A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-wing aircraft and other hybrid aircraft with powered rotors such as cyclogyros/cyclocopters and gyrodynes. Some VTOL aircraft can operate in other modes as well, such as CTOL (conventional take-off & landing), STOL (short take-off & landing), or STOVL (short take-off & vertical landing). Others, such as some helicopters, can only operate as VTOL, due to the aircraft lacking landing gear that can handle taxiing. VTOL is a subset of V/STOL (vertical or short take-off & landing). Some lighter-than-air aircraft also qualify as VTOL aircraft, as they can hover, takeoff and land with vertical approach/departure profiles. Electric vertical takeoff and landing aircraft, or eVTOLs, are being developed along with more autonomous flight control technologies and mobility-as-a-service (MaaS) to enable advanced air mobility (AAM), that could include on-demand air taxi services, regional air mobility, freight delivery, and personal air vehicles (PAVs). Besides the ubiquitous helicopters, there are currently two types of VTOL aircraft in military service: tiltrotor aircraft, such as the Bell Boeing V-22 Osprey, and thrust-vectoring airplanes, such as the Harrier family and new F-35B Lightning II Joint Strike Fighter (JSF). In the civilian sector currently only helicopters are in general use (some other types of commercial VTOL aircraft have been proposed and are under development ). Generally speaking, VTOL aircraft capable of STOVL use it wherever possible, since it typically significantly increases takeoff weight, range or payload compared to pure VTOL. History Props, proprotors and advanced rotorcraft The idea of vertical flight has been around for thousands of years, and sketches for a VTOL (helicopter) show up in Leonardo da Vinci's sketch book. Manned VTOL aircraft, in the form of primitive helicopters, first flew in 1907 but would take until after World War Two to perfect. In addition to helicopter development, many approaches have been tried to develop practical aircraft with vertical take-off and landing capabilities including Henry Berliner's 1922–1925 experimental horizontal rotor fixed wing aircraft, and Nikola Tesla's 1928 patent and George Lehberger's 1930 patent for relatively impractical VTOL fixed wing airplanes with a tilting engines. In the late 1930s British aircraft designer Leslie Everett Baynes was issued a patent for the Baynes Heliplane, another tilt rotor aircraft. In 1941 German designer