The Lockheed XV-4 Hummingbird (originally designated VZ-10) was a U.S. Army project in the 1960s, one of many attempts to produce a V/STOL vertical take off / landing jet. At a design speed of 336 mph, the Hummingbird was slower than some propeller-powered transports.
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 11,607 lb aircraft could be lifted by a 6,600 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
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