Swept wing A swept wing is a wing planform favored for high subsonic and supersonic speeds , and is found on almost all jet aircraft in one form or another , as well as some high speed propeller aircraft . Compared with straight wings common to slower 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 , increasing performance . The concept was first investigated in Germany as early as 1935 , but it found no application until just before the end of the Second World War . Swept wings became common on second - generation post - war fighters like the MiG - 15 and F - 86 Sabre , which demonstrated a decisive superiority over the slower first generation of straight - wing jet fighters during the Korean War . Since then swept wings have become almost universal on all but the slowest jets ( such as the A - 10 ) . The term " swept wing " is normally used to mean " swept back " , but other swept variants include forward sweep , variable sweep wings and pivoting wings . The delta wing also incorporates the same advantages as part of its layout . The characteristic " sweep angle " is normally measured by drawing a line from root to tip , 25 % of the way back from the leading edge , and comparing that to the longitudinal axis of the aircraft . Typical sweep angles vary from 0 for a straight - wing aircraft , to 45 degrees or more for fighters and other high - speed designs . Subsonic and transonic behavior . As an aircraft enters the transonic speeds just below the speed of sound , an effect known as wave drag starts to appear . As airflow accelerates around curved surfaces , near the speed of sound this can cause the airflow to reach supersonic speeds . When this occurs , an oblique shock wave is generated at the point where the flow slows back to subsonic speed . Since this occurs on curved areas , these shock waves 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 to make up for this energy loss . Thus the shocks are seen as a form of drag . Since the shocks form when the local air velocity reaches supersonic speeds , there is a certain " critical mach " speed ( or drag divergence mach number ) 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 . Sweeping the wing has the effect of reducing the curvature of the body as seen from the airflow , by the cosine of the angle of sweep . For instance , a wing with a 45 degree sweep will see a reduction in effective curvature to about 70 % of its straight - wing value . This has the effect of increasing the critical Mach by 30 % . When applied to large areas of the aircraft , like the wings and empennage , this allows the aircraft to reach speeds closer to Mach 1 . One of the simplest and best explanations of how the swept wing works was offered by Robert T . Jones : " Suppose a cylindrical wing ( constant chord , incidence , etc . ) is placed 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 , 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 they 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 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 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 wing to create the Boeing 720 . 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 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 wing s , 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 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 " 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 had a 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 and large compound flaps to the wings has largely resolved the issue . On fighter designs , the addition of leading edge extension 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 , 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 approximately 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 or HFB - 320 Hansa Jet . But larger sweep suitable for high - speed aircraft , like fighters , was generally impossible until the introduction of fly by wire systems that could react quickly enough to damp out these instabilities . The Grumman X - 29 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 . Historically , many low - speed aircraft have had swept wings in order to avoid problems with their center of gravity , 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 meeting in 1935 in Italy , Dr . Adolf Busemann suggested the use of swept wings for supersonic 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 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 who then passed them on to Willy Messerschmitt 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 . 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 . At the time the presentation was largely of academic interest , and soon forgotten . Even notable attendees including Theodore von Kármán and Eastman Jacobs 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 testing had demonstrated the effect was real , and practical . With the introduction of jets in the later half of World War II applying sweep became relevant . The German jet - powered Messerschmitt Me 262 and rocket - powered Messerschmitt Me 163 suffered from compressibility effects that made them very difficult to control at high speeds . In addition , the speeds put them into the 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 s . The first fighter in the world specifically designed in order to take full advantage of the swept wing ' s aerodynamic properties was the Blohm & Voss P . 211 . 