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The Coandă-1910, designed by Romanian inventor Henri Coandă, was an unconventional sesquiplane aircraft powered by a ducted fan. Called the "turbo-propulseur" by Coandă, its experimental engine consisted of a conventional piston engine driving a multi-bladed centrifugal blower which exhausted into a duct. The unusual aircraft attracted attention at the Second International Aeronautical Exhibition in Paris in October 1910, being the only exhibit without a propeller, but the aircraft was not displayed afterwards, and it fell from public awareness. Coandă used a similar turbo-propulseur to drive a snow sledge, but he did not develop it further for aircraft.
Decades later, after the practical demonstration of motorjets and turbojets, Coandă began to tell various conflicting stories about how his early experiments were precursors to the jet, even that his turbo-propulseur was the first motorjet engine with fuel combustion in the airstream. He also claimed to have made a single brief flight in December 1910, crashing just after takeoff, the aircraft being destroyed by fire. Two aviation historians countered Coandă's version of events, saying there was no proof that the engine had combustion in the airstream, and no proof that the aircraft ever flew. In 1965, Coandă brought drawings forward to prove his claim of combustion ducting, but these were shown to be reworked, differing substantially from the originals. Many aviation historians were dismissive, saying that Coandă's turbo-propulseur design involved a weak stream of "plain air", not a powerful jet of air expanding from fuel combustion.
In 2010, based on the notion that Coandă invented the first jet, the centennial of the jet aircraft was celebrated in Romania. A special coin and stamp were issued, and construction began on a working replica of the aircraft. At the European Parliament, an exhibition commemorated the building and testing of the Coandă-1910.<!--citations in body-->
Early developments
Coandă was interested in achieving reactive propelled flight as early as 1905, conducting tests of rockets attached to model aircraft at the Romanian Army arsenal in Bucharest. In secret, at Spandau in Germany, Coandă successfully tested a flying machine equipped with a single tractor propeller, and two counter-rotating propellers providing lift, powered by a 50-horsepower (37 kW) Antoinette engine. Positioned along the fuselage centreline, the smaller rear lift propeller was mounted vertically, while the larger front one was inclined slightly forwards at 17 degrees. According to later claims, Coandă tested the aircraft at Cassel, witnessed by the Chancellor of the German Empire Bernhard von Bülow. It was around this time that Coandă's interest in jet propulsion began, claiming that the aircraft and a jet-propelled model were displayed in December 1907 at the Sporthalle indoor sports arena in Berlin. In 1909 he was employed as technical director of the Liège-Spa Aeroclub, and at the end of that year, with the help of car manufacturer Joachim he built the Coandă-Joachim glider. Caproni was present when the glider was flown at Spa-Malchamps, Belgium.
1910s
thumb|left|upright|"The Only Aeroplanes Without Propellers". This promotional brochure was available at the Paris salon in 1910.
With the opening of the École supérieure d'aéronautique et de constructions mécaniques on 15 November 1909, Coandă moved to Paris. As a continuation of his Belgian experiments, and especially looking for a way to test wing aerofoils at higher speeds, he contacted Ernest Archdeacon, the co-founder of L'Aero-Club de France, who in turn directed Coandă to Gustav Eiffel and Paul Painlevé. With their assistance, he gained approval to test different wing configurations and air resistance on a platform built by Eiffel at the front of a locomotive on the North of France railway. In March, he started flying lessons at Reims in a Hanriot monoplane.
Helped by his schoolfriend Cammarotta-AdornoIn, Coandă started to build his aircraft and the unusual powerplant in a workshop in the courtyard of his house where he tested the thrust of the powerplant on a dynamometer; these are described in detail in the April 1910 edition of La Technique Aéronautique. He filed for several patents for the mechanism and aircraft on 30 May 1910, with later additions to the existing patents.
Coandă exhibited the aircraft at the Second International Aeronautical Exhibition held from 15 October to 2 November 1910. Together with Henri Fabre's Hydravion, the first floatplane, Coandă's aircraft and devices used for aerodynamic experiments were placed "in solitary state" in an upstairs gallery, separated from the more usual types of aircraft on the main exhibition floor.
