Tiltwing aircraft have wings that are horizontal for forward flight and are capable of tilting to a vertical position with their engines to allow for vertical takeoffs and landings. Tiltwings are similar to but differ from tiltrotors, like the V-22 Osprey, which maintains the horizontal position of its wing when transitioning between vertical and horizontal flight. The positive aspect of this is improved hover lift efficiency due to less interference from the wings. A negative impact is an increased impact from crosswinds in hover due to the large surface area of the vertical wing.
Some early tiltwing concepts were the Vertol VZ-2 (1957), Hiller X-18 (1959), Kaman K-16B (1959), and LTV XC-142 (1964).
The Vertol VZ-2 was a research aircraft built for NASA to investigate tiltwings. Of note were small ducted fans in the tail to improve controllablity at low speeds. The VZ-2 successfully made 450 flights with 34 transition flights before the program ended in 1965.
The Hiller X-18 was another tiltwing testbed developed for the U.S. Air Force, and received an X-series experimental plane designation. The aircraft was constructed using parts obtained from Chase YC-122 Avitruc, Lockheed XFV-1, and Convair XFY-1 Pogo aircraft. The X-18 diverted is thrust at the tail to provide pitch control at low speeds. There were 20 flights, with the last occurring in 1961 during which the pilots lost control during hover at 10,000 feet before safely landing. It was eventually cancelled in 1964 and cut up for scrap.
The Kaman K-16B was developed for the U.S. Navy to evaluate the tiltwing concept, and was converted from the Grumman Goose amphibious aircraft. Of note was that the wing could only obtain a maximum of a 50 degree angle of incidence, and did not go completely vertical, but was estimated to have sufficient thrust to allow for essentially vertical takeoffs and landings. The K-16B only underwent wind tunnel testing and several tethered tests before the project was cancelled in 1962.
The Ling-Temco-Vought LTV XC-142 was an experimental tiltwing aircraft that was the result of a joint effort between the U.S. Army, Navy, and Air Force. After building five aircraft and successfully demonstrating its capabilities over several hundred flights, the program ended as each of the services pulled out due to a lack of interest in pursuing the capability.
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