The Wings q51o

the wings Wing construction is basically the same in all types of aircraft. Most modern aircraft have all metal wings, but many older aircraft had wood and fabric wings. Ailerons and flaps will be studied later in this chapter.

fig 1 - 5 wood and fabric wing structure

To maintain its all-important aerodynamic shape, a wing must be designed and built to hold its shape even under extreme stress. Basically, the wing is a framework composed chiefly of spars, ribs, and (possibly) stringers (see figure 1-5). Spars are the main of the wing. They extend lengthwise of the wing (crosswise of the fuselage). All the load carried by the wing is ultimately taken by the spars. In flight, the force of the air acts against the skin. From the skin, this force is transmitted to the ribs and then to the spars. Most wing structures have two spars, the front spar and the rear spar. The front spar is found near the leading edge while the rear spar is about two-thirds the distance to the trailing edge. Depending on the design of the flight loads, some of the all-metal wings have as many as five spars. In addition to the main spars, there is a short structural member which is called an aileron spar. The ribs are the parts of a wing which the covering and provide the airfoil shape. These ribs are called forming ribs. and their primary purpose is to provide shape. Some may have an additional purpose of bearing flight stress, and these are called compression ribs. The most simple wing structures will be found on light civilian aircraft. High-stress types of military aircraft will have the most complex and strongest wing structure.

fig 1 - 6 wing and fuselage attachments

Three systems are used to determine how wings are attached to the aircraft fuselage depending on the strength of a wing's internal structure. The strongest wing structure is the full cantilever which is attached directly to the fuselage and does not have any type of external, stress-bearing structures. The semi-cantilever usually has one, or perhaps two, ing wires or struts attached to each wing and the fuselage. The externally braced wing is typical of the biplane (two wings placed one above the other) with its struts and flying and landing wires (see figure 1-6).

In order to confer lateral stability to an aircraft, the wings may be angled upwards from the fuselage towards the wingtips. This is known as a dihedral. Some wings may be inclined the opposite way and this is called anhedral and allows aircraft to be very manoeuvrable, as is needed for military or aerobatic aircraft.

Ribs In an aircraft, ribs are forming elements of the structure of a wing, especially in traditional construction. By analogy with the anatomical definition of "rib", the ribs attach to the main spar, and by being repeated at frequent intervals, form a skeletal shape for the wing. Usually ribs incorporate the airfoil shape of the wing, and the skin adopts this shape when stretched over the ribs.

Type of ribs There are several types of ribs. Form-ribs, plate-type ribs, truss ribs, closed-ribs, forged ribs and milled ribs, where form-ribs are used for light to medium loading and milled ribs are as strong as it can get. Form-ribs are made from a sheet of metal bent into shape, such as a U-profile. This profile is placed on the skin, just like a stringer, but then in the other direction. Plate-type ribs consist of sheet-metal, which has upturned edges and (often has) weight-saving holes cut into it. Truss ribs are built up out of profiles that are ed together. These ts require great attention during design and manufacture. The ribs may be light or heavy in design which make them suitable for a wide range of loads. Closed-ribs are constructed from profiles and sheet metal and are suitable for closing off sections of the wing (e.g.: the fuel tank). Here too, particular care must be taken with the ts and this type of rib is also suitable for application in a variety of loading conditions. Forged ribs are manufactured using heavy press-machinery. The result is fairly rough; for more refined parts, high-pressure presses are required, which are very expensive. Forged pieces (usually) have to undergo further treatment (for smoother edges and holes). Forged ribs are used for sections where very high loads apply - near the undercarriage for example.

Milled ribs are solid structures. They are manufactured by milling away excess material from a solid block of metal (usually using computer-controlled milling machines). The shape of these ribs is always accurately defined. Such ribs are used under similar conditions as those for forged ribs. Ribs are made out of wood, metal, plastic, composites, foam. The wings of kites, [1] hang gliders,[2] paragliders,[3] powered kites,[4] powered hang gliders, ultralights, windmills [5] are aircraft that have versions that use ribs to form the wing shape. For full size and flying model aircraft wing structures that are usually made of wood, ribs can either be in one piece (forming the airfoil at that rib's "station" in the wing), or be in a three-piece format, with the rib web being the part that the one-piece rib consisted of, with capstrips for the upper and lower edging of the rib, running from the leading edge to the trailing edge, being the other two component parts.

Spar

Spar (aviation) Spar Main spar of a de Havilland DH.60 Moth

In a fixed-wing aircraft, the spar is often the main structural member of the wing, running spanwise at right angles (or thereabouts depending on wing sweep) to the fuselage. The spar carries flight loads and the weight of the wings while on the ground. Other structural and forming such as ribs may be attached to the spar or spars, with stressed skin construction also sharing the loads where it is used. There may be more than one spar in a wing or none at all. However, where a single spar carries the majority of the forces on it, it is known as the main spar. [1] Spars are also used in other aircraft aerofoil surfaces such as the tailplane and fin and serve a similar function, although the loads transmitted may be different to those of a wing spar.

