Cable Connections.

The earliest form of terminal connection for stranded cable consisted of a loop, the free end being bound to the main part of the wire and soldered. With the addition of a binding or serving of wire round the loop to prevent injury, due to contact with the wiring lug, or strainer eye, this wire, in a recent test, gave an efficiency of 100 per cent. for all diameters up to ¼ in.

This result, considering the elementary nature of the joint, is surprising. Unfortunately the effect of corrosion due to acid and solder is a somewhat doubtful quantity; moreover, the appearance of the joint is far from neat. An attachment which at one time achieved some popularity is shown by [Fig. 108], and is especially suitable for the single-strand wire. This consists of a cone-shaped forked end with a taper hole, into which the cable is inserted, the free end being unstranded, spread out and soldered. The attachment has been used on what was at one time one of our best products. The efficiency obtained with this fitting is in the neighbourhood of 100 per cent.

In the method indicated by [Fig. 109] a piece of flat copper tube is passed over the wire, the free end of the latter being bent round a brass thimble, and then passed through the copper tube, in a similar manner to the connection for the solid wire in [Fig. 102]. The tube is then given several turns, and the complete joint well soldered. This system is reliable, and has given good results.

A distinctive terminal is indicated by [Fig. 110], consisting of a brass ferrule just sufficiently wide to accommodate the two thicknesses of wire. The bolts are of the counter-sunk head variety, so that the operation of screwing a bolt home also forces the wires into the protuberances in the sides of the ferrule. Although the foregoing methods have all been extensively used, they have now given place to the thimble splice, [Fig. 111], which, as a general proposition, is undoubtedly the better terminal connection. The brass thimble protects the strands from the wearing effect produced by contact with the turnbuckle or wiring lug. It is the usual practice to wrap the splice with a binding or serving of fine copper wire, or waxed twine. The efficiency of this joint with a properly made splice may be safely taken as 85 per cent. of the total strength of the wire. With this joint the point of failure, as evidenced by numerous tests, always occurs at, or near, the last tuck in the splice, at which point the extra thickness of the splice is just merging into the normal thickness of the wire. The disadvantage with all terminal connections which necessitate the use of solder is the impossibility of determining just how much the heating operation affects the strength of the wire, and also the effects of corrosion, set up by the various species of flux used in the process of soldering.

Relative Strengths.

For a given diameter the solid-wire stay possesses the greatest strength, the next best being the single-stranded cable, as the following comparison of stay strength, taken from the Report of the National Advisory Committee for Aeronautics, 1915, of America, will show:—

Material.Diameter. Strength of
material.		 Strength
of stay.
inch.lbs.lbs.
Wire, solid 3/16 5500 5100
Strand, single 3/16 4600 4100
7 × 19 multi-strand 3/16 4200 3500

Streamline Wires.

Although in the quest for increased speed the number of exposed wires were reduced to a minimum, the aggregate resistance still remained considerable, this leading to the development of the swaged streamline wire, the introduction of which is generally ascribed to the Royal Aircraft Factory; and these wires are now generally used for all exposed wiring. The points in favour of them are that, properly fitted, a considerable reduction in resistance is obtained, there is a lessened liability to slacken after some use, this rendering rigging a more certain operation, and the nature of its connection obviates the use of turnbuckles.