Gas turbine engine having gearbox support shear stress ratio

Abstract

A gas turbine engine for an aircraft including an engine core including a turbine, compressor, and core shaft connecting the turbine and compressor; a fan located upstream of the engine core including a plurality of fan blades; a gearbox that can receive input from the core shaft and can output drive to the fan at a lower rotational speed than the core shaft, an epicyclic gearbox including a sun gear, planet gears, a ring gear, and a planet carrier on which the planet gears are mounted; and a gearbox support. A first gearbox support shear stress ratio: $\frac{\begin{matrix} torsional shear stress of the gearbox support \\ at maxiumum take off conditions \end{matrix}}{radial bending stiffness of the gearbox support}$
is less than or equal to 4.9×10.sup.1 m.sup.−1, and/or a second gearbox ratio: $\frac{\begin{matrix} torsional shear stress of the gearbox support \\ at maximum take off conditions \end{matrix}}{tilt stiffness of the gearbox support}$
is less than or equal to 4.1×10.sup.3 rad/m.sup.3.

Claims

1. A gas turbine engine for an aircraft comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; a gearbox that is configured to: (i) receive an input from the core shaft, and (ii) output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox being an epicyclic gearbox comprising a sun gear, a plurality of planet gears, a ring gear, and a planet carrier on which the plurality of planet gears is mounted; and a gearbox support arranged to at least partially support the gearbox within the gas turbine engine, wherein: the gas turbine engine is configured to have a first gearbox support shear stress ratio of: $\frac{\begin{matrix} a torsional shear stress of the gearbox \\ support at maximum take - off conditions \end{matrix}}{a radial bending stiffness of the gearbox support}$ in a range from 3.5×10.sup.−1 m.sup.−1 to 4.9×10.sup.1 m.sup.−1; and the maximum take-off conditions are defined as conditions when the gas turbine engine is operated at maximum take-off thrust at International Standard Atmosphere (ISA) sea level pressure and temperature +15° C. with a fan inlet velocity of between 0.25 and 0.27 Mach Number (Mn).

2. The gas turbine engine according to claim 1, wherein the gas turbine engine is configured such that the first gearbox support shear stress ratio is in a range from 0.70 m.sup.−1 to 20 m.sup.−1.

3. The gas turbine engine according to claim 1, wherein the radial bending stiffness of the gearbox support is in a range from 1.0×10.sup.7 N/m to 4.0×10.sup.8 N/m.

4. The gas turbine engine according to claim 1, wherein the radial bending stiffness of the gearbox support is in a range from 3.0×10.sup.7 N/m to 2.0×10.sup.8 N/m.

5. The gas turbine engine according to claim 1, wherein the gas turbine engine is configured such that the torsional shear stress of the gearbox support at the maximum take-off conditions is in a range from 1.40×10.sup.8 N/m.sup.2 to 4.90×10.sup.8 N/m.sup.2.

6. The gas turbine engine according to claim 1, wherein the gas turbine engine is configured such that the torsional shear stress of the gearbox support at the maximum take-off conditions is in a range from 2.0×10.sup.8 N/m.sup.2 to 3.5×10.sup.8 N/m.sup.2.

7. The gas turbine engine of claim 1, wherein: a) a diameter of the fan is in a range from 240 cm to 280 cm, and the gas turbine engine is configured such that the first gearbox support shear stress ratio is in a range from 0.70 m.sup.−1 to 35 m.sup.−1; or b) the diameter of the fan is in a range from 330 cm to 380 cm, and the gas turbine engine is configured such that the first gearbox support shear stress ratio is in a range from 0.50 m.sup.−1 to 12 m.sup.−1.

8. The gas turbine engine according to claim 1, wherein the gas turbine engine is configured to have a second gearbox support shear stress ratio of: $\frac{\begin{matrix} the torsional shear stress of the gearbox \\ support at maximum take - off conditions \end{matrix}}{a tilt stiffness of the gearbox support}$ in a range from 6.6 rad/m.sup.3 to 4.1×10.sup.3 rad/m.sup.3.

9. The gas turbine engine according to claim 1, wherein at least one of the following is satisfied: a) the torsional strength of the gearbox support is in a range from 1.60×10.sup.5 Nm to 2.00×10.sup.7 Nm; b) a cross sectional area of the gearbox is in a range from 2.4×10.sup.−1 m.sup.2 to 1.10 m.sup.2; and c) a planet gear spacing angle in radians (β) is defined as 2π/N, where N is the number of planet gears, and the planet gear spacing angle (β) is in a range from 9.0×10.sup.−1 rad to 2.1 rad.

10. The gas turbine engine according to claim 1, wherein the gas turbine engine is configured such that a torque transmitted through the gearbox support, at the maximum take-off conditions, is in a range from 6.00×10.sup.4 Nm to 5.00×10.sup.5 Nm.

11. The gas turbine engine according to claim 10, wherein: a) the gearbox is in a planetary configuration, and the gas turbine engine is configured such that the torque transmitted through the gearbox support, at the maximum take-off conditions, is in a range from 6.00×10.sup.4 Nm to 3.00×10.sup.5 Nm; or b) the gearbox is in a star configuration, and the gas turbine engine is configured such that the torque transmitted through the gearbox support, at the maximum take-off conditions, is in a range from 1.10×10.sup.5 Nm to 5.00×10.sup.5 Nm.

12. The gas turbine engine according to claim 1, wherein: the gearbox has a gear ratio in a range of 3.2 to 4.5.

13. The gas turbine engine according to claim 1, wherein the gas turbine engine is configured to have a specific thrust in a range from 70 to 90 Nkg{circumflex over ( )}−1.

14. The gas turbine engine according to claim 1, wherein: the gas turbine engine is configured to have a bypass ratio at cruise conditions in a range of 12.5 to 18, and the cruise conditions are defined as: (i) conditions at mid-cruise of an aircraft to which the gas turbine engine is attached, or (ii) conditions experienced by the aircraft and the gas turbine engine at a midpoint between a top of a climb and a start of a descent.

15. The gas turbine engine according to claim 1, wherein the fan has a fan diameter greater than 240 cm and less than or equal to 380 cm.

16. A gas turbine engine for an aircraft comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; a gearbox that is configured to: (i) receive an input from the core shaft, and (ii) output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox being an epicyclic gearbox comprising a sun gear, a plurality of planet gears, a ring gear, and a planet carrier on which the plurality of planet gears is mounted; and a gearbox support arranged to at least partially support the gearbox within the gas turbine engine, wherein: the gas turbine engine is configured to have a first gearbox support shear stress ratio of: $\frac{\begin{matrix} a torsional shear stress of the gearbox \\ support at maximum take - off conditions \end{matrix}}{a tilt stiffness of the gearbox support}$ in a range from 6.6 rad/m.sup.3 to 4.1×10.sup.3 rad/m.sup.3; and the maximum take-off conditions are defined as conditions when the gas turbine engine is operated at maximum take-off thrust at International Standard Atmosphere (ISA) sea level pressure and temperature +15° C. with a fan inlet velocity of between 0.25 and 0.27 Mach Number (Mn).

17. The gas turbine engine according to claim 16, wherein the gas turbine engine is configured such that the first gearbox support shear stress ratio is in a range from 1.25×10.sup.1 rad/m.sup.3 to 1.4×10.sup.3 rad/m.sup.3.

18. The gas turbine engine according to claim 16, wherein: a) the tilt stiffness of the gearbox support is in a range from 1.2×10.sup.5 Nm/rad to 2.1×10.sup.7 Nm/rad; and/or b) the gas turbine engine is configured such that the torsional shear stress of the gearbox support at the maximum take-off conditions is in a range from 1.40×10.sup.8 N/m.sup.2 to 4.90×10.sup.8 N/m.sup.2.

19. The gas turbine engine according to claim 16, wherein: a) a diameter of the fan is in a range from 240 cm to 280 cm, and the gas turbine engine is configured such that the first gearbox support shear stress ratio is in a range from 2.9×10.sup.1 rad/m.sup.3 to 2.9×10.sup.3 rad/m.sup.3; or b) the diameter of the fan is in a range from 330 cm to 380 cm, and the gas turbine engine is configured such that the first gearbox support shear stress ratio is in a range from 1.0×10.sup.1 rad/m.sup.3 to 7.0×10.sup.2 rad/m.sup.3.

20. The gas turbine engine according to claim 16, wherein the gas turbine engine is configured to have a second gearbox support shear stress ratio of: $\frac{\begin{matrix} the torsional shear stress of the gearbox \\ support at maximum take - off conditions \end{matrix}}{a radial bending stiffness of the gearbox support}$ in a range from 3.5×10.sup.−1 m.sup.−1 to 4.9×10.sup.1 m.sup.−1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments will now be described by way of example only, with reference to the Figures, in which:

(2) FIG. 1 is a sectional side view of a gas turbine engine;

(3) FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

(4) FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

(5) FIG. 4 is a schematic diagram illustrating the radial bending stiffness of a cantilevered beam;

(6) FIG. 5 is a schematic diagram illustrating the tilt stiffness of a cantilevered beam;

(7) FIG. 6 is a schematic diagram illustrating the torsional stiffness of a shaft;

(8) FIG. 7 is a close up sectional view of the region of a gas turbine engine around its gearbox;

(9) FIGS. 8 and 9 are schematic diagrams illustrating how the radial bending stiffness of a gearbox support may be defined;

(10) FIGS. 10 and 11 are schematic diagrams illustrating how the tilt stiffness of a gearbox support may be defined;

(11) FIG. 12 shows a schematic sectional view of a gearbox support used with a gearbox in a star configuration;

(12) FIG. 13 shows a schematic sectional view of a gearbox support used with a gearbox in a planetary configuration;

(13) FIG. 14 is a schematic diagram illustrating an alternative interface between a fan shaft and fan;

(14) FIGS. 15 and 16 are schematic diagrams illustrating how fan shaft end radial bending stiffnesses may be defined;

(15) FIGS. 17 and 18 are schematic diagrams illustrating how fan shaft end tilt stiffnesses may be defined;

(16) FIG. 19 shows an aircraft having a gas turbine engine attached to each wing;

(17) FIG. 20 shows a method of operating a gas turbine engine on an aircraft; and

(18) FIG. 21 shows a graph of applied load against displacement to illustrate measurement of the stiffness of a component.

