Swept wing - AbsoluteAstronomy.com

A swept wing is a wing planform

Planform

In aviation, a planform is the shape and layout of a fixed-wing aircraft's fuselage and wing. Of all the myriad planforms used, they can typically be grouped into those used for low-speed flight, found on general aviation aircraft, and those used for high-speed flight, found on many military...

favored for high subsonic jet speeds first investigated by Germany during the Second World War. Since the introduction of the MiG-15

Mikoyan-Gurevich MiG-15

The Mikoyan-Gurevich MiG-15 was a jet fighter developed for the USSR by Artem Mikoyan and Mikhail Gurevich. The MiG-15 was one of the first successful swept-wing jet fighters, and it achieved fame in the skies over Korea, where early in the war, it outclassed all straight-winged enemy fighters in...

and North American F-86 which demonstrated a decisive superiority over the slower first generation of straight-wing jet fighters during the Korean War

Korean War

The Korean War was a conventional war between South Korea, supported by the United Nations, and North Korea, supported by the People's Republic of China , with military material aid from the Soviet Union...

, swept wings have become almost universal on all but the slowest jets

Jet aircraft

A jet aircraft is an aircraft propelled by jet engines. Jet aircraft generally fly much faster than propeller-powered aircraft and at higher altitudes – as high as . At these altitudes, jet engines achieve maximum efficiency over long distances. The engines in propeller-powered aircraft...

(such as the A-10). Compared with straight wings common to propeller-powered aircraft, they have a "swept" wing root to wingtip direction angled beyond (usually aftward) the spanwise axis. This has the effect of delaying the drag rise caused by fluid compressibility near the speed of sound as swept wing fighters such as the F-86 were among the first to be able to exceed the speed of sound in a slight dive, and later in level flight.

Unusual variants of this design feature are forward sweep

Forward-swept wing

A forward-swept wing is an aircraft wing configuration in which the quarter-chord line of the wing has a forward sweep. The configuration was first proposed in 1936 by German aircraft designers.Perceived benefits of a forward-swept wing design include...

, variable sweep wings and pivoting wings. Swept wings as a means of reducing wave drag

Wave drag

In aeronautics, wave drag is a component of the drag on aircraft, blade tips and projectiles moving at transonic and supersonic speeds, due to the presence of shock waves. Wave drag is independent of viscous effects.- Overview :...

were first used on jet fighter aircraft

Fighter aircraft

A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...

. The four-engine propeller-driven Tu-95

Tupolev Tu-95

The Tupolev Tu-95 is a large, four-engine turboprop-powered strategic bomber and missile platform. First flown in 1952, the Tu-95 entered service with the former Soviet Union in 1956 and is expected to serve the Russian Air Force until at least 2040...

aircraft also has swept wings.

The angle of sweep which characterizes a swept wing is conventionally measured along the 25% chord

Chord (aircraft)

In aeronautics, chord refers to the imaginary straight line joining the trailing edge and the center of curvature of the leading edge of the cross-section of an airfoil...

line. If the 25% chord line varies in sweep angle, the leading edge is used; if that varies, the sweep is expressed in sections (e.g., 25 degrees from 0 to 50% span, 15 degrees from 50% to wingtip).

Subsonic and transonic behavior

As an aircraft enters the transonic

Transonic

Transonic speed is an aeronautics term referring to the condition of flight in which a range of velocities of airflow exist surrounding and flowing past an air vehicle or an airfoil that are concurrently below, at, and above the speed of sound in the range of Mach 0.8 to 1.2, i.e. 600–900 mph...

speeds just below the speed of sound, an effect known as wave drag

Wave drag

starts to appear. Using conservation of momentum principles in the direction normal to surface curvature, airflow accelerates around curved surfaces, and near the speed of sound the acceleration can cause the airflow to reach supersonic speeds. When this occurs, an oblique shock wave

Shock wave

A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...

is generated at the point where the flow slows down back to subsonic speed. Since this occurs on curved areas, they are normally associated with the upper surfaces of the wing, the cockpit canopy, and the nose cone of the aircraft, areas with the highest local curvature.

Shock waves require energy to form. This energy is taken out of the aircraft, which has to supply extra thrust

Thrust

Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....

to make up for this energy loss. Thus the shocks are seen as a form of drag

Drag (physics)

In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

. Since the shocks form when the local air velocity reaches supersonic speeds over various features of the aircraft, there is a certain "critical mach" speed (or drag divergence mach number

Drag divergence Mach number

The drag divergence Mach number is the Mach number at which the aerodynamic drag on an airfoil or airframe begins to increase rapidly as the Mach number continues to increase...

