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.

A method of providing an engine family includes providing a first engine having a low pressure turbine driving a low pressure compressor at a first speed ratio, and a high pressure turbine driving a high pressure compressor. The method includes providing a second engine by changing the first speed ratio of the first engine to a second speed ratio.

A tiltrotor aircraft having a propulsion configuration that divorces the engine core power from the thrust fan, using a combined gearbox with a plurality of clutches to couple and decouple one or more rotor systems and one or more thrust fans. The aircraft can be operable for vertical takeoff and landing (VTOL) in a helicopter mode, forward flight in a proprotor mode, and high-speed forward flight in an airplane (jet) mode. The propulsion configuration provides shaft horsepower (SHP) to rotors for VTOL flight, while also providing SHP to the thrust fan for high speed flight. Allowing the rotor and the thrust fan to be clutched on and off, sequentially, enables transition from rotor-borne VTOL flight to wing-borne thrust fan flight, and back.

A system includes a gas turbine engine having a low speed spool, a high speed spool, and a combustor. The system also includes a low spool motor configured to augment rotational power of the low speed spool. The system further includes a controller configured to cause fuel flow. The controller is operable to control the low spool motor to drive rotation of the low speed spool responsive to a thrust command while the controller does not command fuel flow to the combustor.

A turbomachine engine including a high-pressure compressor, a high-pressure turbine, a combustion chamber in flow communication with the high-pressure compressor and the high-pressure turbine, and a power turbine in flow communication with the high-pressure turbine. At least one of the high-pressure compressor, the high-pressure turbine, and the power turbine comprises a ceramic matrix composite (CMC) material. The turbomachine engine includes a low-pressure shaft coupled to the power turbine and characterized by a midshaft rating (MSR) between two hundred (ft/sec).sup.1/2 and three hundred (ft/sec).sup.1/2. The low-pressure shaft has a redline speed between fifty and two hundred fifty feet per second (ft/sec). The turbomachine engine is configured to operate up to the redline speed without passing through a critical speed associated with a first-order bending mode of the low-pressure shaft.

A turbomachine engine includes a fan section having a fan shaft, and a core engine having one or more compressor sections, one or more turbine sections that includes a power turbine, and a combustion chamber in flow communication with the compressor sections and turbine sections. The turbomachine engine includes a low-speed shaft coupled to the power turbine and having a midshaft that extends from a forward bearing to an aft bearing. The low-speed shaft is characterized by a midshaft rating (MSR) between two hundred (ft/sec).sup.½ and three hundred (ft/sec).sup.½. The low-speed shaft has a redline speed between fifty and two hundred fifty feet per second (ft/sec). The turbomachine engine includes a gearbox assembly that couples the fan shaft to the low-speed shaft and characterized by a gearbox assembly mode less than 95% of a midshaft mode of the midshaft or greater than 105% of the midshaft mode.

A coupling device for rotably coupling a shaft with a gearbox in a geared turbo fan aircraft engine, wherein the coupling device includes a connection to the shaft at a first end and a connection to the gearbox at a second end, the first and the second ends being axially separated and at least one curved shape between the first end and the second end extending from the gearbox radially inwards to the shaft and the at least one curved shape including at least one cross-section in the axial direction of the engine with a logarithmic profile or a power profile.

A gas turbine engine (10) includes a compressor section, a turbine section, and an accessory gearbox (100). A turning unit (200) for the gas turbine engine includes an output assembly (204) configured to be mechanically coupled to the gas turbine engine, and an electric motor (202). The electric motor is operable to rotate, through the output assembly, one or more components of the compressor section or the turbine section at a rotational speed less than about fifty revolutions per minute during a shut-down condition of the gas turbine engine.

A planet-carrier cage is provided for a turbomachine speed reducer having a planetary gear set. The cage contains a central sun gear and an annular row of planet gears arranged around the sun gear axis and engaging both the sun gear and an internal gear that surrounds the cage. A periphery of the cage has axial receiving elements configured to receive axial fingers secured to a cage carrier of the speed reducer. Each receiving element is penetrated by a radial spindle that guides the rotation of a connection means, such as a swivel joint or a bearing, which is supported by the fingers. The spindles include means for projecting lubricating oil into regions in which the planet gears mesh with the internal gear.

An example system for providing mechanical power to an aircraft accessory with a turbine engine, where the turbine engine includes a low-speed spool and a high-speed spool, includes an accessory gearbox disposed between the low-speed spool and the high-speed spool and a clutch disposed within or external to the accessory gearbox. The accessory gearbox is configured to drive the aircraft accessory, and the clutch is configured to enable either the high-speed spool or the low-speed spool to provide mechanical power to the aircraft accessory via the accessory gearbox.