Wing configuration


The wing configuration or planform of a fixed-wing aircraft is its arrangement of lifting and related surfaces.
Aircraft designs are often classified by their wing configuration. For example, the Supermarine Spitfire is a conventional low wing cantilever monoplane of straight elliptical planform with moderate aspect ratio and slight dihedral.
Many variations have been tried. Sometimes the distinction between them is blurred, for example the wings of many modern combat aircraft may be described either as cropped compound deltas with swept trailing edge, or as sharply tapered swept wings with large leading edge root extensions. Some are therefore duplicated here under more than one heading. This is particularly so for [|variable geometry] and combined wing types.
File:Sukhoi Su-47 in formation, 2005.jpg|thumb|A forward-swept-wing Sukhoi Su-47 alongside the more conventional swept-back Su-27 and Su-30MK2.
Most of the configurations described here have flown on full-size aircraft. A few theoretical designs are also notable.
Note on terminology: Most fixed-wing aircraft have left hand and right hand wings in a symmetrical arrangement. Strictly, such a pair of wings is called a wing plane or just plane. However, in certain situations it is common to refer to a plane as a wing, as in "a biplane has two wings", or alternatively to refer to the whole thing as a wing, as in "a biplane wing has two planes". Where the meaning is clear, this article follows common usage, only being more precise where needed to avoid real ambiguity or incorrectness.

Number and position of main planes

Fixed-wing aircraft can have different numbers of wings:
  • Monoplane: one wing plane. Since the 1930s most aeroplanes have been monoplanes. The wing may be mounted at various positions relative to the fuselage:
  • * Low wing: mounted near or below the bottom of the fuselage.
  • * Mid wing: mounted approximately halfway up the fuselage.
  • * Shoulder wing: mounted on the upper part or "shoulder" of the fuselage, slightly below the top of the fuselage. A shoulder wing is sometimes considered a subtype of high wing.
  • * High wing: mounted on the upper fuselage. When contrasted to the shoulder wing, applies to a wing mounted on a projection above the top of the main fuselage.
  • * Parasol wing: raised clear above the top of the fuselage, typically by cabane struts, pylon or pedestal.
A fixed-wing aircraft may have more than one wing plane, stacked one above another:
  • Biplane: two wing planes of similar size, stacked one above the other. The biplane is inherently lighter and stronger than a monoplane and was the most common configuration until the 1930s. The very first Wright Flyer I was a biplane.
  • * Unequal-span biplane: a biplane in which one wing is shorter than the other, as on the Curtiss JN-4 Jenny of the First World War.
  • * Sesquiplane: literally "one-and-a-half planes" is a type of biplane in which the lower wing is significantly smaller than the upper wing, either in span or chord or both. The Nieuport 17 of World War I was notably successful.
  • * Inverted sesquiplane: has a significantly smaller upper wing. The Fiat CR.1 was in production for many years.
  • * Busemann biplane: a theoretical supersonic wing configuration, in which shock waves between the wing planes interfere to reduce their energy and wave drag.
  • 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 manoeuvrability, 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 never saw 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 two hundred wing foils. See also the tandem wing, below.
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.
  • A tandem wing design has two wings, one behind the other: see [|Tailplanes and foreplanes] below. Some early types had tandem stacks of multiple planes, such as the nine-wing Caproni Ca.60 flying boat with three triplane stacks in tandem.
  • A cruciform wing is a set of four individual wings arranged in the shape of a cross. The cross may take either of two forms:
  • * Wings equally spaced around the cross-section of the fuselage, lying in two planes at right angles, as on a typical missile.
  • * Wings lying together in a single horizontal plane about a vertical axis, as in the cruciform rotor wing or X-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, as on the Fokker D.VII. A strut may act in compression or tension at different points in the flight regime.
  • * Wire braced: alone 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.
  • Closed wing: two wing planes are merged or 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. The first officially witnessed plane to take off and fly, the Santos-Dumont 14-bis, used this configuration. Tandem box wings have also been studied.
  • * Annular box wing: 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.
  • * Annular : 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.
  • * Annular : the wing is shaped like a disc with a hole in it. A number of Lee-Richards annular monoplanes flew shortly before the First World War.
  • * Joined wing: a tandem-wing layout in which the front low wing sweeps back and/or the rear high wing sweeps forwards such that they join at or near the tips to form a continuous surface in a hollow diamond or triangle shape. The Ligeti Stratos is a rare example.
  • ** Rhomboidal wing: a joined wing consisting of four surfaces in a diamond arrangement. The Edwards Rhomboidal biplane of 1911 had both wings in the same plane but failed to fly.
Wings can also be characterised as:
  • Rigid: stiff enough to maintain the aerofoil profile in varying conditions of airflow. A rigid wing may have external bracing and/or a fabric covering.
  • Flexible:
  • * The surface may be flexible, typically a thin membrane. Requires external bracing and/or wind pressure to maintain the aerofoil shape. Common types include the Rogallo wing, parafoil and most kites.
  • * An otherwise rigid structure may be designed to flex, either because it is inherently aeroelastic as in the aeroisoclinic wing, or because shape changes are actively introduced.

