Aircraft power plants including combustion engines, and associated methods for recuperating waste heat from such aircraft power plants are described. A method includes transferring the heat rejected by the internal combustion engine to supercritical CO.sub.2 (sCO.sub.2) used as a working fluid in a heat engine. The heat engine converts at least some the heat transferred to the sCO.sub.2 to mechanical energy to perform useful work onboard the aircraft.

A hybrid electric gas turbine engine includes a fan section having a fan, a turbine section having a turbine drivably connected to the fan through a main shaft that extends along a central longitudinal axis, a gas generating core extending along a first axis that is radially offset from the central longitudinal axis, a first electric motor drivably connected to the main shaft, wherein the electric motor is colinear with the main shaft, and an electric compressor extending along a second axis that is radially offset from the central longitudinal axis, the electric compressor in fluid communication with the second turbine section.

A compound engine assembly including an air conduit having an inlet in fluid communication with ambient air around the compound engine assembly, a compressor having an inlet in fluid communication with the air conduit, an engine core including at least one rotary internal combustion engine and having an inlet in fluid communication with an outlet of the compressor, a turbine section having an inlet in fluid communication with an outlet of the engine core and configured to compound power with the engine core; and at least one heat exchanger in fluid communication with the air conduit, each heat exchanger configured to circulate a fluid of the engine assembly in heat exchange relationship with an airflow from the air conduit circulating therethrough. A method of supplying air to a compound engine assembly is also discussed.

A compound engine assembly including an air conduit having an inlet in fluid communication with ambient air around the compound engine assembly, a compressor having an inlet in fluid communication with the air conduit, an engine core including at least one rotary internal combustion engine and having an inlet in fluid communication with an outlet of the compressor, a turbine section having an inlet in fluid communication with an outlet of the engine core and configured to compound power with the engine core; and at least one heat exchanger in fluid communication with the air conduit, each heat exchanger configured to circulate a fluid of the engine assembly in heat exchange relationship with an airflow from the air conduit circulating therethrough. A method of supplying air to a compound engine assembly is also discussed.

A hybrid-electric propulsion system includes a gas turbine engine, an electric machine coupled to and rotatably driven by the gas turbine engine to produce AC electric power, an energy storage system, and a propulsion unit. The gas turbine engine includes a combustor and a recuperator that places an exhaust air flow that is downstream from the combustor in a heat exchange relationship with a compressed air flow that is upstream from the combustor to transfer thermal energy from the exhaust flow to the compressed flow. The propulsion unit includes a fan and an electric motor rotably coupled to the fan, the electric motor being driven by electric power from one of the electric machine or the energy storage system.

A propulsion system for an aircraft includes an electric propulsion engine configured to be mounted to the aircraft at an aft end of the aircraft. The electric propulsion engine includes a fan rotatable about a central axis of the electric propulsion engine. The fan includes a fan shaft mechanically coupled to a power gearbox. The electric propulsion engine also includes an electric motor having a driveshaft, with the electric motor coupled to the power gearbox through the drive shaft. The electric motor rotates the fan through the power gearbox. The driveshaft includes a flexible element for accommodating a misalignment of the electric motor and the power gearbox.

A propulsion system for an aircraft includes an electric propulsion engine configured to be mounted to the aircraft at an aft end of the aircraft. The electric propulsion engine includes a fan rotatable about a central axis of the electric propulsion engine. The fan includes a fan shaft mechanically coupled to a power gearbox. The electric propulsion engine also includes an electric motor having a driveshaft, with the electric motor coupled to the power gearbox through the drive shaft. The electric motor rotates the fan through the power gearbox. The driveshaft includes a flexible element for accommodating a misalignment of the electric motor and the power gearbox.

A propulsion system for an aircraft includes an electric propulsion engine configured to be mounted to the aircraft at an aft end of the aircraft. The electric propulsion engine includes a power gearbox mechanically coupled to an electric motor. The electric propulsion engine further includes a fan rotatable about a central axis of the electric propulsion engine by the electric motor through the power gearbox. Moreover, the electric propulsion engine includes an attachment assembly for mounting at least one of the electric motor or the power gearbox. The attachment assembly includes a torsional damper for accommodating a torsional vibration of the electric motor or the power gearbox.

A propulsion system for an aircraft includes an electric propulsion engine configured to be mounted to the aircraft at an aft end of the aircraft. The electric propulsion engine includes a power gearbox mechanically coupled to an electric motor. The electric propulsion engine further includes a fan rotatable about a central axis of the electric propulsion engine by the electric motor through the power gearbox. Moreover, the electric propulsion engine includes an attachment assembly for mounting at least one of the electric motor or the power gearbox. The attachment assembly includes a torsional damper for accommodating a torsional vibration of the electric motor or the power gearbox.

A hybrid-electric propulsion system for an aircraft is provided herein that can include a propulsor and a turbomachine comprising a high pressure turbine drivingly coupled to a high pressure compressor through a high pressure spool. An auxiliary power unit can be operably coupled with a starter motor. An electrical system can comprise a first electric machine coupled to the turbomachine. The first electric machine can be separate from the starter motor. A controller can be configured to provide electrical power from an electric power source to the first electric machine to drive the first electric machine to start, or assist with starting, the turbomachine.