THE 456th FIGHTER INTERCEPTOR SQUADRON
THE PROTECTORS OF S. A. C.
Why Delta Wings?
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Definitions and Use
A wing is a surface used to produce an aerodynamic force normal to the direction of motion by traveling in air or another gaseous medium. The first use of the word was for the foremost limbs of birds, but has been extended to include other animal limbs and man-made devices.
The commonest use of wings is to flyby deflecting air downwards to produce lift, but wings are also commonly used as a way to produce down force and hold objects to the ground (for example racing cars)
Terms used to describe aeroplane wings
- Leading edge: the front edge of the wing
- Trailing edge: the back edge of the wing
- Span: distance from wing tip to wing tip
- Chord: distance from wing leading edge to wing trailing edge, usually measured parallel to the long axis of the fuselage
- Aspect ratio: ratio of span to standard mean chord
Aeroplane wings may feature some of the following:
- A rounded leading edge cross-section
- A sharp trailing edge cross-section
- Leading-edge devices such as slats or slots
- Trailing-edge devices such as flaps
- Ailerons (usually near the wingtips) to provide roll control
- Spoilers on the upper surface to disrupt lift
- Dihedral wings, which have an angle between them, have inherent stability in roll. As the aircraft rolls, one wing generates more lift, rolling the aircraft back into position.
- Swept wings are good for fast aircraft. They present the wing at an angle to the airflow, so that the wing "sees" a slower airflow.
- Elliptical wings are theoretically optimum for efficiency at subsonic speeds.
- Delta wings: have reasonable performance at subsonic and supersonic speeds.
- Wave-Riders: are efficient supersonic wings.
- Rogallo wings are two hollow half-cones of fabric, one of the simplest wings to construct.
- Swing-wings (or variable geometry wings) are able to move in flight to give the benefits of dihedral and delta wing. Although they were originally proposed for the un-built Boeing 2707, they are currently only found on some military fighter aircraft.
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The Boeing 2707 was intended to be the first American supersonic airliner. It would have been built at the Boeing plant in Renton. Washington, but increasing outcry over the environmental effects of the aircraft, notably sonic booms, led to its cancellation in 1971 before the two prototypes had been completed.
The Science of Wings
The amount of lift produced by a wing increases with the angle of attack (the angle between the onset flow and the chord line) but this relationship ends once the stall angle is reached. At this angle the airflow starts to separate from the upper surface, and any further increase in angle of attack gives no more lift (it may actually reduce) and gives a large increase in drag.
Wing design is complicated and very tightly associated with the science of aerodynamics.
- A helicopter uses a rotating wing with a variable pitch or angle to provide a directional force.
- The space shuttle uses its wings only for lift during its descent.
The delta-wing is a wing planform in the form of a large triangle. Its use was pioneered by Alexander Lippisch prior to WWII in Germany, but none of his designs entered service. After the war the delta became the favored design for high-speed use, and was used almost to exclusion of other planforms by Convair [ The Consolidated Vultee Aircraft Corporation, universally known as Convair, was the result of a 1943 merger between Consolidated Aircraft and Vultee Aircraft, resulting in a leading aircraft manufacturer of the United States. In 1954, Convair merged with Electric Boat to form General Dynamics, and the aircraft operation became the Convair Division of the merged company. It produced aircraft until 1965 then shifted to space and airframe projects, continuing until 1996, when the division was entirely shut down. ] in the United States and Dassault in France. In early use delta-winged aircraft were often found with no other horizontal control surfaces, creating a tailless design, but most modern versions use a canard [ In aeronautics, canard (French for duck is a type of fixed-wing aircraft in which the tailplane is ahead of the main lifting surfaces, rather than behind them as in conventional aircraft. The earliest models, were seen by observers to resemble a flying duck — hence the name. The term canard has also come to mean the tail surface itself, when mounted in that configuration. ] in front of the wing to modify the airflow over it, most notably during lower altitude flight.
The primary advantage of the design is that the wing's leading edge remains behind the shock wave generated by the nose of the aircraft when flying at supersonic speeds, which was a distinct improvement on traditional wing designs. Another advantage is that as the angle of attack
Angle of Attack is a term used in aerodynamics to describe the angle between the wing's chord and the direction of the relative wing, effectively the direction in which the aircraft is currently moving. The amount of lift generated by a wing is directly related to the angle of attack, with greater angles generating more lift. This remains true up to the stall point, where lift starts to decrease again because of airflow separation. Planes flying at high angles of attack can suddenly enter a stall if, for example, a strong wind gust changes the direction of the relative wind, an effect that is seen primarily in low-speed aircraft.
