From Wikipedia, the free encyclopedia
For rocket vertical takeoff and landing, see
VTVL.
The
Harrier Jump Jet, one of the most famous and successful fixed-wing single-engine VTOL aircraft
A
vertical take-off and landing (
VTOL)
aircraft is one that can hover,
take off, and land vertically. This classification includes
fixed-wing aircraft as well as
helicopters and other aircraft with powered rotors, such as
cyclogyros/cyclocopters and
tiltrotors.
[1][2][3][4] 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). 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 (vertical and/or short take-off and landing).
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.
Generally speaking, VTOL aircraft capable of V/STOL use it wherever
possible, since it typically significantly increases takeoff weight,
range or payload compared to pure VTOL.
Rotary wing
Helicopter
The helicopter's form of VTOL allows it to take off and land
vertically, to hover, and to fly forwards, backwards, and laterally.
These attributes allow helicopters to be used in congested or isolated
areas where
fixed-wing aircraft
would usually not be able to take off or land. The capability to
efficiently hover for extended periods of time is due to the
helicopter's relatively long, and hence efficient rotor blades, and
allows a helicopter to accomplish tasks that fixed-wing aircraft and
other forms of vertical takeoff and landing aircraft could not perform
at least as well until 2011.
On the other hand, the long rotor blades restrict the maximum speed
to about 250 miles per hour of at least conventional helicopters, as
retreating blade stall causes lateral instability.
Tiltrotor and propeller
In addition to the
helicopter, many approaches have been tried to develop practical aircraft with vertical take-off and landing capabilities.
Nikola Tesla patented
[5] a vertical take-off and landing vehicle concept in 1928.
In May 1951, both Lockheed and Convair were awarded contracts in the
attempt to design, construct, and test two experimental VTOL fighters.
Lockheed produced the
XFV, and Convair producing the
Convair XFY Pogo,
nicknamed the "Pogo". Both experimental programs proceeded to flight
status and completed test flights 1954–1955, when the contracts were
cancelled.
[6] Similarly, the X-13 flew a series of test flights between 1955 and 1957, but also suffered the same fate.
[7]
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.
[citation needed]
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.
[citation needed]
A different British VTOL project was the
gyrodyne,
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 the
Fairey Gyrodyne, this type of aircraft later evolved into the much larger twin-engined
Fairey Rotodyne, that used
tipjets to power the rotor on take-off and landing but which then used two
Napier Eland turboprops
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.
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.
[citation needed]
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.
[8]
Although tiltrotors such as the
Focke-Achgelis Fa 269 of the mid-1940s and the
Centro Técnico Aeroespacial "Convertiplano" of the 1950s reached testing or mock-up stages, the
V-22 Osprey is considered the world's first production
tiltrotor aircraft. It has 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.
[9]
Jet
Compared to rotating wings, due to their high exhaust velocity, jets
are comparatively inefficient in hover, but jet engines are compact and
this gives advantages when much higher top speeds are needed, such as
for fighters.
History
In 1947,
Ryan X-13 Vertijet,
a tailsitter design, was ordered by the US Navy, who then further
issued a proposal in 1948 for an aircraft capable of vertical takeoff
and landing (VTOL) aboard platforms mounted on the afterdecks of
conventional ships. Both
Convair and
Lockheed
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.
"Flying Bedstead"- Rolls-Royce Thrust Measuring Rig
Another more influential early functional 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 Short SC.1 a VTOL delta aircraft
The
Short SC.1
(Belfast, Northern Ireland) was the first British fixed-wing vertical
take-off and landing (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 and/or the
nozzle controls
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 in the 1970s. Before the Soviet Union broke up, a
supersonic VTOL aircraft was developed as the Yak-38's successor, the
Yak-141, which never went into production.
[10]
In the 1960s and early 1970s, Germany planned three different VTOL aircraft. 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 aircraft, and the
Dornier Do 31E-3 (troop) transport.
[11]
Aircraft designed to operate in orbital 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.
[12]
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.
V/STOL
The Harrier is usually flown in
STOVL mode which enables it to carry a higher fuel or weapon load over a given distance.
In V/STOL the VTOL 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.
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 has also been retired in December 2010, after being operated by the British
Royal Air Force and
Royal Navy. The United States Marine Corps, and the Italian and Spanish Navies use the
AV-8B 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
Lockheed Martin F-35 Lightning II.
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