Delta wing

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For the race car, see DeltaWing.
HAL Tejas of the Indian air force has a tailless delta wing configuration
The MiG-21 had a tailed delta wing configuration (with a conventional tail)
The delta wing Avro Vulcan bomber

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 (Δ).

History[edit]

Delta wing[edit]

Triangular stabilizing fins for rockets were described ca. 1529-1556 by Conrad Haas and in the 17th century by Kazimierz Siemienowicz.[1][2][3]

The lifting delta wing was pioneered by Alexander Lippisch in Germany after WWI. He flew the first tailless delta aircraft in 1931, followed by four improved designs.[4][5] None of these designs was easy to handle at low speed and none saw widespread service.[6][7] During the war Lippisch studied a number of advanced delta-wing interceptor aircraft, one progressing as far as a glider prototype.[8]

A pioneering designer of the slender delta was Aleksandr Moskalev in the Soviet Union, who in 1934 designed the Sigma 4 Interceptor.[citation needed]

The British later developed aircraft based on the data from Lippisch, notably the Avro Vulcan strategic bomber and the Gloster Javelin fighter. The Javelin incorporated a tailplane in order to rectify some of the perceived weaknesses of the pure delta, to improve low-speed handling and high-speed manoeuvrability and to allow a greater center of gravity range.[9]

Supersonic deltas[edit]

In America Robert T. Jones, working at NACA during World War II, developed a theory for supersonic delta wings. First published in January 1945, this approach differed from Lippisch's earlier work on thick delta wings by combining a delta planform with a thin airfoil. This design proved to be superior and would form the basis of all practical supersonic deltas such as those first made by Convair.[10][11]

The tailless delta became a favored design for high-speed use, and was used almost to the exclusion of other designs by Convair and by Dassault Aviation in France, notably with the popular Dassault Mirage III. Convair's F-102 Delta Dagger was the first fighter with a tailless delta wing in service with any air force anywhere in the world.[citation needed]

The tailed delta configuration was again adopted by the TsAGI (Central Aero and Hydrodynamic Institute, Moscow), to take advantage of both high angle-of-attack flying capability and high speeds. It 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.[citation needed]

Saab AB used a close-coupled damped canard foreplane[12] in front of the main wing of the Viggen fighter. The close coupling actively modifies the airflow over the wing, most notably during flight at high angles of attack. 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 and lowering the landing speed.

Low-speed effects[edit]

At low speeds a delta wing requires a high angle of attack to maintain lift. A slender delta creates a characteristic vortex pattern over the upper surface which enhances lift. Some types with intermediate sweep have been given retractable "moustaches" or fixed leading-edge root extensions (LERX) to encourage vortex formation.

The vortex lift comes at the cost of increased drag and powerful engines are needed to maintain flight.

Supersonic effects[edit]

At moderate supersonic speeds the wing flies inside the shock cone of the leading edge root. This allows air below the leading edge to flow out, up and around it, then back inwards again in a conical flow pattern. The lift distribution and other aerodynamic characteristics are strongly influenced by this sideways flow.[13]

One characteristic of this flight regime is that drooping the leading edge within the cone increases lift but not drag.[14] Such conical leading edge droop was introduced on the production Convair F-102A Delta Dagger at the same time that the prototype design was reworked to include area-ruling. It also appeared on Convair's next two deltas, the F-106 Delta Dart and B-58 Hustler.[15]

At high supersonic speeds the shock cone from the leading edge root lies along the wing surface behind the leading edge. It is no longer possible for the sideways flow to occur and the aerodynamic characteristics change considerably.[13]

Properties[edit]

Wind tunnel model of the Avro 720, a delta-winged aircraft, in The Science Museum's Blythe House store

The primary advantage of the delta wing is that, with a large enough angle of rearward sweep, the wing's leading edge will not contact the shock wave boundary formed at the nose of the fuselage as the speed of the aircraft approaches and exceeds transonic to supersonic speed. The rearward sweep angle vastly lowers the airspeed normal to the leading edge of the wing, thereby allowing the aircraft to fly at high subsonic, transonic, or supersonic speed, while the over wing speed of the lifting air is kept to less than the speed of sound. The delta planform gives the largest total wing area (generating useful lift) for the wing shape, with very low wing per-unit loading, permitting high manoeuvrability in the airframe. As the delta's platform carries across the entire aircraft, it can 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. 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.