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In military terminology, angle of attack is often referred to as alpha (α), the symbol used to denote it on most diagrams. Using a variety of additional aerodynamic surfaces (a.k.a. high-lift devices) like leading edge extensions, fighter aircraft have increased the potential flyable alpha from about 20 degrees to over 45, and in some designs, 90 degrees or more. That is, the plane remains flyable when the wing's chord is at right angles to the direction of motion.
increases the leading edge of the wing generates a huge vortex [ vortex is a spinning turbulent flow which resembles a tornado. Or, maybe it is better to say that a tornado is a well known example of a large vortex. ] which remains attached to the upper surface of the wing, making the delta have very high stall points. The combination of these two features is a dream come true, a normal wing built for high speed use is typically dangerous at low speeds, but in this regime the delta transitions to a mode of lift based on the vortex it generates.
Lippisch studied a number of ramjet powered (sometimes coal-fueled!) delta-wing interceptor aircraft [ An interceptor aircraft (or simply interceptor) is a type of fight aircraft designed specifically to intercept and destroy enemy air craftt, particularly bombers. A number of such aircraft were built in the period starting just prior to World War II and ending in the late 1960's, when they became less important due to the shifting of the strategic bombing role to ICBMs. ] during the war, one progressing as far as a glider prototype. After the war Lippisch was taken to the United States, where he ended up working at Convair. Here the other engineers became very interested in his interceptor designs, and started work on a larger version known as the F-92. This project was eventually cancelled as impractical, but a prototype flying test bed was almost complete by that point, and was later flown widely as the XF-92. The design generated intense interest around the world. Soon almost every aircraft design, notably interceptors, were designed around a delta-wing. Examples include the Convair F-102, F106 & B-58 Hustler, the Avro- Arrow and the MiG-21
Deltas fell out of favor due to some undesirable characteristics, notably flow-separation at high angles of attack (swept-wings have similar problems), and high drag at low altitudes. This limited them primarily to the high-speed, high-altitude interceptor roles. A modification, the compound delta, added another much more highly swept delta wing in front of the main one, to create the vortex in a more controlled fashion and thereby reduce the low-speed drag.
As the performance of jet engines grew, fighters with more traditional planforms found they could perform almost as well as the deltas, but do so while maneuvering much harder and at a wider range of altitudes. Today a remnant of the compound delta can be found on most fighter aircraft, in the form of leading edge extensions. These are effectively very small delta wings placed so they remain out of the airflow in cruising flight, but start to generate a vortex at high angles of attack. The vortex is then captured on the top of the wing to provide additional lift, thereby combining the delta's high-alpha "trick" with a conventional highly efficient wing planform.
Dr. Alexander Martin Lippisch (November 2, 1894 - February 11, 1976) was a German pioneer of aerodynamics who made important contributions to the understanding of flying wings and ground effect craft. His most famous design was the Messerschmitt Me 163 rocket-powered interceptor.
Lippisch was born in Munich, Germany. He later recalled that his interest in aviation was first kindled by watching a demonstration by Orville Wright in September 1909 in Berlin. He was, however, planning to follow in his father’s footsteps and enter art school when World War I intervened. During his service with the German Army from 1915 – 1918, Lippisch had the chance to fly as an aerial photographer and mapper.
Following the war, Lippisch worked for a while with the Zeppelin Company, and it was at this time that he first became interested in tail-less aircraft. In 1921 the first such design of his would reach fruition in the form of the Lippisch-Espenlaub E-2 glider, built by Gottlob Espenlaub. This was the beginning of a research program that would result in some fifty designs throughout the 1920s and 30s. Lippisch’s growing reputation saw him appointed the director of Rhon-Rossitten Gesellschaft (RRG), a glider research group.
Lippisch’s work led to a series of tail-less designs numbered Storch I – Storch IX between 1927 and 1933. These were greeted with almost complete indifference by both government and private industry. During this time, one of Lippisch’s designs, the Ente (Duck), would enter history as the first aircraft to fly under rocket power. It was a sign of things to come.
Experience with the Storch series led Lippisch to concentrate increasingly on delta-winged designs. These would find expression in five aircraft (simply numbered Delta I – Delta V) built between 1931 and 1939. In 1933, RGG had been reorganized into the Deutsche Forschungsanstalt für Segelflug (DFS - German Institute for Sailplane Flight) and the Delta IV and Delta V were designated as the DFS 39 and DFS 40 respectively.
