Experimental and Analytical Evaluation of Efficiency of Helicopter Planetary Stage
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER
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Mechanical efficiency of a helicopter transmission planetary stage was studied. Experiments were done by using two identical planetary stages in a back-to-back, test-and-slave arrangement with separate lubrication systems. A total of 124 different conditions were tested. The parameters varied were speed, torque, type of lubricant, lubricant system temperature, and lubricant flow rate. Experimentally measured efficiency ranged from 98.64 to 99.83 depending on operating conditions. Performance of the planetary stage was also studied analytically. Test hardware and conditions were modeled and analyzed by using computer programs that predict power losses from gear meshes, from gear windage, and from planet bearings. Two different models for calculating power loss due to oil displacement from the gear mesh were also studied, and the results were included in the analytical predictions of efficiency. Experimental results were compared with the analytical predictions. The analysis predicted higher efficiencies than were measured experimentally. Results of this study showed trends similar to those of previous investigations.