A wet wing is an aerospace engineering technique where an aircraft's wing structure is sealed and used as a fuel tank. Wet wings are also called integral fuel tanks. By eliminating the need for fuel bladders, aircraft can weigh less and the wing root bending moment caused by the lift generated by the wings in flight is decreased. This offers further reduction in weight by allowing structural components to be designed lighter as the components do not need to support larger forces.
Wet wings are common among most civilian designs, from large transport aircraft, such as airliners, to small general aviation aircraft. Because the tanks are an integral part of the structure, they cannot be removed, and require access panels for routine maintenance and visual inspections.
A disadvantage of the wet wing is that every rivet, bolt and nutplate, hose and/or tubing that penetrates the wing must be sealed to prevent fuel leaking or seeping around these hardware components. This sealant must allow for expansion and contraction due to rapid temperature changes (e.g., when cold fuel is pumped into a warm wing tank) and must retain its sealing properties when submerged in fuel and when left dry for long periods of time. Working with this sealant can be difficult and replacing old sealant inside a small wing tank can be even worse if the old sealant needs to be removed as well before new sealant can be applied.