DETAILED DESCRIPTION

(19) FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

(20) In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

(21) An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun wheel, or sun gear, 28 of the epicyclic gear arrangement 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to precess around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

(22) The linkages 36 may be referred to as a fan shaft 36, the fan shaft 36 optionally comprising two or more shaft portions coupled together. For example, the fan shaft 36 may comprise a gearbox output shaft portion 36a extending from the gearbox 30 and a fan portion 36b extending between the gearbox output shaft portion and the fan 23. In the embodiment shown in FIGS. 1 and 2, the gearbox 30 is a planetary gearbox and the gearbox output shaft portion 36a is connected to the planet carrier 34—it may therefore be referred to as a carrier output shaft 36a. In star gearboxes 30, the gearbox output shaft portion 36a may be connected to the ring gear 38—it may therefore be referred to as a ring output shaft 36a. In the embodiment shown in FIGS. 1 and 2, the fan portion 36b of the fan shaft 36 connects the gearbox output shaft portion 36a to the fan 23. The output of the gearbox 30 is therefore transferred to the fan 23, to rotate the fan, via the fan shaft 36. In alternative embodiments, the fan shaft 36 may comprise a single component, or more than two components. Unless otherwise indicated or apparent to the skilled person, anything described with respect to an engine 10 with a star gearbox 30 may equally be applied to an engine with a planetary gearbox 30, and vice versa.

(23) Note that the terms “low pressure turbine” and “low pressure compressor” as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the “low pressure turbine” and “low pressure compressor” referred to herein may alternatively be known as the “intermediate pressure turbine” and “intermediate pressure compressor”. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

(24) The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the claimed invention. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

(25) The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

(26) It will be appreciated that the arrangement shown in FIGS. 2 and 3 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 2 example) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have any desired degree of stiffness or flexibility as defined or claimed elsewhere herein.

(27) By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 2 (for example as described in connection with other embodiments disclosed herein which have a star gearbox arrangement).

(28) Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

(29) Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

(30) Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 18, 20 meaning that the flow through the bypass duct 22 has its own nozzle 18 that is separate to and radially outside the core engine nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area.

(31) Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example.

(32) The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

(33) The following general definitions of stiffnesses may be used herein:

(34) Radial Bending Stiffness

(35) A radial bending stiffness is a measure of deformation for a given force applied in any one selected radial direction (i.e. any direction perpendicular to and passing through the engine axis). The radial bending stiffness is defined with reference to FIG. 4 in terms of the deformation of a cantilevered beam 401. As illustrated in FIG. 4, a force, F, applied at the free end of the beam in a direction perpendicular to the longitudinal axis of the beam causes a linear perpendicular deformation, δ. The radial bending stiffness is the force applied for a given linear deformation i.e. F/δ. In the present application, the radial bending stiffness is taken relative to the rotational axis of the engine 9, and so relates to the resistance to linear deformation in a radial direction of the engine caused by a radial force. The beam, or equivalent cantilevered component, extends along the axis of rotation of the engine, the force, F, is applied perpendicular to the axis of rotation of the engine, along any radial direction, and the displacement δ is measured perpendicular to the axis of rotation, along the line of action of the force. The radial bending stiffness as defined herein has SI units of N/m. In the present application, unless otherwise stated, the radial bending stiffness is taken to be a free-body stiffness i.e. stiffness measured for a component in isolation in a cantilever configuration, without other components present which may affect its stiffness.

(36) When the force is applied perpendicular to the cantilevered beam, and at the free end of the beam, the resultant curvature is not constant but rather increases towards the fixed end of the beam.

(37) Tilt Stiffness

(38) A tilt stiffness is defined with reference to FIG. 5, which shows the resulting deformation of a cantilevered beam 401 under a moment M applied at its free end. The tilt stiffness is a measure of the resistance to rotation of a point on the component at which a moment is applied. As can be seen in FIG. 5, an applied moment at the free end of the cantilevered beam induces a constant curvature along the length of the beam between its free and fixed ends. The applied moment M causes a rotation θ of the point at which it is applied. For any component of constant section (like the beam), the angle θ is constant along the length of the component. The tilt stiffness as defined herein therefore has SI units of Nm/rad.

(39) Torsional Stiffness

(40) Torsional stiffness is a measure of deformation for a given torque. FIG. 6 illustrates the definition of the torsional stiffness of a shaft 401 or other body. A torque, τ, applied to the free end of the beam causes a rotational deformation, θ (e.g. twist) along the length of the beam. The torsional stiffness is the torque applied for a given angle of twist i.e. r/O. The torsional stiffness has SI units of Nm/rad.

(41) The following general definitions of other parameters may also be used herein:

(42) Torque

(43) Torque, which may also be referred to as moment, is the rotational equivalent of linear force, and can be thought of as a twist to an object. The magnitude, τ, of torque, τ, of a body depends on three quantities: the force applied (F), the lever arm vector connecting the origin to the point of force application (r), and the angle (A) between the force and lever arm vectors:
τ=r×F
τ=|τ|=|r×F|=|r∥F|sin A where τ is the torque vector and r is the magnitude of the torque; r is the position vector or “lever arm” vector (a vector from the selected point on the body to the point where the force is applied); F is the force vector; × denotes the cross product; and A is the angle between the force vector and the lever arm vector (sin(A) is therefore one when the force vector is perpendicular to the position vector, such that τ=rF, i.e. magnitude of the force multiplied by distance between the selected point on the body and the point of application of the force).

(44) Torque has dimensions of [force]×[distance] and may be expressed in units of Newton metres (N.Math.m).

(45) The net torque on a body determines the rate of change of the body's angular momentum.

(46) Moment of Inertia

(47) Moment of inertia, otherwise known as angular mass or rotational inertia, is a quantity that determines the torque needed for a desired angular acceleration of a body about a rotational axis—this is substantially equivalent to how mass determines the force needed for a particular acceleration.

(48) Moment of inertia depends on the body's mass distribution and the axis chosen, with larger moments requiring more torque to change the body's rotation rate. Moment of inertia has dimensions of [mass]×[distance].sup.2 and may be expressed in units of kilogram meter squared (kg.Math.m.sup.2). Moment of inertia I is defined as the ratio of the net angular momentum L of a body to its angular velocity ω around a principal axis:

(49) 0 $I = \frac{L}{ω}$

(50) Provided that the shape of the body does not change, its moment of inertia appears in Newton's law of motion as the ratio of an applied torque τ on a body to the angular acceleration a around the principal axis:
τ=Iα

(51) For bodies constrained to rotate in a plane, only the moment of inertia about an axis perpendicular to the plane matters, and I can therefore be represented as a scalar value. The skilled person would appreciate that a fan of a gas turbine engine (and more generally a fan rotor of the gas turbine engine comprising the fan disc and blades, and optionally also the fan shaft and/or other related components) is constrained to rotate in only one plane—a plane perpendicular to the engine axis—and that the fan's moment of inertia can therefore be defined by a single, scaler, value.

(52) The fan's moment of inertia about the engine axis can therefore be measured or defined using any standard methodology

(53) Torsional Shear Stress

(54) Shear stress is the component of stress coplanar with a material cross section; the stress tending to produce shear. Shear stress arises from a force vector component parallel to the cross section of the material. Shear stress may be defined as the external force acting on an object or surface parallel to the slope or plane in which it lies.

(55) When a shaft or other body is subjected to a torque, or twisting, a shearing stress is produced in the body—the shearing stress may be referred to as a torsional shear stress as it results from a torque. The shear stress varies from zero along the axis of the torque rotation to a maximum at the part of the body furthest from the axis; a radial distance from the axis at which the shear stress is to be measured is therefore selected. In the arrangements being described, a mid-height of the component of which the torsional shear stress is being measured is selected. For example, if the component has an outer radius of 20 cm, a mid-height position of 10 cm from the axis 9 is selected.

(56) Torsional shear stress has dimensions of [force]/[distance].sup.2 and may be expressed in units of Pascals (Pa) or Newtons/metre squared (N/m.sup.2).

(57) Shear Strength

(58) Shear strength is the strength of a body against the body failing in shear—Shear strength is a material's ability to resist forces that can cause the internal structure of the material to slide against itself. A shear load is a force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force.

(59) The ultimate shear strength of a material is the maximum shear stress that may be sustained before the material will rupture. The proof strength of a material is the stress at which a particular degree of permanent deformation occurs—for example, a 0.2% proof strength is the stress at which a 0.2% permanent deformation occurs.

(60) The strength of the body against shearing when a rotational, or twisting, shear load is applied may be referred to as torsional shear strength. The skilled person would appreciate that the shear strength of a component is important for selecting the dimensions and materials to be used for the manufacture or construction of the component. Shear strength has the same units as torsional shear stress, as it is a maximum supportable shear stress; it may therefore be expressed in units of Pa or N/m.sup.2.

(61) As used herein, the listed shear strength of a material is the 0.2% proof shear strength of the material unless otherwise specified. The skilled person would appreciate that this is lower than the ultimate shear strength.

(62) Shear strength of a material generally varies with temperature. The shear strength as used herein may be defined at room temperature.

(63) For metals (including metal alloys), shear strength generally decreases gradually with increasing temperature until a threshold temperature is reached, beyond which the material strength decreases rapidly. The shear strength may therefore be approximately constant below the threshold temperature. The threshold temperature may be around 400-500° C. for various steel grades. As the temperatures in and around the gearbox 30 generally do not exceed 120° C., well below the threshold temperature for likely materials for gearbox, gearbox support structure, and shaft construction, the shear strength may not be significantly different from the room temperature shear strength—the choice of a specific temperature for strength assessment may therefore have little effect.

(64) Torsional Strength

(65) The torsional strength of a specific component is defined as the ability of a component to withstand an applied torque without failure (i.e. without yield or structural failure). The torsional strength is therefore a measure of the torque capacity of a component. The torsional strength may be measured by applying a varying torque to a component and determining the torque at which the component fails. The torsional strength can be considered as the torque applied to the component at the point where the shear strength of that component is reached causing it to fail. The torsional strength as defined herein has dimensions of [force]×[distance] and may be expressed in units of Nm.

(66) More specific definitions of stiffnesses and other parameters relating to embodiments described herein are provided below for ease of understanding.

(67) Gearbox Support Stiffness

(68) FIG. 7 shows a region of the engine core 11 around the gearbox in close up. The same reference numbers have been used for components corresponding to those shown in FIGS. 1 to 3. In the arrangement shown in FIG. 7 the gearbox 30 has a star arrangement, in which the ring gear 38 is coupled to the fan shaft 36 and the carrier 34 is held in a fixed position relative to the static structure of the engine core (e.g. relative to the stationary supporting structure 24).

