VTOL is an abbreviation for Vertical Take-Off and Landing aircraft. See also V/STOL. This classification includes fixed-wing aircraft that can hover, take off and land vertically as well as helicopters and other aircraft with powered rotors, such as tiltrotors. Autogyros, balloons, airships and rockets are not normally considered VTOL, but may be termed VTVL (Vertical Takeoff with Vertical Landing). 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) mode. 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.

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 aircraft using directed jet thrust such as the Harrier family.

History

In addition to the helicopter, many approaches have been tried to develop practical aircraft with vertical take-off and landing capabilities. An early contribution to VTOL was Rolls-Royce's Thrust Measuring Rig ("flying bedstead") of 1953. This led to the first VTOL engines as used in the first British VTOL aircraft, the Short SC.1 (1957) which used 4 vertical lift engines with a horizontal one for forward thrust.

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.

The idea of using the same engine for vertical and horizontal flight by altering the path of the thrust led to the Bristol Siddeley Pegasus engine which used rotating ducts to direct thrust over a range of angles. This was developed side by side with an airframe, the Hawker P.1127, which became subsequently the Kestrel and then entered production as the Hawker Siddeley Harrier, though the supersonic Hawker Siddeley P.1154 was canceled in 1965. The French in competition with the P.1154 had developed a version of the Dassault Mirage III capable of attaining Mach 1. The Dassault Mirage IIIV achieved transition from vertical to horizontal flight in March 1966, reaching Mach 1.3 in level flight a short time later.

The Harrier is often flown in STOVL mode which enables it to carry a higher fuel or weapon load over a given distance. Now retired from British Royal Navy service, the Indian Navy operates Sea Harriers mainly from its aircraft carrier INS Viraat. The latest version of the Harrier, the BAE Harrier II is operated by the British Royal Air Force and Royal Navy. The United States Marine Corps, and the Italian and Spanish Navies use the AV-8 Harrier II, an equivalent derivative of the Harrier II. The Harrier II/AV-8 will be replaced in the air arms of the US and UK by a STOVL variant of the F-35 Lightning II.

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.

The Yakovlev Yak-38 was the Soviet Navy's VTOL aircraft for their light carriers, cargoships, and capital ships. It was developed from the Yakovlev Yak-36 experimental aircraft. Before the Soviet Union collapsed, a supersonic VTOL aircraft was developed as the Yak-38's successor, the Yak-141, which never went into production.



In the 1960s and early 70s Germany planned three different VTOL planes. One used the F-104 as a base for research for a V/STOL aircraft. Although two models (X1 and X2) were built, the project was canceled due to high costs and political problems as well as changed needs in the Luftwaffe and NATO. The EWR VJ 101C did perform free VTOL take-offs and landings, as well as test flights beyond mach 1 in the mid- and late 60s. One of the test-aircraft is preserved in the Deutsches Museum in Munich, Germany. The others were the VFW-Fokker VAK 191B light fighter and reconnaissance plane, and the Dornier Do 31E-3 (troop) transport.

Canadair CL-84 Dynavert

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. 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.

Aircraft designed to operate in extraterrestrial environments often utilize VTOL. An example of this type of aircraft is the LLRV. Spacecraft typically operate in environments where runways or even a suitably flat surface for skids is nonexistent.

V-22

The V-22 Osprey is the world's first production tiltrotor aircraft, with one three-bladed proprotor, turboprop engine, and transmission nacelle mounted on each wingtip. The Osprey is a multi-mission aircraft with both a vertical takeoff and landing (VTOL) and short takeoff 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.

Gallery

Image:F-35 compilation.ogg|F-35 flight, transition to STOVL configuration, vertical take off, inflight re-fueling, vertical hover and landingImage:F-35 verticle landing.ogg|F-35 vertical landing

See also

• STOL
• VSTOL
• Powered lift
• List of VTOL aircraft
• Military flying saucers
• Tiltrotor
• Mono tiltrotor
• Tiltwing
• Tailsitter
• McDonnell Douglas DC-X
• Reusable Vehicle Testing
• Quad
• Vertical airship

References

1. "Vertical Takeoff & Landing Aircraft," John P. Campbell, The MacMillan Company, New York, 1962.
2. "VTOL – Military Research Aircraft," Mike Rogers, Orion Books, New York, 1989.
3. "Vertical Take-Off and Landing (VTOL) Aircraft," edited by I.B. Laskowitz, Annals of the New York Academy of Sciences, Vol 107, Art.1, March 25, 1963.
4. "Straight Up - A History of Vertical Flight," Steve Markman and Bill Holder, Schiffer Publishing, 2000.

External links

• Doak VZ-4 image
• V/STOL Wheel of Misfortune