Question: The Cierva C.8 was built by Juan de la Cierva in association with a company founded in what year?
Sentence (from "Juan de la Cierva"): In 1923, after four years of experimentation, De la Cierva developed the articulated rotor, which resulted in the world's first successful flight of a stable rotary-wing aircraft, with his C.4 prototype.
Relevant evidence: No