(69) The fan shaft 36 is mounted within the engine by a fan shaft mounting structure 503. The fan shaft mounting structure 503 comprises at least two bearings connected to or otherwise in engagement with the fan shaft at points spaced apart axially along the length of the engine. The fan shaft mounting structure 503 may take a number of different forms, and may comprise one or more separate supporting structures provided to support the fan shaft. It may also include other structures provided to support the fan shaft such as inter-shaft bearings. It therefore includes any supporting structure that extends between a bearing in contact with the fan shaft and a stationary structure of the engine (e.g. of the engine core).

(70) In the arrangement shown in FIG. 7, the fan shaft mounting structure 503 comprises two bearings, a first supporting bearing 506a and a second supporting bearing 506b, via which it is coupled to the fan shaft 36. The supporting bearings 506a, 506a are spaced apart along the axial length of the fan shaft 36. In the described arrangement, both supporting bearings 506a, 506b are provided at positions that are forward of the gearbox 30. In other arrangements, one of the two supporting bearing 506a, 506b used to support the fan shaft 36 may be located at a position rearward of the gearbox 30. In yet other arrangements, more than two supporting bearings may be provided as part of the fan shaft mounting structure or fan shaft mounting structure.

(71) The engine core 11 comprises a gearbox support 40 (corresponding to the linkage described with reference to FIG. 2) arranged to support or mount (e.g. to at least partially support or mount) the gearbox 30 in a fixed position within the engine. The gearbox support is coupled at a first end to the stationary supporting structure 24 which extends across the core duct 502 carrying the core airflow A as illustrated in FIG. 7. In the presently described arrangement, the stationary support structure 24 is an engine section stator (ESS) that acts as both a structural component to provide a stationary mounting for core components such as the gearbox support, and as a guide vane provided to direct airflow from the fan 23. In other embodiments, the stationary supporting structure 24 may comprise a strut extending across the core gas flow path and a separate stator vane provided to direct airflow. In the presently described arrangement, the gearbox support 40 is coupled at a second end to the planet carrier 34. The gearbox support 40 therefore acts against rotation of the planet carrier 34 relative to the static structure of the engine core (e.g. relative to the stationary supporting structure 24).

(72) In embodiments where the gearbox 30 is in a planetary arrangement, the gearbox support 40 is coupled to the ring gear 38 so as to resist its rotation relative to the static structure of the engine core (e.g. relative to the stationary supporting structure 24).

(73) The gearbox support 40 is defined between the point at which it connects to the gearbox (e.g. to the planet carrier in the presently described arrangement) and a point at which it connects to the stationary supporting structure 24. The gearbox support may be formed by any number of separate components providing a coupling between those two points.

(74) The gearbox support 40 has a degree of flexibility characterized by its radial bending stiffness and its tilt stiffness.

(75) Gearbox Support Radial Bending Stiffness:

(76) The radial bending stiffness of the gearbox support 40 is defined with reference to FIGS. 8 and 9. The radial bending stiffness can be considered to represent the resistance of the gearbox support to a force applied to it in a radial direction of the engine. The radial bending stiffness is determined by treating the gearbox support 40 as a free body that is fixed at its point of connection with the stationary supporting structure 24 of the engine, and which has a radial force F.sub.1 applied at its point of connection with the gearbox 30 as illustrated in FIG. 8. Deformation of the gearbox support 40 caused by the applied force F.sub.1 is illustrated in FIG. 9, with the shape of the support with no force applied shown in broken lines for comparison. The radial bending stiffness is defined in terms of the radial displacement, δ.sub.1, of the gearbox support at the position at which the force F.sub.1 is applied. The force, F.sub.1, is shown radially towards the engine axis 9 in FIG. 8, but could equivalently be a force radially away from the engine axis 9. The radial bending stiffness of the gearbox support 40 is therefore given by F.sub.1/δ.sub.1. The gearbox 30 is shown for reference in FIG. 9 remaining in a stationary position despite the deformation of the gearbox support 40 to which it is connected—this is for illustration purposes only and reflects the gearbox support 40 being treated as a free body in order to determine the stiffness.

(77) In various embodiments, the radial bending stiffness of the gearbox support may be greater than or equal to 1.0×10.sup.7 N/m, and optionally greater than or equal to 2.0×10.sup.7 N/m or greater than or equal to 3.0×10.sup.7 N/m.

(78) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the radial bending stiffness of the gearbox support may be greater than or equal to 1.0×10.sup.7 N/m or greater than or equal to 2.7×10.sup.7 N/m. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the radial bending stiffness of the gearbox support may be greater than or equal to 3.2×10.sup.7 N/m or greater than or equal to 4.0×10.sup.7 N/m

(79) In various embodiments, the radial bending stiffness of the gearbox support may be in the range from 1.0×10.sup.7 N/m to 4.0×10.sup.8 N/m, and optionally in the range from 2.0×10.sup.7 N/m to 3×10.sup.8 N/m or further optionally in the range from 3.0×10.sup.7 N/m to 2.0×10.sup.8 N/m.

(80) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the radial bending stiffness of the gearbox support may be in the range from 1.0×10.sup.7 N/m to 3.1×10.sup.8 N/m and optionally in the range from 2.7×10.sup.7 N/m to 3.7×10.sup.7 N/m (and may be equal to 3.2×10.sup.7 N/m).

(81) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the radial bending stiffness of the gearbox support may be in the range from 3.2×10.sup.7 N/m to 4.0×10.sup.8 N/m, and optionally in the range from 4.0×10.sup.7 N/m to 5.0×10.sup.7 N/m (and may be equal to 4.5×10.sup.7 N/m).

(82) Gearbox Support Tilt Stiffness:

(83) The tilt stiffness of the gearbox support 40 is defined with reference to FIGS. 10 and 11. The tilt stiffness can be considered to represent the resistance of the gearbox support to an applied moment. The tilt stiffness is determined by treating the gearbox support 40 as a free body that is fixed at its point of connection with the stationary supporting structure 24. In order to measure the tilt stiffness, a moment M.sub.1 is applied at the point of connection between the gearbox support 40 and the gearbox 30 as illustrated in FIG. 10. Deformation of the gearbox support 40 caused by the applied moment M.sub.1 is illustrated in FIG. 11, with the shape of the support with no moment applied shown in broken lines. The tilt stiffness is defined in terms of the angular displacement, θ.sub.1, of the gearbox support 40 at the position at which the moment M.sub.1 is applied. The tilt stiffness is therefore given by M.sub.1/θ.sub.1. The gearbox 30 is again shown for reference in FIG. 11 remaining in a stationary position despite the deformation of the gearbox support 40 to which it is connected.

(84) In various embodiments, the tilt stiffness of the gearbox support may be greater than or equal to 1.2×10.sup.5 Nm/rad, and optionally greater than or equal to 2.4×10.sup.5 Nm/rad or optionally greater than or equal to 3.9×10.sup.5 Nm/rad.

(85) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the tilt stiffness of the gearbox support may be greater than or equal to 1.2×10.sup.5 Nm/rad or greater than or equal to 4.5×10.sup.5 Nm/rad. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the tilt stiffness of the gearbox support may be greater than or equal to 5.0×10.sup.5 Nm/rad or greater than or equal to 6.0×10.sup.5 Nm/rad.

(86) In various embodiments, the tilt stiffness of the gearbox support may be in the range from 1.2×10.sup.5 Nm/rad to 2.1×10.sup.7 Nm/rad, and optionally in the range from 2.4×10.sup.5 Nm/rad to 1.6×10.sup.7 Nm/rad, and further optionally in the range from 3.9×10.sup.5 Nm/rad to 9.0×10.sup.6 Nm/rad.

(87) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the tilt stiffness of the gearbox support may be in the range from 1.2×10.sup.5 Nm/rad to 7.0×10.sup.6 Nm/rad and optionally in the range from 4.5×10.sup.5 Nm/rad to 6.5×10.sup.5 Nm/rad (and may be equal to 5.5×10.sup.5 Nm/rad).

(88) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the tilt stiffness of the gearbox support may be in the range from 5.0×10.sup.5 Nm/rad to 2.1×10.sup.7 Nm/rad, and optionally in the range from 6.0×10.sup.5 Nm/rad to 2.6×10.sup.6 Nm/rad (and may be equal to 1.6×10.sup.6 Nm/rad).

(89) Gearbox Support Torsional Shear Stress and Torsional Strength

(90) As described elsewhere herein the gearbox support is provided to locate the gearbox within the engine. In order to resist relative rotation of the gearbox compared to the stationary structure of the engine a torque is transmitted through the gearbox support. This varies over the operating cycle of the engine as different levels of torque are transmitted through the gearbox (as defined elsewhere herein) at different stages of the flight cycle of the aircraft to which the engine is mounted.

(91) The torque transmitted through the gearbox support is defined as the torque at the point of connection between the gearbox support 40 and the gearbox 30.

(92) The torsional strength of the gearbox support 40 is defined as the level of torque applied at the point of connection between the gearbox support 40 and the gearbox 20 that would result in failure of the gearbox support.

(93) When measuring the torsional strength or torque transmitted through the gearbox support 40 the gearbox support is considered to be a free body that is fixed at its point of connection with the stationary supporting structure 24 of the engine with a torque applied at the point of connection to the gearbox (i.e. in a similar manner as the application of the force or moment used to determine the radial bending stiffness and tilt stiffness of the gearbox support).

(94) In the arrangement illustrated in FIG. 7, the point of connection between the gearbox support 40 and the gearbox 30 is the point of connection to the planet carrier 34 of the gearbox. Where the gearbox is in a planetary configuration, this point of connection would be between the gearbox support 40 and the ring gear 38.

(95) In various embodiments, the torsional strength of the gearbox support may be greater than or equal to 1.60×10.sup.5 Nm, and optionally greater than or equal to 1.8×10.sup.5 Nm.

(96) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torsional strength of the gearbox support may be greater than or equal to 1.8×10.sup.5 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torsional strength of the gearbox support may be greater than or equal to 4.0×10.sup.5 Nm or greater than or equal to 5.5×10.sup.5 Nm.

(97) In various embodiments, the torsional strength of the gearbox support may be in the range from 1.60×10.sup.5 Nm to 2.00×10.sup.7 Nm, and optionally in the range from 1.8×10.sup.5 Nm to 1.5×10.sup.6 Nm.

