Cierva

24. Juan de la Cierva started building aircraft in Spain as early as 1912; in 1919 he started to consider the use of a rotor to generate lift at low airspeed, and eliminate the risk of stall. To achieve this, he used the ability of a lifting rotor to autorotate. In 1923, de la Cierva's first successful autogyro was flown in Spain by Lt. Gomez Spencer. This pioneering work was carried out in de la Cierva's native Spain. In 1925 he brought his C.6 to England and demonstrated it to the Air Ministry at Farnborough, Hampshire. This machine had a four blade rotor with flapping hinges but relied upon conventional airplane controls for pitch, roll and yaw. It was based upon an Avro 504K fuselage, initial rotation of the rotor was achieved by the rapid uncoiling of a rope passed around stops on the undersides of the blades.

Avro-built C.8 was a refinement of the C.6, with the more powerful 180 hp Lynx radial engine, and several C.8s were built. The C.8R incorporated drag hinges, due to blade flapping motion causing high blade root stresses in the rotor plane of rotation; this modification, however, resulted in other problems such as ground resonance for which drag hinge dampers were fitted.

The resolution of these fundamental rotor problems opened the way for progressive improvements; confidence built up rapidly, and after several cross country flights a C.8L4 was entered for the 1928 Kings Cup Air Race. Although forced to withdraw, the C.8L4 subsequently completed a 4,800 km (3,000 mi) tour of the British Isles. Later that year it flew from London to Paris, extending the tour to include Berlin, Brussels and Amsterdam, thus becoming the first rotating wing aircraft to cross the English Channel.

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