Stranded Cable.
The gradual increase in engine power and total weight of aeroplanes led to the adoption of stranded cable for all important loaded wires, this being made in two distinct ways.
The cable employed for interplane bracing is composed of a number of fine wires, varying from nineteen to thirty-seven according to the different diameters, the end section being indicated by [Fig. 106].
Figs. 103–112.—Methods of forming wire connections.
Where extra flexibility is required, such as for control wires running round pulleys, the cable is composed of a number of strands, generally seven, which in turn consists of a number of fine wires, usually nineteen, the end section being shown by [Fig. 107]. English practice designates this form of cable as extra flexible, and the single rope of nineteen wires as straining cord. American classification is practically the reverse, in that the single rope is known as stranded cable, and the multi-strand as cord. Although the factor of strength is an important one it does not entirely govern the selection of a wire, as other considerations, such as flexibility and fatigue strain, influence greatly the efficiency of a stay under active service conditions. Under test the solid wire possesses the greatest ultimate breaking weight, the next best being the single rope. It must be understood that in flight a wire is subjected to constant and intensive vibration, which must have a deleterious effect on the material, and for this reason a flaw or slight fracture in a solid wire may escape notice until complete failure in the air; whereas the cable, by the unstranding of the damaged wires, would give warning of wear. Chiefly owing to the difficulty of forming a satisfactory splice in the single-strand cable, modern practice inclines toward the use of the multi-strand cable for all purposes, as the construction of this wire lends itself to the forming of a successful splice.