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The wingbox is a structural component in an aircraft designed to provide support and rigidity to the wings. Designs vary, depending on the size and function of an aircraft, but generally this is the strongest section of the fuselage and it can include a number of supportive spars, as well as chambers designed to isolate impacts. Usually, this component is not readily visible, although people can assume it lies between the wing roots, the parts of the plane where the wings attach.
Aircraft in flight experience concentrated shear stresses on their wings. Without adequate support, the wings would eventually fold up against the side of the plane. The wingbox absorbs some of this stress and distributes it across a supportive framework, preventing the wings from wobbling or bending. In addition to holding the wings in place, it helps absorb impacts sustained during events like turbulence to keep the plane in the air.
As new aircraft are developed, engineers think about the stresses they will endure and start planning out a wingbox. They consider the best materials to use, looking for things known to be lightweight and very strong, and they also determine the best layout of support trusses, as well as factors like the size of various supports included in the wingbox. Engineers submit components to materials testing to make sure they can hold up to force on their own, and prototypes of the aircraft may be put through a process known as destructive testing, where very rigorous test methods are used to see what kinds of conditions need to be present for events like breaking off the wings to occur.
Wingbox design can present significant hurdles to aircraft development in some cases. If it is too heavy, a common problem when people are trying to exceed the tolerances for handling shear stresses, it can interfere with the function of the aircraft. In addition, the components can take up significant space in the plane, limiting room for cargo and passengers.
The considerable strength of the wingbox makes it an appealing site to attach landing gear. Since the design is already geared for intense stresses, it is well suited as an area to fix wheels and other gear. This allows designers to eliminate the need to develop a secondary area of additional reinforcements and strength to support the aircraft during takeoff and landing. In addition, there is usually some room built into the wingbox in the form of the compartments inside, providing a space for retractable gear that might otherwise interfere with other systems in the plane.