(98) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torsional strength of the gearbox support may be in the range from 1.8×10.sup.5 Nm to 7.0×10.sup.5 Nm and optionally in the range from 1.8×10.sup.5 Nm to 2.6×10.sup.5 Nm (and may be equal to 2.2×10.sup.5 Nm).

(99) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torsional strength of the gearbox support may be in the range from 4.0×10.sup.5 Nm to 2.0×10.sup.7 Nm and optionally in the range from 5.5×10.sup.5 Nm to 7.5×10.sup.5 Nm (and may be equal to 6.5×10.sup.5 Nm).

(100) Torque Transmitted Through the Gearbox Support at MOT Conditions:

(101) In various embodiments, the torque transmitted through the gearbox support at maximum take-off conditions may be greater than or equal to 6.00×10.sup.4 Nm, and optionally greater than or equal to 7.2×10.sup.4 Nm.

(102) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque transmitted through the gearbox support at maximum take-off conditions may be greater than or equal to 7.0×10.sup.4 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torque transmitted through the gearbox support at maximum take-off conditions may be greater than or equal to 1.8×10.sup.5 Nm.

(103) In various embodiments, the torque transmitted through the gearbox support at maximum take-off conditions may be in the range from 6.00×10.sup.4 Nm to 5.00×10.sup.5 Nm, and optionally in the range from 7.2×10.sup.4 Nm to 4.2×10.sup.5 Nm.

(104) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque transmitted through the gearbox support at maximum take-off conditions may be in the range from 7.0×10.sup.4 Nm to 1.9×10.sup.5 Nm.

(105) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, torque transmitted through the gearbox support at maximum take-off conditions may be in the range from 1.8×10.sup.5 Nm to 4.5×10.sup.5 Nm.

(106) The values in the paragraphs above may apply to any gearbox configuration (i.e. star or planetary, or other gearbox arrangements).

(107) In various embodiments, for example in which the gearbox is in a star configuration, the torque transmitted through the gearbox support at maximum take-off conditions may be greater than or equal to 1.10×10.sup.5 Nm, and optionally greater than or equal to 1.3×10.sup.5 Nm.

(108) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm and/or in which the gearbox is in a star configuration, the torque transmitted through the gearbox support at maximum take-off conditions may be greater than or equal to 1.2×10.sup.5 Nm or greater than or equal to 1.4×10.sup.5 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm and/or in which the gearbox is in a star configuration, the torque transmitted through the gearbox support at maximum take-off conditions may be greater than or equal to 3.0×10.sup.5 Nm or is greater than or equal to 3.4×10.sup.5 Nm.

(109) In various embodiments, for example in which the gearbox is in a star configuration, the torque transmitted through the gearbox support at maximum take-off conditions may be in the range from 1.10×10.sup.5 Nm to 5.00×10.sup.5 Nm, and optionally in the range from 1.3×10.sup.5 Nm to 4.2×10.sup.5 Nm.

(110) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm and/or in which the gearbox is in a star configuration, the torque transmitted through the gearbox support at maximum take-off conditions may be in the range from 1.2×10.sup.5 Nm to 1.9×10.sup.5 Nm and optionally in the range from 1.4×10.sup.5 Nm to 1.8×10.sup.5 Nm (and may be equal to 1.6×10.sup.5 Nm).

(111) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm and/or the gearbox is in a star configuration, torque transmitted through the gearbox support at maximum take-off conditions may be in the range from 3.0×10.sup.5 Nm to 4.5×10.sup.5 Nm and optionally in the range from 3.4×10.sup.5 Nm to 4.2×10.sup.5 Nm (and may be equal to 3.8×10.sup.5 Nm).

(112) In various embodiments, for example in which the gearbox is in a planetary configuration, the torque transmitted through the gearbox support at maximum take-off conditions may be greater than or equal to 6.00×10.sup.4 Nm, and optionally greater than or equal to 7.2×10.sup.4 Nm.

(113) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm and/or in which the gearbox is in a planetary configuration, the torque transmitted through the gearbox support at maximum take-off conditions may be greater than or equal to 7.0×10.sup.4 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm and/or in which the gearbox is in a planetary configuration, the torque transmitted through the gearbox support at maximum take-off conditions may be greater than or equal to 1.8×10.sup.5 Nm.

(114) In various embodiments, for example in which the gearbox is in a planetary configuration, the torque transmitted through the gearbox support at maximum take-off conditions may be in the range from 6.00×10.sup.4 Nm to 3.00×10.sup.5 Nm, and optionally in the range from 7.2×10.sup.4 Nm to 2.6×10.sup.5 Nm.

(115) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm and/or in which the gearbox is in a planetary configuration, the torque transmitted through the gearbox support at maximum take-off conditions may be in the range from 7.0×10.sup.4 Nm to 1.1×10.sup.5 Nm.

(116) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm and/or in which the gearbox is in a planetary configuration, torque transmitted through the gearbox support at maximum take-off conditions may be in the range from 1.8×10.sup.5 Nm to 2.5×10.sup.5 Nm.

(117) Torque Transmitted Through the Gearbox Support at Cruise Conditions:

(118) In various embodiments, the torque transmitted through the gearbox support at cruise conditions may be greater than or equal to 2.00×10.sup.4 Nm, and optionally greater than or equal to 2.2×10.sup.4 Nm.

(119) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque transmitted through the gearbox support at cruise conditions may be greater than or equal to 2.2×10.sup.4 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torque transmitted through the gearbox support at cruise conditions may be greater than or equal to 6.8×10.sup.4 Nm.

(120) In various embodiments, the torque transmitted through the gearbox support at cruise conditions may be in the range from 2.00×10.sup.4 Nm to 2.00×10.sup.5 Nm, and optionally in the range from 2.2×10.sup.4 Nm to 1.7×10.sup.5 Nm.

(121) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque transmitted through the gearbox support at cruise conditions may be in the range from 2.2×10.sup.4 Nm to 6.6×10.sup.4 Nm.

(122) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torque transmitted through the gearbox support at cruise conditions may be in the range from 6.8×10.sup.4 Nm to 1.8×10.sup.5 Nm.

(123) The values in the paragraphs above may apply to any gearbox configuration (i.e. star or planetary, or other gearbox arrangements).

(124) In various embodiments, for example in which the gearbox is in a star configuration, the torque transmitted through the gearbox support at cruise conditions may be greater than or equal to 4.00×10.sup.4 Nm, and optionally greater than or equal to 4.8×10.sup.4 Nm.

(125) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm and/or in which the gearbox is in a star configuration, the torque transmitted through the gearbox support at cruise conditions may be greater than or equal to 4.5×10.sup.4 Nm or greater than or equal to 5.0×10.sup.4 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm and/or the gearbox is in a star configuration, the torque transmitted through the gearbox support at cruise conditions may be greater than or equal to 1.2×10.sup.5 Nm.

(126) In various embodiments, for example in which the gearbox is in a star configuration, the torque transmitted through the gearbox support at cruise conditions may be in the range from 4.00×10.sup.4 Nm to 2.00×10.sup.5 Nm, and optionally in the range from 4.8×10.sup.4 Nm to 1.7×10.sup.5 Nm.

(127) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm and/or the gearbox is in a star configuration, the torque transmitted through the gearbox support at cruise conditions may be in the range from 4.5×10.sup.4 Nm to 6.6×10.sup.4 Nm and optionally in the range from 5.0×10.sup.4 Nm to 6.0×10.sup.4 Nm (and may be equal to 5.5×10.sup.4 Nm).

(128) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm and/or the gearbox is in a star configuration, torque transmitted through the gearbox support at cruise conditions may be in the range from 1.2×10.sup.5 Nm to 1.8×10.sup.5 Nm and optionally in the range from 1.2×10.sup.5 Nm to 1.8×10.sup.5 Nm (and may be equal to 1.5×10.sup.5 Nm).

(129) In various embodiments, for example in which the gearbox is in a planetary configuration, the torque transmitted through the gearbox support at cruise conditions may be greater than or equal to 2.00×10.sup.4 Nm, and optionally greater than or equal to 2.2×10.sup.4 Nm.

(130) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm and/or in which the gearbox is in a planetary configuration, the torque transmitted through the gearbox support at cruise conditions may be greater than or equal to 2.2×10.sup.4 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm and/or the gearbox is in a planetary configuration, the torque transmitted through the gearbox support at cruise conditions may be greater than or equal to 6.8×10.sup.4 Nm.

(131) In various embodiments, for example in which the gearbox is in a planetary configuration, the torque transmitted through the gearbox support at cruise conditions may be in the range from 2.00×10.sup.4 Nm to 1.30×10.sup.5 Nm, and optionally in the range from 2.2×10.sup.4 Nm to 1.1×10.sup.5 Nm.

(132) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm and/or the gearbox is in a planetary configuration, the torque transmitted through the gearbox support at cruise conditions may be in the range from 2.2×10.sup.4 Nm to 3.3×10.sup.4 Nm.

(133) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm and/or the gearbox is in a planetary configuration, torque transmitted through the gearbox support at cruise conditions may be in the range from 6.8×10.sup.4 Nm to 1.1×10.sup.5 Nm.

(134) Gearbox Support Torsional Shear Stress

(135) The gearbox support 40 has a torsional shear stress that also represents the resistance of the gearbox support 40 to a torque applied by the gearbox 30. The torsional shear stress is as defined elsewhere herein.

(136) In various embodiments, the torsional shear stress of the gearbox support at maximum take-off conditions may be less than or equal to 4.90×10.sup.8 N/m.sup.2, and optionally less than or equal to 3.5×10.sup.8 N/m.sup.2.

(137) In various embodiments, the torsional shear stress of the gearbox support at maximum take-off conditions may be in the range from 1.40×10.sup.8 N/m.sup.2 to 4.90×10.sup.8 N/m.sup.2, and optionally in the range from 2.0×10.sup.8 N/m.sup.2 to 3.5×10.sup.8 N/m.sup.2.

(138) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm or in the range from 330 to 380 cm, the torsional shear stress of the gearbox support at maximum take-off conditions may be in the range from 2.3×10.sup.8 N/m.sup.2 to 3.7×10.sup.8 N/m.sup.2 (and may be equal to 2.5×10.sup.8 N/m.sup.2).

