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A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (Δ).
Although long studied, the delta wing did not find significant practical applications until the Jet Age, when it proved suitable for high-speed subsonic and supersonic flight. At the other end of the speed scale, the Rogallo wing proved a practical design for the hang glider and other ultralight aircraft. The delta wing form has unique aerodynamic characteristics and structural advantages. Many design variations have evolved over the years, with and without additional stabilising surfaces.
Its long root chord also allows a deeper structure for a given aerofoil section. This both enhances its weight-saving characteristic and provides greater internal volume for fuel and other items, without a significant increase in drag. However, on supersonic designs the opportunity is often taken to use a thinner aerofoil instead, in order to actually reduce drag.
Ordinarily, this flow separation leads to a loss of lift known as the stall. However, for a sharply-swept delta wing, as air spills up round the leading edge it flows inwards to generate a characteristic vortex pattern over the upper surface. The lower extremity of this vortex remains attached to the surface and also accelerates the airflow, maintaining lift. For intermediate sweep angles, a retractable "moustache" or fixed leading-edge root extension (LERX) may be added to encourage and stabilise vortex formation. The ogee or "wineglass" double-curve, seen for example on Concorde, incorporates this forward extension into the profile of the wing.
In this condition, the centre of lift approximates to the centre of the area covered by the vortex.
The sideways effect also leads to an overall reduction in lift and in some circumstances can also lead to an increase in drag. It may be countered through the use of leading-edge slots, wing fences and related devices.
This allows air below the leading edge to flow out, up and around it, then back inwards creating a sideways flow pattern similar to subsonic flow. The lift distribution and other aerodynamic characteristics are strongly influenced by this sideways flow.Mason, Chap. 10, pp. 9–12.
The rearward sweep angle lowers the airspeed normal to the leading edge of the wing, thereby allowing the aircraft to fly at high subsonic flight, transonic, or supersonic speed, while the subsonic lifting characteristics of the airflow over the wing are maintained.
Within this flight regime, drooping the leading edge within the shock cone increases lift, but not drag to any significant extent.Boyd, Migotzky and Wetzel; "A Study of Conical Camber for Triangular and Sweptback Wings", Research Memorandum A55G19, NACA, 1955.[1] 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 rule. It also appeared on Convair's next two deltas, the F-106 Delta Dart and B-58 Hustler.Mason, Chap. 10, p. 16.
Cropped delta – tip is cut off. This helps maintain lift outboard and reduce wingtip flow separation (stalling) at high angles of attack. Most deltas are cropped to at least some degree.
In the compound delta, double delta or cranked arrow, the leading edge is not straight. Typically the inboard section has increased sweepback, creating a controlled high-lift vortex without the need for a foreplane. Examples include the Saab Draken fighter, the experimental General Dynamics F-16XL, and the Hawker Siddeley HS. 138 VTOL concept. The ogee delta (or ogival delta) used on the Anglo-French Concorde supersonic airliner is similar, but with the two sections and cropped wingtip merged into a smooth ogee curve.
Tailless delta | Cropped delta | Compound delta | Cranked arrow | Ogival delta | Tailed delta |
Tailed delta – adds a conventional tailplane (with horizontal tail surfaces), to improve handling. Common on Soviet types such as the Mikoyan-Gurevich MiG-21.
Canard delta – Many modern fighter aircraft, such as the JAS 39 Gripen, the Eurofighter Typhoon and the Dassault Rafale use a combination of canard foreplanes and a delta wing.
When used with a T-tail, as in the Gloster Javelin, like other wings a delta wing can give rise to a "deep stall" in which the high angle of attack at the stall causes the turbulent wake of the stalled wing to envelope the tail. This makes the elevator ineffective and the airplane cannot recover from the stall.. In the case of the Javelin, a stall warning device was developed and implemented for the Javelin following the early loss of an aircraft to such conditions.Patridge 1967, p. 6. Gloster's design team had reportedly opted to use a tailed delta configuration out of necessity, seeking to achieve effective manoeuvrability at relatively high speeds for the era while also requiring suitable controllability when being flown at the slower landing speeds desired.Patridge 1967, pp. 3–4.
An unloaded or free-floating canard can allow a safe recovery from a high angle of attack. Depending on its design, a canard surface may increase or decrease longitudinal stability of the aircraft...
A canard delta foreplane creates its own trailing vortex. If this vortex interferes with the vortex of the main delta wing, this can adversely affect the airflow over the wing and cause unwanted and even dangerous behaviour. In the close-coupled configuration, the canard vortex couples with the main vortex to enhance its benefits and maintain controlled airflow through a wide range of speeds and angles of attack. This allows both improved manoeuvrability and lower stalling speeds, but the presence of the foreplane can increase drag at supersonic speeds and hence reduce the aircraft's maximum speed.