) where this effect becomes noticeable. This is normally when the shocks start generating over the wing, which on most aircraft is the largest continually curved surface, and therefore the largest contributor to this effect.

One of the simplest and best explanations of how the swept wing works was offered by Robert T. Jones

Robert T. Jones

Robert T. Jones, , was an aerodynamicist and aeronautical engineer for NACA and later NASA. He was known at NASA as "one of the premier aeronautical engineers of the twentieth century",.-Designer:...

:
"Suppose a cylindrical wing (constant chord, incidence, etc.) is place in an airstream at an angle of yaw - ie., it is swept back. Now, even if the local speed of the air on the upper surface of the wing becomes supersonic, a shock wave cannot form there because it would have to be a sweptback shock - swept at the same angle as the wing - ie., it would be an oblique shock. Such an oblique shock cannot form until the velocity component normal to it becomes supersonic."

One limiting factor in swept wing design is the so-called "middle effect". If a swept wing is continuous - an oblique swept wing

Oblique wing

An oblique wing is a variable geometry wing concept. On an aircraft so equipped, the wing is designed to rotate on center pivot, so that one tip is swept forward while the opposite tip is swept aft...

, the pressure iso-bars will be swept at a continuous angle from tip to tip. However, if the left and right halves are swept back equally, as is common practice, the pressure iso-bars on the left wing in theory will meet the pressure iso-bars of the right wing on the centerline at a large angle. As the iso-bars cannot meet in such a fashion, they will tend to curve on each side as the near the centerline, so that the iso-bars cross the centerline at right angles to the centerline. This causes an "unsweeping" of the iso-bars in the wing root region. To combat this unsweeping, German aerodynamicist Dietrich Küchemann

Dietrich Küchemann

Dietrich Küchemann CBE FRS FRAeS was a German aerodynamicist who made several important contributions to the advancement of high-speed flight...

proposed and had tested a local indentation of the fuselage above and below the wing root. This proved to not be very effective. During the development of the Douglas DC-8

Douglas DC-8

The Douglas DC-8 is a four-engined narrow-body passenger commercial jet airliner, manufactured from 1958 to 1972 by the Douglas Aircraft Company...

airliner, uncambered airfoils were used in the wing root area to combat the unsweeping. Similarly, a decambered wing root glove was added to the Boeing 707

Boeing 707

The Boeing 707 is a four-engine narrow-body commercial passenger jet airliner developed by Boeing in the early 1950s. Its name is most commonly pronounced as "Seven Oh Seven". The first airline to operate the 707 was Pan American World Airways, inaugurating the type's first commercial flight on...

wing to create the Boeing 720

Boeing 720

The Boeing 720 is a four-engine narrow-body short- to medium-range passenger jet airliner. Developed by Boeing in the late 1950s from the Boeing 707, the 720 has a shorter fuselage and less range...

Supersonic behavior

Airflow at supersonic speeds generates lift through the formation of shock waves, as opposed to the patterns of airflow over and under the wing. These shock waves, as in the transonic case, generate large amounts of drag. One of these shock waves is created by the leading edge of the wing, but contributes little to the lift. In order to minimize the strength of this shock it needs to remain "attached" to the front of the wing, which demands a very sharp leading edge. To better shape the shocks that will contribute to lift, the rest of an ideal supersonic airfoil is roughly diamond-shaped in cross-section. For low-speed lift these same airfoils are very inefficient, leading to poor handling and very high landing speeds.

One way to avoid the need for a dedicated supersonic wing is to use a highly swept subsonic design. Airflow behind the shock waves of a moving body are reduced to subsonic speeds. This effect is used within the intakes of engines meant to operate in the supersonic, as jet engines are generally incapable of ingesting supersonic air directly. This can also be used to reduce the speed of the air as seen by the wing, using the shocks generated by the nose of the aircraft. As long as the wing lies behind the cone-shaped shock wave, it will "see" subsonic airflow and work as normal. The angle needed to lie behind the cone increases with increasing speed, at Mach 1.3 the angle is about 45 degrees, at Mach 2.0 it is 60 degrees. For instance, at Mach 1.3 the angle of the Mach cone formed off the body of the aircraft will be at about sinμ = 1/M (μ is the sweep angle of the Mach cone)

Generally it is not possible to arrange the wing so it will lie entirely outside the supersonic airflow and still have good subsonic performance. Some aircraft, like the English Electric Lightning

English Electric Lightning

The English Electric Lightning is a supersonic jet fighter aircraft of the Cold War era, noted for its great speed and unpainted natural metal exterior finish. It is the only all-British Mach 2 fighter aircraft. The aircraft was renowned for its capabilities as an interceptor; Royal Air Force ...

or Convair F-106 Delta Dart are tuned entirely for high-speed flight and feature highly swept planforms without regard to the low-speed problems this creates. In other cases the use of variable geometry wings, as on the Grumman F-14 Tomcat, allows an aircraft to move the wing to keep it at the most efficient angle regardless of speed, although the cost in complexity and weight makes this a rare feature.

