Caisson is a power of the wing and other elements of the airframe. This beam-type structure with front and back walls, top and bottom - stressed skin. His trim takes the tangent and the normal stress. Basically, the bending moment is seen stringers and skin. The caisson longitudinal strength members may serve spars having a weakened zone. Caisson is the most common type of aircraft structures (wings and other elements).

The very design of caisson - a special case of a monobloc-wing (mainly bending moment is perceived by plating and stringers). In such designs spars may be completely absent or have weak zones, which are comparable with the cross section of the stringers.

It is worth noting that the ribs are installed much more often than in the spar. As for the bending moment, it is perceived as part of the contour. The tail part and the sock usually do not participate in the perception of the main loads, and for their operational and technological reasons they are made removable - often harnesses of wiring harnesses, pipelines, various assemblies and units are placed inside. The caisson wing design is characterized by volumes that are sufficient to accommodate fuel or other aggregates. And in the first case, all the space of the caisson is necessarily sealed with kerosene-resistant sealants - threaded joints, joints, riveting, which eliminates fuel leakage.

The advantages of the monoblock scheme include high strength, survivability and lower weight, unlike the spar wing. 

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