Mr. Foord: It has been truly said that “lubrication is the heart of an engine,” and I think this saying applies in the strongest possible sense to aircraft engines.

The reasons for this are manifold and one has only to consider the overall thermal efficiency, the low weight/power ratio and consequent minimum scantlings and bearing surfaces, and the high working temperatures of this class of prime mover compared with other types, to realise that the duty the lubricant has to perform is far and away more severe than is the general case.

If one takes into consideration all the various properties which the aircraft engine designer demands for the lubricant, it must be recognised that from an ideal point of view, there is no really satisfactory lubricant for the work and that the only thing that can be done in order to give the best all round results is to effect a compromise.