Methods and systems of operating a gas turbine engine in a low-power condition are provided. In one embodiment, the method includes supplying fuel to a combustor by supplying fuel to a first fuel manifolds and a second fuel manifold of the gas turbine engine. The method also includes, while supplying fuel to the combustor by supplying fuel to the first fuel manifold: stopping supplying fuel to the second fuel manifold; and using a pump to drive gas into the second fuel manifold to flush fuel in the second fuel manifold into the combustor and hinder coking in the second fuel manifold and associated fuel nozzles.

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 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.

An aircraft propulsion system is disclosed and includes a first gas turbine engine including a first input shaft driving a first gear system, a first fan driven by the first gear system, a first generator supported on the first input shaft and a fan drive electric motor providing a drive input to the first fan, a second gas turbine engine including a second input shaft driving a second gear system, a second fan driven by the second gear system, a second generator supported on the second input shaft and a second fan drive electric motor providing a drive input to the second fan and a controller controlling power output from each of the first and second generators and directing the power output between each of the first and second fan drive electric motors.

There are described methods and systems for operating an aircraft having two or more engines. One method comprises operating the two or more engines of the aircraft in an asymmetric operating regime, wherein a first of the engines is in an active mode to provide motive power to the aircraft and a second of the engines is in a standby mode to provide substantially no motive power to the aircraft; governing the first engine in the active mode using a first governing logic; and governing the second engine in the standby mode using a second governing logic, the second governing logic based on a target compressor speed and variable geometry mechanism (VGM) settings that are adjusted using trim values dependent on at least one parameter of the second engine in the standby mode.

There are described methods and systems for operating an aircraft having two or more engines. One method comprises operating the two or more engines of the aircraft in an asymmetric operating regime, wherein a first of the engines is in an active mode to provide motive power to the aircraft and a second of the engines is in a standby mode to provide substantially no motive power to the aircraft; governing the first engine in the active mode using a first governing logic; and governing the second engine in the standby mode using a second governing logic, the second governing logic based on a target compressor speed and variable geometry mechanism (VGM) settings that are adjusted using trim values dependent on at least one parameter of the second engine in the standby mode.

A turboshaft engine for a rotorcraft includes a first spool and an independently rotatable second spool. The first spool includes a low pressure compressor, a first set of variable guide vanes disposed at an entry of the low pressure compressor, and a low pressure turbine drivingly engaged to the low pressure compressor. The second spool includes a high pressure compressor, a second set of variable guide vanes disposed at an entry of the high pressure compressor, the second set of variable guide vanes independently operable relative to the first set of variable guide vanes, and a high pressure turbine drivingly engaged to the high pressure compressor. One or both of the low pressure compressor and the high pressure compressor includes a mixed flow rotor.

A turboshaft engine for a rotorcraft includes a first spool and an independently rotatable second spool. The first spool includes a low pressure compressor, a first set of variable guide vanes disposed at an entry of the low pressure compressor, and a low pressure turbine drivingly engaged to the low pressure compressor. The second spool includes a high pressure compressor, a second set of variable guide vanes disposed at an entry of the high pressure compressor, the second set of variable guide vanes independently operable relative to the first set of variable guide vanes, and a high pressure turbine drivingly engaged to the high pressure compressor. One or both of the low pressure compressor and the high pressure compressor includes a mixed flow rotor.

Methods and systems for operating a rotorcraft comprising a plurality of engines are provided. A request to enter into an asymmetric operating regime (AOR), in which at least one active engine of the plurality of engines is operated in an active mode to provide motive power to the rotorcraft and at least one standby engine of the plurality of engines is operated in a standby mode to provide substantially no motive power, is obtained. Engine usage data for the plurality of engines, including at least one first engine and at least one second engine, is determined. Based on the engine usage data, one of the at least one first and second engines is operated as the at least one active engine for the AOR, and the other one of the at least one first and second engines is operated as the at least one standby engine for the AOR.

Methods and systems for operating a rotorcraft comprising a plurality of engines are provided. A request to enter into an asymmetric operating regime (AOR), in which at least one active engine of the plurality of engines is operated in an active mode to provide motive power to the rotorcraft and at least one standby engine of the plurality of engines is operated in a standby mode to provide substantially no motive power, is obtained. Engine usage data for the plurality of engines, including at least one first engine and at least one second engine, is determined. Based on the engine usage data, one of the at least one first and second engines is operated as the at least one active engine for the AOR, and the other one of the at least one first and second engines is operated as the at least one standby engine for the AOR.