The aircraft's construction was a novelty for the time. In contrast to the monoplane described in the July 1910 patent application, though the construction photographs indicate that it had a wooden framework. Forward of the tail was a small horizontal stabiliser. The fuel tank was located in the fuselage between the engine and the cockpit. placed in the forward section of the fuselage drove a rotary compressor through a 1:4 gearbox (1,000 rpm on the Clerget turned the compressor at 4,000 rpm), which drew air in from the front and expelled it rearward under compression and with added heat. The compressor, with a diameter of 50 centimetres (20 in), was located within a cowling at the front of the fuselage. According to later Coandă descriptions, cast aluminium components were also made by Clerget to create an engine with a weight of – equivalent to a power-to-weight ratio of , a considerable achievement at the time.
Coandă's 1910s-era patents describe the inline piston engine's exhaust gases as being routed through heating channels or heat exchangers in contact with the central air flow, then sucked into the compressor inlet to reduce back-pressure on the engine while adding more heat and mass to the airflow. ducted fan or a suction turbine.
thumb|An overhead view, showing the [[Clerget engine's four upright cylinders aft of the rotary compressor. Upper and lower wings are mounted on steel tubes extending from the fuselage. A man stands in the fuselage near two Antoinette VII-style trim and steering wheels.]]
Aviation reporters from The Aero and La Technique Aeronautique were doubtful that the engine could provide sufficient thrust. The writer said the turbo-propulseur was "claimed to give an enormous wind velocity", but the intake area seemed too small to produce the stated thrust, and that "it also appears as if enormous power would be necessary to drive it", more than supplied by the Clerget. Another Bucharest newspaper listed the aircraft in November as "sold twice-over". It may be that Weymann expressed his willingness to buy the aircraft once tests had been carried out. This work is reflected by additions to the powerplant-related patents of 3 December. According to Gérard Hartmann in his Dossiers historiques et techniques aéronautique française, the propulsion system generated only of thrust, and to generate enough thrust for the aircraft to take off (estimated by Coandă at ) Coandă would have had to spin the "turbine" (the rotary compressor) at a speed of 7,000 rpm with the risk of it exploding. This was not tried, but Hartmann concluded that the experiment proved that the solution worked perfectly. With the help of Despujols, a boat maker, and the motor manufacturer Gregoire, Coandă supervised the building of a motor sled, powered by a 30 hp (22 kW) Gregoire engine driving the turbo-propulseur. The sledge was blessed by Russian Orthodox priests at the Despujols plant near Paris on 2 December 1910. Starting the next day, it was exhibited for two weeks at the 12th Automobile Salon of France, alongside Gregoire-powered automobiles on the Gregoire stand. A number of automobile and general interest magazines published photographs or sketches of the sledge. A version of Coandă's turbo-propulseur design was shown for the second time in late 1910 at the Grand Palais of Paris. and improvements of the Coandă-1910.
Coandă described a different, more sturdy system for the attachment of the wings, which also enabled changes in the angle of attack and the centre of gravity. He aimed to obtain more power from the propulsion system, and design drawings show the arrangement of two air-cooled rotary engines on the sides of the fuselage. The placement of the engines indicates that Coandă did not intend to inject fuel into the jet stream and ignite it as the cooling of the engines would have been compromised. The patent was annotated with an additional claim on 19 July 1911 which brought significant changes including the addition of retractable landing gear with dampers inside aerodynamic fairings with skids, removal of the horizontal stabiliser, a supporting surface was provided for each engine and their accessories were covered to improve aerodynamics. Though Coandă continued to study rotary propulsion mechanisms, Antoniu believes that Coandă never implemented a practical solution because of the lack of funds.
In May 1911 Coandă filed English-language patents on the turbo-propulseur design in the United Kingdom and the United States, as well as a second French-language patent filed in Switzerland, and he described it for the 1911 publication of L'Annuaire de l'Air. At the third aviation salon in Paris 1911, Coandă displayed a scale model of the aircraft which used two Gnome rotary engines mounted back to back, connected by a bevel gear to a single two-bladed propeller. The combination of two engines connected to one propeller was originally intended to drive a new turbine, but Coandă was unable to fund one.
Henri Mirguet writing for L'Aérophile magazine in January 1912 said that the new 1911 aircraft retained the fuselage, the frame and the wing of Coandă's 1910 design, but did not keep the turbo-propulseur or "the wooden wingloading surface including the forward longitudinal ribs". The aircraft was flown on 21 October 1911, but with modest results as the latest modifications, especially those related to the powerplant, did not compensate for the increased total weight of the aircraft. At the military contest, it did not meet the requirement for independent operation of each engine.
