Vertical take-off and landing (VTOL) refer to the ability of aircraft to be able to land and take-off in a vertical manner. A well-known example of VTOL aircraft is the helicopter.
The helicopter was one of the first successful forms of VTOL-capable aircraft, with Étienne Oehmichen of France and Raúl Pateras-Pescara de Castelluccio of Argentina being the first two to have successfully developed rotor-based helicopters that took off, hovered, and flew. Following this, several other VTOL aircraft that were developed later on use technology that is similar in principle with the helicopter, and these rotor-based aircraft were used by various countries during World War II. Some examples include Sikorsky R-4, used by the United States, and Focke-Wulf Fw 61, used by Germany.
This development sets the trend to follow for further VTOL aircraft advancements. VTOL innovations have been particularly noted by the military, which leads to advancements by aeronautical technology companies. Experimentation with alternative propulsion models of VTOL aircraft, manifested in the invention of the Harrier Jet around the late 1950s. Instead of being powered by rotors, the Harrier used jet engine as its propeller.
Rotorcrafts were the earliest form of VTOL aircraft. Rotorcrafts are generally energy-efficient, requiring less fuel than any powered-lift aircrafts. This makes the vehicle ideal for practical applications where the vehicle would need to hover for longer periods of time. Nonetheless, not all rotor-based aircrafts are able to do a vertical take off and landing. The autogyro, for example, uses a conventional take off and landing (CTOL). On the other hand, some, like the gyrodyne, has STOVL capability allowing it to take off and land vertically from a short runway. One of the VTOL rotorcraft still in mass production today is the Bell/Boeing V-22.
These aircrafts range from those utilizing ducted fan, propeller, and turbojets to lift the vehicle to the air vertically. Though the three aircrafts require higher fuel consumption - with the turbojets requiring the most - powered-lift aircrafts are capable for longer-distance flights and are able to perform more complex manueveurs in the air. One of the powered-lift VTOL aircraft that is in mass production uses jet turbines, which is the McDonnell/British Aerospace Harrier.