    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. 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. Structurally efficient, high instantaneous roll rate, low supersonic drag. They tend to be used on fighter aircraft, such as the Lockheed F-104 Starfighter, and on very high-speed aircraft including the North American X-15.
  • Moderate aspect ratio: general-purpose wing, very widely used, for example on the Douglas DC-3 transport.
  • High aspect ratio: long and slender wing. More efficient aerodynamically, having less induced drag at subsonic speeds. They tend to be used by high-altitude subsonic aircraft such as the Lockheed U-2 spy plane and by high-performance sailplanes such as the Glaser-Dirks DG-500.
Most variable geometry configurations vary the aspect ratio in some way, either deliberately or as a side effect.

Chord variation along span

The wing chord may be varied along the span of the wing, for both structural and aerodynamic reasons.
  • Constant chord: parallel leading & trailing edges. Simplest to make, and common where low cost is important, such as on the Piper J-3 Cub but inefficient as the outer section generates little lift while adding both weight and drag. Sometimes known in North America as the Hershey Bar wing due to its similarity in shape to a popular chocolate bar.
  • Tapered: wing narrows towards the tip. Structurally and aerodynamically more efficient than a constant chord wing, and easier to make than the elliptical type.
  • * Trapezoidal: a tapered wing with straight leading and trailing edges: may be unswept or swept. The straight tapered wing is one of the most common wing planforms, as seen on the Messerschmitt Bf 109.
  • * Inverse or reverse tapered: wing is widest near the tip. Structurally 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. Typically braced to maintain stiffness. Used on the Westland Lysander army cooperation aircraft to increase visibility for the crew.
  • Constant chord with tapered outer section: common variant seen for example on many Cessna types.
  • Elliptical: leading and trailing edges are curved such that the chord length varies elliptically with respect to span. Sometimes mistakenly said to be the most efficient, and also difficult to make. Famously used on the Supermarine Spitfire.
  • * Semi-elliptical: only the leading or trailing edge is elliptical with the other being straight, as with the elliptical trailing edges of the Seversky P-35.
  • Bird wing: a curved shape appearing similar to a bird's outstretched wing. Popular during the pioneer years, and achieved some success on the Etrich Taube where its planform was inspired by the zanonia seed.
  • Bat wing: a form with radial ribs. The 1901 Whitehead No. 21 has been the subject of claims to the first controlled powered flight.
  • Circular: approximately circular planform. The Vought V-173 used large propellers near the tips, which helped to counteract its strong wingtip vortices, and had an outboard tail plane for stability.
  • * Flying saucer: circular flying wing. Inherently unstable, as the Avro Canada Avrocar demonstrated.
  • * Disc wing: a variant in which the entire disc rotates. Popular on toys such as the Frisbee.
  • * Flat annular wing: the circle has a hole in, forming a closed wing. The Lee-Richards annular monoplanes flew shortly before the First World War.
  • 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 Dassault Mirage III series.
  • * Tailed delta: adds a conventional tailplane, to improve handling. Used on the Mikoyan-Gurevich MiG-21.
  • * Cropped delta: wing tips are cut off. This helps avoid tip drag at high angles of attack. The Fairey Delta 1 also had a tail. At the extreme, merges into the "tapered swept" configuration.
  • * Compound delta or double delta: inner section has a steeper leading edge sweep as on the Saab Draken. This improves the lift at high angles of attack and delays or prevents stalling. By contrast, the Saab Viggen has an inner section of reduced sweep to avoid interference from its canard foreplane.
  • * 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 transport.