sixth airframe was the static test article. Of the last three flying Tritons, it was the fourth one that flew the most as the third and fifth airframes only made a few flights before getting grounded for mechanical issues. The airframe summary is as follows: 
  • Triton 01: Prototype, Jumo 004 powered. Eight test flights. Retired in November 1947.
  • Triton 02: Identical to prototype, but never flown as it was set aside for the French Rateau engine which never became available for use. 
  • Triton 03: Modified for the Nene turbojet. Only two test flights before getting grounded for mechanical issues. It can be seen today at the French aerospace museum at Le Bourget. 
  • Triton 04: Most successful one of the group. 189 test flights. Final flight in November 1950.
  • Triton 05: Damaged due to a forced landing after only eight test flights. 
  • Triton 06: Static test article not intended to fly. 

While modest in performance compared to the jet aircraft of the late 1940s, the Triton gave French industry its first jet experience and many of the prominent test pilots of the time got their first jet time on the Triton given it's trainer layout. Not a bad accomplishment for an aircraft that was designed in secret not out of security but out of fear of the Nazi regime. Lucien Servanty stayed on with Sud-Ouest which became Sud Aviation in 1957. He rose to engineering prominence at Sud Aviation and headed the French design team for the Concorde before his death in Toulouse in 1973. 

Source: X-Planes of Europe: Secret Research Aircraft from the Golden Age 1946-1974 by Tony Buttler and Jean-Louis Delezenne. Hikoki Publications, 2012, pp 22-26. Photos: Wikipedia, Walter Van Tilborg Collection. 

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