(139) In various embodiments, the torsional shear stress of the gearbox support at cruise conditions may be greater than or equal to 7.00×10.sup.7 N/m.sup.2, and optionally greater than or equal to 8.2×10.sup.7 N/m.sup.2.

(140) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torsional shear stress of the gearbox support at cruise conditions may be greater than or equal to 8.0×10.sup.7 N/m.sup.2. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torsional shear stress of the gearbox support at cruise conditions may be greater than or equal to 8.5×10.sup.7 N/m.sup.2 or greater than or equal to 9.0×10.sup.7 N/m.sup.2.

(141) In various embodiments, the torsional shear stress of the gearbox support at cruise conditions may be in the range from 7.00×10.sup.7 N/m.sup.2 to 1.90×10.sup.8 N/m.sup.2, and optionally in the range from 8.2×10.sup.7 N/m.sup.2 to 1.5×10.sup.8 N/m.sup.2.

(142) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torsional shear stress of the gearbox support at cruise conditions may be in the range from 8.0×10.sup.7 N/m.sup.2 to 1.5×10.sup.8 N/m.sup.2 and optionally in the range from 8.0×10.sup.7 N/m.sup.2 to 9.2×10.sup.7 N/m.sup.2 (and may be equal to 8.6×10.sup.7 N/m.sup.2).

(143) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torsional shear stress of the gearbox support at cruise conditions may be in the range from 8.5×10.sup.7 N/m.sup.2 to 1.9×10.sup.8 N/m.sup.2 and optionally in the range from 9.0×10.sup.7 Nm.sup.2 to 1.2×10.sup.8 N/m.sup.2 (and may be equal to 9.6×10.sup.7 N/m.sup.2).

(144) The maximum take-off conditions and cruise conditions referred to in this section may be as defined elsewhere herein.

(145) The shear stress may be measured through the highest loaded plane section of the component (i.e. the gearbox support). It excludes the effects of stress concentrations at small radii and holes. The skilled person will understand that for the shear stress of the gearbox support defined herein since the predominant load is a torque, the effective radius also affects the measurement of the shear as well as the area.

(146) Fan Moment of Inertia

(147) The fan 23 has a moment of inertial I.sub.F. The moment of inertia of the fan is measured based on the total mass of the rotor forming the fan, i.e. including the total mass of the plurality of fan blades, the fan hub and any support arm or other linkages provided to connect the fan to the fan shaft. The moment of inertial therefore includes all rotating components apart from the fan shaft. The moment of inertia is the mass moment of inertia or rotational inertia of the fan with respect to rotation around the principal rotational axis 9 of the engine. Rotation of the fan will cause a gyroscopic effect meaning that the fan shaft will tend to maintain a steady direction of its axis of rotation. During maneuvering of the aircraft to which the gas turbine engine is mounted the orientation of the axis of rotation of the fan shaft will however change. The gyroscopic effect will result in a reaction force at the fan shaft mounting structure to resist the tendency of the fan shaft to maintain its orientation. The moment of inertia of the fan will have an effect on the magnitude of the gyroscopic effect produced, and so has an impact on the design of the fan shaft and the fan shaft mounting structure as is discussed elsewhere herein.

(148) In various embodiments, the moment of inertia of the fan may be greater than or equal to 7.40×10.sup.7 kgm.sup.2, and optionally greater than or equal to 8.3×10.sup.7 kgm.sup.2.

(149) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the moment of inertia of the fan may be greater than or equal to 7.4×10.sup.7 kgm.sup.2 or 8.6×10.sup.7 kgm.sup.2. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the moment of inertia of the fan may be greater than or equal to 3.0×10.sup.8 kgm.sup.2 or 4.0×10.sup.8 kgm.sup.2.

(150) In various embodiments, the moment of inertia of the fan may be in the range from 7.40×10.sup.7 kgm.sup.2 to 9.00×10.sup.8 kgm.sup.2, and optionally in the range from 8.3×10.sup.7 kgm.sup.2 to 6.5×10.sup.8 kgm.sup.2.

(151) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the moment of inertia of the fan may be in the range from 7.4×10.sup.7 kgm.sup.2 to 1.5×10.sup.8 kgm.sup.2 and optionally in the range from 8.6×10.sup.7 kgm.sup.2 to 9.6×10.sup.7 kgm.sup.2 (and may be equal to 9.1×10.sup.7 kgm.sup.2).

(152) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the moment of inertia of the fan may be in the range from 3.0×10.sup.8 kgm.sup.2 to 9.0×10.sup.8 kgm.sup.2 and optionally in the range from 4.0×10.sup.8 kgm.sup.2 to 5.0×10.sup.8 kgm.sup.2 (and may be equal to 4.5×10.sup.8 kgm.sup.2).

(153) Relative Fan and Gearbox Positions

(154) Referring again to FIG. 7, a fan-gearbox axial distance 110 is defined as the axial distance between the axial position P of the gearbox output position (also labelled X in FIGS. 15 to 18) and the fan axial centreline Q. The fan axial centreline is defined as the axial midpoint of the fan blades forming the fan. The gearbox output position is defined as the point of connection between the fan shaft 36 and the gearbox. This may be defined differently for different types of gearbox as is described below.

(155) In various embodiments, the fan-gearbox axial distance may be greater than or equal to 0.35 m, and optionally greater than or equal to 0.37 m.

(156) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan-gearbox axial distance may be greater than or equal to 0.38 m or greater than or equal to 0.40 m. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan-gearbox axial distance may be greater than or equal to 0.48 m or greater than or equal to 0.50 m.

(157) In various embodiments, the fan-gearbox axial distance may be in the range from 0.35 m to 0.8 m, and optionally in the range from 0.37 m to 0.75 m.

(158) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan-gearbox axial distance may be in the range from 0.38 m to 0.65 m and optionally in the range from 0.40 m to 0.44 m (and may be equal to 0.42 m).

(159) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan-gearbox axial distance may be in the range from 0.48 m to 0.8 m and optionally in the range from 0.50 m to 0.66 m (and may be equal to 0.58 m).

(160) The fan shaft 36 is defined as the torque transfer component that extends from the output of the gearbox to the fan input. It therefore includes part or all of any gearbox output shaft and fan input shaft that may be provided between those points. For the purposes of defining the stiffness of the fan shaft 36 it is considered to extend between a fan input position and a gearbox output position, and includes all of the torque transfer components between those points. It does not therefore include any components of the gearbox (e.g. the planet carrier or connecting plate coupled to it) which transmit discrete forces, rather than the fan shaft torque. The gearbox output position therefore may be defined as the point of connection between the fan shaft 36 and the gearbox 30. The fan input position may be defined as the point of connection between the fan shaft 36 and the fan.

(161) Referring to FIG. 12, where the gearbox is in a star configuration, the gearbox output position is defined as the point of connection 702 between the ring gear 38 and the fan shaft 36. More specifically, it is the point of connection to the annulus of the ring gear 38 (with any connection component extending from the outer surface of the annulus being considered to be part of the ring gear). Where the point of connection is formed by an interface extending in a direction having an axial component, the point of connection is considered to be the axial centreline of that interface as illustrated in FIG. 7.

(162) The fan shaft 36 includes all torque transmitting components up to the point of connection 702 with the ring gear 38. It therefore includes any flexible portions or linkages 704 of the fan shaft 36 that may be provided, and any connection(s) 706 (e.g. spline connections) between them.

(163) Where the gearbox 30 is in a planetary configuration, the gearbox output position is again defined as the point of connection between the fan shaft 36 and the gearbox 30. An example of this is illustrated in FIG. 13, which shows a carrier comprising a forward plate 34a and rearward plate 34b, with a plurality of pins 33 extending between them and on which the planet gears are mounted. The fan shaft 36 is connected to the forward plate 34a via a spline connection 708. In an arrangement such as this, the gearbox output position is taken as any point on the interface between the fan shaft 36 and the forward plate 34a. The forward plate 34a is considered to transmit discrete forces, rather than a single torque, and so is taken to be part of the gearbox 30 rather than the fan shaft.

(164) FIG. 13 shows only one example of a type of connection between the fan shaft and planet carrier 34. In embodiments having different connection arrangements, the gearbox output position is still taken to be at the interface between components transmitting a torque (i.e. that are part of the fan shaft) and those transmitting discrete forces (e.g. that are part of the gearbox). The spline connection 708 is only one example of a connection that may be formed between the fan shaft and gearbox (i.e. between the fan shaft and the forward plate 34b in the presently described arrangement). In other embodiments, the interface which forms the gearbox output position may be formed by, for example, a curvic connection, a bolted joint or other toothed or mechanically dogged arrangement.

(165) The fan input position is defined as a point on the fan shaft at the axial midpoint of the interface between the fan and the fan shaft. In the presently described arrangement, the fan 23 comprises a support arm 23a (as can be seen, for example, in FIG. 7) arranged to connect the fan 23 to the fan shaft 36. The support arm 23a is connected to the fan shaft by a spline coupling 36c that extends along the length of a portion of the fan shaft 36. The fan input position is defined as the axial midpoint of the spline coupling. The spline coupling shown is only one example of a coupling that may form the interface between the fan and fan shaft. In other embodiments, for example, a curvic connection, a bolted joint or other toothed or mechanically dogged arrangement may be used. For example, a flange coupling may be provided between the support arm 23a and the fan shaft 36. In such an embodiment, the support arm can be connected at the rear of the fan hub. In this embodiment the fan input position is the axial midpoint of the flange coupling. FIG. 14 illustrates an arrangement in which an alternative coupling is provided between the fan 23 and the fan shaft 36. Similarly to FIG. 7, the fan 23 is coupled to the fan shaft 36 via a support arm 23a. In this arrangement however, a flange coupling 36d is provided between the support arm 23a and the fan shaft 36. In this embodiment, the support arm 23a is connected at the rear of the fan hub. The flange coupling 36d may be a curvic coupling. In other embodiments, other forms of flange coupling may be provided. In the embodiment of FIG. 14, the fan input position is the axial midpoint (labelled Y) of the flange coupling.

(166) The fan shaft 36 has a degree of flexibility characterized by its radial bending stiffness and tilt stiffness.

(167) Fan Shaft End Stiffness at Gearbox Output:

(168) The stiffness of the fan shaft where it couples to the gearbox 30 is defined with reference to FIGS. 15 to 18.

