The method of designing and calculating the optimum oil-supply pressure for jet-lubricated high speed aviation spur gears applied in helicopter transmission is analysed. The optimum oil nozzle arrangement and oil jet velocity are obtained based on related theoretical and experimental research results. A thick-walled orifice is taken as the model of the oil nozzle to derive the oil-supply pressure that meets the ideal oil jet velocity. The optimum oil-supply pressure for a set of test spur gears used in the helicopter transmission is calculated under different gear operating speed and with different oil nozzle configuration. It is shown that the optimum oil-supply pressure increases as the increase of the gear running speed, but decreases as the increase of the flow velocity coefficient of the nozzle. The oil-supply pressure of oil nozzles in the out-of-mesh-side is larger than that of oil nozzles in the into-mesh-side, and it is necessary to adopt nozzles with larger flow velocity coefficient when the gear operating speed is considerate high in order to restrain the optimum oil-supply pressure less than the upper limit of 1Mpa.
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