For questions about vehicles capable of vertical take-off and landing.
VTOL (Vertical TakeOff and Landing) describes aircraft that can, as the name indicates, perform takeoffs and landings vertically. Similar acronyms include stol (Short TakeOff and Landing), V/STOL (Vertical/Short TakeOff and Landing), STOVL (Short TakeOff and Vertical Landing), and V/STOVL (Vertical/Short TakeOff and Vertical Landing).
There are three main ways an aircraft can take off and/or land vertically:
- Using rotating wings (i.e., being a rotorcraft), so that the wings can see high-speed airflow even when the aircraft has no horizontal movement (helicopters, tiltrotors). Not all rotorcraft are fully VTOL-capable, however; an autogyro cannot take off vertically, as its main rotor is unpowered and relies on airflow through the rotor disk to rotate its blades (autogyros can, however, land vertically).
- Being lighter than air, so that the aircraft floats into the air under its own buoyancy (airships, balloons; these are collectively known as aerostats).
- Directing the thrust from a jet-engine (or, occasionally, rocket) downwards in order to push the aircraft upwards. Most VTOL combat aircraft (popularly known as "jump jets") use this method. There are three main ways of doing this:
- A tailsitting aircraft sits vertically when on the ground, with its tail pointing straight down. This was tried on a number of very early VTOL aircraft, but was abandoned due to the extreme difficulty of landing an aircraft when you can't see the ground, as well as problems with transitioning between vertical and horizontal flight and the need for a ladder when entering or egressing the cockpit.
- Vertically-mounted auxiliary engines (known as lift engines or lift jets) can be used to provide vertical thrust while allowing takeoffs and landings to be made in the conventional horizontal orientation, but the extra engines used only for takeoff and landing impose a considerable weight penalty, degrading aircraft-performance. As a result, this solution has only been used on a few varieties of aircraft, and usually only as a supplement to vectored thrust (see below).
- thrust-vectoring can be used to redirect the gas flow from a horizontally-mounted engine downwards. This poses some engineering challenges, but allows the aircraft to take off and land vertically without needing to use heavy additional engines or sit on its tail.
Wikipedia has more information on:
