Wingbox

Lore & Background

The wingbox derives its name from the box-like shape formed by the forward and rear wing spars and the upper and lower wing skins. While internal wing structure commonly provides much of the strength via spars, ribs and stringers, the external skin typically carries a proportion of the loads as well. On many aircraft, the inner volume of the wingbox has been used to store fuel, a design referred to as a wet wing. In recent years, there has been increasing use of composite materials within the wingbox, particularly carbon fibre, due to its very high strength-to-weight ratio. In January 2017, European aerospace conglomerate Airbus Group announced the creation of the world's first single-piece composite center wingbox, stating it represented a 20 per cent reduction in manufacturing cost by being easier to assemble. Due to its crucial structural role, the wingbox is subjected to considerable analysis and scrutiny. Various techniques to calculate and verify stresses have been devised, and the use of increasingly capable calculations and tests has been credited with enabling lighter and more efficient wings. Towards the latter part of the twentieth century, computer aided design (CAD) technology, such as the software package CATIA, became commonplace in aerospace programmes. Physical verification of structural performance is normally demanded in the certification process of civil airliners, leading manufacturers to produce non-flying test units subjected to ground-based testing with loads up to 1.5 times the maximum aerodynamic forces expected. Destructive testing of wing elements has been around since the earliest days of aviation, with techniques becoming increasingly sophisticated, particularly since the invention of the strain gauge in 1938. Non-destructive testing is performed during initial certification and throughout an aircraft's life to safeguard against fatigue failure and inspect potential damage, using techniques such as visual inspection, ultrasonic testing, radiographic testing, electromagnetic testing, acoustic emissions, and shearography. When replacement of a wingbox is identified, it is a costly procedure, often leading operators to end an aircraft's operating life instead. In Summer 2019, the United States Air Force grounded over 100 of its Lockheed Martin C-130 Hercules transport aircraft for inspection and remedial work upon discovering excessive wingbox cracking. Aircraft intended for lengthy service lives have often received replacement wingboxes as part of life extension programmes.

Reader's Guide

The wingbox is the primary load-carrying structure of the wing, forming its structural centre and interfacing with the fuselage via the centre wingbox. Its significance lies in its role as the attachment point for other wing components and its capacity to store fuel in wet wing designs. The trend toward composite materials, especially carbon fibre, has been pursued to achieve lower weights, with Airbus Group announcing in January 2017 the first single-piece composite center wingbox, which reduced manufacturing cost by 20 per cent. The wingbox's critical structural role demands extensive analysis and testing. Computer aided design (CAD) tools like CATIA became commonplace in the latter part of the twentieth century, enabling lighter and more efficient wings. Certification of civil airliners requires physical verification through ground-based testing of non-flying units at loads up to 1.5 times maximum expected aerodynamic forces. Destructive testing has existed since early aviation, with strain gauges (invented 1938) widely used since the Second World War. Non-destructive testing, including ultrasonic and radiographic methods, is performed throughout an aircraft's life to detect fatigue failure. Replacement of a wingbox is intensive and costly, often leading to retirement of the aircraft, though life extension programmes sometimes include replacement. In Summer 2019, the U.S. Air Force grounded over 100 C-130 Hercules aircraft due to excessive wingbox cracking, underscoring the component's criticality.

Did You Know?

• The wingbox is so called because the forward and rear spars and upper and lower skins form a natural box shape.
• The inner volume of the wingbox is often used to store fuel, known as a wet wing design.
• In January 2017, Airbus Group announced the world's first single-piece composite center wingbox, reducing manufacturing cost by 20 per cent.
• The strain gauge, invented in 1938, has been in widespread use in aerospace since the Second World War for destructive testing.