The Influence of Engine Oils on Aircraft-Engine Performance 350097
OIL cooling of aircraft powerplants is increasingly difficult. The weight and drag of the oil coolers necessary with the present maximum “Oil-in” temperature of 185 deg. fahr. (85 deg. cent.) are both decidedly objectionable. It appears possible to increase the “oil-in” temperature to about 220 deg. fahr. (104 deg. cent.) with oils which can be produced by the newer refining methods.
The use of an “oil-in” temperature of 220 deg. fahr. would render possible a material reduction in weight, size and drag of oil coolers in comparison with present practice. Oils suitable for use at 220 deg. fahr. “oil-in” temperature would not be likely to cause a material increase of engine-starting difficulty, as they would only be used in summer when the shearing resistance of the oil has slight influence on engine starting.
The approximate temperature cycle encountered by the oil in its passage through a modern aircraft-engine is discussed. The not generally realized importance of oil as a heat transfer agent in the high-duty aircraft-engine is briefly referred to. The lack of adequate knowledge of oil stability is dealt with.
It is stated that only extensive service tests of an unknown oil will, in the light of present knowledge, determine its stability. Further, that the stability, as determined by examination of the used oil and by engine effects, is usually similar but not always so, and that the latter is much the most important.