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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.

Research information on solid lubricants has been compiled for consideration in the possible use of such materials in aircraft electrical equipment. Solid lubricants are capable of lubricating at the maximum temperatures (600° F) for aircraft electrical equipment. Many solids that adhere well to metals may be useful lubricants; those with layer-lattice structure usually give low friction. Solid lubricants are most commonly used as bonded films but the use of fluid carriers and surface reaction products have considerable merit.

This paper summarizes the results and findings of a program to design, develop, and evaluate actuator rod seals for use in advanced aircraft high-temperature hydraulic systems. The rod seals are intended to function efficiently and reliably for 3000 hr in the temperature range of -40-500 F. Preliminary studies of various material and design combinations showed that a polyimide low-pressure second-stage V-seal in a two-stage configuration had the greatest potential in long-term duty cycle testing in a simulated actuator test system. Modifications of this seal that provided for improved fatigue life and more efficient loading met the test objectives of 20 X 106 short-stroke cycles of operation at 500 F. Severity of this testing was equivalent to 3000 hr of duty cycle operation. The validity of design techniques used to achieve performance goals was shown.