Experimental Study of Split-Path Transmission Load Sharing.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CEN TER
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Split path transmissions are promising, attractive alternatives to the common planetary transmissions for helicopters. The split path design offers two parallel paths for transmitting torque from the engine to the rotor. Ideally, the transmitted torque is shared equally between the two load paths however, because of manufacturing tolerances, the design must be sized to allow for other than equal load sharing. To study the effect of tolerances, experiments were conducted using the NASA split-path test gearbox. Two gearboxes, nominally identical except for manufacturing tolerances, were tested. The clocking angle was considered to be a design parameter and used to adjust the load sharing of an otherwise fixed design. The torque carried in each path was measured for a matrix of input torques and clocking angles. The data were used to determine the optimal value and a tolerance for the clocking angles such that the most heavily loaded split path carried no greater than 53 percent of an input shaft torque of 367 N-m. The range of clocking angles satisfying this condition was -0.0012 or - 0.0007 rad for box I and 0.0023 or - 0.0009 rad for box 2. This study indIcates that split-path gearboxes can be used successfully in rotorcraft and can be manufactured with existing technology.