Most high-speed aircraft have a wing that spends at least some of its time in the supersonic airflow. But since the shock cone moves towards the fuselage with increased speed (that is, the cone becomes narrower), the portion of the wing in the supersonic flow also changes with speed. Since these wings are swept, as the shock cone moves inward, the lift vector moves forward as the outer, rearward portions of the wing are generating less lift. This results in powerful pitching moments and their associated required trim changes.

Disadvantages

When a swept wing travels at high speed, the airflow has little time to react and simply flows over the wing almost straight from front to back. At lower speeds the air does have time to react, and is pushed spanwise by the angled leading edge, towards the wing tip. At the wing root, by the fuselage, this has little noticeable effect, but as one moves towards the wingtip the airflow is pushed spanwise not only by the leading edge, but the spanwise moving air beside it. At the tip the airflow is moving along the wing instead of over it, a problem known as spanwise flow.

The lift from a wing is generated by the airflow over it from front to rear. With increasing span-wise flow the boundary layers on the surface of the wing have longer to travel, and so are thicker and more susceptible to transition to turbulence or flow separation, also the effective aspect ratio of the wing is less and so air "leaks" around the wing tips reducing their effectiveness. The spanwise flow on swept wings produces airflow that moves the stagnation point on the leading edge of any individual wing segment further beneath the leading edge, increasing effective angle of attack of wing segments relative to its neighbouring forward segment. The result is that wing segments farther towards the rear operate at increasingly higher angles of attack promoting early stall of those segments. This promotes tip stall on back swept wings, as the tips are most rearward, while delaying tip stall for forward swept wings, where the tips are forward. With both forward and back swept wings, the rear of the wing will stall first. This creates a nose-up pressure on the aircraft. If this is not corrected by the pilot it causes the plane to pitch up, leading to more of the wing stalling, leading to more pitch up, and so on. This problem came to be known as the Sabre dance in reference to the number of North American F-100 Super Sabre

F-100 Super Sabre

The North American F-100 Super Sabre was a supersonic jet fighter aircraft that served with the United States Air Force from 1954 to 1971 and with the Air National Guard until 1979. The first of the Century Series collection of USAF jet fighters, it was the first USAF fighter capable of...

s that crashed on landing as a result.

The solution to this problem took on many forms. One was the addition of a fin known as a wing fence
Wing fence
Wing fences, also known as boundary layer fences and potential fences are fixed aerodynamic devices attached to aircraft wings. Not to be confused with wingtip fences, wing fences are flat plates fixed to the upper surfaces parallel to the airflow. They are often seen on swept-wing aircraft...

on the upper surface of the wing to redirect the flow to the rear (see the MiG-15 as an example.) Another closely related design was addition of a dogtooth notch to the leading edge (Avro Arrow). Other designs took a more radical approach, including the Republic XF-91 Thunderceptor's wing that grew wider towards the tip to provide more lift at the tip. The Handley Page Victor

Handley Page Victor

The Handley Page Victor was a British jet bomber aircraft produced by the Handley Page Aircraft Company during the Cold War. It was the third and final of the V-bombers that provided Britain's nuclear deterrent. The other two V-bombers were the Avro Vulcan and the Vickers Valiant. Some aircraft...

had a planform

Planform

based on a crescent compound sweep or scimitar wing that had substantial sweep-back near the wing root where the wing was thickest, and progressively reducing sweep along the span as the wing thickness reduced towards the tip.

Modern solutions to the problem no longer require "custom" designs such as these. The addition of leading edge slats

Leading edge slats

Slats are aerodynamic surfaces on the leading edge of the wings of fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. A higher coefficient of lift is produced as a result of angle of attack and speed, so by deploying slats an aircraft can fly at slower...

and large compound flaps

Flap (aircraft)

Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...

to the wings has largely resolved the issue. On fighter designs, the addition of leading edge extension

Leading edge extension

A leading edge extension is a small extension to an aircraft wing surface, forward of the leading edge. Different kinds of extensions have been used for different reasons.-Leading edge slats:...

s, included for high maneuverability, also serve to add lift during landing and reduce the problem.

