was the world's first airplane to vary the sweepback of its wings in
flight. Its first flight was on June 20, 1951.
Presumably, after decades of designing
and building airplanes, a person would suspect that all airplanes with a
similar purpose would look the same. All fighters would look alike, all
passenger jets would look alike, and so on. But this has not happened.
Even more than five decades after the dawn of the jet age, jet fighters
designed around the same time can look radically different. The level of
technological capability can explain most of these differences; cultural
factors are also a factor, although generally of less importance.
Aeronautical engineers, like any other group of people sharing similar
interests, can become enthusiastic about certain ideas at the same time
and overlook their drawbacks. That is what happened with variable-sweep
The swept-back wing used for the B-47
and common to many aircraft that followed demonstrated that airplanes
could use wing designs other than the straight wing to achieve certain
performance goals. Straight wings were clearly advantageous for short
takeoffs and landings, low speed, and fuel-efficient flight, but swept
wings were ideal for high-speed, particularly supersonic, flight.
All aircraft represent numerous
compromises made by their designers. Some aircraft need to fly at very
high speeds whereas others need to fly very slowly. Some have to be highly
fuel-efficient whereas others have to accomplish their missions without
regard to cost. Designers, therefore, try to optimize each aircraft so
that it does its required mission as best it can. But sometimes aircraft
are required to do things that demand design features that oppose each
other. The best example is an aircraft that can fly at high supersonic
speeds but still needs to be able to land at relatively low speeds, such
as on the deck of an aircraft carrier.
Experiments with variable-sweep wings
began in France about 1911. Dr. Adolf Buseman, a German designer,
presented a theoretical concept for a practical moveable wing at a
convention in Rome just before World War II. His theory, supported with
research by Dr. Albert Betz of the Göttingen Aerodynamics Research
Institute, led Messerschmitt to begin developing a variable-sweep wing
design, the P-1101, in 1942. The war ended before the aircraft could be
produced. It is also doubtful that existing engines provided high enough
speed for the design to make an appreciable difference in performance.
Beginning in the late 1940s, as
technological capabilities improved, designers in the United States began
to examine the possibility of moving the wing of an aircraft while it was
in flight, so that it extended straight out from the fuselage for takeoff
and landing and swept back for high-speed operations. Such an airplane
might be able to accomplish its demanding missions without paying a
In the early 1950s, Bell Aircraft built
the experimental X-5 aircraft for the U.S. Air Force and the National
Advisory Committee for Aeronautics (NACA). It had a wing that could be
moved backward and forward in flight-a variable-sweep wing. Grumman
Aircraft built the F-10-F for the U.S. Navy, also with variable-sweep
wings. Both designs proved that the concept of movable wings worked.
A few years later, in 1959, engineers at
NASA's Langley Research Centre discovered the two-pivot variable-sweep
concept-as opposed to the single-pivot used in earlier experiments. This
development led to the success of the variable-wing idea.
In the late 1950s, the U.S. Air Force
submitted specifications for a plane with variable-sweep wings that could
fly at supersonic speeds and could also cruise for long distances at high
altitudes to reach its distant targets. Secretary of Defence Robert
McNamara wanted to combine this requirement with Army needs for close air
support and a Navy requirement for air defence of the naval fleet. This
soon led in December 1960 to the Tactical Fighter Experimental (TFX)
program. This was to consist of aircraft suitable for use by the Air
Force, which would operate it in the close air support role for Army
ground forces and also use it in its own roles, and by the Navy in
aircraft carrier roles.
The Department of Defence selected
General Dynamics to develop two versions of the TFX, the F-111A for the
Air Force and the F-111B for the Navy. Roll out took place on October 15,
1964, and Secretary McNamara stated that the Air Force and Navy now had an
aircraft with the range of a transport, capacity and endurance of a
bomber, and agility of a fighter. However, the Navy cancelled its portion
of the program, in August 1968, finding that the plane was too heavy for
use aboard aircraft carriers. Commonality between the aircraft used by the
two services had also dropped significantly by that time with the adoption
of different engines. The Navy subsequently selected Grumman Aircraft to
develop the F-14 Tomcat interceptor, which also had a variable-sweep, or
The F-111 Aardvark, as it become known,
was a medium-size tactical fighter-bomber capable of flying at high speeds
at very low altitudes, hugging the terrain. It achieved this by using a
variable-sweep wing. For takeoff or long flights to and from its targets,
it operated as a straight-wing aircraft. For high-speed dashes at low
altitudes toward its target, the wings swept back and acted much like a
delta wing. Several versions of the F-111 were developed-a supersonic
bomber for dropping conventional and nuclear bombs, a strike aircraft, and
a version for electronic warfare.
