Planes that can take off directly into the air without the need for a runway are, theoretically, an absolute dream for the military. Vertical take-off and landing (VTOL) craft require less physical space and infrastructure to get into the air compared to traditional planes. That means more fighters on a single aircraft carrier or smaller airports in more remote places.
While VTOL has its roots in military applications, culminating in the long-delayed F-35B, VTOL has also grown as an attractive option in both private and civil use, primarily for use in possible "air taxis" or "flying cars" that would make use of helipads, but wouldn't be helicopters exactly.
A vertical take-off and landing (VTOL) aircraft is one that can hover, take off, and land vertically. This classification can include a variety of types of aircraft including fixed-wing aircraft as well as helicopters and other aircraft with powered rotors, such as cyclocopters and tiltrotors. Some VTOL aircraft can operate in other modes as well, such as CTOL (conventional take-off and landing), STOL (short take-off and landing), and/or STOVL (short take-off and vertical landing). Others, such as some helicopters, can only operate by VTOL, due to the aircraft lacking landing gear that can handle horizontal motion. VTOL is a subset of V/STOL (vertical and/or short take-off and landing).
Besides the ubiquitous helicopter, there are currently two types of VTOL aircraft in military service: craft using a tiltrotor, such as the Bell Boeing V-22 Osprey,
and another using directed jet thrust, 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 as of 2017). Generally speaking, VTOL aircraft capable of STOVL use it wherever possible, since it typically significantly increases take-off weight, range or payload compared to pure VTOL.
The idea of vertical flight has been around for thousands of years and sketches for a VTOL (helicopter) shows up in Leonardo da Vinci's sketchbook. 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 aircraft with 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 Heinrich Focke's began work on the Focke-Achgelis Fa 269, which had two rotors that tilted downward for vertical takeoff, but wartime bombing halted development.
In May 1951, both Lockheed and Convair were awarded contracts in the attempt to design, construct, and test two experimental VTOL fighters. Lockheed produced the XFV, and Convair produced the Convair XFY Pogo.
Both experimental programs proceeded to flight status and completed test flights from 1954–1955 when the contracts were cancelled. Similarly, the X-13 VertiJet flew a series of test flights between 1955 and 1957, but also suffered the same fate.
The use of vertical fans driven by engines was investigated in the 1950s. The US built an aircraft where the jet exhaust drove the fans, while British projects not built included fans driven by mechanical drives from the jet engines.
NASA has flown other VTOL craft such as the Bell XV-15 research craft (1977), as have the Soviet Navy and Luftwaffe. Sikorsky tested an aircraft dubbed the X-Wing, which took off in the manner of a helicopter. The rotors would become stationary in mid-flight, and function as wings, providing lift in addition to the static wings. Boeing X-50 is a Canard Rotor/Wing prototype that utilizes a similar concept.
A different British VTOL project was the gyrodyne, where a rotor is powered during take-off and landing but which then freewheels during flight, with separate propulsion engines providing forward thrust. Starting with the Fairey Gyrodyne, this type of aircraft later evolved into the much larger twin-engined Fairey Rotodyne, that used tip jets to power the rotor on take-off and landing but which then used two Napier Eland turboprops driving conventional propellers mounted on substantial wings to provide propulsion, the wings serving to unload the rotor during horizontal flight.
The Rotodyne was developed to combine the efficiency of a fixed-wing aircraft at cruise with the VTOL capability of a helicopter to provide short-haul airliner service from city centres to airports.
The first production tiltrotor aircraft CL-84-1 (CX8402) on display at the Canada Aviation and Space Museum in Ottawa, Ontario
The CL-84 was a Canadian V/STOL turbine tilt-wing monoplane designed and manufactured by Canadair between 1964 and 1972. The Canadian government ordered three updated CL-84s for military evaluation in 1968, designated the CL-84-1. From 1972 to 1974, this version was demonstrated and evaluated in the United States aboard the aircraft carriers USS Guam and USS Guadalcanal, and at various other centres. These trials involved military pilots from the United States, the United Kingdom and Canada. During testing, two of the CL-84s crashed due to mechanical failures, but no loss of life occurred as a result of these accidents. No production contracts resulted.
Although tiltrotors such as the Focke-Achgelis Fa 269 of the mid-1940s and the Centro Técnico Aeroespacial "Convertiplano" of the 1950s reached testing or mock-up stages,
the V-22 Osprey is considered the world's first production tiltrotor aircraft. It has one three-bladed proprotor, turboprop engine, and transmission nacelle mounted on each wingtip. The Osprey is a multi-mission aircraft with both vertical take-off and landing (VTOL) and short take-off and landing capability (STOL). It is designed to perform missions like a conventional helicopter with the long-range, high-speed cruise performance of a turboprop aircraft. The FAA classifies the Osprey as a model of powered lift aircraft.
Attempts were made in the 1960s to develop a commercial passenger aircraft with VTOL capability. The Hawker Siddeley Inter-City Vertical-Lift proposal had two rows of lifting fans on either side. However, none of these aircraft made it to production after they were dismissed as too heavy and expensive to operate.
Uber has expressed interest in VTOL technology for taxis with Airbus as a potential partner. A German company, Lilium, has had successful test runs and the city of Dubai wants to incorporate VTOL planes into future transportation solutions.