In 1951, Bell Aircraft began a long and ardent affair with the tilt-rotor aircraft. The first prototype of this type of aircraft -- the XV-3 -- was, like every helicopter of the period, underpowered. Nonetheless, in a fifteen-year test program, this prototype made over 250 flights, including 110 conversions from vertical to horizontal flight. The success of these tests has sustained Bell's basic faith in the concept.
