The wings are airfoils attached to each side of the fuselage and are the main lifting surfaces which support the airplane in flight. There are numerous wing designs, sizes, and shapes used by the various manufacturers. Each fulfill a certain need with respect to performance expected for the particular airplane. How the wing produces lift is explained in subsequent chapters.
Wings are of two main types - cantilever and semicantilever (Fig. 2-3). The cantilever wing requires no external bracing; the stress is carried by internal wing spars, ribs, and stringers. Generally, in this type wing the "skin" or metal wing covering is constructed to carry much of the wing stresses. Airplanes with wings so stressed are called stressed skin types. Treated aluminum alloy is most commonly used as the wing covering (Fig. 2-4). The semicantilever wing is braced both externally by means of wing struts attached to the fuselage, and internally by spars and ribs.
The principal structural parts of the wing are spars, ribs, and stringers. These are reinforced by trusses, I beams, tubing, or other appropriate devices. The wing ribs actually determine the shape and thickness of the wing (airfoil). In most modern airplanes, the fuel tanks are either an integral pat of the wing's structure, or consist of flexible containers mounted inside of the wing structure.