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Two aircraft reciprocating piston engines were run to their recommended 200 hour overhaul periods utilizing 200 hour oil changes and 100 hour filter changes. The oil was tested each 200 hours for contamination, additive depletion, and wear-metal concentrations. Up-on completion of the study, both engines were disassembled and compared with two engines that were operated 600 hours beyond their recommended 2000 hour overhauls using normal oil and filter change periods. Results indicated that oil could be used safely for 200 hours under closely monitored conditions for a particular aircraft fleet operation.

Six, one hundred eighty brake horsepower aircraft reciprocating piston engines have been operated for one year using three different multi-viscosity oils. Two of the oils were semi-synthetic blends and the third was an ashless dispersant. These three oils were compared with six (6) identical aircraft using a single grade aviation oil. Preliminary results have indicated that the engines utilizing multi-viscosity oils exhibited improved cold-weather starting characteristics, averaged lower oil consumption, and displayed similar wear rates when compared to the six control aircraft using straight-weight oil.

Six, one hundred eighty horsepower aircraft piston engines have been operated through their normal overhaul life using three different ashless dispersant multi-viscosity aircraft oils. Two of these oils achieved their multi-viscosity characteristics by utilizing some synthetic base stock while the third utilized additional viscosity-index (V-I) improver. The performance of these three oils was compared with that of a conventional, single-grade AD oil in six identical control aircraft engines. The results of this test indicates that multi-viscosity oils provide improved cold-weather starting, less consumption, and comparable wear rates to the six control engines.

Documented articles have been published on the very early development of aircraft piston engine oils covering the transition from castor oil to various types of nonadditive, mineral-base lubricants. This documentation covers the history and development of these lubricants up to and including the World War II era and into the late 1940's. A considerable amount of research and development of greatly improved lubricants has occurred since that time. Although numerous articles have dealt with certain phases of this development, no attempt has been made to organize this period into a chronological and thorough historical perspective. This paper attempts to fill the gap in the development of aircraft piston engine lubricants during the past 40 years.