US Patent 7937927 Counter-rotating gearbox for tip turbine engine

A tip turbine engine (10) provides an axial compressor rotor (46) that is counter-rotated relative to a fan (24). A planetary gearset (90) couples rotation of a fan (46) to an axial compressor rotor (46), such that the axial compressor rotor (46) 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 (54) between the final stage of compressor blades (52) and inlets (66) to the hollow fan blades (28) of the fan are eliminated. As a result, the length of the axial compressor (22) and the overall length of the tip turbine engine (10) are decreased.