The Bell-constructed X-14 was an open-cockpit, all-metal VTOL monoplane powered by two turbojet engines equipped with thrust deflectors. It first flew in 1957, and was constructed using the wings, ailerons, and undercarriage of a Beech Bonanza and the tail surfaces of a Beech T-34 Mentor airplane. In 1959, the Viper engines were replaced by General Electric J85 engines and the aircraft was delivered to the NASA Ames Research Center as the X-14A where it was used as a test aircraft until early 1963.