(169) The radial bending stiffness of the fan shaft 36 at the output of the gearbox 30 is measured by applying a force F.sub.2 to the fan shaft at the gearbox output position defined above (illustrated in FIG. 15). The fan shaft 36 is treated as a free body, and is held fixed at the position of all of bearing positions at which it is supported i.e. the first and second bearings 506a, 506b in the arrangement of FIG. 15. As a result of force F.sub.2 the fan shaft 36 deforms so that the gearbox output position is displaced by a distance of δ.sub.2 (as illustrated in FIG. 16). The radial bending stiffness of the fan shaft 36 at the output of the gearbox is then given by F.sub.2/δ.sub.2.

(170) In various embodiments, the radial bending stiffness of the fan shaft at the output of the gearbox may be greater than or equal to 4.00×10.sup.6 N/m, and optionally greater than or equal to 3.7×10.sup.7 N/m.

(171) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the radial bending stiffness of the fan shaft at the output of the gearbox may be greater than or equal to 3.7×10.sup.7 N/m. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the radial bending stiffness of the fan shaft at the output of the gearbox may be greater than or equal to 3.9×10.sup.7 N/m or greater than or equal to 5.0×10.sup.7 N/m.

(172) In various embodiments, the radial bending stiffness of the fan shaft at the output of the gearbox may be in the range from 4.00×10.sup.6 N/m to 1.5×10.sup.9 N/m, and optionally in the range from 3.7×10.sup.7 N/m to 1.0×10.sup.9 N/m.

(173) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the radial bending stiffness of the fan shaft at the output of the gearbox may be in the range from 3.7×10.sup.7 N/m to 5.0×10.sup.8 N/m and optionally in the range from 3.7×10.sup.7 N/m to 4.3×10.sup.7 N/m (and may be equal to 4.0×10.sup.7 N/m).

(174) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the radial bending stiffness of the fan shaft at the output of the gearbox may be in the range from 3.9×10.sup.7 N/m to 1.5×10.sup.9 N/m, and optionally in the range from 5.0×10.sup.7 N/m to 9.0×10.sup.7 N/m (and may be equal to 7.0×10.sup.7 N/m).

(175) The tilt stiffness of the fan shaft 36 at the output of the gearbox 30 is measured by applying a moment M.sub.2 to the fan shaft at the gearbox output position defined above (illustrated in FIG. 17). The fan shaft 36 is again treated as a free body, and is held fixed at the position of all of the bearing positions at which it is supported i.e. the first and second bearings 506a, 506b in the arrangement of FIG. 15. As a result of moment M.sub.2 the fan shaft 36 deforms so that the gearbox output position is displaced by an angular displacement of θ.sub.2 as illustrated in FIG. 17. The tilt stiffness of the fan shaft 36 at the output of the gearbox is then given by M.sub.2/θ.sub.2.

(176) In various embodiments, the tilt stiffness of the fan shaft at the output of the gearbox may be greater than or equal to 7.00×10.sup.4 Nm/rad, and optionally greater than or equal to 9.5×10.sup.5 Nm/rad.

(177) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the tilt stiffness of the fan shaft at the output of the gearbox may be greater than or equal to 9.5×10.sup.5, and optionally may be greater than or equal to 9.5×10.sup.5 Nm/rad. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the tilt stiffness of the fan shaft output of the gearbox may be greater than or equal to 1.1×10.sup.6 Nm/rad and optionally may be greater than or equal to 2.0×10.sup.6 Nm/rad.

(178) In various embodiments, the tilt stiffness of the fan shaft at the output of the gearbox may be in the range from 7.00×10.sup.4 Nm/rad to 7.00×10.sup.7 Nm/rad, and optionally in the range from 9.5×10.sup.5 Nm/rad to 3.5×10.sup.7 Nm/rad.

(179) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the tilt stiffness of the output of the gearbox may be in the range from 9.5×10.sup.5 Nm/rad to 2.0×10.sup.7 Nm/rad and optionally in the range from 9.5×10.sup.5 Nm/rad to 2.4×10.sup.6 Nm/rad (and may be equal to 1.2×10.sup.6 Nm/rad).

(180) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the tilt stiffness of the fan shaft at the output of the gearbox may be in the range from 1.1×10.sup.6 Nm/rad to 7.0×10.sup.7 Nm/rad, and optionally in the range from 2.0×10.sup.6 Nm/rad to 5.2×10.sup.6 Nm/rad (and may be equal to 3.6×10.sup.6 Nm/rad).

(181) Torque Transmission by the Gearbox

(182) The gearbox provides a torque conversion between the toque at its input (i.e. the core shaft) and its output (i.e. the fan shaft). The torque transmitted through the gearbox is defined as the torque at the output position of the gearbox (the output position being as defined elsewhere herein). The torque transmitted through the gearbox varies over the operating cycle of the engine.

(183) In various embodiments, the torque transmitted through the gearbox at maximum take-off conditions may be greater than or equal to 7.00×10.sup.4 Nm, and optionally greater than or equal to 1.0×10.sup.5 Nm.

(184) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque transmitted through the gearbox at maximum take-off conditions may be greater than or equal to 1.1×10.sup.5 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torque transmitted through the gearbox at maximum take-off conditions may be greater than or equal to 1.5×10.sup.5 Nm or greater than or equal to 2.0×10.sup.5 Nm.

(185) In various embodiments, the torque transmitted through the gearbox at maximum take-off conditions may be in the range from 7.00×10.sup.4 Nm to 5.00×10.sup.5 Nm, and optionally in the range from 1.0×10.sup.5 Nm to 3.5×10.sup.5 Nm.

(186) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque transmitted through the gearbox at maximum take-off conditions may be in the range from 1.1×10.sup.5 Nm to 1.5×10.sup.5 Nm and optionally in the range from 1.1×10.sup.5 Nm to 1.3×10.sup.5 Nm (and may be equal to 1.2×10.sup.5 Nm).

(187) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torque transmitted through the gearbox at maximum take-off conditions may be in the range from 1.5×10.sup.5 Nm to 5.0×10.sup.5 Nm and optionally in the range from 2.0×10.sup.5 Nm to 3.8×10.sup.5 Nm (and may be equal to 2.9×10.sup.5 Nm).

(188) In various embodiments, the torque transmitted through the gearbox at cruise conditions may be greater than or equal to 2.30×10.sup.4 Nm, and optionally greater than or equal to 3.1×10.sup.4 Nm.

(189) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque transmitted through the gearbox at cruise conditions may be greater than or equal to 3.2×10.sup.4 Nm or greater than or equal to 3.8×10.sup.4 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torque transmitted through the gearbox at cruise conditions may be greater than or equal to 7.3×10.sup.4 Nm or greater than or equal to 9.8×10.sup.4 Nm.

(190) In various embodiments, the torque transmitted through the gearbox at cruise conditions may be in the range from 2.30×10.sup.4 Nm to 1.80×10.sup.5 Nm, and optionally in the range from 3.1×10.sup.4 Nm to 1.5×10.sup.5 Nm.

(191) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque transmitted through the gearbox at cruise conditions may be in the range from 3.2×10.sup.4 Nm to 7.2×10.sup.4 Nm and optionally in the range from 3.8×10.sup.4 Nm to 4.6×10.sup.4 Nm (and may be equal to 4.2×10.sup.4 Nm).

(192) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, torque transmitted through the gearbox at cruise conditions may be in the range from 7.3×10.sup.4 Nm to 1.8×10.sup.5 Nm and optionally in the range from 9.8×10.sup.4 Nm to 1.4×10.sup.5 Nm (and may be equal to 1.1×10.sup.5 Nm).

(193) Gearbox CSA

(194) The cross sectional area (CSA) of the gearbox is defined as the area of the pitch circle of the ring gear. The pitch circle of a gear is an imaginary circle that rolls without slipping with the pitch circle of any other gear with which the first gear is meshed. The pitch circle passes through the points where the teeth of two gears meet as the meshed gears rotate—the pitch circle of a gear generally passes through a mid-point of the length of the teeth of the gear. The CSA of the gearbox can be found by measuring the pitch circle diameter (PCD) of the gear. The PCD can be roughly estimated by taking the average of the diameter between tips of the gear teeth and the diameter between bases of the gear teeth.

(195) In various embodiments, the CSA of the gearbox may be greater than or equal to 2.4×10.sup.−1 m.sup.2 and optionally greater than or equal to 2.6×10.sup.−1 m.sup.2.

(196) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the CSA of the gearbox may be greater than or equal to 2.4×10.sup.−1 m.sup.2 or greater than or equal to 2.5×10.sup.−1 m.sup.2. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the CSA of the gearbox may be greater than or equal to 4.5×10.sup.−1 m.sup.2 or greater than or equal to 5.5×10.sup.−1 m.sup.2.

(197) In various embodiments, the CSA of the gearbox may be in the range from 2.4×10.sup.−1 m.sup.2 to 1.10 m.sup.2, and optionally in the range from 2.6×10.sup.−1 m.sup.2 to 9.0×10.sup.−1 m.sup.2.

(198) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the CSA of the gearbox may be in the range from 2.4×10.sup.−1 m.sup.2 to 5.0×10.sup.−1 m.sup.2 and optionally in the range from 2.5×10.sup.−1 m.sup.2 to 3.4×10.sup.−1 m.sup.2 (and may be equal to 2.9×10.sup.−1 m.sup.2).

(199) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the CSA of the gearbox may be in the range from 4.5×10.sup.−1 m.sup.2 to 1.1 m.sup.2, and optionally in the range from 5.5×10.sup.−1 m.sup.2 to 6.4×10.sup.−1 m.sup.2 (and may be equal to 5.9×10.sup.−1 m.sup.2).

(200) Angle Between Adjacent Planet Gears

(201) A planet gear spacing angle in radians (β) is defined as 2π/N, where N is the number of planet gears 32 provided in the gearbox. The planet gear spacing angle is illustrated in FIG. 3. The planet gearbox spacing angle corresponds to the average angle (in rad) between all the adjacent pairs of planet gears.

(202) In various embodiments, the planet gear spacing angle (β) may be greater than or equal to 9.0×10.sup.−1 rad, and optionally in the range between 9.0×10.sup.−1 rad to 2.1 rad, and further optionally in the range between 1.1 rad and 1.3 rad (and may be equal to 1.26 rad)

(203) Parameter Ratios

(204) The inventor has discovered that the ratios (and/or products) of some properties have a considerable impact on the operation of the gearbox and its inputs/outputs/support structure. Some or all of the below may apply to any embodiment:

(205) In various embodiments, a radial bending stiffness to moment of inertia ratio may be defined as:

(206) $\frac{\begin{matrix} the radial bending stiffness of at least one of \\ the fan shaft (36) at the output of gearbox and \\ the gearbox support (40) \end{matrix}}{the moment of inertia of the fan (23)}$

(207) In various embodiments, the radial bending stiffness to moment of inertia ratio may be greater than or equal to 2.5×10.sup.−2 Nkg.sup.−1 m.sup.−3 (i.e. (N/m)/(kg.Math.m.sup.2)) and optionally greater than or equal to 0.05 Nkg.sup.−1 m.sup.−3.