01 which , however , never saw mass - production . The Focke - Wulf Ta 183 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 , 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 , where two additional copies with US built engines carried on the research as the Bell X - 5 . The last jet fighter designed by Willy Messerschmitt , the Egyptian Helwan HA - 300 had swept leading - edged delta wings in this case . Technology impact . The Soviet Union 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 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 " Utka " pusher canard 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 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 , 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 , 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 engineer Robert T . Jones started looking at highly swept delta wings 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 , 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 - 46 and B - 48 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 into strut - mounted pods under the wings since Boeing was concerned that the uncontained failure of an internal engine could potentially destroy the aircraft . With the engines mounted away from the wings on struts equipped with fuse pins , an out - of - balance engine would simply shatter the pins and fall harmlessly away , sparing the aircraft from destructive vibrations . The resulting B - 47 design had performance rivaling the fastest fighters and trounced the straight - winged competition . Boeing ' s winning jet - transport formula of swept wings and engines mounted on pylons under the wings has since been universally adopted . In fighters , North American Aviation 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 XP - 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 . The Air Ministry 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 and Supermarine Swift . The German research was also " leaked " to SAAB 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 turboprop 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 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 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 , 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 have employed relatively short - span fixed wings with relatively large wing area . Sweep theory . Sweep theory is an aeronautical engineering description of the behavior of airflow over a wing when the wing ' s leading edge encounters the airflow at an oblique angle . The development of sweep theory resulted in the swept wing design used by most modern jet aircraft , as this design performs more effectively at transonic and supersonic speeds . In its advanced form , sweep theory led to the experimental oblique wing concept . Overview . Adolf Busemann introduced the concept of the swept wing and presented this 1935 at the 5 . Volta - Congress in Rome . Sweep theory in general was a subject of development and investigation throughout the 1930s and 1940s , but the breakthrough mathematical definition of sweep theory is generally credited to NACA ' s Robert T . Jones in 1945 . Sweep theory builds on other wing lift theories . Lifting line theory describes lift generated by a straight wing ( a wing in which the leading edge is perpendicular to the airflow ) . Weissinger theory describes the distribution of lift for a swept wing , but does not have the capability to include chordwise pressure distribution . There are other methods that do describe chordwise distributions , but they have other limitations . Jones ' sweep theory provides a simple , comprehensive analysis of swept wing performance . Description . To visualize the basic concept of simple sweep theory , consider a straight , non - swept wing of infinite length , which meets the airflow at a perpendicular angle . The resulting air pressure distribution is equivalent to the length of the wing ' s chord ( the distance from the leading edge to the trailing edge ) . If we were to begin to slide the wing sideways ( spanwise ) , the sideways motion of the wing relative to the air would be added to the previously perpendicular airflow , resulting in an airflow over the wing at an angle to the leading edge . This angle results in airflow traveling a greater distance from leading edge to trailing edge , and thus the air pressure is distributed over a greater distance ( and consequently lessened at any particular point on the surface ) . This scenario is identical to the airflow experienced by a swept wing as it travels through the air . The airflow over a swept wing encounters the wing at an angle . That angle can be broken down into two vectors , one perpendicular to the wing , and one parallel to the wing . The flow parallel to the wing has no effect on it , and since the perpendicular vector is shorter ( meaning slower ) than the actual airflow , it consequently exerts less pressure on the wing . In other words , the wing experiences airflow that is slower - and at lower pressures - than the actual speed of the aircraft . One of the factors that must be taken into account when designing a high - speed wing is compressibility , which is the effect that acts upon a wing as it approaches and passes through the speed of sound . The significant negative effects of compressibility made it a prime issue with aeronautical engineers . Sweep theory helps mitigate the effects of compressibility in transonic and supersonic aircraft because of the reduced pressures . This allows the mach number of an aircraft to be higher than that actually experienced by the wing . There is also a negative aspect to sweep theory . The lift produced by a wing is directly related to the speed of the air over the wing . Since the airflow speed experienced by a swept wing is lower than what the actual aircraft speed is , this becomes a problem during slow - flight phases , such as takeoff and landing . There have been various ways of addressing the problem , including the variable - incidence wing design on the F - 8 Crusader and swing wings on aircraft such as the F - 14 , F - 111 , and the Panavia Tornado .