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Avertical and/or short take-off and landing (V/STOL) aircraft is anairplane able totake off or land vertically or on short runways. Vertical takeoff and landing (VTOL) aircraft are a subset of V/STOL craft that do not require runways at all. Generally, a V/STOL aircraft needs to be able to hover. Helicopters are not considered under the V/STOL classification as the classification is only used for aeroplanes, aircraft that achievelift in forward flight by planing the air, thereby achieving speed andfuel efficiency that is typically greater than the capability of helicopters.
The main advantage of V/STOL aircraft is in their military performance, such as closer basing to the enemy, which reduces response time and tanker support requirements. In the case of theFalklands War, it also permitted high-performance fighter air cover and ground attack without a large aircraft carrier equipped withaircraft catapult. V/STOL was developed to allow fast jets to be operated from clearings in forests, from very short runways, and from smallaircraft carriers that would previously only have been able to carryhelicopters.
A rolling takeoff, sometimes with a ramp (ski-jump), reduces the amount of thrust required to lift an aircraft from the ground (compared with vertical takeoff), and hence increases the payload and range that can be achieved for a given thrust. For instance, the Harrier is incapable of taking off vertically with full weapons and fuel load. Hence V/STOL aircraft generally use a runway if it is available. In other words, short takeoff and vertical landing (STOVL) or conventional takeoff and landing (CTOL) operation is preferred to vertical takeoff and landing (VTOL) operation.
Onaircraft carriers, non-catapult-assisted fixed-wing short takeoffs are accomplished with the use ofthrust vectoring, which may also be used in conjunction with a runway "ski-jump". There are 16 aircraft carriers that operate these STOVL aircraft: United States (9), Japan (2), United Kingdom (2), Italy (2), and Spain (1). Use of STOVL tends to allow aircraft to carry a larger payload compared tovertical take-off and landing (VTOL), while still only requiring a short runway. The most famous examples are theHawker Siddeley Harrier and theBAe Sea Harrier. Although technically a V/STOL aircraft, they are operationally STOVL aircraft due to the extra weight carried at take-off for fuel and armaments. The same is true of the B variant of theLockheed Martin F-35 Lightning II, which demonstrated VTOL capability in test flights but is operationally a STOVL.[1]
Vertical take-off and landing (VTOL) is a subset of V/STOL. This classification can include a variety of types ofaircraft as well asthrust-vectoringfixed-wing aircraft and other hybrid aircraft with poweredrotors such ascyclogyros andgyrodynes.[2]
Some VTOL aircraft can operate in other modes as well, such asCTOL (conventional take-off and landing),STOL (short take-off and landing), or STOVL (short take-off and vertical landing). Others, such as some helicopters, can only operate as VTOL, due to the aircraft's lack oflanding gear that can handletaxiing. Somelighter-than-air aircraft also qualify as VTOL aircraft, as they can hover, take off and land with vertical approach/departure profiles.[3]
Electric vertical takeoff and landing aircraft, oreVTOLs, are being developed along with more autonomous flight control technologies and mobility-as-a-service (MaaS) to enable advanced air mobility (AAM), that could include on-demand air taxi services, regional air mobility, freight delivery, andpersonal air vehicles (PAVs).[4]
Besides the ubiquitous helicopters, there are currently two types of VTOL aircraft in military service:tiltrotor aircraft, such as theBell Boeing V-22 Osprey, and thrust-vectoring airplanes, such as theHarrier family and newF-35B Lightning IIJoint 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[update]). Generally speaking, VTOL aircraft capable of STOVL use the latter wherever possible, since it typically significantly increases takeoff weight, range, or payload compared to pure VTOL.[5]
Of dozens of V/STOL designs tried from the 1950s to 1980s, only the subsonic Hawker Siddeley Harrier and Yak-38 Forger reached operational status, with the Forger being withdrawn after the fall of theSoviet Union.