The swept wing also has several more problems. One is that for any given length of wing, the actual span from tip-to-tip is shorter than the same wing that is not swept. Low speed drag is strongly correlated with the aspect ratio

Aspect ratio (wing)

In aerodynamics, the aspect ratio of a wing is essentially the ratio of its length to its breadth . A high aspect ratio indicates long, narrow wings, whereas a low aspect ratio indicates short, stubby wings....

, the span compared to chord, so a swept wing always has more drag at lower speeds. Another concern is the torque applied by the wing to the fuselage, as much of the wing's lift lies behind the point where the wing root connects to the plane. Finally, while it is fairly easy to run the main spars of the wing right through the fuselage in a straight wing design to use a single continuous piece of metal, this is not possible on the swept wing because the spars will meet at an angle.

Forward sweep

Sweeping a wing forward has the same effect as rearward in terms of drag reduction, but has other advantages in terms of low-speed handling where tip stall problems simply go away. In this case the low-speed air flows towards the fuselage, which acts as a very large wing fence. Additionally, wings are generally larger at the root anyway, which allows them to have better low-speed lift.

However, this arrangement also has serious stability problems. The rearmost section of the wing will stall first causing a pitch-up moment pushing the aircraft further into stall similar to a swept back wing design. Thus swept-forward wings are unstable in a fashion similar to the low-speed problems of a conventional swept wing. However unlike swept back wings, the tips on a forward swept design will stall last, maintaining roll control.

Forward-swept wings can also experience dangerous flexing effects compared to aft-swept wings that can negate the tip stall advantage if the wing is not sufficiently stiff. In aft-swept designs, when the airplane maneuvers at high load factor the wing loading and geometry twists the wing in such a way as to create washout (tip twists leading edge down). This reduces the angle of attack at the tip, thus reducing the bending moment on the wing, as well as somewhat reducing the chance of tip stall. However, the same effect on forward-swept wings produces a wash-in effect which increases the angle of attack promoting tip stall.

Small amounts of sweep do not cause serious problems, and had been used on a variety of aircraft to move the spar into a convenient location, as on the Junkers Ju 287

Junkers Ju 287

-Bibliography:* Hitchcock, Thomas H. Junkers 287 . Acton, MA: Monogram Aviation Publications, 1974. ISBN 0-914144-01-4.-External links:*...

or HFB-320 Hansa Jet

HFB-320 Hansa Jet

|-See also:-References:*Sloot, Emiel. "Hansa Jet Retirement". Air International, October 1994, Vol 47 No 4. pp. 234–235. ISSN 0306-5634.*Taylor, John W. R.. Jane's All The World's Aircraft 1965–66. London: Sampson Low, Marston & Company, 1965....

. But larger sweep suitable for high-speed aircraft, like fighters, was generally impossible until the introduction of fly by wire

Fly by Wire

Fly by Wire: The Geese, the Glide, the Miracle on the Hudson is a book written in 2009 by William Langewiesche about US Airways Flight 1549 with emphasis on the role played by the advanced fly-by-wire flight control system of the aircraft....

systems that could react quickly enough to damp out these instabilities. The Grumman X-29

Grumman X-29

|-See also:-References:NotesBibliography* Thruelsen, Richard. The Grumman Story. New York: Praeger Publishers, Inc., 1976. ISBN 0-275-54260-2....

was an experimental technology demonstration project designed to test the forward swept wing for enhanced maneuverability in 1984. The Su-47 Berkut is another notable example using this technology. However no highly swept-forward design has entered production.

History

The first aircraft with swept wings were those designed by the British designer J.W.Dunne in the first decade of the 20th century. Dunne successfully employed severely swept wings in his tailless aircraft as a means of creating positive longitudinal static stability

Longitudinal static stability

Longitudinal static stability is the stability of an aircraft in the longitudinal, or pitching, plane during static conditions. This characteristic is important in determining whether an aircraft will be able to fly as intended...

. Historically, many low-speed aircraft have had swept wings in order to avoid problems with their center of gravity

Center of gravity of an aircraft

The center-of-gravity is the point at which an aircraft would balance if it were possible to suspend it at that point. It is the mass center of the aircraft, or the theoretical point at which the entire weight of the aircraft is assumed to be concentrated. Its distance from the reference datum is...

, to move the wing spar into a more convenient location, or to improve the sideways view from the pilot's position. For instance, the Douglas DC-3 had a slight sweep to the leading edge of its wing. The wing sweep in low-speed aircraft was not intended to help with transonic performance, and although most have a small amount of wing sweep they are rarely described as swept wing aircraft. The Curtiss XP-55 was the first American swept wing airplane, although it was not considered successful. The swept wing had appeared before World War I, conceived as a means of permitting the design of safe, stable, and tailless flying wings. It imposed “self-damping” inherent stability upon the flying wing, and, as a result, many flying wing gliders and some powered aircraft appeared in the interwar years.

Introduction

The idea of using swept wings to reduce high-speed drag was first developed in Germany in the 1930s. At a Volta Conference

Volta Conference

The Volta Conference was the name given to each of the international conferences held in Italy by the Royal Academy of Science in Rome, and funded by the Alessandro Volta Foundation...

meeting in 1935 in Italy, Dr. Adolf Busemann

Adolf Busemann

Adolph Busemann was a German aerospace engineer and influential early pioneer in aerodynamics, specialising in supersonic airflows...

suggested the use of swept wings for supersonic

Supersonic

Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...

flight. He noted that the airspeed over the wing was dominated by the normal component of the airflow, not the freestream velocity, so by setting the wing at an angle the forward velocity at which the shock waves would form would be higher (the same had been noted by Max Munk in 1924, although not in the context of high-speed flight). Albert Betz

Albert Betz

Albert Betz was a German physicist and a pioneer of wind turbine technology.In 1910 he graduated as a naval engineer from Technische Hochschule Berlin...

immediately suggested the same effect would be equally useful in the transonic. After the presentation the host of the meeting, Arturo Crocco, jokingly sketched "Busemann's airplane of the future" on the back of a menu while they all dined. Crocco's sketched showed a classic 1950's fighter design, with swept wings and tail surfaces, although he also sketched a swept propeller powering it.

Hubert Ludewieg of the High-Speed Aerodynamics Branch at the AVA Göttingen in 1939 conducted the first wind tunnel tests to investigate Busemann's theory. Two wings, one with no sweep, and one with 45 degrees of sweep were tested at Mach numbers of 0.7 and 0.9 in the 11 x 13 cm wind tunnel. The results of these tests confirmed the drag reduction offered by swept wings at transonic speeds. The results of the tests were communicated to Albert Betz

Albert Betz

Albert Betz was a German physicist and a pioneer of wind turbine technology.In 1910 he graduated as a naval engineer from Technische Hochschule Berlin...

who then passed them on to Willy Messerschmitt

Willy Messerschmitt

Wilhelm Emil "Willy" Messerschmitt was a German aircraft designer and manufacturer. He was born in Frankfurt am Main, the son of a wine merchant...

in December 1939. The tests were expanded in 1940 to include wings with 15, 30 and -45 degrees of sweep and Mach numbers as high as 1.21.

At the time, however, there was no way to power an aircraft to these sorts of speeds, and even the fastest aircraft of the era were only approaching 400 km/h (249 mph). Large engines at the front of the aircraft made it difficult to obtain a reasonable fineness ratio, and although wings could be made thin and broad, doing so made them considerably less strong. The British Supermarine Spitfire

Supermarine Spitfire

The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s...

used as thin a wing as possible for lower high-speed drag, but later paid a high price for it in a number of aerodynamic problems such as control reversal

Control reversal

Control reversal is an adverse effect on the controllability of aircraft. The flight controls reverse themselves in a way that is not intuitive, so pilots may not be aware of the situation and therefore provide the wrong inputs; in order to roll to the left, for instance, they have to push the...

. German design instead opted for thicker wings, accepting the drag for greater strength and increased internal space for landing gear, fuel and weapons.

At the time the presentation was largely of academic interest, and soon forgotten. Even notable attendees including Theodore von Kármán

Theodore von Karman

Theodore von Kármán was a Hungarian-American mathematician, aerospace engineer and physicist who was active primarily in the fields of aeronautics and astronautics. He is responsible for many key advances in aerodynamics, notably his work on supersonic and hypersonic airflow characterization...

and Eastman Jacobs

Eastman Jacobs

Eastman Nixon Jacobs was a leading aerodynamicist who worked for NACA's Langley Research Center from the 1920s to the 1940s. He was responsible for advancing many fields in aerodynamics, dealing particularly with wind tunnels, airfoils, turbulence, boundary layers, and Schlieren...

did not recall the presentation 10 years later when it was re-introduced to them. Buseman was in charge of aerodynamics research at Braunschweig, and in spite of the limited interest he began a research program studying the concept. By 1939 wind tunnel

Wind tunnel

A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...

testing had demonstrated the effect was real, and practical.