Following the 1911 exhibition, at the personal request of Sir George White, Coandă moved to the United Kingdom to take a position as chief engineer or chief designer at British and Colonial Aeroplane Company for a few years. In the next four decades Coandă worked on a great variety of inventions. During World War II he revived his earlier turbo-propulseur engine when he was contracted by the German Army in late 1942 to develop an air propulsion system for military ambulance snow sledges much like the one made for the Russian Grand Duke. The German contract concluded after one year, yielding no plans for production. Though Coandă had experimented with a variety of nozzles, and said that he had achieved a degree of success, no turbojet-engine-style fuel injection or combustion in the air stream was attempted. In the same year Geoffrey G. Smith chronicled technological development in his book Gas Turbines and Jet Propulsion for Aircraft, but did not mention Coandă.
In 1950's l'aviation d'Ader et des temps héroiques, the authors assert that Coandă flew the first jet aircraft at Issy-les-moulineaux for 30 metres (100 ft), ending with a crash. In 1953, Flights treatment of aircraft in the 50 years since the Wright brothers' flight included the Coandă-1910 "ducted fan" and said of Coandă that he "believes that he 'took off for a few feet, then came down hurriedly and broke two teeth, quoting J.W. Adderley's 1952 letter to the editor of Flight after Adderley's discussion with Coandă in Paris at the end of World War II. Adderley said he "can definitely confirm that the power unit was of the ducted-fan type, similar in basic principles to the Caproni-Campini aircraft of the 1930s" (referring to the Caproni Campini N.1). Coandă himself spoke on the subject, notably before the Wings Club at New York's Biltmore Hotel on 18 January 1956 where he said "I intended to inject fuel into the air stream which would be ignited by the exhaust gases also channelled through the same circular vent", implying that he never finished the powerplant. Martin Caidin wrote "The Coanda Story" for the May 1956 issue of Flying, based on a personal interview. Houart's version put the fuel tank in the overhead wing, which was metal. In further statements, Coandă said that his 1910 aircraft had movable leading edge slots, retractable landing gear and a fuel supply which was held in the overhead wing to reduce fuselage profile and thus drag.
Rocket engineer G. Harry Stine worked alongside Coandă from 1961 to 1965 at Huyck Corporation, and interviewed him in 1962. In 1967, the magazine Flying printed an account written by Stine, which described the landing gear as retracting into the lower wing, with the fuel tank hidden in the upper wing. Stine wrote that Coandă flew on 10 December 1910, and described the heat from the "two jet exhausts" as being "too much for me" after the powerplant was mounted in the aircraft.
In 1965, Historian Emeritus Paul E. Garber of the NASM interviewed Coandă, who related that the December 1910 flight was no accident, that he had seated himself in the cockpit intending to test five factors: aircraft structure, the engine, the wing lift, the balance of controls, and the aerodynamics. He said that the heat from the engine was "fantastic", but that he placed mica sheets and deflecting plates to direct the jet blast away from the wooden fuselage. Gibbs-Smith wrote that "there has recently arisen some controversy about this machine, designed by the Romanian-born and French-domiciled Henri Coanda, which was exhibited at the Paris salon in October 1910. Until recently it has been accepted as an all-wood sesquiplane, with cantilever wings, powered by a 50 hp Clerget engine driving a 'turbo-propulseur' in the form of a large but simple ducted air fan. This fan was fitted right across the machine's nose and the cowling covered the nose and part of the engine: the resulting 'jet' of plain air was to propel the aeroplane."
In 2010, Antoniu wrote that he thought Gibbs-Smith speculated on the basis of the evidence of absence that the aircraft was never tested or flown, but that Gibbs-Smith did not find any concrete evidence to support his position. Similarly, Antoniu was unable to find concrete proof of a test flight. Antoniu also wrote that Gibbs-Smith did not check the French patents claimed by Coandă in 1910 and 1911, describing the retractable gear, leading edge wing slot and upper wing fuel tank, and that he did not see photographs from private collections demonstrating aspects about which he wrote.
thumb|Coandă's US patent diagram for "Improvement in Propellers", filed 1911 and granted 1914
In 1980, NASM historian Frank H. Winter examined the 1965 drawings and specifications Coandă prepared while at Huyck Corporation and wrote an article about Coandă's claim: "There is a wholly new description of the inner workings of the machine that does not occur in any of the accounts given [in the 1910s] and which defies all of the patent specifications." He said Coandă told various conflicting stories about his claimed 1910 flight, and that Coandă produced a set of altered drawings as proof of his claims: