Wing configuration

Fixed-wing aircraft, popularly called aeroplanes, airplanes or just planes may be built with many wing configurations.

This page provides a breakdown of types, allowing a full description of any aircraft's wing configuration. For example the Spitfire wing may be classified as a conventional low wing cantilever monoplane with straight elliptical wings of moderate aspect ratio and slight dihedral.

Sometimes the distinction between types is blurred, for example the wings of many modern combat aircraft may be described either as cropped compound deltas with (forwards or backwards) swept trailing edge, or as sharply tapered swept wings with large "Leading Edge Root Extension" (or LERX).

All the configurations described have flown (if only very briefly) on full-size aircraft, except as noted.

Some variants may be duplicated under more than one heading, due to their complex nature. This is particularly so for variable geometry and combined (closed) wing types.

Contents 1 Number and position of main-planes 2 Wing support 3 Wing planform 3.1 Aspect ratio 3.2 Wing sweep 3.3 Planform variation along span 4 Horizontal stabilizer 5 Dihedral and anhedral 6 Wings vs. bodies 7 Variable geometry 7.1 Variable planform 7.2 Variable chord 7.3 Polymorphism 8 Minor aerodynamic surfaces 9 Minor surface features 10 Notes 11 References 12 External links

Number and position of main-planes

Fixed-wing aircraft can have different numbers of wings:

• Monoplane - one wing. Most aeroplanes have been monoplanes since before the Second World War. The wing may be mounted at various heights relative to the fuselage:
  • Low wing - mounted on the lower fuselage.
  • Mid wing - mounted approximately half way up the fuselage.
  • Shoulder wing - mounted on the upper part or "shoulder" of the fuselage, either flush with or slightly below the top of the fuselage. Sometimes treated as as distinct from the high wing,^[1] and sometimes described as a high wing ^[2] where it may be regarded as a sub-type.
  • High wing - mounted on the upper fuselage. When contrasted to the shoulder wing, applies to a wing projecting slightly above the top of the fuselage.
  • Parasol wing - mounted on "cabane" struts above the fuselage.

Low wing

Mid wing

Shoulder wing

High wing

Parasol wing

A fixed wing aircraft may have more than one wing plane, stacked one above another:

• Biplane - two planes of approximately equal size, stacked one above the other. The most common type until the 1930s, when the cantilever monoplane took over. The very first aeroplane to fly, the Wright Flyer I was a biplane, and the configuration remained dominant for three decades.
  • Unequal-span bibplane - a variant on the biplane in which one wing (usually the lower) is shorter than the other. The Curtiss JN-4 "Jenny" was widely produced during and after the First World War.
  • Sesquiplane - literally "one-and-a-half planes" is a variant on the biplane in which the lower wing is significantly smaller than the upper wing, both in span and in chord. The Nieuport 17 of WWI was notably successful.
  • Inverted sesquiplane - has a significantly smaller upper wing. The Fiat CR.1 was in production for many years.

Biplane

Unequal-span biplane

Sesquiplane

Inverted sesquiplane

• Triplane - three planes stacked one above another. Triplanes such as the Fokker Dr.I enjoyed a brief period of popularity during the First World War due to their small size and high manoeuvrability as fighters, but were soon replaced by improved biplanes.

• Quadruplane - four planes stacked one above another. A small number of the Armstrong Whitworth F.K.10 were built in the First World War but it never saw operational military service.

• Multiplane - many planes, sometimes used to mean more than one or more than some arbitrary number. The term is occasionally applied to arrangements stacked in tandem as well as vertically. The 1907 Multiplane of Horatio Frederick Phillips flew successfully with 200 wing foils, while the nine-wing Caproni Ca.60 flying boat was airborne briefly before crashing.

Triplane

Quadruplane

Multiplane

A staggered design has the upper wing slightly forward of the lower. Long thought to reduce the interference caused by the low pressure air over the lower wing mixing with the high pressure air under the upper wing however the improvement is minimal and its primary benefit is to improve access to the fuselage. It is common on many successful biplanes and triplanes. Backwards stagger is also seen in a few examples such as the Beechcraft Staggerwing.

Unstaggered biplane

Forwards stagger

Backwards stagger

A Tandem wing design has two similar-sized wings, one behind the other - see Horizontal stabiliser below. Some early types had tandem stacks of multiple planes - see the article on multiplanes.

Wing support

To support itself a wing has to be rigid and strong and consequently may be heavy. By adding external bracing, the weight can be greatly reduced. Originally such bracing was always present, but it causes a large amount of drag at higher speeds and has not been used for faster designs since the early 1930s.

The types are:

• Cantilevered - self-supporting. All the structure is buried under the aerodynamic skin, giving a clean appearance with low drag.
• Braced: the wings are supported by external structural members. Nearly all multi-plane designs are braced. Some monoplanes, especially early designs such as the Fokker Eindecker, are also braced to save weight. Braced wings are of two types:
  • Strut braced - one or more stiff struts help to support the wing. A strut may act in compression or tension at different points in the flight regime.
  • Wire braced - alone (as on the Boeing P-26 Peashooter) or, more usually, in addition to struts, tension wires also help to support the wing. Unlike a strut, a wire can act only in tension.

Cantilever

Strut braced

Wire braced

A braced multiplane may have one or more "bays", which are the compartments created by adding interplane struts; the number of bays refers to one side of the aircraft's wing panels only. For example, the de Havilland Tiger Moth is a single-bay biplane where the Bristol F.2 Fighter is a two-bay biplane.^[3]

Single-bay biplane

Two-bay biplane

• Combined or closed wing - two wings are joined structurally at or near the tips in some way. This stiffens the structure, and can reduce aerodynamic losses at the tips. Variants include:
  • Box wing - upper and lower planes are joined by a vertical fin between their tips. Some Dunne biplanes were of this type. Tandem box wings have also been studied (see Joined wing description below).
  • Rhomboidal wing - a tandem layout in which the front wing sweeps back and the rear wing sweeps forwards such that they join at or near the tips to form a continuous surface in a hollow diamond shape. The Edwards Rhomboidal biplane of 1909 failed to fly.^[4] The design has recently seen a revival of interest where it is referred to as a joined wing . The Small Diameter Bomb, a smart guided bomb, has a rhomboidal wing.
  • Annular or ring wing - may refer to various types:
    • Flat - the wing is shaped like a circular disc with a hole in it. A Lee-Richards type was one of the first stable aircraft to fly, shortly before the First World War. [4]
    • Cylindrical - the wing is shaped like a cylinder. The Coléoptère had concentric wing and fuselage. It took off and landed vertically, but never achieved transition to horizontal flight. Examples with the wing mounted on top of the fuselage have been proposed but never built. [5] [6])
    • A type of box wing whose vertical fins curve continuously, blending smoothly into the wing tips. An early example was the Blériot III, which featured two annular wings in tandem.

Box wing

Annular box wing

Cylindrical wing

Rhomboidal wing

Flat annular wing

Wings can also be characterised as:

• Rigid - stiff enough to maintain the aerofoil profile in varying conditions of airflow.
• Flexible - usually a thin membrane. Requires external bracing or wind pressure to maintain the aerofoil shape. Common types include Rogallo wings and kites.

Wing planform

The wing planform is the silhouette of the wing when viewed from above or below.

See also Variable geometry types which vary the wing planform during flight.

Aspect ratio

The aspect ratio is the span divided by the mean or average chord.^[5] It is a measure of how long and slender the wing appears when seen from above or below.

• Low aspect ratio - short and stubby wing. More efficient structurally, more maneuverable and with less drag at high speeds. They tend to be used by fighter aircraft, such as the Lockheed F-104 Starfighter, and by very high-speed aircraft (e.g. North American X-15).

• Moderate aspect ratio - general-purpose wing (e.g. the Lockheed P-80 Shooting Star).

• High aspect ratio - long and slender wing. More efficient aerodynamically, having less drag, at low speeds. They tend to be used by high-altitude subsonic aircraft (e.g. the Lockheed U-2), subsonic airliners (e.g. the Bombardier Dash 8) and by high-performance sailplanes (e.g. Glaser-Dirks DG-500).

Low aspect ratio

Moderate aspect ratio

High aspect ratio

Most Variable geometry configurations vary the aspect ratio in some way, either deliberately or as a side effect.

Wing sweep

Wings may be swept back, or occasionally forwards, for a variety of reasons. A small degree of sweep is sometimes used to adjust the centre of lift when the wing cannot be attached in the ideal position for some reason, such as a pilot's visibility from the cockpit. Other uses are described below.

• Straight - extends at right angles to the line of flight. The most efficient structurally, and common for low-speed designs, such as the P-80 Shooting Star.
• Swept back - (references to "swept" often assume swept back). From the root, the wing angles backwards towards the tip. In early tailless examples, such as the Dunne aircraft, this allowed the outer wing section to act as a conventional tail empennage to provide aerodynamic stability. At transonic speeds swept wings have lower drag, but can handle badly in or near a stall and require high stiffness to avoid aeroelasticity at high speeds. Common on high-subsonic and supersonic designs e.g. the English Electric Lightning.
• Forward swept - the wing angles forwards from the root. Benefits are similar to backwards sweep, also at significant angles of sweep it avoids the stall problems and has reduced tip losses allowing a smaller wing, but requires even greater stiffness because of much higher liability to aeroelastic flutter and for this reason is not often used. A civil example is the HFB-320 Hansa Jet and in military Sukhoi Su-47.

Some types of variable geometry vary the wing sweep during flight:

• Swing-wing - also called "variable sweep wing". The left and right hand wings vary their sweep together, usually backwards. Seen in a few types of combat aircraft, the first being the General Dynamics F-111.
• Oblique wing - a single full-span wing pivots about its mid point, so that one side sweeps back and the other side sweeps forward. Flown on the NASA AD-1 research aircraft.

Straight

Swept

Forward swept

Variable sweep (swing-wing)

Oblique wing

Planform variation along span

The wing chord may be varied along the span of the wing, for both structural and aerodynamic reasons.

• Elliptical - leading and/or trailing edges are curved such that the chord length varies elliptically with respect to span. Aerodynamically the most efficient, but difficult to make. Famously used on the Supermarine Spitfire. The wings of the Seversky P-35 were semi-elliptical,^[6] having a straight leading edge and progressively curved trailing edge. (Note that in aerodynamics theory, the term "elliptical" describes the optimal lift distribution over a wing).
• Constant chord - leading & trailing edges are parallel. Simple to make, and common where low cost is important, e.g. in the Piper J-3 Cub but inefficient as much of the outboard area generates no lift, but adds drag through greater wetted area, and increases the stresses on the root structure making it heavier. These disadvantages are only significant on large or fast aircraft. Sometimes known as the Hershey Bar wing in North America due to its similarity in shape to the chocolate bar.^[7][8]
• Tapered - wing narrows towards the tip, with straight edges. Structurally and aerodynamically more efficient than a constant chord wing, and easier to make than the elliptical type. It is the most commonly used type of wing planform, as seen on the Grumman F6F Hellcat.

• Trapezoidal - a low aspect ratio tapered wing, having little or no sweep such that the leading edge sweeps back and the trailing edge sweeps forwards. Used for example on the Lockheed F-22 Raptor.
• Reverse tapered - wing widens towards the tip. Structurally very inefficient, leading to high weight. Flown experimentally on the XF-91 Thunderceptor in an attempt to overcome the stall problems of swept wings.
• Compound tapered - taper reverses towards the root, to increase visibility for the pilot. Typically needs to be braced to maintain stiffness. Used on the Westland Lysander observation aircraft.

Elliptical

Constant chord

Tapered

Trapezoidal

Reverse tapered

Compound tapered

• Constant chord with tapered outer section - description of a planform used on many Cessna and other types such as the English Electric Canberra.
• Bird like - a curved shape appearing similar to a bird's outstretched wing. Popular during the pioneer years, and achieved some success on the Etrich Taube.
• Bat like - a form with radial ribs which was used for some early designs, especially if the wings were foldable. The Whitehead No. 21 of 1901 is sometimes claimed as the first powered aircraft to fly, over two years before the Wright Flyer.
• Circular - approximately circular planform. The Vought XF5U attempted to counteract the large tip vortices by using large propellers rotating in the opposite sense to the vortices.
  • Flying saucer - tailless circular flying wing. The Avrocar demonstrated the inherent instability of the design, while the Moller M200G uses computer control to achieve artificial stability in hover mode.
  • Flat annular wing - the circle has a hole in, forming a closed wing (see above). A Lee-Richards type was one of the first stable aircraft to fly, shortly before the First World War.^[9]

Constant chord, tapered outer

Birdlike

Batlike

Circular

Flying saucer

Flat annular

• Delta - triangular planform with swept leading edge and straight trailing edge. Offers the advantages of a swept wing, with good structural efficiency and low frontal area. Disadvantages are the low wing loading and high wetted area needed to obtain aerodynamic stability. Variants are:
  • Tailless delta - a classic high-speed design, used for example in the widely built Dassault Mirage III series.
  • Tailed delta - adds a conventional tailplane, to improve handling. Popular 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. At the extreme, merges into the "tapered swept" configuration.
  • Compound delta or double delta - inner section has a (usually) steeper leading edge sweep e.g. Saab Draken. This improves the lift at high angles of attack and delays or prevents stalling. Seen in tailless form on the Tupolev Tu-144. The HAL Tejas has an inner section of reduced sweep.
  • Ogival delta - a smoothly blended "wineglass" double-curve encompassing the leading edges and tip of a cropped compound delta. Seen in tailless form on the Concorde supersonic transports.

Tailless delta

Tailed delta

Cropped delta

Compound delta

Ogival delta

The angle of sweep may also be varied, or cranked, along the span:

• Crescent - wing outer section is swept less sharply than the inner section. Used for the Handley Page Victor.
• Cranked arrow - similar to a compound delta, but with the trailing edge also kinked inwards. Trialled experimentally on the General Dynamics F-16XL. (See also Cranked wing below.)
• M-wing - the inner wing section sweeps forward, and the outer section sweeps backwards. The idea has been studied from time to time, but no example has ever been built.^[10][11]
• W-wing - the inner wing section sweeps back, and the outer section sweeps forwards. The reverse of the M-wing. The idea has been studied even less than the M-wing and no example has ever been built.^[11]

Crescent

Cranked arrow

M-wing

W-wing

Horizontal stabilizer

The classic aerofoil section wing is unstable in pitch, and requires some form of horizontal stabilising surface. Also it cannot provide any significant pitch control, requiring a separate control surface (elevator) elsewhere. The elevator may be hinged to a fixed horizontal stabiliser, or the whole stabiliser may pivot to double as the elevator.

• Conventional - "tailplane" surface at the rear of the aircraft, forming part of the tail or empennage.
• Canard - "foreplane" surface at the front of the aircraft. Common in the pioneer years, but from the outbreak of World War I no production model appeared until the Saab Viggen.
• Tandem - two main wings, one behind the other. The two act together to provide stability and both provide lift. An example is the Rutan Quickie. According to NASA research, the wings must differ in aerodynamic characteristics or the aircraft will tend to oscillate in pitch. Either span, chord or wing section must be different between the two wings.
• Tandem triple or triplet - having both conventional and canard surfaces. This may be for manoeuvrability, or the canard surfaces may be used for active vibration damping, to smooth out air turbulence giving the crew a more comfortable ride and reducing fatigue on the airframe. Popularly (but incorrectly) referred to as a tandem triplane. An example is the Sukhoi Su-33.
• Tailless - no separate surface, at front or rear. Either the lifting and stabilising surfaces are combined in a single plane, or the aerofoil profile is modified to provide inherent stability. The whole wing tip sections of the Short SB.4 Sherpa acted as elevons. Recently, aircraft having a tailplane but no vertical tail fin have also been described as "tailless".

Conventional

Canard

Tandem

Tandem triple

Tailless

Dihedral and anhedral

Angling the wings up or down spanwise from root to tip can help to resolve various design issues, such as stability and control in flight.

