Even before the dawn of jet aircraft, aeronautical
engineers have wanted to reduce the amount of runway required by fast
aircraft, preferably eliminating runways completely. They wanted an
aircraft that takes off and lands like a helicopter but flies with the
efficiency of an airplane. These types of aircraft are generally
classified either as Vertical Takeoff and Landing (VTOL) or Short Takeoff
and Landing (STOL), and the two categories are often grouped together as
V/STOL. However, designing such aircraft has been difficult and there have
been few successes.
XFV-1 is a "tail-sitter" aircraft.
It points straight up, which permits the entire thrust of its propulsion
system to be converted directly into vertical lift.
However, this feature also makes it difficult to land since the pilot
needs to ease down onto the ground.
From the 1940s until today, slightly more than 40
vertical/short takeoff and landing aircraft have been tested. However,
only four have actually gone into production: the British Harrier "jump
jet" and its derivatives, the Soviet An-72/74 transport aircraft, the
Soviet Yak-38 naval fighter, and the Bell/Boeing V-22 Osprey. Most of the
other aircraft were highly experimental or proof-of-concept types never
intended to lead to an actual production aircraft.
The biggest problem with achieving V/STOL flight is
that conventional wings provide a good amount of lift for a
relatively low amount of forward thrust. Getting an aircraft off the
ground with little or no forward motion requires that engine thrust—and
not wing lift—support a significant portion of the aircraft's weight—or
all of it. This usually requires big engines, lots of fuel, and
complicated flight controls, all of which weigh more.
Another problem is that these aircraft are often hard
for the pilot to control during transition from horizontal flight to
vertical flight and back again. Computerized flight control systems and
better cockpit displays have helped with this. Some experimental V/STOL
aircraft also simply have had a hard time accelerating in forward flight
after lifting off the ground.
One early V/STOL aircraft was the XVW-1, which Lockheed
tested in 1954. This "tailsitter" aircraft had two large contra-rotating
propellers on its nose. In horizontal flight, the aircraft looked like
many piston-engine fighters, although with a large tail. When on the
ground, it actually sat on its tail. The plane would rise straight up
during takeoff and transition to forward flight. The Convair XFY-1 Pogo,
developed at the same time, operated similarly. Both were extremely
difficult to control in vertical flight (the pilots had to look over their
shoulders to see the ground when landing), and both were grounded in 1956.
The Ryan X-13 Vertijet tailsitter was more successful. It used a single
large jet engine for thrust and even landed and took off in the Pentagon
parking lot. But it too never progressed beyond the experimental stage.
In the late 1950s and early 1960s, several European
experimental V/STOL jets were developed. The French firm Dassault
developed two versions of the Mirage III-V with small lift jets in the
fuselage for lifting the aircraft off the ground. Germany's EWR developed
the VJ101C, with wingtip-mounted pairs of tilting jet engines and lift
jets behind the cockpit.
In the early 1960s, the British firm Hawker developed
the experimental P.1127 Kestrel. This aircraft had a single Rolls-Royce
Pegasus jet engine in the fuselage that vented its exhaust through four
ports in the fuselage—two on each side. The ports could be directed
downward to lift the aircraft off the ground, and then rotated back to
direct the thrust to the rear, thus changing the aircraft from vertical to
The Kestrel was soon developed into the British
Aerospace GR.3 Harrier single-seat attack aircraft, which entered service
in 1969. The Harrier is often called a "jump jet" and can operate from
relatively unprepared locations. The Harrier proved to be successful and
was later modified into a naval fighter version and also adopted by the
U.S. Marine Corps as well as by other navies. Despite its success, the
Harrier rarely takes off and lands vertically because this severely limits
its lifting capabilities and its range. It usually makes short takeoffs
and landings, sometimes rolling forward to lift off a "ski jump" ramp,
both on the ground and on small aircraft carriers.
The Soviet Yak-38 "Forger" single-seat naval fighter
was similar to the Harrier. It operated from the USSR's four multipurpose
cruiser/aircraft carriers during the 1970s and 1980s. Unlike the Harrier,
the Forger had three jet engines, two of which provided vertical lift and
the third that could be vectored to provide both vertical lift and
horizontal thrust. The Forger could not make rolling takeoffs like the
Harrier but had to rise straight up, using more fuel. It was severely
limited in range and performance and was withdrawn from service in the
Probably the most commonly tested type of V/STOL
aircraft has been the various tilting propulsion designs, often
collectively called "convertiplanes." These aircraft tilt propellers,
rotors, ducted propellers, or even their entire wings from vertical to
The XV-15 was so successful that it ultimately led to
the V-22 Osprey, which was intended to be a multipurpose aircraft for the
U.S. Marine Corps, the U.S. Coast Guard, and some special purpose
missions, such as the recovery of downed pilots deep behind enemy lines
(called Combat Search and Rescue, or CSAR). The V-22, which looks like a
more muscular version of the XV-15, offered greater range, speed and
lifting capability than conventional large transport helicopters. By
essentially operating as a conventional aircraft in forward flight, it
avoided the limitations of helicopters, such as less speed and range. One
of the key developments for the Osprey was a transmission shaft running
through the wing and connecting both engines. If one engine failed, the
other engine could keep both propellers rotating.
Some aircraft use large flaps or other devices on their
wings to dramatically increase lift at low speeds or even to deflect
engine thrust downwards. The American YC-14 and YC-15 aircraft, tested in
the 1970s, evaluated these technologies, some of which eventually made
their way to the successful Boeing C-17 cargo plane (which is not
considered a STOL aircraft but which can operate from shorter runways).
The Soviet An-72 cargo aircraft also operates in this manner.