(208) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the radial bending stiffness to moment of inertia ratio may be greater than or equal to 0.05 Nkg.sup.−1 m.sup.−3. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the radial bending stiffness to moment of inertia ratio may be greater than or equal to 0.025 Nkg.sup.−1 m.sup.−3.

(209) In various embodiments, the radial bending stiffness to moment of inertia ratio may be in the range from 2.5×10.sup.−2 Nkg.sup.−1 m.sup.−3 to 6.0 Nkg.sup.−1 m.sup.−3, and optionally in the range from 0.05 Nkg.sup.−1 m.sup.−3 to 3.0 Nkg.sup.−1 m.sup.−3, and further optionally in the range from 0.05 Nkg.sup.−1 m.sup.−3 to 0.6 Nkg.sup.−1 m.sup.−3.

(210) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the radial bending stiffness to moment of inertia ratio may be in the range from 0.05 Nkg.sup.−1 m.sup.−3 to 4.0 Nkg.sup.−1 m.sup.−3.

(211) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the radial bending stiffness to moment of inertia ratio may be in the range from 0.025 Nkg.sup.−1 m.sup.−3 to 2.0 Nkg.sup.−1 m.sup.−3.

(212) In various embodiments, in addition to or alternatively to the radial bending stiffness to moment of inertia ratio, a product of the parameters making up that ratio may be defined. This product (referred to as the radial bending stiffness to moment of inertia product) may be defined as:
(the radial bending stiffness of at least one of the fan shaft (36) at the output of the gearbox and the gearbox support (40))×(the moment of inertia of the fan (23))

(213) In various embodiments, the radial bending stiffness to moment of inertia product may be greater than or equal to 2.0×10.sup.14 Nkgm (i.e. (N/m).Math.(kg.Math.m.sup.2)), and optionally greater than or equal to 4.0×10.sup.14 Nkgm, and further optionally greater than or equal to 2.0×10.sup.15 Nkgm.

(214) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the radial bending stiffness to moment of inertia product may be greater than or equal to 1.5×10.sup.15 Nkgm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the radial bending stiffness to moment of inertia product may be greater than or equal to 2.0×10.sup.15 Nkgm.

(215) In various embodiments, the radial bending stiffness to moment of inertia product may be in the range from 2.0×10.sup.14 Nkgm to 1.4×10.sup.18 Nkgm, and optionally in the range from 4.0×10.sup.14 Nkgm to 7.0×10.sup.17 Nkgm, and further optionally in the range from 2.0×10.sup.15 Nkgm to 7.0×10.sup.17 Nkgm.

(216) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the radial bending stiffness to moment of inertia product may be in the range from 1.5×10.sup.15 Nkgm to 1.3×10.sup.17 Nkgm.

(217) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the radial bending stiffness to moment of inertia product may be in the range from 2.0×10.sup.15 Nkgm to 1.4×10.sup.18 Nkgm.

(218) In various embodiments, a fan shaft radial bending stiffness to moment of inertia ratio may be defined as:

(219) $\frac{\begin{matrix} the radial bending stiffness of \\ the fan shaft (36) at the output of the gearbox \end{matrix}}{the moment of inertia of the fan (23)}$

(220) In various embodiments, the fan shaft radial bending stiffness to moment of inertia ratio may be greater than or equal to 2.5×10.sup.−2 Nkg.sup.−1 m.sup.−3 (i.e. (N/m)/(kg.Math.m.sup.2)), and optionally greater than or equal to 0.05 (N/m)/(kg.Math.m.sup.2).

(221) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan shaft radial bending stiffness to moment of inertia ratio may be greater than or equal to 0.05 Nkg.sup.−1 m.sup.−3 or greater than or equal to 0.4 Nkg.sup.−1 m.sup.−3. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan shaft radial bending stiffness to moment of inertia ratio may be greater than or equal to 0.025 Nkg.sup.−1 m.sup.−3 or optionally greater than or equal to 0.06 Nkg.sup.−1 m.sup.−3.

(222) In various embodiments, the fan shaft radial bending stiffness to moment of inertia ratio may be in the range from 2.5×10.sup.−2 Nkg.sup.−1 m.sup.−3 to 6.0 Nkg.sup.−1 m.sup.−3, and optionally in the range from 0.05 Nkg.sup.−1 m.sup.−3 to 3.0 Nkg.sup.−1 m.sup.−3, and further optionally in the range from 0.05 Nkg.sup.−1 m.sup.−3 to 0.6 Nkg.sup.−1 m.sup.−3.

(223) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan shaft radial bending stiffness to moment of inertia ratio may be in the range from 0.05 Nkg.sup.−1 m.sup.−3 to 0.6 Nkg.sup.−1 m.sup.−3 and optionally in the range from 0.4 Nkg.sup.−1 m.sup.−3 to 0.5 Nkg.sup.−1 m.sup.−3 (and may be equal to 0.44 Nkg.sup.−1 m.sup.−3).

(224) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan shaft radial bending stiffness to moment of inertia ratio may be in the range from 0.025 Nkg.sup.−1 m.sup.−3 to 0.6 Nkg.sup.−1 m.sup.−3, and optionally in the range from 0.06 Nkg.sup.−1 m.sup.−3 to 0.26 Nkg.sup.−1 m.sup.−3 (and may be equal to 0.16 Nkg.sup.−1 m.sup.−3).

(225) In various embodiments, in addition to or alternatively to the fan shaft radial bending stiffness to moment of inertia ratio, a product of the parameters making up that ratio may be defined. This product (referred to as the fan shaft radial bending stiffness to moment of inertia product) may be defined as:
the radial bending stiffness of the fan shaft (36) at the output of the gearbox×the moment of inertia of the fan (23)

(226) In various embodiments, the fan shaft radial bending stiffness to moment of inertia product may be greater than or equal to 3.0×10.sup.14 Nkgm (i.e. (N/m).Math.(kg.Math.m.sup.2)), and optionally greater than or equal to 6.0×10.sup.14 Nkgm, and further optionally greater than or equal to 2.0×10.sup.15 Nkgm.

(227) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan shaft radial bending stiffness to moment of inertia product may be greater than or equal to 2.0×10.sup.15 Nkgm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan shaft radial bending stiffness to moment of inertia product may be greater than or equal to 2.3×10.sup.15 Nkgm.

(228) In various embodiments, the fan shaft radial bending stiffness to moment of inertia product may be in the range from 3.0×10.sup.14 Nkgm to 1.4×10.sup.18 Nkgm, and optionally in the range from 6.0×10.sup.14 Nkgm to 7.0×10.sup.17 Nkgm, and further optionally in the range from 2.0×10.sup.15 Nkgm to 7.0×10.sup.17 Nkgm.

(229) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan shaft radial bending stiffness to moment of inertia product may be in the range from 2.0×10.sup.15 Nkgm to 7.5×10.sup.16 Nkgm.

(230) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan shaft radial bending stiffness to moment of inertia product may be in the range from 2.3×10.sup.15 Nkgm to 1.4×10.sup.18 Nkgm.

(231) In various embodiments, a gearbox support radial bending stiffness to moment of inertia ratio may be defined as

(232) $\frac{the radial bending stiffness of the gearbox support (40)}{the moment of inertia of the fan (23)}$

(233) In various embodiments, the gearbox support radial bending stiffness to moment of inertia ratio may be greater than or equal to 3.0×10.sup.−2 Nkg.sup.−1 m.sup.−3 (i.e. (N/m)/(kg.Math.m.sup.2)), and optionally greater than or equal to 0.06 Nkg.sup.−1 m.sup.−3.

(234) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the gearbox support radial bending stiffness to moment of inertia ratio may be greater than or equal to 0.06 Nkg.sup.−1 m.sup.−3 or greater than or equal to 0.25 Nkg.sup.−1 m.sup.−3. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the gearbox support radial bending stiffness to moment of inertia ratio may be greater than or equal to 0.03 Nkg.sup.−1 m.sup.−3 or greater than or equal to 0.06 Nkg.sup.−1 m.sup.−3.

(235) In various embodiments, the gearbox support radial bending stiffness to moment of inertia ratio may be in the range from 3.0×10.sup.−2 Nkg.sup.−1 m.sup.−3 to 4.0 Nkg.sup.−1 m.sup.−3, and optionally in the range from 0.06 Nkg.sup.−1 m.sup.−3 to 2.0 Nkg.sup.−1 m.sup.−3, and further optionally in the range from 0.06 Nkg.sup.−1 m.sup.−3 to 0.48 Nkg.sup.−1 m.sup.−3.

(236) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the gearbox support radial bending stiffness to moment of inertia ratio may be in the range from 0.06 Nkg.sup.−1 m.sup.−3 to 4.0 Nkg.sup.−1 m.sup.−3 and optionally in the range from 0.25 Nkg.sup.−1 m.sup.−3 to 0.45 Nkg.sup.−1 m.sup.−3 (and may be equal to 0.35 Nkg.sup.−1 m.sup.−3).

(237) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the gearbox support radial bending stiffness to moment of inertia ratio may be in the range from 0.03 Nkg.sup.−1 m.sup.−3 to 2.0 Nkg.sup.−1 m.sup.−3, and optionally in the range from 0.06 Nkg.sup.−1 m.sup.−3 to 0.6 Nkg.sup.−1 m.sup.−3 (and may be equal to 0.1) Nkg.sup.−1 m.sup.−3.

(238) In various embodiments, in addition to or alternatively to the gearbox support radial bending stiffness to moment of inertia ratio, a product of the parameters making up that ratio may be defined. This product (referred to as the gearbox support radial bending stiffness to moment of inertia product) may be defined as:
the radial bending stiffness of the gearbox support (40)×the moment of inertia of the fan (23)

(239) In various embodiments, the gearbox support radial bending stiffness to moment of inertia product may be greater than or equal to 2.0×10.sup.14 Nkgm (i.e. (N/m).Math.(kg.Math.m.sup.2)), and optionally greater than or equal to 4.0×10.sup.14 Nkgm or further optionally greater than or equal to 2.0×10.sup.15 Nkgm.

