The Cierva C.1 was an

experimental An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs when a ...

autogyro An autogyro (from Greek and , "self-turning"), also known as a ''gyroplane'', is a type of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. Forward thrust is provided independently, by an engine-driven propeller. Whi ...

built by Juan de la Cierva in Spain in 1920, the forerunner of his successful series of autogyros. The C.1 was created by taking the fuselage from a Deperdussin fixed-wing aircraft and mounting two rotors shaft above it.text about La cierva (with C.1 photo). In Spanish
/ref> This shaft carried two coaxial contra-rotating rotors, and atop it a fin for increased lateral stability. When tested, the C.1 refused to take off, which Cierva attributed to interference between the two sets of rotors leading to each set autorotating at a different speed. He considered the possibility of mechanically linking the rotors, but dismissed the idea on the grounds of weight and complexity, and his subsequent efforts would all feature single main rotors. Despite its failure to fly, the C.1 demonstrated the principle of

autorotation Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor. Bensen, Ig ...

in a full-sized aircraft for the first time, as it was taxied around the ground.

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