Lubricant Effects on Efficiency of a Helicopter Transmission

Efficiency tests were conducted using 11 different lubricants in the NASA Lewis Research Center's 500 hp torque regenerative helicopter transmission test stand. The test transmission was the OH58A helicopter main transmission. The mechanical power input to the test transmission was 224 kw (300 hp) at 6060 rpm. Tests were run at oil-in temperatures of 355 K (180° F) and 372 K (210° F). The efficiency was calculated from a heat balance on the water running through an oil-to-water heat exchanger while the trans­ mission was heavily insulated. The following results were obtained: 1) Among the 11 different lubricants, the efficiency rangeo tram 98.3 to 98.8 percent, which is a 50 percent variation relative to the losses associated with the maximum efficiency measureo. 2) For a given lubricant, the efficiency increased as temperature increased and thus as viscosity decreased. There were two exceptions which could not be explained on the basis of available data. 3) Between lubricants, efficiency was not correlated with viscosity. There were relatively large variations in efficiency with the different lubricants whose viscosity generally fell in the 5 to 7 cs range. 4) The lubricants had no significant effect on the vibration signature of the transmission.