Vertical Take-Off and Landing
Vertical takeoff and landing (VTOL) aircraft include fixed-wing aircraft that can hover, take off and land vertically, as well as helicopters and other aircraft with powered rotors, such as tiltrotors. Some VTOL aircraft can operate in other modes as well, such as CTOL (conventional takeoff and landing), STOL (short takeoff and landing), and/or STOVL (short takeoff 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.
To take off or land vertically, the powerful exhaust streams from a jet engine can be directed downward as well as backward, and their direction can be changed in mid-flight. This allows fixed-wing aircraft, such as the Harrier or the F-35B, to take off vertically, fly forward, stop in mid-air, back up, and land vertically. They can also take off and land like a normal airplane. A helicopter’s spinning blades create thrust like a large propeller, but the thrust is directed vertically. This allows the vehicle to take off and land vertically and to hover. To move forward, the helicopter tilts slightly to direct some of its thrust forward.
A tiltrotor is an aircraft that uses a pair tiltrotors mounted on rotating engines at the end of a fixed wing to generate vertical and horizontal thrust. It combines the vertical capability of a helicopter with the speed and range of a fixed-wing aircraft. For vertical flight, the rotors are angled so the plane of rotation is horizontal, like a helicopter. As the aircraft gains speed, the rotors are tilted forward, with the plane of rotation eventually becoming vertical. The wing then provides lift, and the rotor provides thrust like a propeller.