• Dihedral - the tips are higher than the root as on the Boeing 737, giving a shallow 'V' shape when seen from the front. Adds lateral stability.
• Anhedral - the tips are lower than the root, as on the Ilyushin Il-76; the opposite of dihedral. Used to reduce stability where some other feature results in too much stability thus making manoeuvering difficult. A popular choice in modern fighters since the configuration makes them more agile in battle. In level flight, computers assist the pilot in preventing the plane from teetering about.

Some biplanes have different angles of dihedral/anhedral on different wings; e.g. the first Short Sporting Type, known as the Shrimp, had a flat upper wing and a slight dihedral on the lower wing.

Dihedral

Anhedral

Biplane with dihedral on both wings

Biplane with dihedral on lower wing

The dihedral angle may vary along the span.

• Gull wing - sharp dihedral on the wing root section, little or none on the main section, as on the Göppingen Gö 3 glider. Typically done to raise wing-mounted engines higher above the ground or water.
• Inverted gull - anhedral on the root section, dihedral on the main section. The opposite of a gull wing. Typically done to reduce the length and weight of wing-mounted undercarriage legs and allow for the use of a larger propeller. Two well-known examples of the inverted gull wing are World War II's American F4U Corsair, and the German Junkers Ju 87 Stuka dive bomber.

Gull wing

Inverted gull wing

• Cranked - tip section dihedral differs from the main section. The wingtips may crank upwards as on the F-4 Phantom II or downwards as on the Dunne monoplane and Northrop XP-56 Black Bullet. (Note that the term "cranked" varies in usage.^[12][13][14] Here, it is used to help clarify the relationship between changes of dihedral nearer the wing tip vs. nearer the wing root. See also Cranked arrow planform.)
• The channel wing is an unusual variation where the frontal profile follows the arc of a propeller down, around and back up, before continuing outwards in a conventional manner. Since 1942 several examples have flown, notably the Custer Channel Wing aircraft, but none has entered production.

Upward cranked tips

Downward cranked tips

Channel wing

Wings vs. bodies

Some designs have no clear join between wing and fuselage, or body. This may be because one or other of these is missing, or because they merge into each other:

• Flying wing - the aircraft has no distinct fuselage or tail empennage (although fins and small pods, blisters, etc. may be present); one example is the B-2 Spirit.
• Blended body or blended wing-body - smooth transition between wing and fuselage, with no hard dividing line. Reduces wetted area and hence, if done correctly, aerodynamic drag. The McDonnell XP-67 Bat was also designed to maintain the aerofoil section across the entire aircraft profile.
• Lifting body - the aircraft has no significant wings, and relies on the fuselage to provide aerodynamic lift i.e. X-24 .

Flying wing

Blended body

Lifting body

Some proposed designs, typically a sharply-swept delta planform having a deep centre section tapering to a thin outer section, fall across these categories and may be interpreted in different ways, for example as a lifting body with a broad fuselage, or as a low-aspect-ratio flying wing with a deep center chord.

Variable geometry

A variable geometry aircraft is able to change its physical configuration during flight.

Some types of variable geometry craft transition between fixed wing and rotary wing configurations. For more about these hybrids, see powered lift.

Variable planform

• Swing-wing or variable sweep wing. The left and right hand wings vary their sweep together, usually backwards. The first successful wing sweep in flight was carried out by the Bell X-5 in the early 1950s.
• Oblique wing - a single full-span wing pivots about its mid point, as used on the NASA AD-1, so that one side sweeps back and the other side sweeps forward.
• Telescoping wing - the outer section of wing telescopes over or within the inner section of wing, varying span, aspect ratio and wing area, as used on the FS-29 TF glider.^[15] The Makhonine Mak-123 was an early example.^[16]
• Extending wing or expanding wing - part of the wing retracts into the main aircraft structure to reduce drag and low-altitude buffet for high-speed flight, and is extended only for takeoff, low-speed cruise and landing. The Gérin Varivol biplane, which flew in 1936, extended the leading and trailing edges to increase wing area.^[17]

Variable sweep (swing-wing)

Oblique wing

Telescoping wing

Extending wing

• Folding wing - part of the wing extends for takeoff and landing, and folds away for high-speed flight. The outer sections of the XB-70 Valkyrie wing folded down, to increase lift and reduce drag through generation of 'compression lift' during supersonic flight. (Many aircraft have wings that may be folded for storage on the ground or on board ship. These are not folding wings in the sense used here).

