The open rotor engine is a next generation aero-engine that satisfies the demand for high fuel efficiency and low CO2 emission. A differential planetary gear system is incorporated in the open rotor engine to connect the turbine output shaft and fan rotors in order to counter-rotate the fan rotors as well as allow the turbine and fan rotors to operate at more efficient speeds. The open rotor gear system is required to have not only 20,000 hp high power transmission, but also an increasingly high efficiency, high reliability and light weight. To achieve these requirements, the following design works were conducted; (1) a low misalignment and lightweight carrier, (2) a flexible structure to absorb the displacement caused by the flight load, (3) an optimum gear tooth modification and (4) reduction of oil churning and windage losses. Also, extensive analyses and simulations such as lube oil flow CFD, FEA and tooth contact analysis were conducted. A full scale prototype gear system was manufactured and validation tests were conducted using a newly constructed test rig to validate the design concept. A slow roll test, rated performance test and efficiency test were conducted. And the design concept was found to be valid. This paper describes details of the prototype design and the results of the validation tests.

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