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.
Cold War era During the 1950s, aircraft designers around the world engaged in programmes to develop fixed-wing aircraft that could not only perform both a vertical take-off and vertical landing, but transition into and out of conventional flight as well. As observed by the aviation author Francis K. Mason, a combat aircraft that possessed such qualities would have effectively eliminate the traditional reliance on relatively vulnerable runways by taking off and landing vertically as opposed to the conventional horizontal approach. Accordingly, the development of viable
vertical take-off and landing (VTOL) aircraft was particularly attractive to military planners of the early
postwar era. As the
thrust-to-weight ratio of
turbojet engines increased sufficiently for a single engine be able to lift an aircraft, designers began to investigate ways of maintaining stability while an aircraft was flying in the VTOL stage of flight. One company that opted to engage in VTOL research was the
French engine manufacturer
SNECMA who, beginning in 1956, built a series of wingless test rigs called the
Atar Volant. Only the first of these was unpiloted and the second flew freely, both stabilized by gas jets on outrigger pipes The third had a tilting seat to allow the pilot to sit upright when the
fuselage was level and had the lateral air intakes planned for the free flying aircraft, though it always operated attached to a movable cradle. The pilot for these experiments was Auguste Morel. However, the Atar Volant was not an end onto itself; its long term purpose was to serve as precursors to a larger fixed-wing aircraft. Independently of this work, substantial influence on the direction of development came from the Austrian design engineer
Helmut von Zborowski, who had designed an innovative doughnut-shaped
annular wing that could function "as power plant, airframe of a flying wing aircraft and drag-reducing housing". It was theorised that such a wing could function as a
ramjet engine and propel an aircraft at
supersonic speeds, suitable for an
interceptor aircraft. The eye-catching design of the Coléoptère rapidly made waves in the public conscious, even internationally; author Jeremy Davis observed that the aircraft had even influenced international efforts, having allegedly motivated the
United States Navy to contract American helicopter manufacturer
Kaman Aircraft to design its own annular-wing vehicle, nicknamed the Flying Barrel. The XFY successfully demonstrated the full transition between flight modes on 5 November 1954. A somewhat similar aircraft was the
Lockheed XFV Salmon, which paired a straight wing with an
X tail; however, the XFV never achieved the crucial flight transition. However, it became evident during flight testing that such VTOL aircraft would be flown only by the most experienced pilots, even if all technical problems were disregarded; thus, it was not feasible to place VTOL fighters—as previously hoped for—on every ship. Also, whereas jet-engined fighters had top speeds that approached Mach 2, the turboprop VTOL fighter was at a disadvantage due to its maximum speed being below Mach 1. As a result of these circumstances, work on the XFY was halted. During 1955, the United States commenced flight testing of a jet-powered design, the Ryan
X-13 Vertijet. Two prototypes were constructed, both of which flew, made successful transitions to and from horizontal flight, and
landed. The X-13's final test flight was conducted near
Washington DC during 1957. An inherent problem with all these tail-sitter designs was poor pilot visibility, especially of the ground, during vertical descent and landing. Ultimately, most work on applying the concept towards manned aircraft were abandoned upon the arrival of more practical form of VTOL appeared, in the form of
thrust vectoring, as used by production aircraft such as the
Hawker Siddeley Harrier and
Yakovlev Yak-38. An
unmanned aerial vehicle (UAV) does not suffer the problem of pilot attitude. The
Dornier Aerodyne is of ducted-fan configuration similar to a
coleopter, and a test UAV flew successfully in hover mode in 1972, before development was discontinued. Another contemporary UAV project was the
NSRDC BQM-108 that was developed by the
United States Navy; although work was discontinued almost immediately after its single successful test flight. During the 1970s, several studies and
wind tunnel models were made of a tail-sitting version of the
General Dynamics F-16 Fighting Falcon that was intended for use on board ships; however, it was decided not to pursue further development of the concept due to the large thrust requirement involved, as well as the need for extensive apparatus to handle take-off and landing.
In the present At present, most of the tail sitter projects or proposals fall under the category of
unmanned aircraft such as Bell Apt or
Northrop Grumman Tern.
Pivotal BlackFly eVTOL with its "tilt-aircraft architecture" can also be considered a type of tail sitter. ==List of tail-sitters==