Conventional wings are of three general, monospar, two spar and multiple star. True stressed skin wings may have shear webs but no true “spars”. The monospar wing has only one spar, the two spar wing has two spars as the name indicates, and the multispar wing has more than two spars. A wing spar, sometimes called wing beam, is a principle spanwise member of the wing structure. In the metal wing all principle parts are made of aluminum alloy, and the tie rods or brace wires are made of steel. In the wood wing, the spars may be the only members made of wood or both the spars and the compression struts may be of wood. The wires carrying drag loads are called drag wires, and those carrying the loads opposite drag are called antidrag wires. The wing spar for the wood wing must be made of aircraft quality spruce meeting the requirements set forth Federal Aviation Administration Advisory Circular 43.13-1A.

Wing for a Jet Airliner.

The construction of the wing for a modern Jet Airliner such as the Douglas DC-8 provides an understanding of how the great strength required for such a wing is attained. When we consider the weight of the wing itself plus the two jet engines hung under the wing on each side of the airplane plus the weight of the fuel carried in the wing. It seems almost impossible that the wing could be made strong enough to carry the weight alone, much less the additional loads imposed upon it in flight and upon landing. The basic structure of the wing consists of three spars with conventional sheet-aluminum alloy webs and vertical stiffeners. Between the spars are ribs and bulkheads to provide additional strength and form separations between the tank sections. A wing designed and constructed so it is also a fuel tank called a “wet wing”.