Also in 1909, British aeronautical pioneer J. W. Dunne patented his tailless stable aircraft with conical wing development. The patent included a broad-span biconical delta, with each side bulging upwards towards the rear in a manner characteristic of the modern Rogallo wing.J.W. Dunne; Provisional Patent: Improvements Relating to Aeroplanes, UK Patent No. 8118, Date of Application 5 April 1909. Copy on Espacenet During the following year, in America U. G. Lee and W. A. Darrah patented a similar biconical delta winged aeroplane with an explicitly rigid wing. It also incorporated a proposal for a flight control system and covered both gliding and powered flight.Woodhams, Mark and Henderson, Graeme; "Did we really fly Rogallo wings?", Skywings, June 2010.Lee, U. G. and Darrah, H.; US patent 989,7896, filed 15 February 1910, granted 18 April 1911. None of these early designs is known to have successfully flown although, in 1904, Lavezzani's hang glider featuring independent left and right triangular wings had left the ground, and Dunne's other tailless swept designs based on the same principle would fly.
The practical delta wing was pioneered by German aeronautical designer Alexander Lippisch in the 1930s, using a thick cantilever wing without any tail. His first such designs, for which he coined the name "Delta", used a very gentle angle so that the wing appeared almost straight and the wing tips had to be cropped sharply (see below). His first such delta flew in 1931, followed by four successively improved examples.. These prototypes were not easy to handle at low speed and none saw widespread use.
The work of French designer Nicolas Roland Payen somewhat paralleled that of Lippisch. During the 1930s, he had developed a tandem delta configuration with a straight fore wing and steep delta aft wing, similar to that of Causarás. The outbreak of the Second World War brought a halt to flight testing of the Pa-22, although work continued for a time after the project garnered German attention. During the postwar era, Payen flew an experimental tailless delta jet, the Pa.49, in 1954, as well as the tailless pusher-configuration Arbalète series from 1965. Further derivatives based on Payen's work were proposed but ultimately went undeveloped.
Following the war, the British developed a number of subsonic jet aircraft that harnessed data gathered from Lippisch's work. One such aircraft, the Avro 707 research aircraft, made its first flight in 1949.Hygate, Barrie; British Experimental Jet Aircraft, Argus, 1990. British military aircraft such as the Avro Vulcan (a strategic bomber) and Gloster Javelin (an all-weather fighter) were among the first delta-equipped aircraft to enter production. Whereas the Vulcan was a classic tailless design, the Javelin incorporated a tailplane in order to improve low-speed handling and high-speed manoeuvrability, as well as to allow a greater centre of gravity range.. Gloster proposed a refinement of the Javelin that would have, amongst other changes, decreased wing thickness in order to achieve supersonic speeds of up to Mach 1.6.Buttler, 2017, pp. 94, 98-100.
During the late 1940s, the British aircraft manufacturer Fairey Aviation became interested in the delta wing,Wood 1975, p. 73. its proposals led to the experimental Fairey Delta 1 being produced to Air Ministry Specification E.10/47.Wood 1975, p. 74. A subsequent experimental aircraft, the Fairey Delta 2 set a new World air speed record on 10 March 1956, achieving 1,132 mph (1,811 km/h) or Mach 1.73. "Individual History: Fairey FD-2 Delta WG777/7986M." Royal Air Force Museum, Retrieved: 13 December 2016. "50 years ago: 16 Mar 1956." Flight International, 10 March 2006.Wood 1975, p. 77. "Fairey FD2." Royal Air Force Museum, Retrieved: 13 December 2016. This raised the record above 1,000 mph for the first time and broke the previous record by 310 mph, or 37 per cent; never before had the record been raised by such a large margin.Wood 1975, p. 79.
In its original tailless form, the thin delta was used extensively by the American aviation company Convair and by the French aircraft manufacturer Dassault Aviation. The supersonic Convair F-102 Delta Dagger and transonic Douglas F4D Skyray were two of the first operational jet fighters to feature a tailless delta wing when they entered service in 1956. Dassault's interest in the delta wing produced the Dassault Mirage family of combat aircraft, especially the highly successful Mirage III. Amongst other attributes, the Mirage III was the first Western European combat aircraft to exceed Mach 2 in horizontal flight. "Mirage III." Dassault Aviation, 18 December 2015.
The tailed delta configuration was adopted by the TsAGI (Central Aero and Hydrodynamic Institute, Moscow), to improve high angle-of-attack handling, manoeuvrability and centre of gravity range over a pure delta planform. The resulting TsAGI S-12 airfoil was used in the Mikoyan-Gurevich MiG-21 ("Fishbed"), which became the most widely built combat aircraft of the 1970s.Sweetman, Bill & Gunston, Bill; Soviet Air Power: An Illustrated Encyclopedia. Salamander, 1978, p. 122.
The close-coupled canard has since become common on supersonic fighter aircraft. Notable examples include the multinational Eurofighter Typhoon, France's Dassault Rafale, Saab's own Gripen (a successor to the Viggen) and Israel's IAI Kfir. One of the main reasons for its popularity has been the high level of agility in manoeuvring that it is capable of.Warwick 1980, p. 1260.Roskam 2002, p. 206.
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