A tail-sitter, or tailsitter, is a type of VTOL aircraft that takes off and lands on its tail, then tilts horizontally for forward flight. Originating in the 1920s with the inventor Nikola Tesla, the first aircraft to adopt a tail-sitter configuration were developed by Nazi Germany during the Second World War. Development of such aircraft spiked during the late 1940s and 1950s, as aircraft designers and defence planners alike recognised the potential value of fixed-wing aircraft that could perform both a vertical take-off and vertical landing while also transitioning into and out of conventional flight. Inherent problems with tail-sitter aircraft were poor pilot visibility and control difficulties, especially during vertical descent and landing. Programmes to develop manned tail-sitters were typically terminated in the form of the more practical thrust vectoring approach, as used by aircraft such as the Hawker Siddeley Harrier and Yakovlev Yak-38.
Description A tail-sitter sits vertically on its tail for takeoff and landing, then tilts the whole aircraft forward for horizontal flight. This is very different from the many other kinds of VTOL technologies, which have horizontally-oriented fuselages. Tail-sitters change fuselage orientation after take-off. They start off with the back of the aircraft to the ground (a vertical orientation), and then reorient to a horizontal orientation in flight. Some tail-sitters then landed conventionally in horizontally-oriented configuration, while others had a much more ambitious goal of landing vertically with the aircraft's back to the ground, a highly hazardous procedure for many reasons, prime of which was increased fuel consumption and limited pilot visibility.
History
Early work The concept of a tail-sitting aircraft can be attributed to originate with the inventor Nikola Tesla, who filed for an associated patent during 1928. However, no immediate attempt to implement this concept into a functional aircraft would emerge for almost two decades. During the Second World War, Nazi Germany worked on the Focke-Wulf Triebflügel ("thrust-wing") fighter that incorporated the tail-sitter concept into its design. It featured three wings that were mounted radially as a rotor on a rotating section of the fuselage, these were driven by small jet engines positioned on the wingtips to propel the aircraft via this wing rotation. For takeoff and landing, it would fly vertically (akin to a helicopter) before tilting over horizontally to fly as a self-propelled wing generating both lift and thrust. The contemporary Heinkel Lerche project had an annular wing forming a duct around a conventional propeller, and in the transition from vertical to forward flight the lift would have transferred to the wing.
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