The wing configuration or planform of a fixed-wing aircraft (including both gliders and powered aeroplanes) 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 (forwards or backwards) swept trailing edge, or as sharply tapered swept wings with large leading edge root extensions (or LERX). Some are therefore duplicated here under more than one heading. This is particularly so for variable geometry and combined (closed) wing types. Most of the configurations described here have flown (if only very briefly) 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: A fixed-wing aircraft may have more than one wing plane, stacked one above another: 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.

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: Wings can also be characterised as:

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. It is a measure of how long and slender the wing appears when seen from above or below. 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.

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

Sweep variation along span

The angle of a swept wing may also be varied, or cranked, along the span:

Asymmetrical

On a few asymmetrical aircraft the left and right hand sides are not mirror-images of each other:

Tailplanes and foreplanes

The classic aerofoil section wing is unstable in pitch, and requires some form of horizontal stabilizing surface. Also it cannot provide any significant pitch control, requiring a separate control surface (elevator) mounted elsewhere - usually on the horizontal stabilizer.

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. Some biplanes have different degrees of dihedral/anhedral on different wings. The Sopwith Camel had a flat upper wing and dihedral on the lower wing, while the Hanriot HD-1 had dihedral on the upper wing but none on the lower. In a cranked or polyhedral wing the dihedral angle varies along the span. (Note that the description "cranked" varies in usage. See also Cranked arrow planform.)

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: Some designs may fall into multiple categories depending on interpretation, for example many UAVs or drones can be seen either as a tailless blended wing-body or as a flying wing with a deep centre 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

Variable section

Polymorphism

A polymorphic wing is able to change the number of planes in flight. The Nikitin-Shevchenko IS "folding fighter" prototypes were able to morph between biplane and monoplane configurations after takeoff by folding the lower wing up into a cavity in the underside of the upper wing. The slip wing is a variation on the polymorphic idea, in which a low-wing monoplane is fitted with a second detachable "slip" wing above it to assist takeoff. The upper wing is then released and discarded once in the air. The idea was first flown on the experimental Hillson Bi-mono.

Minor independent surfaces

Aircraft may have additional minor aerodynamic surfaces. Some of these are treated as part of the overall wing configuration:

Additional minor features

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

High lift

High-lift devices maintain lift at low speeds and delay the stall to allow slower takeoff and landing speeds:

Spanwise flow control

On a swept wing, air tends to flow sideways as well as backwards and reducing this can improve the efficiency of the wing:

Vortex creation

Vortex devices maintain airflow at low speeds and delay the stall, by creating a vortex which re-energises the boundary layer close to the wing.

Drag reduction