Last updated

The wingbox of a fixed-wing aircraft refers to the primary load-carrying structure of the wing, which forms the structural centre of the wings and also the attachment point for other wing components such as leading edge flaps, trailing edge flaps and wing-tip devices. The wingbox continues beyond the visible wing roots and interfaces with the fuselage in the centre wingbox, which forms the structural core of an aircraft.

The wingbox is so called since, on many designs, the combination of the forward and rear wing spars and the upper and lower wing skins together form a natural "box" shape running through the wing. [1] While internal wing structure commonly provides much of the strength via a combination of spars, ribs and stringers, the external skin also typically carries a proportion of the loads too. On many aircraft, the inner volume of the wingbox has also be used to store fuel, which is commonly referred to as being a wet wing design. [1]

In recent years, there has been an increasing use of composite materials within the wingbox; this trend has largely been pursued to achieve lower weights over designs only using conventional materials. [2] [3] Specifically, carbon fibre has become a popular material due to its very high strength-to-weight ratio. [4] During January 2017, European aerospace conglomerate Airbus Group announced that they had created the world's first single-piece composite center wingbox, stating that it represented a 20 per cent reduction in the cost of manufacture by being easier to assemble. [5]

Evaluating and testing

Due to its crucial structural role, the wingbox is subjected to considerable analysis and scrutiny in order to be certain of its capabilities, as well to achieve optimum performance. As such, various techniques to calculate and verify the stresses involved have been devised by aerospace engineers and employed by aircraft manufacturers. [1] The use of increasingly capable calculations and tests has been directly credited with enabling the production of lighter and more efficient wings. [2] Towards the latter part of the twentieth century, the use of computer aided design (CAD) technology became commonplace in aerospace programmes; as such, software packages such as CATIA plays a major role in the design and manufacturing process. [1]

Furthermore, physical verification of the structural performance of the wingbox is normally demanded in the certification process of civil airliners by the certification authorities. Accordingly, it is commonplace for aircraft manufacturers to produce non-flying test units which are subjected to ground-based testing, exerting loads of up to 1.5 times the maximum aerodynamic forces expected to be encountered at any point throughout its operating life. [6] Destructive testing of wing elements has been around since the earliest days of aviation, although the specific techniques employed have become increasingly sophisticated, particularly since the invention of the strain gauge in 1938, which has been in widespread use within the aerospace industry since the Second World War. [7]

Non-destructive testing is also performed not only during the initial certification process but often throughout an individual aircraft's life to safeguard against fatigue failure or inspect potential damage inflicted. [8] Common techniques include visual inspection, ultrasonic testing, radiographic testing, electromagnetic testing, acoustic emissions, and shearography. [9] [10] Sometimes, via such techniques, the need to replace an individual aircraft's wingbox is identified; although this is a quite intensive and costly procedure, leading to operators often choosing to end an aircraft's operating life instead, such replacements are occasionally performed. [11] [12] During Summer 2019, the United States Air Force was compelled to ground over 100 of its Lockheed Martin C-130 Hercules transport aircraft for inspection and remedial work upon discovering excessive wingbox cracking. [13] Aircraft intended for lengthy service lives have often received replacement wingboxes as a part of life extension programmes. [14]

Related Research Articles

<span class="mw-page-title-main">Fuselage</span> Main body of an aircraft

The fuselage is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage, which in turn is used as a floating hull. The fuselage also serves to position the control and stabilization surfaces in specific relationships to lifting surfaces, which is required for aircraft stability and maneuverability.

<span class="mw-page-title-main">Wingtip device</span> Aircraft component fixed to the end of the wings to improve performance

Wingtip devices are intended to improve the efficiency of fixed-wing aircraft by reducing drag. Although there are several types of wing tip devices which function in different manners, their intended effect is always to reduce an aircraft's drag by partial recovery of the tip vortex energy. Wingtip devices can also improve aircraft handling characteristics and enhance safety for following aircraft. Such devices increase the effective aspect ratio of a wing without greatly increasing the wingspan. Extending the span would lower lift-induced drag, but would increase parasitic drag and would require boosting the strength and weight of the wing. At some point, there is no net benefit from further increased span. There may also be operational considerations that limit the allowable wingspan.

<span class="mw-page-title-main">Fatigue (material)</span> Initiation and propagation of cracks in a material due to cyclic loading

In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts of the fracture surface. The crack will continue to grow until it reaches a critical size, which occurs when the stress intensity factor of the crack exceeds the fracture toughness of the material, producing rapid propagation and typically complete fracture of the structure.