The idea of vertical flight has been around for thousands of years, and sketches for a VTOL (helicopter) show up inLeonardo da Vinci's sketch book. Manned VTOL aircraft, in the form of primitive helicopters, first flew in 1907, but would take until after World War Two to be perfected.[6][7]
In addition tohelicopter development, many approaches have been tried to develop practical aircraft with vertical take-off and landing capabilities, includingHenry Berliner's 1922–1925 experimental horizontal-rotor fixed-wing aircraft, andNikola Tesla's 1928 patent, and George Lehberger's 1930 patent for relatively impractical VTOL fixed wing airplanes with tilting engines.[8][9][10] In the late 1930s, British aircraft designerLeslie Everett Baynes was issued a patent for theBaynes Heliplane, another tiltrotor aircraft. In 1941, German designerHeinrich Focke's began work on theFocke-Achgelis Fa 269, which had two rotors that tilted downward for vertical takeoff, but wartime bombing halted development.[10]
In May 1951, bothLockheed andConvair were awarded contracts in the attempt to design, construct, and test two experimental VTOL fighters. Lockheed produced theXFV, and Convair producing theConvair XFY Pogo. Both experimental programs proceeded to flight status and completed test flights 1954–1955, when the contracts were cancelled.[11] Similarly, theRyan X-13 Vertijet flew a series of test flights between 1955 and 1957, but also suffered the same fate.[12]
In 1962, Lockheed built theXV-4 Hummingbird for theU.S. Army. It sought to "augment" available thrust by injecting the engine exhaust into an ejector pump in the fuselage. First flying vertically in 1963, it suffered a fatal crash in 1964. It was converted into the XV-4B Hummingbird for theU.S. Air Force as a testbed for separate, vertically mounted lift engines, similar to those used in theYakovlev Yak-38 'Forger'. That plane flew and later crashed in 1969.[13] TheRyan XV-5 Vertifan, which was also built for the U.S. Army at the same time as the Hummingbird, experimented with gas-driven lift fans. That plane used fans in the nose and each wing, covered by doors which resembled half garbage can lids when raised. However, it crashed twice, and proved to generate a disappointing amount of lift, and was difficult to transition to horizontal flight.
Rockwell International built, and then abandoned, theRockwell XFV-12 supersonic fighter which had an unusual wing which opened up likewindow blinds to create an ejector pump for vertical flight. It never generated enough lift to get off the ground despite developing 20,000lbf of thrust. The French had a nominally Mach 2Dassault Mirage IIIV fitted with no less than 8 lift engines that flew (and crashed), but did not have enough space for fuel or payload for combat missions. The GermanEWR VJ 101 used swiveling engines mounted on the wingtips with fuselage mounted lift engines, and the VJ 101C X1 reached supersonic flight (Mach 1.08) on 29 July 1964. The supersonicHawker Siddeley P.1154, which competed with the Mirage IIIV for use in NATO, was cancelled even as the aircraft were being built.
NASA has flown other VTOL craft such as theBell XV-15 research craft (1977), as have theSoviet Navy andLuftwaffe.Sikorsky tested an aircraft dubbed theX-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 aCanard Rotor/Wing prototype that utilizes a similar concept.[14]
A different British VTOL project was thegyrodyne, 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 theFairey Gyrodyne, this type of aircraft later evolved into the much larger twin-enginedFairey Rotodyne, that usedtipjets to power the rotor on take-off and landing but which then used twoNapier Elandturboprops 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.
