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The tremendously increased use of ball bearings in modern aircraft has emphasized the need for a closer evaluation of lubricants for these bearings. Operational experience during the war and recent commercial practice has indicated that many of our present standardized test methods for grease evaluation for aircraft are in need of replacement or, in some cases, just an overhaul. It is quite natural that methods which had proved quite satisfactory for automotive and commercial practice should be the first to be employed in qualifying greases for aircraft use.—The tremendous impetus of war and global operation resulted in the present test methods more-or-less adapted to aircraft greases. Such early and commendable methods are found in the early Army-Navy AN grease specifications. As the result of the vast amount of aircraft activity during the war, service data began to trickle back to the aircraft manufacturers and to the Services' technical centers indicating, somewhat vaguely in many cases, the equipment in which the lubricants were failing. There evolved from these reports and much additional pleading for service experience, the third step in this evolutionary process which is now taking place, namely the actual tailoring of test methods to the peculiar functional requirements of aircraft. The newer AN specifications and requirements of commercial aircraft manufacturers contain numerous tests which at least have the appearance of being functional tests, that is, the grease is required to qualify itself in a test method which attempts to duplicate the requirements it must actually meet in service. This cannot be done without some element of hazard. Good reliable service experience is still too rare to be able to predict with certainty the actual environmental conditions that the grease will be subjected to even if the mechanical device used in an absolute duplicate of its service counterpart. Every effort should be bent toward designing the environmental conditions of the test not toward needless severity, but rather toward optimum requirements. There have been too many instances of setting environmental conditions fora functional test which have excluded greases that proved eminently satisfactory in service.
Moreton, D. H.
Chairman of S.A.E. Subcommittee S-5c, Douglas Aircraft Co., Santa Monica, Calif.