Bell Aircraft XV-3
The Bell XV-3 (Bell 200) was a tiltrotor aircraft first flown in 1955. Like its predecessors, the XV-3 had the engines in the fuselage and drive shafts transferring power out to tilting wingtip rotor assemblies. It was fitted with ejection seats that fired downwards; they were never needed.
The original military designation was XH-33, classifying it as a helicopter, but its designation was changed to XV-3 in the convertiplane series. The designation was changed once again in 1962 to XV-3A when the V- prefix was changed to mean VTOL.
The XV-3 was successfully able to hover and transition to forwards flight, but had a number of stability, aerodynamic, and structural problems. The largest problem was aeroelastic stability, where vibrations of the rotors, tilt assemblies, wings, and fuselage would cause aerodynamic instability for the whole aircraft. It flew in August 1955 but crashed two months later. The second XV-3 made its first flight on 12 December 1958 and was able to make the conversion from vertical to horizontal flight 6 days afterward. The XV-3 was flown for 125 flight hours by 10 test pilots between 1955 and November, 1968. It accomplished 110 transitions from hovering to forward flight.
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