With the introduction of jets

Jet engine

A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

in the later half of World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

applying sweep became relevant. The German jet-powered Messerschmitt Me 262

Messerschmitt Me 262

The Messerschmitt Me 262 Schwalbe was the world's first operational jet-powered fighter aircraft. Design work started before World War II began, but engine problems prevented the aircraft from attaining operational status with the Luftwaffe until mid-1944...

and rocket-powered Messerschmitt Me 163

Messerschmitt Me 163

The Messerschmitt Me 163 Komet, designed by Alexander Lippisch, was a German rocket-powered fighter aircraft. It is the only rocket-powered fighter aircraft ever to have been operational. Its design was revolutionary, and the Me 163 was capable of performance unrivaled at the time. Messerschmitt...

suffered from compressibility effects that made them very difficult to control at high speeds. In addition, the speeds put them into the wave drag

Wave drag

regime, and anything that could reduce this drag would increase the performance of their aircraft, notably the notoriously short flight times measured in minutes. This resulted in a crash program to introduce new swept wing designs, both for fighters as well as bomber

Bomber

A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...

s. The Focke-Wulf Ta 183

Focke-Wulf Ta 183

The Focke-Wulf Ta 183 Huckebein was a design for a jet-powered fighter aircraft intended as the successor to the Messerschmitt Me 262 and other day fighters in Luftwaffe service during World War II. It was developed only to the extent of wind tunnel models when the war ended, but the basic design...

was a swept wing fighter design with a layout very similar to that later used on the MiG-15 that was not produced before war's end.

A prototype test aircraft, the Messerschmitt Me P.1101

Messerschmitt Me P.1101

|-See also:-References:NotesBibliography* Myrha, David. Messerschmitt P.1101- X Planes of the Third Reich Series. Atglen, PA: Schiffer Military History, 1999. ISBN 0-7643-0908-0....

, was built to research the tradeoffs of the design and develop general rules about what angle of sweep to use. None of the fighter or bomber designs were ready for use by the time the war ended, but the P.1101 was captured by US forces and returned to the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, where two additional copies with US built engines carried on the research as the Bell X-5

Bell X-5

-See also:-Bibliography:* Hallion, Richard P. On The Frontier: Flight Research At Dryden 1946-1981 . Washington, DC: National Aeronautics and Space Administration, 1984 . ISBN 1-58834-134-8....

. The last jet fighter designed by Willy Messerschmitt

Willy Messerschmitt

Wilhelm Emil "Willy" Messerschmitt was a German aircraft designer and manufacturer. He was born in Frankfurt am Main, the son of a wine merchant...

the HA-300 had swept wings, Delta Wing

Delta wing

The delta wing is a wing planform in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta .-Delta-shaped stabilizers:...

in this case.

Technology impact

The Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

was intrigued about the idea of swept wings on aircraft at the end of World War II in Europe, when their "captured aviation technology" counterparts to the western Allies spread out across the defeated Third Reich. Artem Mikoyan was asked by the Soviet government, principally by the government's TsAGI

TsAGI

TsAGI is a transliteration of the Russian abbreviation for Центра́льный аэрогидродинами́ческий институ́т or "Tsentralniy Aerogidrodinamicheskiy Institut", the Central Aerohydrodynamic Institute....

aviation research department, to develop a test-bed aircraft to research the swept wing idea-the result was the late 1945-flown, unusual MiG-8

Mikoyan-Gurevich MiG-8

|-See also:-References:Bibliography* Gordon, Yefim and Komissarov, Dmitry. OKB Mikoyan: A History of the Design Bureau and its Aircraft. Hinckley, England: Midland Publishing, 2009 ISBN 1-85780-307-5...

Utka pusher

Pusher configuration

In a craft with a pusher configuration the propeller are mounted behind their respective engine. According to Bill Gunston, a "pusher propeller" is one mounted behind engine so that drive shaft is in compression...

canard

Canard (aeronautics)

In aeronautics, canard is an airframe configuration of fixed-wing aircraft in which the forward surface is smaller than the rearward, the former being known as the "canard", while the latter is the main wing...

layout aircraft, with its rearwards-located wings being swept back for this type of research. When applied to the jet-powered Mig-15, its maximum speed of 1075 km/h (668 mph) outclassed the straight-winged American jets and piston-engined fighters first deployed to Korea.

von Kármán travelled to Germany near the end of the war as part of Operation Paperclip

Operation Paperclip

Operation Paperclip was the Office of Strategic Services program used to recruit the scientists of Nazi Germany for employment by the United States in the aftermath of World War II...

, and reached Braunschweig on May 7, discovering a number of swept wing models and a mass of technical data from the wind tunnels. One member of the US team was George S. Schairer

George S. Schairer

George S. Schairer was an aerodynamicst at Consolidated Aircraft and Boeing whose design innovations became standard on virtually all types of military and passenger jet planes.-Early life:...

