The performance of transmission systems, especially those of high criticality and specific torque capacity such as those in helicopters, depends strongly on lubricant behaviour.
However, economic load capacity evaluation of lubricants involves the correlation of test results obtained from simple tests in order to predict service performance, which is an unreliable step. In this paper the role of the thermal characteristics of the test machine is explored and the results used to resolve the apparent contradictions in the ranking order obtained from different test methods.
A simple method for calculating the bulk and surface temperatures in disc machines is given together with corresponding experimental confirmation. The performance of two lubricants that show a reversal in ranking order at a particular temperature is examined.
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