US Patent 8950171 Counter-rotating gearbox for tip turbine engine

A tip turbine engine provides an axial compressor rotor that is counter-rotated relative to a fan. A planetary gearset couples rotation of a fan to an axial compressor rotor, such that the axial compressor rotor is driven by rotation of the fan in a rotational direction opposite that of the fan. By counter-rotating the axial compressor rotor, a final stage of compressor vanes between the final stage of compressor blades and inlets to the hollow fan blades of the fan are eliminated. As a result, the length of the axial compressor and the overall length of the tip turbine engine are decreased.