Methods and systems for operating an aircraft having two or more engines are described. The 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, receiving a request to exit the asymmetric operating regime, the request having at least one parameter associated therewith, selecting one of a plurality of available exit protocols as a function of the at least one parameter, and applying the exit protocol by commanding the engines accordingly.

A method of operating an engine of a multi-engine aircraft includes sequentially operating the engine through a plurality of cycles, each cycle including a breathing-in phase followed by a breathing-out phase. The breathing-in phase includes: i) in response to a speed of a rotor of the engine being at a sub-idle threshold, opening variable guide vanes upstream a compressor and injecting fuel into the combustor to increase rotor speed to a pre-determined upper threshold, and then ii) in response to the rotor speed reaching the pre-determined upper threshold, reducing a supply rate of fuel into the combustor and substantially closing the variable guide vanes. The breathing-out phase includes maintaining the variable guide vanes closed at least until the speed drops from the pre-determined upper threshold to the pre-determined sub-idle threshold.

A method of operating an engine of a multi-engine aircraft includes sequentially operating the engine through a plurality of cycles, each cycle including a breathing-in phase followed by a breathing-out phase. The breathing-in phase includes: i) in response to a speed of a rotor of the engine being at a sub-idle threshold, opening variable guide vanes upstream a compressor and injecting fuel into the combustor to increase rotor speed to a pre-determined upper threshold, and then ii) in response to the rotor speed reaching the pre-determined upper threshold, reducing a supply rate of fuel into the combustor and substantially closing the variable guide vanes. The breathing-out phase includes maintaining the variable guide vanes closed at least until the speed drops from the pre-determined upper threshold to the pre-determined sub-idle threshold.

An aircraft propulsion system includes a fan section that includes a fan shaft that is rotatable about a fan axis. The fan shaft includes a fan gear. The aircraft propulsion system also includes a boost turbine engine that includes a first output shaft that includes a first gear that is coupled to the fan gear. The boost turbine engine has a first maximum power capacity. The aircraft propulsion system further includes a cruise gas turbine engine that includes a second output shaft that includes a second gear that is coupled to the fan gear. The cruise turbine engine has a second maximum power capacity that is less than the first maximum power capacity of the boost turbine engine. The fan section produces a thrust that corresponds to power input through the fan gear from the boost turbine engine and the cruise turbine engine.

Methods for monitoring engine health of an aircraft having a first engine and a second engine are provided. In one example, the method includes obtaining a first turbine gas temperature of the first engine and a second engine turbine gas temperature of the second engine from a first flight. The first turbine gas temperature and the second turbine gas temperature are related to each other to define a first value. The first value is compared to a data set for monitoring the engine health.

There are provided a gas turbine system and a gas turbine power generator that can achieve an increase in output power and a decrease in fuel efficiency together and curb an increase in cost and weight. There is also provided a gas turbine system that can stably supply a necessary amount of air to a combustor even when a compressor and a turbine on one side are stopped. The gas turbine system 1 includes a plurality of gas turbine units 2 and 3, a single combustor 4, a plurality of pipes 5, a plurality of on-off valves 6, and a control unit 7. In a first operation mode, the control unit 7 controls switching-on/off of the on-off valves 6 such that air is supplied to the combustor 4 from a first compressor 21 and a second compressor 31. In a second operation mode, the control unit 7 controls switching-on/off of the on-off valves 6 such that air compressed in stages while sequentially passing through the first compressor 21 and the second compressor 31 is supplied to the combustor 4, and supplies air to turbines such that they can be expanded in stages.

Systems and method for filling a fuel manifold comprising at least a primary and a second manifold of a gas turbine engine are described. The method comprises providing fuel flow to the secondary manifold of the gas turbine engine, the secondary manifold being partly or completely empty; monitoring at least one engine operational parameter of the gas turbine engine as fuel fills the secondary manifold; and accelerating the engine when a transition threshold is reached, the transition threshold being associated with the engine operational parameter and indicative that fuel has reached the combustor.

Systems and method for filling a fuel manifold comprising at least a primary and a second manifold of a gas turbine engine are described. The method comprises providing fuel flow to the secondary manifold of the gas turbine engine, the secondary manifold being partly or completely empty; monitoring at least one engine operational parameter of the gas turbine engine as fuel fills the secondary manifold; and accelerating the engine when a transition threshold is reached, the transition threshold being associated with the engine operational parameter and indicative that fuel has reached the combustor.

A hybrid-electric propulsion system for an aircraft includes a turbomachine, the turbomachine including a first spool and a second spool. A method for operating the hybrid electric propulsion system includes operating, by one or more computing devices, the turbomachine such that the first spool mechanically drives a prime propulsor of the hybrid-electric propulsion system; and modifying, by the one or more computing devices, a speed relationship parameter defined between the first spool and second spool by providing electrical power to, or drawing electrical power from, an electric machine mechanically coupled to the first spool, the second spool, or both.

An aspect includes a method for motoring control for multiple engines of an aircraft is provided. A controller can determine a motoring time of a first engine starting system to cool a first engine. The controller can compare the motoring time of the first engine starting system with a motoring time of one or more other engine starting systems of one or more other engines of the aircraft. The motoring time of the first engine starting system can be controlled relative to a tolerance of the motoring time of the one or more other engine starting systems by adjusting the motoring time of the first engine starting system relative to the one or more other engine starting systems in a motoring sequence based on comparing the motoring time of the first engine starting system with the motoring time of the one or more other engine starting systems.