US Patent 9278760 Torque split gearbox for rotary wing aircraft

A gearbox system for a dual coaxial counter rotating rotor assembly includes an input shaft to input a first torque into the gearbox system and a transfer shaft operably connected to the input shaft to transfer the first torque therethrough. Two gear sets are operably connected to the transfer shaft. Each gear set includes a first output gear to transfer a second torque acting in a first direction to a first rotor of a rotor assembly and a second output gear to transfer the second torque acting in a second direction opposite the first direction to a second rotor of the rotor assembly. The second torque transferred by each gear set of the two gear sets is substantially equal.