In early 1939, the Reichsluftfahrtsministerium (RLM) – (Reich Aviation Ministry) transferred Lippisch and his team to work at the Messerschmitt factory to design a high-speed fighter aircraft around the rocket engines then under development by Hellmuth Walter. They quickly adapted their then-current design, the DFS 194 to rocket power, successfully flying in early 1940. This was the direct ancestor of the Messerschmitt Me 163 Komet.
Although technically brilliant, the Komet did not prove to be a successful weapon, and friction between Lippisch and Messerschmitt was frequent. In 1943, Lippisch transferred to Vienna’s Luftfahrtforschungsanstalt Wien (LFW), to concentrate on the problems of high-speed flight. That same year, he was awarded a doctoral degree in engineering by the University of Heidelberg.
Wind tunnel research in 1939 had suggested that the delta wing was a good choice for supersonic flight and Lippisch set to work designing a supersonic, ramjet-powered fighter, the Lippisch P-13. By the time the war ended, however, the project had only advanced as far as a development glider, the DM-1.
Like many German scientists, Lippisch was taken to the United states after the war under Project Paper Clip.
[Originally called Operation Overcast, Operation Paperclip was the code name for the operation by the government of the USA to extract rockets (e.g. V-1, V-2), chemical weapons (e.g. Zyklon-B) and medical scientists from Germany, after the collapse of the Nazi government during World War II.
Scientists were deployed atWhite Sands Proving Ground, New Mexico and Fort Bliss, Texas to work on guided missile and ballistic missile technology, and led to the foundation of NASA and the US ICBM program.
Over 700 members of the Nazi scientific community were brought to the US as a direct result of Operation Paperclip, many of whom were still ardent Nazi supporters.
AlthoughPresident Harry S. Truman gave explicit orders not to allow any scientists who were thought to have strong Nazi leanings to enter the US under Operation Paperclip, many dossiers were re-written to "clean-up" the histories of many of the scientists involved, to avoid their knowledge falling into the hands of another power.
Much of the information surrounding Operation Paperclip is still classified. ]
Advances in jet engines were making his original interceptor designs more practical, and Convair became interested in a hybrid jet/rocket design that they proposed as the F-92. In order to gain experience with the delta wing, they first built a jet powered test aircraft, the 7003, which became the first powered delta-wing aircraft to fly. Although the USAF lost interest in the F-92, Convair's experience with the delta-wing design led them to proposing it for most of their projects through the 1950s and into the 1960s, including the F-102 Delta Dagger, F-106 Delta Dart and B-58 Hustler.
From 1950 - 1964 Lippisch worked for the Collins Radio Company in Iowa, which had an aeronautical division. It was during this time that his interest shifted toward ground effect craft. The results were an unconventional VTOL
[ Vertical Take-Off and Landing (VTOL) describes airplanes that can lift off vertically. This classification includes only a very few aircraft; helicopters are not considered VTOL.
In 1928, Nikola Tesla received patents for an apparatus for aerial transportation. It is one of the earliest example of VTOL aircraft. In the late 1950's and early 1960's almost all fighter aircraft designed included some VTOL features. This was a response to the worrying possibility that a first-strike against airfields by nuclear armed bombers would leave a country open to attack by following bombers. The "solution" was to use VTOL fighters that could be moved to open fields around the countryside, making them immune to widespread destruction.
In reality the costs of VTOL performance were huge, and while it turned out to be fairly easy to move the plane, moving the support equipment and fuel was not so easy. By the mid-1960s interest in VTOL had faded, perhaps due much to the widespread introduction ofICBMs as the main nuclear delivery system.
Currently there are believed to be two types of practical VTOL aircraft in operation:
V-22 Osprey "tilt-rotor" and the
- Bell Boeing
British AerospaceHawker Harrier "Jump jet" ]
aircraft (an aerodyne) and an aerofoil boat. Lippisch resigned from Collins because of ill health caused by cancer.
When he recovered in 1996, he formed his own research company, Lippisch Research Corporation, and attracted the interest of the West German government. Prototypes for both the aerodyne and the ground-effect craft were built, but no further development was undertaken. The Kiekhaefer Mercury company was also interested in his ground-effect craft and successfully tested one of his designs as the Aeroskimmer, but also eventually lost interest.
Lippisch died at Cedar Rapids, Iowa.
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