delta wing

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Eurofighter Typhoon

The delta-winged Convair F-106 Delta Dart also employs an area ruled fuselage

The delta wing Avro Vulcan bomber

The delta wing is a wing planform in the form of a triangle, named after the Greek uppercase delta which is a triangle (Δ).

History

Conception of this wing and its name have been suggested in the 17th century by Polish inventor Kazimierz Siemienowicz.^[1][2][3] Its use in the so called "tail-less delta", i.e. without the horizontal tailplane, was pioneered especially by Alexander Lippisch in Germany prior to World War II, although none of his designs saw widespread service.^{[citation needed]}

Alexander Lippisch, Frenchman Payen, and the DFS (German Institute of Flight) studied a number of ramjet powered (sometimes coal-fueled) delta-wing interceptor aircraft during the war, one progressing as far as a glider prototype. Prototype Test Footage. After the war, Lippisch was taken to the United States of America, where he worked at the Convair company in California. Some high-ranking Convair engineers became quite interested in his interceptor designs, and they started work on a larger test version known as the Convair XF-92. The actual F-92 fighter was never needed, and its design was too immature, so it never went into production. The prototype flying test-bed was extensively flight-tested, and its design generated a lot of interest at various airplane manufactures in several different countries. Soon many aircraft designs, particularly interceptors, were designed around a delta wing.

The tail-less delta became the favored design for high-speed use, and was used (almost to the exclusion of other designs) by Convair and by Dassault Aviation in France. A number of British designs also used the delta, including the Avro Vulcan bomber. This early use of tail-less delta wing aircraft was augmented by the tailed delta configuration created in the TsAGI (Central Aero and Hydrodynamic Institute, Moscow), taking advantage of both high angle-of-attack flying capability and high speeds. The tailed delta wing was used in the MiG-21 (Fishbed) and Sukhoi Su-9/Su-11/15 fighters, built by the tens of thousands in several different communist countries.

More recently, with the advent of aircraft with relaxed or no natural stability, and the therefore necessary computer controlled/assisted control systems (fly-by-wire, or FBW), the horizontal control surfaces are often moved forward to become a canard in front of the wing to control the aeroplane as the normal elevator does. This favorably modifies the airflow over the wing, most notably during lower altitude flight. In contrast to the classic tail-mounted elevators, the canards add to the total lift, enabling the execution of extreme maneuvers, improving low-speed handling, lowering the landing speed, or the marked reduction of drag. An example of a canard-equipped delta-winged aircraft was the Tupolev bureau's Tu-144 supersonic transport airliner.

Aerodynamic advantages

The primary advantage of the delta wing 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 is an improvement on traditional wing designs. While this is also true of highly swept wings, the delta's planform carries across the entire aircraft, allowing it to be built much more strongly than a swept wing, where the spar meets the fuselage far in front of the center of gravity. Generally a delta will be stronger than a similar swept wing, as well as having much more internal volume for fuel and other storage.

Another advantage is that as the angle of attack increases the leading edge of the wing generates a vortex which remains attached to the upper surface of the wing, giving the delta a very high stall angle. A normal wing built for high speed use is typically dangerous at low speeds, but in this regime the delta changes over to a mode of lift based on the vortex it generates. The disadvantages, especially marked in the older tailless delta designs, are a loss of total available lift caused by turning up the wing trailing edge or the control surfaces (as required to achieve a sufficient stability) and the high induced drag of this low-aspect ratio type of wing. This causes delta-winged aircraft to 'bleed off' energy very rapidly in turns, a disadvantage in aerial maneuver combat and dogfighting. This can be solved with relaxed stability, strakes and canards.

Additional advantages of the delta wing are simplicity of manufacture, strength, and substantial interior volume for fuel or other equipment. Because the delta wing is simple, it can be made very robust (even if it is quite thin), and it is easy and relatively inexpensive to build - a substantial factor in the success of the MiG-21 and Mirage aircraft.

Delta-wing variations

Pure delta-wings fell out of favour somewhat due to their 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 high-speed, high-altitude interceptor roles.

Some modern aircraft, like the F-16, use a cropped delta along with horizontal tail surfaces.

In another variant known variously as compound delta, double delta or cranked arrow, the inner part of the wing has a very high sweepback, while the outer part has less sweepback, to create the high-lift vortex in a more controlled fashion, reduce the drag and thereby allow for landing the delta at acceptably slow speed. This design can be seen on the Saab Draken fighter, the prototype F-16XL "Cranked Arrow" and in the High Speed Civil Transport study. The ogee delta used on the Anglo-French Concorde Mach 2 airliner is similar, but with a smooth curve joining the two parts rather than an angle.

As the performance of jet engines grew, fighters with other planforms could perform as well as deltas, and 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 parallel to 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 performance with a conventional highly efficient wing planform. Many modern fighter aircraft, such as the JAS 39 Gripen and the Eurofighter Typhoon use a combination of canards and a delta wing.

Aircraft examples

References

• S. S. Sritharan and A. R. Seebass (1984). "A Finite Area Method for Nonlinear Supersonic Conical Flows". AIAA Journal 22: 226-233. 
• S. S. Sritharan (1985). "Delta Wings with Shock-Free Cross Flow". Quarterly of Applied Mathematics XLIII: 275-286. 
• Jingling Guan and S. S. Sritharan (2008). "A Problem of Hyperbolic-Elliptic Type Conservation Laws on Manifolds that Arises in Delta-Wing Aerodynamics". International Journal of Contemporary Mathematical Sciences 3: 721-737. 

http://uwacadweb.uwyo.edu/SMAW/Members%20Stuff/Computational_Simulation_of_Supersonic_Delta-wingsFinal.ppt

External links

Wikimedia Commons has media related to: Delta wings

• Aerodynamics of delta wings
• Analysis of air flow over delta wings