Lockheed XV-4 Hummingbird

The Lockheed XV-4 Hummingbird (originally designated VZ-10) was a U.S. Army project designed and built by the Lockheed Corporation in the 1960s, one of many attempts to produce a V/STOL vertical take off/landing jet. At a design speed of 336 mi/h, the Hummingbird was slower than some propeller-powered transports. Both prototype aircraft were destroyed in accidents.

Design and development
The design used doors at the top and bottom of the fuselage intended to augment thrust ejected into this area with cold air. In theory, a 11607 lb aircraft could be lifted by a 6600 lbf engine. Unfortunately, performance was far below the estimates only 1.04 thrust-to-weight in practice and the prototype crashed on 10 June 1964, killing the pilot. The second aircraft was converted to lift jets instead, also crashing after several tests.

Rockwell's XFV-12 would be even less successful at venting cold air to augment thrust through the wings. The Lockheed F-35 Joint Strike Fighter would later employ a shaft-driven lift fan, also located in the fuselage.

None of the early American V/STOL designs would result in a production aircraft. The British Hawker Siddeley Harrier used vectoring nozzles, while the Russian Yakovlev Yak-38 Forger attack jet used lift jets in conjunction with rotating rear nozzles.

Testing
The first conventional takeoff flight of the first prototype, XV-4A (62–4503), took place on 7 July 1962. Initial tethered flight tests were carried out on 30 November 1962 with the first free hovering flight occurring on 24 May 1963. The first flight to transition from hovering to forward flight took place on 8 November 1963. 62–4503 was destroyed in a fatal crash in Cobb County on 10 June 1964.

Lockheed modified the second prototype aircraft between 1966 and 1968 to XV-4B standard. The two Pratt & Whitney JT12 engines were replaced with six General Electric J85 turbojets four of these units acting as lift jets. This aircraft crashed in Georgia on 14 March 1969, the pilot, Harlan J. Quamme, escaped uninjured by use of the ejection seat.