THE DEVELOPMENT OF RUST PREVENTIVE LUBRICATING OILS FOR RECIPROCATING AIRCRAFT ENGINES

The internal rusting of reciprocating aircraft engines which are temporarily idle or stored under conditions of high temperature and high humidity presents a major maintenance problem. Factors contributing to rust formation are discussed. An attractive means of overcoming this rusting is through the use of rust preventive lubricating oils suitable for both engine break-in and fly-away service. The development of oils of this type has been hampered in the past by the lack of suitable laboratory tests for the evaluation of experimental products. A new laboratory test procedure is described which successfully measures the rust preventive properties of lubricating oils. The test involves operation of a single-cylinder engine using the test oil as a crankcase lubricant and five days’ storage of the cylinder in a humidity cabinet, the temperature and humidity of which are cycled to simulate severe climatic conditions which promote rust. Data are presented which show excellent correlation between laboratory and full-scale engine test results. The test has proved successful in the development of a rust preventive lubricating oil composition incorporating an ashless inhibitor which overcomes the deficiencies of previous rust preventive compounds or oils of the AN-VV-C576b type using metallic inhibitors. Data from full-scale engine tests and commercial experience are presented which confirm the laboratory test results.