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History

Since 400 BC, Chinese children have played with bamboo flying tops. Eventually, this flying top made its way to Europe and is depicted in a 1463 European painting. Pao Phu Tau (抱朴子) was a 4th-century book in China reported to describe some of the ideas inherent to rotary wing aircraft:

Paul Cornu's helicopter in 1907
Paul Cornu's helicopter in 1907
Someone asked the master about the principles of mounting to dangerous heights and traveling into the vast inane. The Master said, "Some have made flying cars with wood from the inner part of the jujube tree, using ox-leather [straps] fastened to returning blades so as to set the machine in motion."

Leonardo da Vinci conceived a machine that could be described as an "aerial screw". He wrote that he made small flying models but could not stop the rotor from making the whole craft rotate. Later machines would more closely resemble the ancient bamboo flying top, with spinning wings rather than screws.

In July 1754, Mikhail Lomonosov showed the Russian Academy of Sciences a small coaxial rotor powered by a wound-up spring, intended to lift meteorological instruments.[9]

In 1783, Christian de Launoy, and his mechanic, Bienvenu, made a model pair of counter-rotating rotors (not coaxial) using turkey's flight feathers as rotor blades, and in 1784 demonstrated it to the French Academy of Sciences.[9]

In 1861, the word "helicopter" was coined by Gustave de Ponton d'Amécourt,[9] a French inventor who demonstrated a small steam-powered model.

From 1860 to 1880, many small helicopter models were designed and made.[9] These included Alphonse Pénaud's model coaxial rotors, powered by twisted rubber bands (1870). Enrico Forlanini's unmanned helicopter was powered by a steam engine. It was the first of its type that rose to a height of 13 meters, where it remained for some 20 seconds, after a vertical take-off from a park in Milan (1877). Emmanuel Dieuaide's design featured counter-rotating rotors and was steam-powered through a hose from a boiler on the ground (1877). Melikoff designed a "man carrier," but it was almost certainly not built (1877). Dandrieux's design had counter-rotating rotors and a 7.7-pound (3.5-kilogram) steam engine. It rose more than 40 feet (12 meters) and flew for 20 seconds (circa 1878).

In the 1880s, Thomas Edison experimented with small helicopter models in the USA. First with a guncotton-powered engine, which caused damage by explosions, and tests were ended. Next he used an electric motor. His tests showed that a large rotor with low blade area was needed.

Ján Bahýľ, a Slovak inventor, developed a model helicopter powered by an internal combustion engine, that in 1901 reached a height of 0.5 meters. On 5 May 1905, his helicopter reached four meters in altitude and flew for over 1,500 meters.[10]

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First flights

In 1906, two French brothers, Jacques and Louis Breguet, began experimenting with airfoils for helicopters and in 1907, those experiments resulted in the Gyroplane No.1. Although there is some discrepancy about the dates, sometime between 14 August and 29 September 1907, the Gyroplane No. 1 lifted its pilot up into the air about two feet (0.6 meters) for a minute.[3] However, the Gyroplane No. 1 proved to be extremely unsteady and required a man at each corner of the airframe to hold it steady. For this reason, the flights of the Gyroplane No. 1 are considered to be the first manned flight of a helicopter, but not a free or untethered flight.

That same year, fellow French inventor Paul Cornu designed and built a helicopter that used two 20-foot (6-meter) counter-rotating rotors driven by a 24 hp (18-kW) Antoinette engine. On 13 November 1907, it lifted its inventor to 1 foot (0.3 meters) and remained aloft for 20 seconds. Although this flight was smaller in its achievement than that of the Breguet brothers, it was greater in accomplishment in that it was the first true free flight with a pilot. The Cornu helicopter would achieve a height of nearly 2 meters but also proved to be unstable and was abandoned after only a few flights.[3]

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Early development

In the early 1920s, Raul Pateras Pescara, an Argentinian working in Europe, demonstrated one of the first successful applications of cyclic pitch.[3] His coaxial, contra-rotating, biplane rotors were able to be warped to cyclically increase and decrease the lift they produced; and the rotor hub could also tilt, both allowing the aircraft to move laterally without a separate propeller to push or pull it. Pescara is also credited with demonstrating the principle of autorotation, the method by which helicopters land safely after engine failure. By January 1924, Pescara's helicopter No. 3 was capable of flights up to 10 minutes.

One of Pescara's contemporaries, Frenchman Etienne Oemichen, set the first helicopter world record recognized by the Fédération Aéronautique Internationale (FAI) on 14 April 1924, flying his helicopter 360 meters (1,181 feet). On 18 April 1924, Pescara beat Oemichen's record, flying for a distance of 736 m (nearly a half mile) in 4 minutes and 11 seconds (about 8 mph, 13 km/h) maintaining a height of six feet.[11] Not to be outdone, Oemichen reclaimed the world record on 4 May when he flew his No. 2 machine again for a 14-minute flight covering 5,550 feet (1.05 mi, 1.692 km) while climbing to a height of 50 feet (15 meters).[11] Oemichen also set the 1-km closed-circuit record at 7 minutes 40 seconds.[3]

Meanwhile, Juan de la Cierva was developing and introducing the first practical rotorcraft in Spain. In 1923, the aircraft that would become the basis for the modern helicopter rotor began to take shape in the form of an autogyro, Cierva's C.4.[12] Cierva had discovered aerodynamic and structural deficiencies in his early designs that could cause his autogyros to flip over after takeoff. The flapping hinges that Cierva designed for the C.4 allowed the rotor to develop lift equally on the left and right halves of the rotor disk. A crash in 1927 led to the development of a drag hinge to relieve further stress on the rotor from its flapping motion.[12] These two developments allowed for a stable rotor system, not only in a hover, but in forward flight.

