A method is provided of operating a single unducted rotor engine, the single unducted rotor engine comprising a single stage of unducted rotor blades. The method includes operating the single unducted rotor engine to define a flight speed, V.sub.0, in a length unit per second and an angular speed, n, in revolutions per second, the single stage of unducted rotor blades defining a diameter, D, in the length unit; wherein operating the single unducted rotor engine comprises operating the single unducted rotor engine to define an advance ratio greater than 3.8 while operating the single unducted rotor engine at a net efficiency of at least 0.8, the advance ratio defined by the equation V.sub.0/(nD).

A gas turbine engine is provided. The gas turbine engine includes a turbomachine comprising a low speed spool; a rotor assembly coupled to the low speed spool; an electric machine mechanically coupled to the low speed spool at a connection point of the low speed spool; and a clutch positioned in the torque path of the low speed spool between the connection point and the rotor assembly

A hybrid propulsion system for an aircraft can include a propulsor assembly having at least one propulsor and a power generation system. The power generation system can include a first power assembly, a second power assembly, a first electric machine, and a second electric machine. The first power assembly can be drivingly coupled to the first electric machine to produce a first amount of electric power. The second power assembly can be drivingly coupled to the second electric machine to produce a second amount of electric power. A controller can be operably coupled to the first power assembly, the first electric machine, or both and to the second power assembly, the second power assembly, or both. The controller can be configured to combine at least a portion of the first and second amount of power for electric transfer to the propulsor assembly.

This method for managing the exiting of a specific-consumption mode of an aircraft comprises a step of identifying a need to reactivate a turbine engine in the nominal mode of said turbine engine, and a step of: normal reactivation of the turbine engine in the nominal mode for the turbine engine for a first duration when a first condition is met; accelerated reactivation of the turbine engine in the nominal mode for the turbine engine for a second duration when a second condition is met; rapid reactivation of the turbine engine in the nominal mode of the turbine engine for a third duration when a third condition is met, the first duration being longer than the second duration, and the second duration being longer than the third duration.