A splined shaft includes splines evenly distributed over the periphery, wherein the splines being spaced apart from each other. At least one portion of the splines are spaced apart by a modified pitch p with respect to the nominal pitch pn of the splines. The ratio of the absolute value of the difference between the modified pitch and the nominal pitch, to the nominal pitch, i.e. |pn−p|/pn, is different from zero, for example between 0.5 and 5%.

A splined shaft includes splines evenly distributed over the periphery, wherein the splines being spaced apart from each other. At least one portion of the splines are spaced apart by a modified pitch p with respect to the nominal pitch pn of the splines. The ratio of the absolute value of the difference between the modified pitch and the nominal pitch, to the nominal pitch, i.e. |pn−p|/pn, is different from zero, for example between 0.5 and 5%.

A gas turbine engine includes a fan assembly having a plurality of fan blades; and a turbomachine. The turbomachine includes a compressor section, a combustion section, and a turbine section in serial flow order. The turbomachine further including a first input power source; a second input power source configured to counter-rotate relative to the first input power source; a power output component operably connected to the fan assembly; and a gear assembly located forward of the combustion section of the turbomachine, the gear assembly configured to receive power from the first input power source and the second input power source and provide power to the power output component, the gear assembly comprising a helical gear.

A gas turbine engine includes a fan assembly having a plurality of fan blades; and a turbomachine. The turbomachine includes a compressor section, a combustion section, and a turbine section in serial flow order. The turbomachine further including a first input power source; a second input power source configured to counter-rotate relative to the first input power source; a power output component operably connected to the fan assembly; and a gear assembly located forward of the combustion section of the turbomachine, the gear assembly configured to receive power from the first input power source and the second input power source and provide power to the power output component, the gear assembly comprising a helical gear.

In accordance with at least on aspect of this disclosure, there is provided a hydrogen fuel system for aircraft. The hydrogen fuel system includes a gas turbine engine and a fuel feed conduit. The fuel feed conduit is defined at least in part by, in fluid series, a liquid hydrogen tank fluidly connected to a combustor of the gas turbine engine, a liquid hydrogen pump to drive fuel to the combustor of the gas turbine engine, an evaporator, and an electric heat source in thermal communication with the evaporator to add heat into a flow of hydrogen passing through the evaporator. In embodiments, the electric energy source associated with the electric heat source to power the electric heat source.

In accordance with at least on aspect of this disclosure, there is provided a hydrogen fuel system for aircraft. The hydrogen fuel system includes a gas turbine engine and a fuel feed conduit. The fuel feed conduit is defined at least in part by, in fluid series, a liquid hydrogen tank fluidly connected to a combustor of the gas turbine engine, a liquid hydrogen pump to drive fuel to the combustor of the gas turbine engine, an evaporator, and an electric heat source in thermal communication with the evaporator to add heat into a flow of hydrogen passing through the evaporator. In embodiments, the electric energy source associated with the electric heat source to power the electric heat source.

In accordance with at least one aspect of this disclosure, there is provided a drive shaft system. In embodiments, the drive shaft system includes a generator shaft extending along a longitudinal axis with a longitudinal bore defined through the generator shaft. A thru shaft extends through the longitudinal bore of the generator shaft. In embodiments, the thru shaft includes, a front coupler mount at a first end operative to receive torque input, and a rear coupler mount at a second end opposite the first end.

In accordance with at least one aspect of this disclosure, there is provided a drive shaft system. In embodiments, the drive shaft system includes a generator shaft extending along a longitudinal axis with a longitudinal bore defined through the generator shaft. A thru shaft extends through the longitudinal bore of the generator shaft. In embodiments, the thru shaft includes, a front coupler mount at a first end operative to receive torque input, and a rear coupler mount at a second end opposite the first end.

In a rotary electric machine housing, a first bearing and a second bearing are provided for supporting a rotating shaft. A lubricating oil is supplied to the first bearing and the second bearing. At least one of the first bearing or the second bearing is sandwiched between the compressed air supplied from one side of the rotating shaft in an axial direction thereof and the compressed air supplied from another side of the rotating shaft in the axial direction.

In a rotary electric machine housing, a first bearing and a second bearing are provided for supporting a rotating shaft. A lubricating oil is supplied to the first bearing and the second bearing. At least one of the first bearing or the second bearing is sandwiched between the compressed air supplied from one side of the rotating shaft in an axial direction thereof and the compressed air supplied from another side of the rotating shaft in the axial direction.