From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Paper on the requirements and testing of aircraft engine lubrication.
| Identifier | ExFiles\Box 154a\2\ scan0008 | |
| Date | 14th June 1938 | |
| Aircraft-Engine Lubrication By E.{Mr Elliott - Chief Engineer} L. Bass and C. H.{Arthur M. Hanbury - Head Complaints} Barton Asiatic Petroleum Co., Ltd. IT may be necessary to compromise among the ring-sticking, sludge-forming, and corrosion properties of oil for civil aircraft engines, the authors suggest. No laboratory tests are yet able to predict the performance of an oil in an aircraft engine, they contend, and therefore, full-scale engine tests are necessary for final judgment. However, they explain, much preliminary work can be carried out in suitable small units. To illustrate the complexity of the problem the authors set forth five requirements for an aircraft-engine lubricant: 1. It must not cause ring-sticking under the full-throttle detonating conditions of take-off. 2. It must not cause ring-sticking under weak-mixture cruising conditions. 3. It must give freedom from sludging so that there is no ring-jamming, so that the oil scrapers are kept free, and so that the overhaul periods are not limited. 4. It must provide protection from cold corrosion. 5. It must not be corrosive to special alloys, such as cadmium-base bearings. Test data which are treated in the appendix of the paper, include specifications of the single-cylinder 250-cc. engines used for ring-sticking tests; and of the 500-cc. single-cylinder engine for sludge-testing. Results of these tests are correlated with single-cylinder aircraft engine, full-scale bench, and flight-test results. In a discussion of engine results, the paper takes up the influence of mechanical conditions; carbon formation; sludging; effect of lead content of the fuel; ring-sticking and dopes; and bearing corrosion. THE demand for a means of rating oils for aircraft engines has still to be satisfied. The importance of this demand tends to increase as time goes on since lubricating-oil requirements of engines become more arduous as their specific power outputs increase. Moreover, the development of oils suitable for the latest high-output engines is retarded if a satisfactory testing technique is not available. The task is one of considerable complexity due to the variable demands made upon the oil. It is no longer the simple function of an oil to lubricate – it also has to cool and protect certain parts from corrosion under a wide range of temperatures and pressures. Additional complication is introduced by the enormous influence which details in design¹ have upon lubricating-oil conditions. We know now that, with a given engine, the lubricating oil must fulfill the following requirements: 1. It must not cause ring-gumming under the highest temperatures and possibly under slightly detonating conditions likely to be met. These conditions will occur on full throttle during take-off. 2. It must not cause ring-gumming under weak-mixture cruising conditions. 3. It must give freedom from sludging so that: a.{Mr Adams} Ring-sticking due to accumulation of carbon and sludge in the ring-grooves does not occur. b. Oil-control rings do not become clogged and, therefore, inoperative. c. Heavy deposits of sludge are avoided which may limit the period between overhauls. 4. It must, as far as possible, provide adequate protection from cold corrosion of working parts during periods of inaction of the engine. 5. It must not be corrosive to special alloys, such as cadmium-base bearings. The relative importance of each of these requirements obviously will depend largely upon operating conditions; it also will vary from one make (or even type) of engine to the next. The difficulties in providing an engine test capable of rating oils for all engines are immediately apparent. One specific engine test may be developed, taking due account of all variables, but the results obtained can only be applicable to the type of engine in which the tests were made. The proper attack of the problem involves the examination of the effect of each operating condition as far as it is possible to segregate them. For preliminary experiments small air-cooled motorcycle engines were selected as test units. These offered considerable advantages for laboratory tests in the direction of ease and the cost of installation and operation. The results obtained have amply justified this decision. The first engines installed were of 250-cc. (15 cu. in.) capacity. Details of these engines, together with a description of the testing equipment, are given in Appendix 1. A good deal of experimenting was necessary to find the [This paper was presented at the Semi-Annual Meeting of the Society, White Sulphur Springs, West Va., June 14, 1938.] ¹See “Aero Engine Design and Lubrication,” by E.{Mr Elliott - Chief Engineer} L. Bass, presented at the General Discussion on Lubrication and Lubricants, Institution of Mechanical Engineers, October, 1937. 8 Vol. 44, No. 1 | ||