TheCL-84 Dynavert was a Canadian V/STOL turbine tilt-wing monoplane designed and manufactured byCanadair 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 USSGuam and USSGuadalcanal, and at various other centres.[15] 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.[16]
Although tiltrotors such as theFocke-Achgelis Fa 269 of the mid-1940s and the Centro Técnico Aeroespacial "Convertiplano" of the 1950s reached testing or mock-up stages, theBell-Boeing V-22 Osprey is considered the world's first productiontiltrotor aircraft. It has one three-bladedproprotor,turboprop engine, and transmissionnacelle 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 conventionalhelicopter with the long-range, high-speed cruise performance of aturboprop aircraft. The FAA classifies the Osprey as a model ofpowered lift aircraft.[17]
Attempts were made in the 1960s to develop a commercial passenger aircraft with VTOL capability. TheHawker 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.[18][19]
In 1983, the Defense Advanced Research Projects Agency (DARPA) initiated the Advanced STOVL (ASTOVL) program to develop a supersonic STOVL fighter (SSF) to replace the Harrier for the U.S. Marine Corps and the U.K. Royal Navy. Several propulsion methods were explored under ASTOVL and assigned to different contractors for research and development. These include the Shaft-Driven Lift Fan (SDLF) byLockheed which had a forwardlift fan powered by a shaft connected to the main engine's low-pressure spool and engaged by a clutch, the Lift-Plus-Lift/Cruise (LPLC) byNorthrop (laterNorthrop Grumman) which had a separate dedicated lift engine alongside the main engine, and the Gas-Driven Lift Fan (GDLF) byMcDonnell Douglas that used the main engine bleed air to power a lift fan; all methods had an aft vectoring nozzle for the main engine.[20]
ASTOVL would continue under theCommon Affordable Lightweight Fighter (CALF) program, which eventually became part of theJoint Strike Fighter program; theLockheed Martin X-35B with the SDLF was eventually selected for full-scale development in 2001, with the production aircraft for operational service becoming the F-35B with theF135-PW-600 engine.NASA uses theabbreviation SSTOVL for Supersonic Short Take-Off / Vertical Landing,[21] and as of 2012, the X-35B/F-35B are the only aircraft to conform with this combination within one flight.[22][23]
In 2018, Opener Aero demonstrated an electrically powered fixed-wing VTOL aircraft, theBlackfly, which the manufacturer claims is the world's first ultralight fixed-wing, all-electric, VTOL aircraft.[24]
In the 21st century, unmanned drones are becoming increasingly commonplace. Many of these have VTOL capability, especially thequadcopter type.[25]
In 1947, theRyan X-13 Vertijet, atailsitter design, was ordered by the US Navy, who then further issued a proposal in 1948 for an aircraft capable of VTOL aboard platforms mounted on the afterdecks of conventional ships. BothConvair andLockheed competed for the contract but in 1950, the requirement was revised, with a call for a research aircraft capable of eventually evolving into a VTOL ship-based convoy escort fighter.[citation needed]
At the end of 1958, the FrenchSNECMA Coléoptère, a tailsitterannular wing design, performed its maiden flight. However the sole prototype was destroyed on its ninth flight in 1959, and financing was never sourced for a second prototype.[citation needed]
Another more influential early functional contribution to VTOL wasRolls-Royce'sThrust Measuring Rig ("flying bedstead") of 1953. This led to the first VTOL engines as used in the first British VTOL aircraft, theShort SC.1 (1957), Short Brothers and Harland, Belfast which used four vertical lift engines with a horizontal one for forward thrust.
TheShort SC.1 was the first British fixed-wing VTOL aircraft. The SC.1 was designed to study the problems with VTOL flight and the transition to and from forward flight. The SC.1 was designed to meet a Ministry of Supply (MoS) request for tender (ER.143T) for a vertical take-off research aircraft issued in September 1953. The design was accepted by the ministry and a contract was placed for two aircraft (XG900 and XG905) to meet Specification ER.143D dated 15 October 1954. The SC.1 was also equipped with the first "fly-by-wire" control system for a VTOL aircraft. This permitted three modes of control of the aerodynamic surfaces or the nozzle controls.
TheRepublic AviationAP-100 was a prototype VTOL 6xGeneral Electric J85 turbojet-engined nuclear-capable strike fighter concept designed byAlexander Kartveli that had three ducted fans in the centre of its fuselage and tail as a possible contender for theTFX Program.[26][27][28] Another design was the A400 AVS that used variable-geometry wings but was found too complicated; however, it led to the development of theAFVG, which in turn helped the development of thePanavia Tornado.
