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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
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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