Foreign Research Progress: Translations Issued by the N.A.C.A.

The coefficient of friction between piston ring and cylinder wall (both average coefficient and coefficient at different points over the stroke) was measured on a test set‐up in relation to rubbing speed, wall pressure and temperature, increase in running‐in time, oil quantity, and type of oil. The average friction coefficients fluctuated between 0·02 and 0·14 and, for the same oil samples and test conditions at medium and high wall pressures, was much greater than the friction coefficients of a well‐oiled journal bearing.