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Aviation History
1934
1934 - 1451.PDF
AUGUST 30, 1934 63 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT aircraft far more accurately than the most skilled human pilot. It is important to remember that while a dis- turbance must actually have occurred before it can be appreciated and corrected by a human pilot, the Auto- matic Pilot detects a disturbance instantly with its growth and almost simultaneously applies the means for its correction. In consequence, the somewhat unpleasant motions of an aircraft in rough weather are very much reduced, and it is therefore probable that public opinion may, in the future, demand the universal use of automatic control in passenger carrying aircraft. The accuracy with which the Automatic Pilot can main- tain the aircraft on its true course must inevitably result in a reduction of the fuel consumption. In practice, the course steered will not deviate by more than four or five degrees per hour, and thus only a very occasional correction is required by the pilot. The additional weight of the equipment is more than balanced on a long flight by the reduced fuel consumption and not infrequently the carrying of a relief pilot or wireless operator is rendered unnecessary. In comparison with the extra safety assured, the economies and the extra comfort afforded, the initial cost of installation is not high. The considerable experi- ence of the working of the Automatic Pilot which has been gained during recent years by its use in several squadrons of the Royal Air Force has demonstrated the safety and tht> value of the installation, and it is safe to predict that within a few years, no passenger or freight carrying air- craft will remain unequipped with gyroscopic control. NICKEL WIRE FOR SPARKING PLUGS By A. G, AREND NICKEL wire has been adopted as representing themost suitable economical metal for the sparkingplugs of internal combustion engines. The intensely hot spark which is formed heats the zone around the gap to a very high temperature. Accordingly, nickel has been adopted as the most suitable metal for the central electrode points, whilst in many cases the side electrodes are stamped from nickel sheet to the required template. The successful manufacture of the nickel wire for this purpose has been the outcome of much research work, because nickel is one of the most impure metals on the market. There are, of course, many classes of the metal, but to the present day it is quite customary to find nickel which contains several per cent, of impurities. Such a metal as this is of little value for drawing purposes, and would only result in brittle and weak wire. It is thus recognised that only the purest form of nickel be used for wire drawing. When it is known that the wire has to be ultimately used in the making of sparking plugs, an addition of about 2 per cent, of manganese is made. This is better suited to withstand the effects of current and heat, but sometimes adds to the difficulties of successful drawing. The best nickel is obtained from the electrolytic process. This is first cut up into long strips which resemble ingots of small section. These are first hot-rolled, and later cold-rolled, until the section has been reduced to a thin rod. Heat treatment has to be performed between the different rolling operations to remove the strains which exist in the crystalline structure of the metal. Much more difficulty is experienced in this heat-treatment, than in the annealing of copper, brass or similar metals for wire production. Brittleness appears during the reduction of the billet, before it has even reached the rod stage. This is due to the ready solubility of nickel oxide in the nickel. The result is that to-day the pure metal from the electrolytic extraction, is not directly rolled, but first melted, and a minute quantity of a deoxidising agent added, which ensures the removal of this undesirable oxygen. The metal is then poured into rod-ingot moulds, which thus economises in part of the rolling operations which would otherwise have been necessary. The final size of the rod is about Jin. diameter, after which it is reduced to the form of wire by drawing through dies. The drawing process does not differ materially from that adopted for the making of copper wire, since the relative ductility of copper and nickel are very similar. (These conditions, however, do not obtain in the rolling of the two metals as copper is much more malleable than nickel.) Ductility simply signifies the power of the metal being permanently extended by traction, and although ductility and malleability are closely associated in most cases, an exception to this exists in the drawing of nickel and copper wire. The plant used for the making of the nickel wire is the same as that used for copper wire. The wire required for sparking plugs is expected to possess a fair amount of rigidity, since although the shape must be capable of being altered from time to time, it must remain in such a position. The melting point of nickel is only surpassed by three FIVE PHOTO-MICROGRAPHS t A specially-drawn Nickel Wire under diflEerent magnifications.
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