<span class="mw-page-title-main">Airbus A400M Atlas</span> Multi-national four-engine turboprop military transport aircraft

The Airbus A400M Atlas is a European four-engine turboprop military transport aircraft. It was designed by Airbus Military as a tactical airlifter with strategic capabilities to replace older transport aircraft, such as the Transall C-160 and the Lockheed C-130 Hercules. The A400M is sized between the C-130 and the Boeing C-17 Globemaster III; it can carry heavier loads than the C-130 and is able to use rough landing strips. In addition to its transport capabilities, the A400M can perform aerial refueling and medical evacuation when fitted with appropriate equipment.

<span class="mw-page-title-main">Airframe</span> Mechanical structure of an aircraft

The mechanical structure of an aircraft is known as the airframe. This structure is typically considered to include the fuselage, undercarriage, empennage and wings, and excludes the propulsion system.

<span class="mw-page-title-main">Grumman X-29</span> 1984 experimental aircraft family by Grumman

The Grumman X-29 was an American experimental aircraft that tested a forward-swept wing, canard control surfaces, and other novel aircraft technologies. The X-29 was developed by Grumman, and the two built were flown by NASA and the United States Air Force. The aerodynamic instability of the X-29's airframe required the use of computerized fly-by-wire control. Composite materials were used to control the aeroelastic divergent twisting experienced by forward-swept wings, and to reduce weight. The aircraft first flew in 1984, and two X-29s were flight tested through 1991.

<span class="mw-page-title-main">GLARE</span>

Glare is a fiber metal laminate (FML) composed of several very thin layers of metal interspersed with layers of S-2 glass-fiber pre-preg, bonded together with a matrix such as epoxy. The uni-directional pre-preg layers may be aligned in different directions to suit predicted stress conditions.

<span class="mw-page-title-main">Blended wing body</span> Aircraft design with no clear dividing line between fuselage and wing cross-sections

A blended wing body (BWB), also known as blended body or hybrid wing body (HWB), is a fixed-wing aircraft having no clear dividing line between the wings and the main body of the craft. The aircraft has distinct wing and body structures, which are smoothly blended together with no clear dividing line. This contrasts with a flying wing, which has no distinct fuselage, and a lifting body, which has no distinct wings. A BWB design may or may not be tailless.

In safe-life design, products are intended to be removed from service at a specific design life.

Acoustic emission (AE) is the phenomenon of radiation of acoustic (elastic) waves in solids that occurs when a material undergoes irreversible changes in its internal structure, for example as a result of crack formation or plastic deformation due to aging, temperature gradients or external mechanical forces. In particular, AE is occurring during the processes of mechanical loading of materials and structures accompanied by structural changes that generate local sources of elastic waves. This results in small surface displacements of a material produced by elastic or stress waves generated when the accumulated elastic energy in a material or on its surface is released rapidly. The waves generated by sources of AE are of practical interest in structural health monitoring (SHM), quality control, system feedback, process monitoring and other fields. In SHM applications, AE is typically used to detect, locate and characterise damage.

<span class="mw-page-title-main">Irkut MC-21</span> Twin-engine Russian jet airliner

The Irkut MC-21 is a single-aisle airliner, developed in Russia by the Yakovlev Design Bureau and produced by its parent Irkut, a branch of the United Aircraft Corporation (UAC), itself a 92%-owned subsidiary of Russia's state-owned aviation giant Rostec.

<span class="mw-page-title-main">Spar (aeronautics)</span> Main structural member of the wing of an aircraft

In a fixed-wing aircraft, the spar is often the main structural member of the wing, running spanwise at right angles to the fuselage. The spar carries flight loads and the weight of the wings while on the ground. Other structural and forming members 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. Where a single spar carries most of the force, it is known as the main spar.

<span class="mw-page-title-main">Hellenic Aerospace Industry</span>

Hellenic Aerospace Industry (HAI) is the leading aerospace company of Greece. The company headquarters is located in Tanagra, 65 kilometers north-west of Athens, with the industrial complex covering an area of 200,000 sq.m.

Carbon fiber-reinforced polymers, carbon-fibre-reinforced polymers, carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic, also known as carbon fiber, carbon composite, or just carbon, are extremely strong and light fiber-reinforced plastics that contain carbon fibers. CFRPs can be expensive to produce, but are commonly used wherever high strength-to-weight ratio and stiffness (rigidity) are required, such as aerospace, superstructures of ships, automotive, civil engineering, sports equipment, and an increasing number of consumer and technical applications.

A crack arrestor is a structural engineering device. Being typically shaped into ring or strip, and composed of a strong material, it serves to contain stress corrosion cracking or fatigue cracking, helping to prevent the catastrophic failure of a device.

<span class="mw-page-title-main">Aircraft design process</span> Establishing the configuration and plans for a new aeroplane

The aircraft design process is a loosely defined method used to balance many competing and demanding requirements to produce an aircraft that is strong, lightweight, economical and can carry an adequate payload while being sufficiently reliable to safely fly for the design life of the aircraft. Similar to, but more exacting than, the usual engineering design process, the technique is highly iterative, involving high level configuration tradeoffs, a mixture of analysis and testing and the detailed examination of the adequacy of every part of the structure. For some types of aircraft, the design process is regulated by civil airworthiness authorities.