Spar loads The wing spar provides the majority of the weight and dynamic load integrity of cantilever monoplanes, often coupled with the strength of the wing 'D' box itself. Together, these two structural components collectively provide the wing rigidity needed to enable the aircraft to fly safely. Biplanes employing flying wires have much of the flight loads transmitted through the wires and interplane struts enabling smaller section and thus lighter spars to be used.

Forces Some of the forces acting on a wing spar are:[2]

• Upward bending loads resulting from the wing lift force that s the fuselage in flight. These forces are often offset by carrying fuel in the wings or employing wing-tip-mounted fuel tanks; the Cessna 310 is an example of this design feature. • Downward bending loads while stationary on the ground due to the weight of the structure, fuel carried in the wings, and wing-mounted engines if used. • Drag loads dependent on airspeed and inertia. • Rolling inertia loads. • Chordwise twisting loads due to aerodynamic effects at high airspeeds often associated with washout, and the use of ailerons resulting in control reversal. Further twisting loads are induced by changes of thrust settings to underwing-mounted engines.[3] The "D" box construction is beneficial to reduce wing twisting. Many of these loads are reversed abruptly in flight with an aircraft such as the Extra 300 when performing extreme aerobatic manoeuvers; the spars of these aircraft are designed to safely withstand great load factors. Spar (aviation) 2

Materials and construction Wooden construction Early aircraft used spars often carved from solid spruce or ash. Several different wooden spar types have been used and experimented with such as spars that are box-section in form; and laminated spars laid up in a jig, and compression glued to retain the wing dihedral. Wooden spars are still being used in light aircraft such as the Robin DR400 and its relatives. A disadvantage of the wooden spar is the deteriorating effect that atmospheric conditions, both dry and wet, and biological threats such as wood-boring insect infestation and fungal attack can have on the component; consequently regular inspections are often mandated to maintain airworthiness. [4] Wood wing spars of multipiece construction usually consist of upper and lower , called spar caps, and vertical sheet wood , known as shear webs or more simply webs, that span the distance between the spar caps. Even in modern times, "homebuilt replica aircraft" such as the replica Spitfires use laminated wooden spars. These spars are laminated usually from spruce or douglas fir (by clamping and glueing). A number of enthusiasts build "replica" Spitfires that will actually fly using a variety of engines relative to the size of the aircraft. [5]

Metal spars Basic metal-sparred wing using a honeycomb 'D' box leading edge

A typical metal spar in a general aviation aircraft usually consists of a sheet aluminium spar web, with "L" or "T" -shaped spar caps being welded or riveted to the top and bottom of the sheet to prevent buckling under applied loads. Larger aircraft using this method of spar construction may have the spar caps sealed to provide integral fuel tanks. Fatigue of metal wing spars has been an identified causal factor in aviation accidents, especially in older aircraft as was the case with Chalk's Ocean Airways Flight 101.[6]

Tubular metal spars The German Junkers J.I armoured fuselage ground-attack sesquiplane

of 1917 used a Hugo Junkers-designed multi-tube network of several tubular wing spars, placed just under the corrugated duralumin wing covering and with each tubular spar connected to the adjacent one with a space frame of triangulated duralumin strips riveted onto the spars, resulting in a substantial increase in structural strength at a time when most other aircraft designs were built almost completely with wood-structure wings. The Junkers allmetal corrugated-covered wing / multiple tubular wing spar design format was emulated after World War I by American aviation designer William Stout for his 1920s-era Ford Trimotor airliner series, and by Russian aerospace designer Andrei Tupolev for such aircraft as his Tupolev ANT-2 of 1922, upwards in size to the then-gigantic Maxim Gorki of 1934. A design aspect of the Supermarine Spitfire wing that contributed greatly to its success was an innovative spar boom design, made up of five square concentric tubes that fitted into each other. Two of these booms were linked together by an alloy web, creating a lightweight and very strong main spar. [7] A version of this spar construction method is also used in the BD-5, which was designed and constructed by Jim Bede in the early 1970s. The spar used in the BD-5 and subsequent BD projects was primarily aluminium tube of approximately 2 inches (5.1 cm) in diameter, and ed at the wing root with a much larger internal diameter aluminium tube to provide the wing structural integrity. Spar (aviation) 3

Geodesic construction In aircraft such as the Vickers Wellington, a geodesic wing spar structure was employed, which had the advantages of being lightweight and able to withstand heavy battle damage with only partial loss of strength.

Composite construction Many modern aircraft use carbon fibre and Kevlar in their construction, ranging in size from large airliners to small homebuilt aircraft. Of note are the developments made by Scaled Composites and the German glider manufacturers Schempp-Hirth and Schleicher.[8] These companies initially employed solid fibreglass spars in their designs but now often use carbon fibre in their high performance gliders such as the ASG 29. The increase in strength and reduction in weight compared to the earlier fibreglass-sparred aircraft allows a greater quantity of water ballast to be carried.[9]

False spars False spars, like main spars, are load bearing structural running spanwise but are not ed to the fuselage. Their most common purpose is to carry moving surfaces, principally ailerons. [10]

References Notes