Various Wires used.
The various wires used in construction may be classified into four distinct types: the solid wire stay, the straining cord or cable used for stay wires, the extra flexible cable used for controls, and the swaged tie rods in plain or streamline form. The earliest form of bracing was of the solid piano wire variety, this having been used on most aeroplanes from the days of the Wrights onward. From the view-point of the early pioneers, this wire was eminently satisfactory, being cheap (a vital consideration) and simple to attach and replace. Although the tensile strength of this wire cannot probably be excelled, its hardness renders somewhat difficult the forming of the end loop without fracture of the wire. For this reason piano wire gradually gave place to a softer grade of wire which, while being strong, was tough and ductile, enabling bends to be made with a lesser danger of fracture. The original connection used for the piano wire stay is shown by [Fig. 103], this consisting of a loop or eye, the free end being turned round a ferrule of soft copper tube, this being sometimes varied by the use of a flat strip of tinned iron, wrapped round and soldered. While this was fairly satisfactory for short stays, it was hardly suitable for the main lift wires of the interplane bracing, owing to the comparative ease with which, under load, the free end pulled or cut through the ferrule, so that after a while the oval spring-wire ferrule, [Fig. 104], came into use. This is made of the same gauge wire as the stay, and is from seven to nine convolutions in length. The eye should be formed as an easy bend, and not kinked, the ferrule being pushed tight against the shoulders, and the free end turned back.