A gas turbine engine assembly according to an exemplary aspect of the present disclosure includes, among other things, a geared architecture configured to rotatably couple a turbine and a compressor of an engine to rotate the compressor at a different speed than the turbine and a fan. A method of adjusting rotational speeds within a gas turbine engine is also disclosed.

A gas turbine engine having a reverse travelling wave first flap mode, Fan RTW, and including a fan located upstream of the engine core; a fan shaft; a front engine structure arranged to support the fan shaft and having a front engine structure nodding mode including a pair of modes at similar, but not equal, natural frequencies in orthogonal directions; and a gearbox. An LP rotor system including the fan system and a gearbox output shaft arranged to drive the fan shaft first reverse and first forward whirl rotor dynamic modes, Rotor RW, and 1FW. The engine has a maximum take-off speed, MTO. A mutual frequency margin of:

[00001]

A highly efficient gas turbine engine includes the fan of the gas turbine engine driven from a turbine via a gearbox, such that the fan has a lower rotational speed than the driving turbine, thereby providing efficiency gains. The efficient fan system is mated to a core that has low cooling flow requirements and/or high temperature capability, and which may have particularly low mass for a given power.

A highly efficient gas turbine engine includes the fan of the gas turbine engine driven from a turbine via a gearbox, such that the fan has a lower rotational speed than the driving turbine, thereby providing efficiency gains. The efficient fan system is mated to a core that has low cooling flow requirements and/or high temperature capability, and which may have particularly low mass for a given power.

A gas turbine engine for an aircraft includes a fan system having a reverse travelling wave first flap mode, Fan RTW, and including a fan located upstream of the engine core; a fan shaft; and a front engine structure arranged to support the fan shaft and having a front engine structure nodding mode comprising a pair of modes at similar, but not equal, natural frequencies in orthogonal directions; and a gearbox. An LP rotor system including the fan system and a gearbox output shaft arranged to drive the fan shaft has a first reverse whirl rotor dynamic mode, Rotor RW, and a first forward whirl rotor dynamic mode, 1FW. The engine has a maximum take-off speed, MTO. A backward whirl frequency margin of:

[00001]$\frac{\begin{array}{c}\mathrm{the}\mathrm{lowest}\mathrm{frequency}\mathrm{of}\mathrm{either}\mathrm{mode}\mathrm{Fan}\mathrm{RTW}\mathrm{or}\mathrm{Rotor}\mathrm{RW}\mathrm{at}\\ \mathrm{the}\mathrm{MTO}\mathrm{speed}\end{array}}{\mathrm{the}\mathrm{MTO}\mathrm{speed}}$

may be in the range from 15 to 50%.

A gas turbine engine for an aircraft includes a fan system having a reverse travelling wave first flap mode, Fan RTW, and including a fan located upstream of the engine core; a fan shaft; and a front engine structure arranged to support the fan shaft and having a front engine structure nodding mode comprising a pair of modes at similar, but not equal, natural frequencies in orthogonal directions; and a gearbox. An LP rotor system including the fan system and a gearbox output shaft arranged to drive the fan shaft has a first reverse whirl rotor dynamic mode, Rotor RW, and a first forward whirl rotor dynamic mode, 1FW. The engine has a maximum take-off speed, MTO. A backward whirl frequency margin of:

[00001]$\frac{\begin{array}{c}\mathrm{the}\mathrm{lowest}\mathrm{frequency}\mathrm{of}\mathrm{either}\mathrm{mode}\mathrm{Fan}\mathrm{RTW}\mathrm{or}\mathrm{Rotor}\mathrm{RW}\mathrm{at}\\ \mathrm{the}\mathrm{MTO}\mathrm{speed}\end{array}}{\mathrm{the}\mathrm{MTO}\mathrm{speed}}$

may be in the range from 15 to 50%.

A gas turbine engine for an aircraft includes a fan system including a fan located upstream of the engine core; a fan shaft; and a front engine structure arranged to support the fan shaft and having a front engine structure nodding mode including a pair of modes at similar, but not equal, natural frequencies in orthogonal directions; and a gearbox. An LP rotor system including the fan system and a gearbox output shaft arranged to drive the fan shaft has a first forward whirl rotor dynamic mode, 1FW. The engine has a maximum take-off speed, MTO. A forward whirl frequency margin of:

[00001]$\frac{\begin{array}{c}\begin{array}{c}\mathrm{the}\mathrm{frequency}\mathrm{difference}\mathrm{between}\mathrm{the}\mathrm{intersection}\mathrm{of}1\mathrm{FW}\mathrm{and}\\ \mathrm{the}\mathrm{first}\mathrm{engine}\mathrm{order}\mathrm{line}\mathrm{and}\mathrm{the}\mathrm{first}\mathrm{engine}\mathrm{order}\end{array}\\ \mathrm{at}\end{array}}{}$

A hybrid multi-spool gas turbine engine, has: a LP spool and a HP spool rotatable about a central axis, the LP spool having an LP compressor and an LP turbine engaged to the LP compressor via an LP shaft, the LP shaft engaged to a rotatable load at a first end thereof, the HP spool having an HP turbine and an HP compressor engaged to the HP turbine via a HP shaft; an accessory gearbox (AGB) engaged to both of the LP shaft and the HP shaft and located proximate a second end thereof, the AGB having at least one accessory output drivingly engageable to at least one accessory and at least one input; and at least one electric motor drivingly engaged to the at least one input of the AGB, the at least one electric motor drivingly engaged to the rotatable load via the AGB and the LP shaft.

A hybrid multi-spool gas turbine engine, has: a LP spool and a HP spool rotatable about a central axis, the LP spool having an LP compressor and an LP turbine engaged to the LP compressor via an LP shaft, the LP shaft engaged to a rotatable load at a first end thereof, the HP spool having an HP turbine and an HP compressor engaged to the HP turbine via a HP shaft; an accessory gearbox (AGB) engaged to both of the LP shaft and the HP shaft and located proximate a second end thereof, the AGB having at least one accessory output drivingly engageable to at least one accessory and at least one input; and at least one electric motor drivingly engaged to the at least one input of the AGB, the at least one electric motor drivingly engaged to the rotatable load via the AGB and the LP shaft.

The invention relates to an aircraft comprising a fuselage (1), which is propelled by a turbine engine with two coaxial fans, namely an upstream fan (7) and a downstream fan (8), driven by two contra-rotating rotors (5, 6) of a power turbine (3). The two fans (7, 8) and the turbine (3) are integrated into a nacelle (14) which projects downstream from the fuselage (1) and through which air flows. According to the invention, at least one of the fans (7, 8) of the aircraft and, in particular, the downstream fan (8) comprises variable-spacing blades, and at least one stator-forming variable-spacing blade ring (25) in the aircraft is placed upstream of the upstream fan (7). The variable-spacing stator blades (25) and the variable-spacing blades of the downstream fan (8) are mutually configured to direct the air flow in a first mode in which the air flows through the nacelle (14) from upstream to downstream and in a second mode in which the air is pushed back upstream through the nacelle (14).