, who was at that time working at the Boeing company. He immediately forwarded a letter to Ben Cohn at Boeing stating that they needed to investigate the concept. He also told Cohn to distribute the letter to other companies as well, although only Boeing and North American made immediate use of it.

In February 1945, NACA

NACA

- Organizations :* National Advisory Committee for Aeronautics, the forerunner of the U.S. federal agency NASA* National Association for Campus Activities, an organization for programmers of university and college activities...

engineer Robert T. Jones

Robert T. Jones

Robert T. Jones, , was an aerodynamicist and aeronautical engineer for NACA and later NASA. He was known at NASA as "one of the premier aeronautical engineers of the twentieth century",.-Designer:...

started looking at highly swept delta wing

Delta wing

The delta wing is a wing planform in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta .-Delta-shaped stabilizers:...

s and V shapes, and discovered the same effects as Busemann. He finished a detailed report on the concept in April, but found his work was heavily criticised by other members of NACA Langley

Langley Research Center

Langley Research Center is the oldest of NASA's field centers, located in Hampton, Virginia, United States. It directly borders Poquoson, Virginia and Langley Air Force Base...

, notably Theodore Theodorsen, who referred to it as "hocus-pocus" and demanded some "real mathematics". However, Jones had already secured some time for free-flight models under the direction of Robert Gilruth, whose reports were presented at the end of May and showed a fourfold decrease in drag at high speeds. All of this was compiled into a report published on June 21, 1945, which was sent out to the industry three weeks later. Ironically, by this point Busemann's work had already been passed around.

Boeing was in the midst of designing the Boeing B-47 Stratojet, and the initial Model 424 was a straight-wing design similar to the B-45

B-45 Tornado

The North American B-45 Tornado was the United States Air Force's first operational jet bomber, and the first jet aircraft to be refueled in the air. The B-45 was an important part of the United States's nuclear deterrent for several years in the early 1950s, but was rapidly succeeded by the Boeing...

, B-46

Convair XB-46

|-See also:-External Links:*...

and B-48

Martin XB-48

|-See also:-References:NotesBibliography* Jones, Lloyd S. U.S. Bombers, B-1 1928 to B-1 1980s. Fallbrook, CA: Aero Publishers, 1962, second edition 1974. ISBN 0-8168-9126-5....

it competed with. A recent design overhaul completed in June produced the Model 432, another four-engine design with the engines buried in the fuselage to reduce drag, and long-span wings that gave it an almost glider-like appearance. By September the Braunschweig data had been worked into the design, which re-emerged as the Model 448, a larger six-engine design with more robust wings swept at about 35 degrees. Another re-work in November moved the engines to pods under the wings, as the Army was concerned about engine fires potentially destroying the aircraft. The resulting design would have performance rivaling the fastest fighters, and trounced the straight-winged competition. The basic layout of engines on pylons under swept wings is still used on most airliners today.

In fighters, North American Aviation

North American Aviation

North American Aviation was a major US aerospace manufacturer, responsible for a number of historic aircraft, including the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F-86 Sabre jet fighter, the X-15 rocket plane, and the XB-70, as well as Apollo Command and Service...

was in the midst of working on a straight-wing jet-powered naval fighter then known as the FJ-1. It was submitted it to the Air Force as the F-86. Larry Green, who could read German, studied the Busemann reports and convinced management to allow a redesign starting in August 1945. A battery of wind tunnel tests followed, and although little else of the design was changed, including the wing profile (NACA 0009), the performance of the aircraft was dramatically improved over straight-winged jets. With the appearance of the Mig-15, the F-86 was rushed into combat and straight-wing jets like the Lockheed P-80 Shooting Star and Republic F-84 Thunderjet were soon relegated to ground attack. Some such as the F-84 and Grumman F-9 Cougar were later redesigned with swept wings from straight-winged aircraft. Later planes such as the North American F-100 Super Sabre would be designed with swept wings from the start, though additional innovations such as the afterburner, area-rule and new control surfaces would be necessary to master supersonic flight.

The British also received the German data, and decided that future high-speed designs would have to use it. A particularly interesting victim of this process was the cancellation of the Miles M-52, a straight-wing design for an attempt on the speed of sound. When the swept wing design came to light the project was cancelled, as it was thought it would have too much drag to break the sound barrier, but soon after the US nevertheless did just that with the Bell X-1

Bell X-1

The Bell X-1, originally designated XS-1, was a joint NACA-U.S. Army/US Air Force supersonic research project built by Bell Aircraft. Conceived in 1944 and designed and built over 1945, it eventually reached nearly 1,000 mph in 1948...