Albert Gillis von Baumhauer, a Dutch aeronautical engineer, began studying rotorcraft design in 1923. His first prototype "flew" ("hopped" and hovered in reality) on 24 September 1925, with Dutch Army-Air arm Captain Floris Albert van Heijst at the controls. The controls that Captain van Heijst used were Von Baumhauer's inventions, the cyclic and collective. Patents were granted to von Baumhauer for his cyclic and collective controls by the British ministry of aviation on 31 January 1927, under patent number 265,272.

In 1930, the Italian engineer Corradino D'Ascanio built his D'AT3, a coaxial helicopter. His relatively large machine had two, two-bladed, counter-rotating rotors. Control was achieved by using auxiliary wings or servo-tabs on the trailing edges of the blades,[13] a concept that was later adopted by other helicopter designers, including Bleeker and Kaman. Three small propellers mounted to the airframe were used for additional pitch, roll, and yaw control. The D'AT3 held modest FAI speed and altitude records for the time, including altitude (18 m), duration (8 minutes 45 seconds) and distance flown (1,078 m).[13]

The Bréguet-Dorand Gyroplane Laboratoire was built in 1933. After many ground tests and an accident, it first took flight on 26 June 1935. Within a short time, the aircraft was setting records with pilot Maurice Claisse at the controls. On 14 December 1935 he set a record for closed-circuit flight with a 500 m diameter. The next year, on 26 September 1936, Claisse set a height record of 158 m. And, finally, on 24 November 1936, he set a flight duration record of one hour, two minutes and 5 seconds over a 44 km closed circuit at 44.7 km/h. The aircraft was destroyed in 1943 by an Allied air strike at Villacoublay airport.

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Birth of an industry

Despite the success of the Gyroplane Laboratoire, the German Focke-Wulf Fw 61, first flown in 1936, would eclipse its accomplishments. The Fw 61 broke all of the helicopter world records in 1937, demonstrating a flight envelope that had only previously been achieved by the autogyro. In February 1938, Hanna Reitsch became the first female helicopter pilot, exhibiting the Fw 61 before crowds in the Deutschlandhalle.

Nazi Germany would use helicopters in small numbers during World War II for observation, transport, and medical evacuation. The Flettner Fl 282 Kolibri synchropter was used in the Mediterranean Sea, while the Focke Achgelis Fa 223 Drache was used in Europe. Extensive bombing by the Allied forces prevented Germany from producing any helicopters in large quantities during the war.

In the United States, Igor Sikorsky and W. Lawrence LePage, were competing to produce the United States military's first helicopter. Prior to the war, LePage had received the patent rights to develop helicopters patterned after the Fw 61, and built the XR-1, utilizing the transverse rotor layout.[14] Meanwhile, Sikorsky, had settled on a simpler, single rotor design, the VS-300. After experimenting with configurations to counteract the torque produced by the single main rotor, he settled on a single, smaller rotor mounted vertically on the tailboom.

Developed from the VS-300, Sikorsky's R-4 became the first mass produced helicopter with a production order for 100 aircraft. The R-4 was the only Allied helicopter to see service in World War II, primarily being used for rescue in Burma, Alaska, and other areas with harsh terrain. Total production would reach 131 helicopters before the R-4 was replaced by other Sikorsky helicopters such as the R-5 and the R-6. In all, Sikorsky would produce over 400 helicopters before the end of World War II.[15]

As LePage and Sikorsky were building their helicopters for the military, Bell Aircraft hired Arthur Young to help build a helicopter using Young's semi-rigid, teetering-blade rotor design, which utilized a weighted stabilizing bar. The subsequent Model 30 helicopter demonstrated the simplicity and ease of the design. The Model 30 was developed into the Bell 47, which became the first aircraft certificated for civilian use in the United States. Produced in several countries, the Bell 47 would become the most popular helicopter model for nearly 30 years.

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Turbine age

In 1951, at the urging of his contacts at the Department of the Navy, Charles H. Kaman modified his Ka-225 helicopter with a new kind of engine, the turboshaft engine. This adaptation of the turbine engine provided a large amount of horsepower to the helicopter with a lower weight penalty than piston engines, with their heavy engine blocks and auxiliary components. On 11 December 1951, the Ka-225 became the first turbine-powered helicopter in the world. Two years later, on 26 March 1954, a modified Navy HTK-1, another Kaman helicopter, became the first twin-turbine helicopter to fly. However, it was the Sud Aviation Alouette II that would become the first helicopter to be produced with a turbine-engine.[16]

Reliable helicopters capable of stable hover flight were developed decades after fixed-wing aircraft. This is largely due to higher engine power density requirements than fixed-wing aircraft. Improvements in fuels and engines during the first half of the 20th century were a critical factor in helicopter development. The availability of lightweight turboshaft engines in the second half of the 20th century led to the development of larger, faster, and higher-performance helicopters. While smaller and less expensive helicopters still use piston engines, turboshaft engines are the preferred powerplant for helicopters today.

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