Turboshaft gearbox output gear arrangement with torque measurement system

A turboshaft gearbox output gear arrangement of a gas turbine engine, comprising:

• a power turbine shaft having a forward end;
• a torque shaft, extending from a forward end to an aft end, the aft end of the torque shaft coupled to and driven by the forward end of the power turbine shaft;
• a gear shaft, extending from a forward end to an aft end, coupled to the torque shaft at a first portion of the torque shaft and driven by the torque shaft;
• a mating gear, driven by the gear shaft, wherein the mating gear defines a gear mesh plane, wherein the mating gear is aft of the first portion of the torque shaft, and wherein the forward and aft ends of the torque and gear shafts extend on each side of the gear mesh plane,
• wherein at least a portion of the gear shaft and the torque shaft are concentric and axially aligned with each other;
• and
• a sensor that engages the gear shaft and the torque shaft to measure twist in the torque shaft,
• wherein angular movement of the gear shaft relative to the torque shaft is indicative of torque reacted in the torque shaft;
• and
• the aft end of the gear shaft and the aft end of the torque shaft defining an interface coupled via a phonic wheel having interlacing teeth, and the sensor engages the interlacing teeth to determine a relative angular displacement indicative of twist,
• wherein the aft end of the gear shaft is axially aligned with a second portion of the torque shaft, wherein the second portion of the torque shaft is aft of the mating gear.

A method of operating a turboshaft gearbox output gear arrangement of a gas turbine engine, comprising:

• driving a power turbine shaft, to thereby drive a torque shaft and a gear shaft that are operationally coupled to one another, and to thereby drive a mating gear driven by the gear shaft;
• measuring a phase shift between a first portion of the torque shaft that is forward of a mesh plane of the mating gear and a second portion of the torque shaft that is aft of the mesh plane utilizing a sensor;
• and
• determining a torque on the torque shaft from the phase shift.