Built under a US Air Force contract, the X-14 used a planar array of diverter vanes to vector the exhaust of two Armstrong Siddeley ASV8 Viper engines (1,750 lb thrust each) at the center of gravity (c.g.). The vanes could be rotated to direct the exhaust from vertical to nearly horizontal. The 25 ft fuselage and tail were from a Beech T-34; the 34 ft span wing was from a Beech Bonanza. The lack of a ejection seat limited hover testing to very low and very high altitudes. The gross weight was originally only 3,100 lb. The landing gear had to be lengthened when the phenomenon of suck-down was first discovered. Engine gyroscopic effects and exhaust gas reingestion were also encountered. First hover flight was achieved on 17 February 1957; first transition was made on 24 May 1958. The Viper engines were replaced with higher power GE J85 engines when it was transferred to NASA in 1960. It was eventually fitted with a digital fly-by-wire control system and continued flying as a V/STOL testbed until 1981!