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vertical takeoff and landing aircraft (VTOL), craft capable of rising and descending vertically from and to the ground, thus requiring no runway. While a balloon or an airship has obvious VTOL capability, both are very inefficient at moving parallel to the earth's surface. The autogiro and the helicopter offer some improvement in this respect, but still have very limited performance. A large number of VTOL designs have been produced and tried. The pogo-stick, or tail-sitting, type was similar in appearance to a conventional airplane except for a special tail on which it took off and landed. This type was abandoned, partly because of the difficulty in maintaining fine control when its fuselage was positioned vertically, e.g., during a landing. Convertiplanes are VTOL craft that can fly horizontally with the same effectiveness as a conventional airplane. Some convertiplanes are conventional-looking aircraft that can tilt their rotors, or oversize propellors, so that the rotors' axes are vertical during takeoff and landing and are horizontal during forward flight. The best-known such tilt-rotor aircraft is the V-22 Osprey, which first flew in 1989. The Harrier is a jet fighter convertiplane that uses vanes to direct the thrust of its engine upward or forward and is capable of flight at approximately the speed of sound; it proved its ability to control a battlefield despite the absence of airports and runways during the 1982 Falklands conflict.
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