Lockheed’s XV-4 Hummingbird was a U.S. Army experimental aircraft intended to test whether a jet-powered vertical-takeoff-and-landing (VTOL) design could serve as a surveillance platform. The program demonstrated hover and transition flight, but the aircraft’s augmented jet-ejector approach delivered less performance than expected. Both prototypes were ultimately lost in crashes: the first in a fatal accident in 1966 and the modified second aircraft in 1969, with its pilot ejecting safely.
The Hummingbird’s history is a reminder that demonstrating a flight mode is not the same as proving a…