History of aicraft piston engines

Meanwhile a subsidiary of the general motors

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Unformatted text preview: figures 44 and 45 show e xamples. Ball or roller bearings occasionally have been used for crankpins (see figs. 20 and 33). Thrust bearings generally have been of the ball type. M ost aircraft engines have used plain journal bearings for the crankpin, a nd, with the exceptions noted above, for the main crankshaft bearings. Before about 1930 such bearings were made of the lead-tin-antimony alloy babbit. This material is excellent for bearings in all respects except i n structural strength, which is low. After about 1930 the increases in power and speed, resulting in increased bearing loads, began to cause serious fatigue failure of plain b abbit bearings. Meanwhile a subsidiary of the General Motors Corporation h ad developed a bearing material consisting of a copper matrix filled in w ith lead. These "copper-lead" bearings were found to have excellent l oad carrying ability as compared to babbit, and were soon adopted as s tandard for all high-output aircraft engines. D uring World War II, U.S. radial engines started to have crankpinbearing failures when overspeeded in combat dives. A bearing consisting of a steel shell lined with a thin layer of cadmium, with a very thin overlay of silver was developed to solve this problem. Variations on this bearing h ave been used in large radial-engines crankpins since that time. Copperlead bearings, when improved with a very thin overlay of tin, have generally been found adequate for V-type engine crankshafts and crankpins. T hese bearing developments have been an important factor in the u p-rating of airplane engines illustrated by figure 7 1. I mprovements in lubrication systems have included the use of full p ressure feed to bearings, rather than gravity or splash feed, or such "total loss" systems as that already described for the Gnome engine (see p. 23). A nother important improvement has been the installation of adequate oil filtering elements within the engine's oil-circulation system. As size and p ower of engines has increased, it has become necessary to limit oil temperature by circulating the lubricant through oil radiators, usually air cooled. T he use of castor oil as a lubricant for most, if not all, aircraft, engines p revious to 1918, has already been mentioned (p. 25). When fresh, this t ype of oil is an excellent lubricant, but has the disadvantages of rapid b reakdown to gummy deposits in the engine, and a very limited supply base. W ork to explore the possibilities of petroleum oils for aircraft-engine l ubrication was started at the United States Navy Aero-Engine Laboratory 82 a t Washington, D . O , in 1917, and within a few months a number of p roprietary mineral oils were found satisfactory and approved for use in all except rotary engines. Since that time, development of mineral oils s uitable for aircraft engines has been energetically carried on by the oil i ndustry. The resulting improved quality of lubricants has been an important factor in increasing the reliability, and the running time between o verhauls, of aircraft piston engines. T he development of engine instruments...
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This document was uploaded on 01/19/2014.

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