. The Air Ministry

Air Ministry

The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...

introduced a program of experimental aircraft to examine the effects of swept wings (as well as delta wings) and introduced their first combat designs as the Hawker Hunter

Hawker Hunter

The Hawker Hunter is a subsonic British jet aircraft developed in the 1950s. The single-seat Hunter entered service as a manoeuvrable fighter aircraft, and later operated in fighter-bomber and reconnaissance roles in numerous conflicts. Two-seat variants remained in use for training and secondary...

and Supermarine Swift

Supermarine Swift

The Supermarine Swift was a British single-seat jet fighter of the Royal Air Force , built by Supermarine during the 1950s. After a protracted development period, the Swift entered service as an interceptor, but, due to a spate of accidents, its service life was short...

.

The German research was also "leaked" to SAAB

Saab

Saab AB is a Swedish aerospace and defence company, founded in 1937. From 1947 to 1990 it was the parent company of automobile manufacturer Saab Automobile, and between 1968 and 1995 the company was in a merger with commercial vehicle manufacturer Scania, known as Saab-Scania.-History:"Svenska...

from a source in Switzerland in late 1945. They were in the process of developing the jet fighter Saab 29 Tunnan, and quickly adapted the existing straight-wing layout to incorporate a 25 degree sweep. Although not well known outside Sweden, the Tunnan was a very competitive design, remaining in service until 1972 in some roles.

The introduction of the German swept wing research to aeronautics caused a minor revolution, especially after the dramatic successes of the B-47 and F-86. Eventually almost all design efforts immediately underwent modifications in order to incorporate a swept wing. The classic Boeing B-52, designed in the 1950s, would remain in service until into the 21st century as a high subsonic long-range heavy bomber despite the development of the triple-sonic North American B-70 Valkyrie, supersonic swing-wing Rockwell B-1 Lancer, and flying wing designs. While the Soviet never matched the performance of the Boeing B-52 Stratofortress with a jet design, the intercontinental range Tupolev Tu-95

Tupolev Tu-95

turboprop

Turboprop

A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...

bomber also remains in service today. With a near-jet class top speed of 920 km/h, it is an unusual in combining swept wings with propeller propulsion and remains the fastest propeller powered production aircraft. By the 1960s, most civilian jets such as the Boeing 707

Boeing 707

adopted swept wings as well.

By the early 1950s nearly every new fighter was either rebuilt or designed from scratch with a swept wing. The Douglas A-4 Skyhawk and Douglas F4D Skyray were examples of delta wings which also have swept leading edges with or without a tail. Most early transonic and supersonic designs such as the MiG-19 and F-100 used long, highly swept wings. Swept wings would reach Mach 2 in the arrow-winged BAC Lightning, and stubby winged Republic F-105 Thunderchief, which was found to be wanting in turning ability in Vietnam combat. By the late 1960s, the F-4 Phantom and Mikoyan-Gurevich MiG-21

Mikoyan-Gurevich MiG-21

The Mikoyan-Gurevich MiG-21 is a supersonic jet fighter aircraft, designed by the Mikoyan-Gurevich Design Bureau in the Soviet Union. It was popularly nicknamed "balalaika", from the aircraft's planform-view resemblance to the Russian stringed musical instrument or ołówek by Polish pilots due to...

which both used variants on tailed delta wings came to dominate front line air forces. Variable geometry wings were employed on the American F-111, Grumman F-14 Tomcat and Soviet Mikoyan Mig-27

Mikoyan MiG-27

The Mikoyan MiG-27 is a variable-geometry ground-attack aircraft, originally built by the Mikoyan design bureau in the Soviet Union and later license-produced in India by Hindustan Aeronautics as the Bahadur . It is based on the Mikoyan-Gurevich MiG-23 fighter aircraft, but optimized for...

, although the idea would be abandoned for the American SST design. After the 1970s, most newer generation fighters optimized for maneuvering air combat since the USAF F-15 and Soviet Mikoyan MiG-29

Mikoyan MiG-29

The Mikoyan MiG-29 is a fourth-generation jet fighter aircraft designed in the Soviet Union for an air superiority role. Developed in the 1970s by the Mikoyan design bureau, it entered service with the Soviet Air Force in 1983, and remains in use by the Russian Air Force as well as in many other...

have employed relatively short-span fixed wings with relatively large wing area.

External links

CFD results showing the 3 dimensional supersonic bubble over the wing of an A 320. Another CFD result showing the MDXX and how the shock vanishes close to the fuselage where the aerofoil is more slender