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The paper discusses the general lubrication problems associated with operation of high-output aircraft engines. Since the paper is concerned with two types of aircraft engines, namely, turbine and reciprocating, a natural division into two parts is made. Part I deals with the problems of turbine engines, and part II deals with the problems of reciprocating engines. In part I it is indicated that the choice of a lubricant is very difficult for the turbine engine particularly, because of the wide temperature range (from -67°F to approximately 400° F). Two solutions to the problem of proper choice of a lubricant are discussed, namely (1) the use of supplemental lubricants, and (2) the use of additive lubricants. Data are presented on supplemental lubricants including the various oxides of iron, molybdenum disulfide and graphite.

The paper describes the bearing and lubricant problems inherent in aircraft turbine engines; these problems are severe because of the occurrence of high rotative speeds and an extremely broad temperature range (including high temperatures as one end of the range). It is indicated that the materials currently used in rolling contact bearings for turbine engines are temperature limited to such an extent that completely new materials are now under consideration. Some data are presented which show acceptable friction and wear properties of some materials for rolling contact bearings and their cages (separators, retainers) at high speeds and at high temperatures. For liquid-lubricated-bearings, considerable improvement in the limiting speeds of rolling contact bearings appears possible with proper cage and bearing design. The design principle involves providing easy flow paths for the lubricant through the bearing.

Synthetic lubricants are coming into prominence for lubrication of aircraft turbine engines, because of the stringent operating temperature requirements. Because many of the surfaces to be lubricated in the turbine engine operate under conditions of boundary or “thin-film” lubrication, the friction and surface-failure properties of the lubricant under these conditions are of extreme importance. In consequence, an investigation was made at the NACA laboratories of the friction properties of several classes of synthetic lubricants over a wide range of sliding velocities. Most synthetics including a diester, a polyether, a silicate ester and a phosphonate ester are more effective boundary lubricants at high sliding velocities than petroleum oils of comparable viscosity at 100° F. The breakdown of effective lubrication takes place at a much higher sliding velocity with these synthetic fluids than with the petroleum oils.