A twin-engine system includes a gas turbine engine comprising a core and a first output shaft drivable by the core. An electric engine has an electric motor configured to drive a second output shaft. A reduction gear box (RGB) has an RGB input drivingly engaged to both the first output shaft and the second output shaft. The RGB has an RGB output to provide rotational output to a rotatable load.

An assembly is provided for a turbine engine. This turbine engine assembly includes a first rotating structure, a turbine engine apparatus, a rotating coupler and a seal assembly. The first rotating structure is configured to rotate about a rotational axis. The turbine engine apparatus includes an electric machine and a second rotating structure. The electric machine includes an electric machine rotor and an electric machine stator. The second rotating structure is configured to rotate about the rotational axis and is coupled to the electric machine rotor. The rotating coupler is coupled to the first rotating structure by a first connection. The rotating coupler is coupled to the second rotating structure by a second connection. The seal assembly includes a rotating seal land and a stationary seal element. The rotating seal land is mounted onto the rotating coupler. The stationary seal element sealingly engages the rotating seal land.

An assembly is provided for a turbine engine. This turbine engine assembly includes a stationary structure, a rotating structure and an electric machine. The rotating structure is rotatably mounted to the stationary structure by a first bearing and a second bearing. The electric machine is between the first bearing and the second bearing. The electric machine includes a rotor and a stator circumscribing the rotor. The rotor is connected to the rotating structure. The stator is connected to the stationary structure.

An electric module for an aircraft turbomachine includes an electric machine stator having an annular shape around an axis (A) and being configured to surround a rotor of the electric machine, and an annular support element of the stator. The support element includes an outer annular surface configured to be swept over by a gas stream (F) from the turbomachine with a view to conductively cooling the stator.

A combined cycle power generation system for an aircraft includes fuel cell and supercritical CO.sub.2 cycles. The fuel cell cycle includes a compressor and turbine disposed on a first shaft, a fuel cell in fluid communication with the compressor and a fuel source, and a combustor in fluid communication with the fuel cell and the turbine. The combustor is configured to combust partially spent fuel from the fuel cell and produce combustion exhaust gas for delivery to the turbine. The supercritical CO.sub.2 cycle includes a compressor and turbine disposed on a second shaft, a supercritical CO.sub.2 fluid circuit in thermal communication with the combustor and configured to deliver CO.sub.2 to the turbine and compressor, and a heat exchanger in thermal communication with the supercritical CO.sub.2 fluid circuit and a source of cooling fluid. A mechanical linkage is configured to transfer power from the second shaft to the first shaft.

A twin-engine system includes a gas turbine engine comprising a core and a first output shaft drivable by the core. An electric engine has an electric motor configured to drive a second output shaft. A reduction gear box (RGB) has an RGB input drivingly engaged to both the first output shaft and the second output shaft. The RGB has an RGB output to provide rotational output to a rotatable load.

An integrated hydrogen-electric engine including an air compressor system, a hydrogen fuel source, a fuel cell stack, a heat exchanger, an elongated shaft, and a motor assembly. The heat exchanger is disposed in fluid communication with the hydrogen fuel source and the fuel cell stack. The elongated shaft supports the air compressor system, the fuel cell stack and the heat exchanger. The motor assembly is disposed in electrical communication with the fuel cell stack.

A reverse-flow gas turbine engine includes a core of the gas turbine engine comprising multiple spools rotatable about a center axis of the gas turbine engine. Each spool is configured to pressurize air and to extract energy from combustion gases. The air and combustion gases are configured to flow through the core in a forward direction from an air inlet at an aft end of the core to an outlet at a forward end of the core. A propeller is disposed forward of the outlet. A reduction gearbox (RGB) is drivingly engaged to the core. An electric motor is drivingly engaged to the propeller and disposed axially between the RGB and the propeller.

An energy storage plant includes a casing for the storage of a working fluid different from atmospheric air, in gaseous phase and in pressure equilibrium with the atmosphere; and a tank for the storage of said working fluid in liquid or super-critical phase with a temperature close to the critical temperature. The critical temperature is close to the ambient temperature. The plant is configured to perform a closed cyclic thermodynamic transformation, first in one direction in a charge configuration and then in an opposite direction in a discharge configuration, between said casing and said tank. In the charge configuration the plant stores heat and pressure and in the discharge configuration generates mechanical energy to drive a driven machine.

An impeller attach mechanism for a turbocharger including a stud extending from a central bore of a compressor impeller toward a turbine wheel, the stud having a first threaded region and a second threaded region; a shaft coupled to the turbine wheel and extending toward the compressor impeller, the shaft having a leading portion, the leading portion having a threaded interior configured to engage the second threaded region of the stud; and an insert having an internal portion and an external portion, the internal portion having a threaded external surface to engage the compressor impeller, the internal portion having a threaded internal surface to engage the first threaded region of the stud, the external portion configured to surround the leading portion of the shaft.