Coandă-1910
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.
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 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.Coandă continued his studies at Liège, Belgium, where with his roommate and friend Giovanni Battista Caproni he built the Coandă-Caproni box glider, based on the plans of gliders designed by Otto Lilienthal and Octave Chanute which he previously studied at Charlottenburg and Spandau. 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
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, it was a sesquiplane which complicated the construction, but in return solved lateral stability control issues. The cantilevered wings were held in place at three points by tubular steel struts without any bracing from flying wires. According to Coandă's description the wings were built with metal spars, but existing photographs of the construction show a completely wooden internal structure. The trailing edges of the upper wing could be twisted separately or together for lateral control or braking during landing, and were controlled by pedals in the two-seat open cockpit. The fuselage, painted reddish-brown and highly polished, was described by The Technical World magazine as having a framework of steel, though the construction photographs indicate that it had a wooden framework. This was triangular in cross-section with convex ribs edged with strips of steel, and strengthened with a covering of heat-shaped moulded plywood. Tubular radiators for engine cooling were located on either side of the cockpit. The vertical struts from the wings were secured to the fuselage with steel collars fixed with screws. The fuselage terminated in a cruciform empennage with control surfaces at 45° angles to vertical and horizontal. Four triangular surfaces at the rear of the tail were controlled using a pair of large Antoinette VII-style steering wheels mounted outside of the cockpit, one on each side, and were used for pitch and directional control. It was an early instance of what are now known as ruddervators. Forward of the tail was a small horizontal stabiliser. The fuel tank was located in the fuselage between the engine and the cockpit.
The most remarkable feature of the aircraft was its engine. Instead of a propeller, a 50 hp inline water-cooled internal combustion engine built by Pierre Clerget at the Clément-Bayard workshop with funding from L'Aero-Club de France, placed in the forward section of the fuselage drove a rotary compressor through a 1:4 gearbox, 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, 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. The turbo-propulseur was claimed to be capable of generating of thrust. The powerplant was referred to in reports at the time by different terms: a turbine without propellers, turbo-propulseur, ducted fan or a suction turbine.
File:Coanda aircraft at 1910 Paris salon.jpg|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 engine was noted in The Aero, reprinted in Aircraft, as being "of remarkably small proportions in relation to the size of the machine." 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.
The Coandă-1910 was reportedly sold to Charles Weymann in October 1910. A daily newspaper from Bucharest wrote in 1910 that the aircraft was constructed in Clerget's workshops and that it "will fly in 6–7 weeks near Paris, piloted by Weymann, one of the pilots celebrated at the Rennes aviation meeting." 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.
At the exhibition, reaction among observers was mixed. Some doubted the aircraft would fly, and focused on more likely machines such as the Sloan, the Voisin, or Louis Paulhan's design. Others gave special notice to the Coandă-1910, calling it original and ingenious. The reporter from La Technique Aeronautique wrote, "In the absence of definitive trials, permitting the precise yield of this machine, it is without doubt premature to say it will supersede the propeller ... the tentative is interesting and we watch it closely." The official exhibition report ignored the turbo-propulseur engine and instead described Coandă's novel wing design, and the unusual empennage. On 15 November 1910, L'Aérophile wrote that if the machine were ever to develop as the inventor hoped, it would be "a beautiful dream".
After the exhibition the aircraft was moved to a Clément-Bayard workshop at Issy-les-Moulineaux for further testing. This work is reflected by additions to the powerplant-related patents of 3 December. A group of modern-day Romanian investigators led by Dan Antoniu, having examined photographs from 1910, concluded that the rotary compressor featured at the exhibition was a hybrid between the one described in the initial 30 May 1910 patent and that shown in a later patent application. They felt that the exhibition machine had a simpler director system, a different rotor with a smaller intake cone, and that the exhaust gas heat transfer system had not been implemented. 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 Coandă would have had to spin the "turbine" 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.
Henri Mirguet writing for L'Aérophile magazine in January 1912, recalled the previous exhibition's machine as the "chief attraction" of the 1910 salon. He wrote that Coandă answered his "pressing—and indiscreet—questions" about the turbo-propulseur-powered aircraft at that earlier exhibit, telling him that the machine had attained a speed of 112 kilometres per hour during several "flight tests", an improbable answer about which Mirguet "reserved judgment", waiting for confirmation that never materialised.