F-111 is a supersonic tactical strike fighter-bomber.
The F-111 has variable sweep wings, allowing the pilot to fly from slow
approach speeds to
supersonic velocity at sea level and more than twice the speed of sound at
The wings angle from 16 degrees (full forward) to 72.5 degrees (full aft).
The F-111 had numerous problems during
its early service, including problems with cracks in the large gearbox
used to move the wings. The plane, though, eventually saw service in
Vietnam, and the F-111F saw considerable action during the Gulf War.
Perhaps its greatest success occurred in a combined U.S. Air Force and
U.S. Navy attack on Libya and its terrorist government in mid-April 1986,
at El Dorado Canyon.
The F-14 adopted by the Navy
incorporated a swing-wing that could be manually controlled by the pilot
or shifted automatically according to the plane's speed. It moved forward
to allow the plane to land on tiny aircraft carrier decks at relatively
low speeds and backward as the plane dashed out to intercept Soviet
bombers. More than 700 F-14s were produced, in several variants, and more
than 70 of them were exported to Iran in the 1970s. It first entered
service in the mid-1970s, and still serves today in 2001, although it is
being retired. Despite its long service, the F-14 has been the most
expensive interceptor aircraft to operate in the U.S. military.
During the 1970s, an Israeli Air Force (IAF)
pilot evaluated the Navy F-14 and the Air Force F-15 Eagle for service in
the IAF. He walked around both airplanes and counted their control
surfaces such as ailerons, flaps, slats, and speed brakes. The F-14 had
more control surfaces and the pilot determined that this would make it
more difficult and expensive to maintain; for this and many other reasons,
the IAF subsequently purchased the F-15 Eagle. In many ways this was an
omen, for the variable-sweep wing, the largest moving part ever developed
for an aircraft, proved to be more trouble than it was worth for many
MiG-23's most significant new feature was its variable sweep wing.
Like the U.S. Air Force's swing wing F-111, the sweep of the wings could
be changed in flight.
With the wings fully swept back, the MiG-23 has greater speed.
But for a period, variable-sweep wings
were in vogue and more than a half dozen major military aircraft were
designed with variable sweep wings during the 1960s and 1970s, with the
number of swing-wing aircraft numbering in the thousands. The Soviets
developed the Su-24 and MiG-27 attack planes and the MiG-23 fighter, all
with swing-wings. The European consortium Panavia developed the Tornado,
produced in both ground attack and interceptor versions. It too had a
variable-sweep wing. Aircraft designers also applied variable-sweep wings
to large bomber-size aircraft. North American Rockwell began the B-1A
bomber in the early 1970s as the U.S. Air Force's new strategic bomber (it
was cancelled in the late 1970s and revived a few years later). The Soviet
design firm Tupolev also developed the Tu-22M Backfire naval attack bomber
and the Tu-160 Blackjack strategic bomber.
By the 1980s, however, no one was
designing variable-sweep aircraft and no new work on this technology has
been incorporated into any new production military aircraft in at least
the last 15 years, although work is still being carried out on wings that
move in other ways. The technology of variable-sweep wings lasted little
more than 20 years before being phased out, although hundreds of the
aircraft continued to fly for years more.
There were several reasons for the move
away from this technology, but the primary reason was that the large metal
gearbox needed to move the wings was complicated and heavy. This increased
maintenance requirements and decreased fuel performance. An aircraft
capable of moving its wing forward for fuel-efficient flight could never
be as efficient as an airplane equipped with a straight wing. The same was
true for aircraft with swept-back wings; they would always be more
efficient than aircraft with swing-wings. The B-1B Lancer, for example,
has never been able to achieve its original range requirements and has to
refuel in the air more often than planned. It also rarely flew at the high
speeds that sweeping back the wings allowed it to do. Ultimately, aircraft
designers decided that the flexibility of the variable-sweep wing was not
worth the compromises it demanded.