TheYakovlev Yak-38 was aSoviet Navy VTOL aircraft intended for use aboard their light carriers, cargoships, and capital ships. It was developed from theYakovlev Yak-36 experimental aircraft in the 1970s. Before the Soviet Union broke up, a supersonic VTOL aircraft was developed as the Yak-38's successor, theYak-141, which never went into production.[29]
In the 1960s and early 1970s, Germany planned three different VTOL aircraft. One used theLockheed F-104 Starfighter as a basis 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 theGerman Air Force and NATO. TheEWR 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 theDeutsches Museum in Munich, Germany, another outside Friedrichshafen Airport. The others were the VFW-FokkerVAK 191B light fighter and reconnaissance aircraft, and theDornier Do 31E-3 (troop) transport.[30]
TheLLRV was aspacecraft simulator for the Apollo lunar lander.[31] It was designed to mimic the flight characteristics of thelunar exploration module (LEM), which had to rely on a reaction engine to land on the Moon.
The idea of using the same engine for vertical and horizontal flight by altering the path of the thrust was conceived byMichel Wibault.[32] It led to theBristol Siddeley Pegasus engine which used four rotatingnozzles to direct thrust over a range of angles.[33] This was developed side-by-side with an airframe, theHawker P.1127, which became subsequently the Kestrel and then entered production as theHawker Siddeley Harrier, though the supersonicHawker Siddeley P.1154 was canceled in 1965. The French in competition with the P.1154 had developed a version of theDassault Mirage III capable of attainingMach 1. TheDassault 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 usually flown in STOVL mode, which enables it to carry a higher fuel or weapon load over a given distance.[5] In V/STOL, the aircraft moves horizontally along the runway before taking off using vertical thrust. This gives aerodynamic lift as well as thrust lift and permits taking off with heavier loads and is more efficient. When landing, the aircraft is much lighter due to the loss of propellant weight, and a controlled vertical landing is possible. An important aspect of Harrier STOL operations aboard naval carriers is the "ski jump" raised forward deck, which gives the craft additional vertical momentum at takeoff.[34]
The March 1981 cover ofPopular Science showed three illustrations for its "Tilt-engine V/STOL – speeds like a plane, lands like a copter" front-page feature story;[35] a followup story was part of the April 2006 issue that mentioned "the fuel-consumption and stability problems that plagued earlier plane/copter."[36]
Retired from the BritishRoyal Navy in 2006,[37] theIndian Navy continued to operateSea Harriers until 2016,[38] mainly from itsaircraft carrierINS Viraat. The latest version of the Harrier, theBAE Harrier II, was retired in December 2010 after being operated by the BritishRoyal Air Force and Royal Navy. TheUnited States Marine Corps and the Italian and Spanish navies all continue to use theAV-8B Harrier II, an American-British variant. Replacing the Harrier II/AV-8B in the air arms of the US and UK is the STOVL variant of theLockheed Martin F-35 Lightning II, the F-35B.[39]
SpaceX developedseveral prototypes of Falcon 9 to validate various low-altitude, low-velocity engineering aspects of itsreusable launch system development program.[40] The first prototype, Grasshopper, made eight successful test[41] flights in 2012–2013. It made its eighth, and final, test flight on October 7, 2013, flying to an altitude of 744 metres (2,441 ft) before making its eighth successful VTVL landing.[42][43] This was the last scheduled test for the Grasshopper rig; next up will be low altitude tests of the Falcon 9 Reusable (F9R) development vehicle in Texas followed by high altitude testing in New Mexico.
On November 23, 2015,Blue Origin's New Shepard booster rocket made the first successful vertical landing following an uncrewed suborbital test flight that reached space.[44] On December 21, 2015,SpaceXFalcon 9 first stage made a successful landing after boosting 11 commercial satellites tolow Earth orbit onFalcon 9 Flight 20.[45] These demonstrations opened the way for substantial reductions in space flight costs.
This is a partial list; there have been many designs for V/STOL aircraft.
Although many aircraft have been proposed and built, with a few being tested, the F-35B is the first and only supersonic V/STOL aircraft to have reached operational service, having entered service in 2016.[46]
SpaceX has constructed a half-acre concrete launch facility in McGregor, and the Grasshopper rocket is already standing on the pad, outfitted with four insect-like silver landing legs.
WATCH: Grasshopper flies to its highest height to date – 744 m (2441 ft) into the Texas sky.
