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 (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. :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. •
Closed wing: two wing planes are merged or joined structurally at or near the tips in some way. •
Annular (planar): 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 (in
aerodynamics theory, the term "elliptical" describes the optimal lift distribution over a wing of given span and not its shape), 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 (
Alsomitra macrocarpa) 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 (see above). 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 (usually) 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.
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 structurally-efficient wing, it has been common for low-speed designs since the very first days of the
Wright Flyer. •
Swept back (aka "swept wing"): The wing sweeps rearwards from the root to the tip. In early tailless examples, such as the
Dunne aircraft, this allowed the outer wing section to act like a conventional
empennage (tail) to provide aerodynamic stability. At
transonic speeds swept wings have lower drag, but can handle poorly in or near a stall and require high stiffness to avoid
aeroelasticity at high speeds. Common on high-subsonic and early supersonic designs such as the
Hawker Hunter. •
Forward swept: the wing angles forward from the root. Benefits are similar to backwards sweep, also it avoids the stall problems and has reduced tip losses allowing a smaller wing, but requires even greater stiffness to avoid
aeroelastic flutter as on the
Sukhoi Su-47. The
HFB 320 Hansa Jet used forward sweep to prevent the wing spar passing through the cabin. Small
shoulder-wing aircraft may use forward sweep to maintain a correct
CoG. 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 military aircraft, such as the
General Dynamics F-111 Aardvark and the
Grumman F-14 Tomcat. •
Oblique wing: a single full-span wing pivots about its midpoint, so that one side sweeps back and the other side sweeps forward. Flown on the
NASA AD-1 research aircraft.
Sweep variation along span The angle of a swept wing may also be varied, or cranked, along the span: •
Crescent: wing outer section is swept less sharply than the inner section, to obtain a best compromise between
transonic shock delay and
spanwise flow control. Used on the
Handley Page Victor. •
Cranked arrow: aerodynamically identical to the compound delta, but with the trailing edge also kinked inwards. Trialled experimentally on the
General Dynamics F-16XL. •
M-wing: the inner wing section sweeps forward, and the outer section sweeps backwards. Allows the wing to be highly swept while minimising the undesirable effects of
aeroelastic bending. Periodically studied, but never used on an aircraft.
Asymmetrical On a few
asymmetrical aircraft the left and right hand sides are not mirror-images of each other: •
Asymmetric layout: the
Blohm & Voss BV 141 had separate fuselage and crew nacelle offset on either side to give the crew a good field of view. •
Asymmetric span: on several Italian fighters such as the
Ansaldo SVA, one wing was slightly longer than the other to help counteract engine torque. •
Oblique wing: one wing sweeps forward and the other back. The
NASA AD-1 had a full-span wing structure with variable sweep. ==Tailplanes and foreplanes==