Eurofighter Typhoon of the German Luftwaffe has a tailless delta wing configuration

Another advantage is that as the angle of attack increases, the leading edge of the wing generates a vortex which energizes the flow, giving the delta a very high stall angle.[citation needed] 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 manoeuvre combat and dogfighting. It also causes a reduction in lift at takeoff and landing until the correct angle of attack is achieved, this means that the rear undercarriage must be more strongly built than with a conventional wing.[citation needed]

A canard-delta suffers from a smaller shift in the center of lift with increasing Mach number than a wing and tail configuration, but the canard is unsuitable to provide an aileron input. The canard configuration also allows a save recovery from a high angle of attack with an unload or free floating canard. This changes a static longitudinal unstable configuration to a static longitudinal stable configuration.[16][17]

When used with a T-tail as in the Gloster Javelin the large delta wing could give rise to a "deep stall"; at high angles of attack the wing nullified airflow over the tail and made the aircraft uncontrollable.[18]

Delta-wing variations[edit]

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.

Many modern fighter aircraft, such as the JAS 39 Gripen, the Eurofighter Typhoon and the Dassault Rafale use a combination of canards and a delta wing.

Tailed delta – adds a conventional tailplane (with horizontal tail surfaces), to improve handling. Common on Soviet types such as the Mikoyan-Gurevich MiG-21.

Cropped delta – tip is cut off. This helps avoid tip drag at high angles of attack. Used for example in all three Eurocanards (cropped, tailless delta combined with a canard).

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 landing 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 (or ogival delta) used on the Anglo-French Concorde Mach 2 airliner is similar, but with a smooth 'ogee' curve joining the two parts rather than an angle.

" "
Tailless delta
" "
Tailed delta
" "
Cropped delta
" "
Compound delta
" "
Cranked arrow
" "
Ogival delta

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.

Aircraft examples[edit]

Production examples[edit]

Research or prototype-only examples[edit]

Notes[edit]

  1. ^ "Corad Haas Raketenpionier in Siebenbürgen" [Corad Haas rocket pioneer in Transylvania]. Beruehmte Siebenbuerger Sachsen (in German). Siebenbürgen und die Siebenbürger Sachsen im Internet. 
  2. ^ New Rocket Guide (pdf), NASA .
  3. ^ Orłowski, Bolesław (Jul 1973), Technology and Culture 14 (3), JStor, pp. 461–73, JSTOR 3102331 .
  4. ^ Ford, Roger (2000). Germany's secret weapons in World War II (1st ed.). Osceola, WI: MBI Publishing. p. 36. ISBN 0-7603-0847-0. 
  5. ^ "New Triangle Plane Is Tailless", Popular Science, December 1931: 65 .
  6. ^ Madelung, Ernst Heinrich; Hirschel, Horst; Prem, Gero (2004). Aeronautical research in Germany: from Lilienthal until today (American ed.). Berlin: Springer. ISBN 3-540-40645-X. 
  7. ^ Wohlfahrt, Karl; Nickel, Michael (1990). Schwanzlose flugzeuge : ihre auslegung und ihre eigenschaften [Tailless aircraft: their design & properties] (in German). Basel: Birkhauser. pp. 577–78. ISBN 3-7643-2502-X. Retrieved 13 February 2011. [Lippisch Delta I and Horten H I] Both these aircraft shown, how not to do it. 
  8. ^ Grommo (17 May 2008), Lippisch P13a Supersonic Ramjet Fighter footage (video), Youtube .
  9. ^ Partridge, J (1967), Number 179 – The Gloster Javelin 1-6, Profile .
  10. ^ Von Karman, Aerodynamics: Selected Topics in the Light of their Historical Development, 1954
  11. ^ Richard Hallion, Lippisch, Gluhareff and Jones: The Emergence of the Delta Planform, Aerospace Historian, March 1979.
  12. ^ Green, W; Swanborough, G (1994), The complete book of fighters, Salamander [page needed].
  13. ^ a b Mason, Chap. 10, Pages 9-12.
  14. ^ Boyd, Migotzky and Wetzel; "A Study of Conical Camber for Triangular and Sweptback Wings", Research Memorandum A55G19, NACA, 1955.[1]
  15. ^ Mason, Chap. 10, Page 16.
  16. ^ Probert, B, Aspects of Wing Design for Transonic and Supersonic Combat (pdf), NATO .
  17. ^ Aerodynamic highlights of a fourth generation delta canard fighter aircraft, Mach flyg .
  18. ^ Gloster Javelin History, UK: Thunder & Lightnings, 4 April 2012 .

References[edit]

External links[edit]