Abstract
The laser-interferometric skin-friction meter is a device used to determine the aerodynamic skin friction through the measurement of the rate of change with time of the thickness of a thin oil film on the test surface. The results from thin-film lubrication theory are used to relate skin friction to the rate of thinning of the film. The limits of applicability of the simplified theory have been studied. Two problems are examined: the response of the oil film to a time-varying skin friction such as is encountered in turbulent boundary layers, and a 'surface-wave instability' encountered at high skin-friction levels.