The term "smart structures" is commonly used for structures which have the ability to adapt to environmental conditions according to the design requirements. As a rule, the adjustments are designed and performed in order to increase the efficiency or safety of the structure. Combining "smart structures" with the "sophistication" achieved in materials science, information technology, measurement science, sensors, actuators, signal processing, nanotechnology, cybernetics, artificial intelligence, and biomimetics, one can talk about Smart Intelligent Structures. In other words, structures which are able to sense their environment, self-diagnose their condition and adapt in such a way so as to make the design more useful and efficient.

Carbon fiber testing is a set of various different tests that researchers use to characterize the properties of carbon fiber. The results for the testing are used to aid the manufacturer and developers decisions selecting and designing material composites, manufacturing processes and for ensured safety and integrity. Safety-critical carbon fiber components, such as structural parts in machines, vehicles, aircraft or architectural elements are subject to testing.

Testia, an Airbus company, is a training, services and products provider for aerostructure testing and Non-Destructive Testing (NDT). It has been fully owned by Airbus since 2013.

<span class="mw-page-title-main">Fatigue testing</span> Determination of a material or structures resiliency against cyclic loading

Fatigue testing is a specialised form of mechanical testing that is performed by applying cyclic loading to a coupon or structure. These tests are used either to generate fatigue life and crack growth data, identify critical locations or demonstrate the safety of a structure that may be susceptible to fatigue. Fatigue tests are used on a range of components from coupons through to full size test articles such as automobiles and aircraft.


  1. 1 2 3 4 Immanuvel, D.; Arulselvan, K.; Maniiarasan, P.; Senthilkumar, S. (2014). "Stress Analysis and Weight Optimization of a Wing Box Structure Subjected To Flight Loads" (PDF). The International Journal of Engineering and Science (IJES). 3 (1): 33–40. ISSN   2319-1813.
  2. 1 2 Moors, G.; Kassapoglou, C.; de Almeida, S.F.M.; Ferreira, C.A.E. (2019). "Weight trades in the design of a composite wing box: effect of various design choices". CEAS Aeronaut Jpournal. 10 (2): 403–417. doi: 10.1007/s13272-018-0321-4 .
  3. Oliveri, Vincenzo; Zucco, Giovanni; Peeters, Daniël; Clancy, Gearoid; Telford, Robert; Rouhi, Mohammad; McHale, Ciarán; O’Higgins, Ronan; Young, Trevor; Weaver, Paul (April 2019) [2 January 2019]. "Design, Manufacture and Test of an In-Situ Consolidated Thermoplastic Variable-Stiffness Wingbox". AIAA Journal. 57 (4): 1671–1683. Bibcode:2019AIAAJ..57.1671O. doi:10.2514/1.J057758. S2CID   128172559.
  4. Cunningham, Justin (13 June 2014). "Aerospace industry moves to carbon fibre wings". Engineering Materials.
  5. "Airbus' new centre wing box design holds great promise for future aircraft". Airbus Group. 13 January 2017.
  6. "Boeing Successfully completes 787 wingbox destructive testing". Composites World. 17 November 2008. Archived from the original on 2011-09-29. Retrieved 2011-08-31.
  7. Hoversten, Paul (30 April 2009). "Then & Now: Under Stress". Air & Space Magazine.
  8. Snider, H. Lawrence; Reeder, Franklin L.; Dirkin, William (July 1972). Residual Strength and Crack Progatation Tests on C-130 Airplane Center Wings with Service-Imposed Fatigue Damage (PDF) (Report). NASA. Archived from the original (PDF) on 2015-02-17.
  9. Gholizade, S. (2016). "A review of non-destructive testing methods of composite materials". Procedia Structural Integrity. 1: 50–57. doi: 10.1016/j.prostr.2016.02.008 .
  10. Bayraktar, E.; Antolovich, S.D.; Bathias, C. (12 September 2008). "New developments in non-destructive controls of the composite materials and applications in manufacturing engineering". Journal of Materials Processing Technology. 206 (1–3): 30–44. doi:10.1016/j.jmatprotec.2007.12.001.
  11. Housman, Damian (15 November 2006). "Air logistics center upgrades center wing boxes on C-130s". Air Force Materiel Command.
  12. "Keeping the C-130s Flying: Center Wing Box Replacements". Defense Industry Daily. 4 April 2007.
  13. Insinna, Valerie (8 August 2019). "US Air Force pauses flight ops for more than a hundred C-130s over 'atypical' cracking". Defense News.
  14. Tomkins, Richard (18 July 2017). "Marshall Aerospace and Defense tapped for C-130J work". United Press International.