Folding wing

Variable chord

• Variable incidence - the wing plane can tilt upwards or downwards relative to the fuselage. Used on the Vought F-8 Crusader to tilt the leading edge up by a small amount for takeoff, to give STOL performance. If powered proprotors are fitted to the wing to allow vertical takeoff or STOVL performance, merges into the powered lift category.
• Variable camber - the leading and trailing edge sections of the wing pivot and/or extend to increase the effective camber and/or area of the wing. This increases lift at low angles of attack, delays stalling at high angles of attack, and enhances manoeuverability.
  • Variable thickness - the upper wing centre section can be raised to increase wing thickness and camber for landing and take-off, and lowered for high speed flight. Charles Rocheville modified one or more aircraft in the course of his researches.^[18][19][20]

Variable incidence wing

Variable camber aerofoil

Variable thickness aerofoil

Polymorphism

A polymorphic wing is able to change the number of planes in flight. The Nikitin-Shevchenko IS "folding fighter" protoypes were able to morph between biplane and monoplane configurations after takeoff by folding the lower wing into a cavity in the upper wing.

Polymorphic wing

Minor aerodynamic surfaces

Additional minor aerodynamic surfaces may form part of the overall wing configuration:

• Winglet - a small vertical fin at the wingtip, usually turned upwards. Reduces the size of vortices shed by the wingtip, and hence also tip drag.
• Chine - narrow extension to the leading edge wing root, extending far along the forward fuselage. As well as improving low speed (high angle of attack) handling, provides extra lift at supersonic speeds for minimal increase in drag. Seen on the Lockheed SR-71 Blackbird.
• Leading edge extension - small fillet used on fighters to improve lift characteristics at high angles of attack.
• Moustache - small high-aspect-ratio canard surface having no movable control surface. Typically is retractable for high speed flight. Deflects air downward onto the wing root, to delay the stall. Seen on the Dassault Milan and Tupolev Tu-144.

Minor surface features

Additional minor features may be applied to an existing aerodynamic surface such as the main wing:

• Leading edge extensions of various kinds.
• Slot - a spanwise gap behind the leading edge section, which forms a small aerofoil or slat extending along the leading edge of the wing. Air flowing through the slot is deflected by the slat to flow over the wing, allowing the aircraft to fly at lower air speeds. Leading edge slats are moveable extensions which open and close the slot.
• Flap - trailing-edge (or leading-edge) wing section which may be angled downwards for low-speed flight, especially when landing. Some types also extend backwards to increase wing area.
• Wing fence - a thin surface extending along the wing chord and for a short distance vertically. Used to control spanwise airflow over the wing.
• Vortex generator - small triangular protrusion on the upper leading wing surface; usually, several are spaced along the span of the wing. The vortices are used to re-energise the boundary layer and reduce drag.
• Anti-shock body - a streamlined "pod" shaped body added to the leading or trailing edge of an aerodynamic surface, to delay the onset of shock stall and reduce transonic wave drag. Examples include the Küchemann carrots on the wing trailing edge of the Handley Page Victor B.2, and the tail fairing on the Hawker Sea Hawk.
• Fairings of various kinds, such as blisters, pylons and wingtip pods, containing equipment which cannot fit inside the wing, and whose only aerodynamic purpose is to reduce the drag created by the equipment.

Notes

References

• Kermode, A.C. (1972); Mechanics of Flight, Chapter 3 (Eighth (metric) edition). Sir Isaac Pitman and Sons Ltd, London. ISBN 0 273 31623 0
• Taylor, John W.R. The Lore of Flight, London: Universal Books Ltd., 1990. ISBN 0-9509620-15.
• "What is it? Aircraft Characteristics That Aid The Spotter". Flight. June 4, 1942. http://www.flightglobal.com/pdfarchive/view/1942/1942%20-%201194.html. 

External links

• High wing, low wing - Flight article on the merits of wing position