(240) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the gearbox support radial bending stiffness to moment of inertia product may be greater than or equal to 1.5×10.sup.15 Nkgm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the gearbox support radial bending stiffness to moment of inertia product may be greater than or equal to 2.0×10.sup.15 Nkgm.

(241) In various embodiments, the gearbox support radial bending stiffness to moment of inertia product may be in the range from 2.0×10.sup.14 Nkgm to 3.0×10.sup.17 Nkgm, and optionally in the range from 4.0×10.sup.14 Nkgm to 1.3×10.sup.17 Nkgm, and yet further optionally in the range from 2.0×10.sup.15 Nkgm to 1.3×10.sup.17 Nkgm.

(242) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the gearbox support radial bending stiffness to moment of inertia product may be in the range from 1.5×10.sup.15 Nkgm to 1.3×10.sup.17 Nkgm.

(243) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the gearbox support radial bending stiffness to moment of inertia product may be in the range from 2.0×10.sup.15 Nkgm to 3.0×10.sup.17 Nkgm.

(244) In various embodiments, a tilt stiffness to moment of inertia ratio may be defined as:

(245) $\frac{\begin{matrix} the tilt stiffness of at least one of the fan shaft (36) \\ at the output of the gearbox and the gearbox support (40) \end{matrix}}{the moment of inertia of the fan (23)}$

(246) In various embodiments, the tilt stiffness to moment of inertia ratio may be greater than or equal to 4.0×10.sup.−4 Nrad.sup.−1 kg.sup.−1 m.sup.−1 (i.e. (Nm/rad)/(kg.Math.m.sup.2)), and optionally greater than or equal to 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(247) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the tilt stiffness to moment of inertia ratio may be greater than or equal to 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the tilt stiffness to moment of inertia ratio may be greater than or equal to 4.0×10.sup.−4 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(248) In various embodiments, the tilt stiffness to moment of inertia ratio may be in the range from 4.0×10.sup.−4 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 2.7×10.sup.−1 Nrad.sup.−1 kg.sup.−1 m.sup.−1, and optionally in the range from 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 0.1 Nrad.sup.−1 kg.sup.−1 m.sup.−1, and further optionally in the range from 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 1.5×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(249) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the tilt stiffness to moment of inertia ratio may be in the range from 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 1.45×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(250) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the tilt stiffness to moment of inertia ratio may be in the range from 4.0×10.sup.−4 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 3.0×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(251) In various embodiments, in addition to or alternatively to the tilt stiffness to moment of inertia ratio, a product of the parameters making up that ratio may be defined. This product (referred to as the tilt stiffness to moment of inertia product) may be defined as:
(the tilt stiffness of at least one of the fan shaft (36) at the output of the gearbox and the gearbox support (40))×(the moment of inertia of the fan (23))

(252) In various embodiments, the tilt stiffness to moment of inertia product may be greater than or equal to 3.0×10.sup.12 Nm.sup.3 rad.sup.−1 kg (i.e. (Nm/rad).Math.(kg.Math.m.sup.2)), and optionally greater than or equal to 6.0×10.sup.12 Nm.sup.3 rad.sup.−1 kg, and further optionally greater than or equal to 2.5×10.sup.13 Nm.sup.3 rad.sup.−1 kg.

(253) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the tilt stiffness to moment of inertia product may be greater than or equal to 2.0×10.sup.13 Nm.sup.3 rad.sup.−1 kg. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the tilt stiffness to moment of inertia product may be greater than or equal to 2.5×10.sup.13 Nm.sup.3 rad.sup.−1 kg.

(254) In various embodiments, the tilt stiffness to moment of inertia product may be in the range from 3.0×10.sup.12 Nm.sup.3 rad.sup.−1 kg to 6.0×10.sup.16 Nm.sup.3 rad.sup.−1 kg, and optionally in the range from 6.0×10.sup.12 Nm.sup.3 rad.sup.−1 kg to 3.0×10.sup.16 Nm.sup.3 rad.sup.−1 kg, and further optionally in the range from 2.5×10.sup.13 Nm.sup.3 rad.sup.−1 kg to 3.0×10.sup.16 Nm.sup.3 rad.sup.−1 kg.

(255) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the tilt stiffness to moment of inertia product may be in the range from 2.0×10.sup.13 Nm.sup.3 rad.sup.−1 kg to 4.0×10.sup.15 Nm.sup.3 rad.sup.−1 kg.

(256) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the tilt stiffness to moment of inertia product may be in the range from 2.5×10.sup.13 Nm.sup.3 rad.sup.−1 kg to 6.0×10.sup.16 Nm.sup.3 rad.sup.−1 kg.

(257) In various embodiments, a fan shaft tilt stiffness to moment of inertia ratio may be defined as:

(258) $\frac{\begin{matrix} the tilt stiffness of the fan shaft (36) \\ at the output of the gearbox \end{matrix}}{the moment of inertia of the fan (23)}$

(259) In various embodiments, the fan shaft tilt stiffness to moment of inertia ratio may be greater than or equal to 4.0×10.sup.−4 Nrad.sup.−1 kg.sup.−1 m.sup.−1 (i.e. (Nm/rad)/(kg.Math.m.sup.2)), and optionally greater than or equal to 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(260) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan shaft tilt stiffness to moment of inertia ratio may be greater than or equal to 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 or greater than or equal to 3.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan shaft tilt stiffness to moment of inertia ratio may be greater than or equal to 4.0×10.sup.−4 Nrad.sup.−1 kg.sup.−1 m.sup.−1 or greater than or equal to 0.7×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(261) In various embodiments, the fan shaft tilt stiffness to moment of inertia ratio may be in the range from 4.0×10.sup.−4 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 0.27 Nrad.sup.−1 kg.sup.−1 m.sup.−1, and optionally in the range from 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 0.1 Nrad.sup.−1 kg.sup.−1 m.sup.−1, and further optionally in the range from 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 1.5×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(262) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan shaft tilt stiffness to moment of inertia ratio may be in the range from 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 1.45×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1 and optionally in the range from 3.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 2.3×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1 (and may be equal to 1.3×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1).

(263) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan shaft tilt stiffness to moment of inertia ratio may be in the range from 4.0×10.sup.−4 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 1.4×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1, and optionally in the range from 7.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 9.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 (and may be equal to 8.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1).

(264) In various embodiments, in addition to or alternatively to the fan shaft tilt stiffness to moment of inertia ratio, a product of the parameters making up that ratio may be defined. This product (referred to as the fan shaft tilt stiffness to moment of inertia product) may be defined as:
the tilt stiffness of the fan shaft (36) at the output of the gearbox×the moment of inertia of the fan (23)

(265) In various embodiments, the fan shaft tilt stiffness to moment of inertia product may be greater than or equal to 5.0×10.sup.12 Nm.sup.3 rad.sup.−1 kg (i.e. (Nm/rad).Math.(kg.Math.m.sup.2)), and optionally greater than or equal to 1.0×10.sup.13 Nm.sup.3 rad.sup.−1 kg or greater than or equal to 6.0×10.sup.13 Nm.sup.3 rad.sup.−1 kg.

(266) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan shaft tilt stiffness to moment of inertia product may be greater than or equal to 6.0×10.sup.13 Nm.sup.3 rad.sup.−1 kg. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan shaft tilt stiffness to moment of inertia product may be greater than or equal to 1.0×10.sup.14 Nm.sup.3 rad.sup.−1 kg.

(267) In various embodiments, the fan shaft tilt stiffness to moment of inertia product may be in the range from 5.0×10.sup.12 Nm.sup.3 rad.sup.−1 kg to 6.0×10.sup.16 Nm.sup.3 rad.sup.−1 kg, and optionally in the range from 1.0×10.sup.13 Nm.sup.3 rad.sup.−1 kg to 3.0×10.sup.16 Nm.sup.3 rad.sup.−1 kg, and further optionally in the range from 6.0×10.sup.13 Nm.sup.3 rad.sup.−1 kg to 3.0×10.sup.16 Nm.sup.3 rad.sup.−1 kg.

(268) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan shaft tilt stiffness to moment of inertia product may be in the range from 6.0×10.sup.13 Nm.sup.3 rad.sup.−1 kg to 3.0×10.sup.15 Nm.sup.3 rad.sup.−1 kg.

(269) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan shaft tilt stiffness to moment of inertia product may be in the range from 1.0×10.sup.14 Nm.sup.3 rad.sup.−1 kg to 6.0×10.sup.16 Nm.sup.3 rad.sup.−1 kg.

(270) In various embodiments, a gearbox support tilt stiffness to moment of inertia ratio may be defined as:

(271) $\frac{the tilt stiffness of the gearbox support (40)}{the moment of inertia of the fan (23)}$

(272) In various embodiments, the gearbox support tilt stiffness to moment of inertia ratio may be greater than or equal to 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 (i.e. (Nm/rad)/(kg.Math.m.sup.2)), and optionally greater than or equal to 2.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(273) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the gearbox support tilt stiffness to moment of inertia ratio may be greater than or equal to 2.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 or greater than or equal to 5.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the gearbox support tilt stiffness to moment of inertia ratio may be greater than or equal to 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 or greater than or equal to 2.6×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(274) In various embodiments, the gearbox support tilt stiffness to moment of inertia ratio may be in the range from 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 7.0×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1, and optionally in the range from 2.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 3.0×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1, and further optionally in the range from 2.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 7.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1.

(275) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the gearbox support tilt stiffness to moment of inertia ratio may be in the range from 2.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 7.2×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 and optionally in the range from 5.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 7.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 (and may be equal to 6.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1).

(276) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the gearbox support tilt stiffness to moment of inertia ratio may be in the range from 1.0×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 3.0×10.sup.−2 Nrad.sup.−1 kg.sup.−1 m.sup.−1, and optionally in the range from 2.6×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 to 4.6×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1 (and may be equal to 3.6×10.sup.−3 Nrad.sup.−1 kg.sup.−1 m.sup.−1).

(277) In various embodiments, in addition to or alternatively to the gearbox support tilt stiffness to moment of inertia ratio, a product of the parameters making up that ratio may be defined. This product (referred to as the gearbox support tilt stiffness to moment of inertia product) may be defined as:
the tilt stiffness of gearbox support (40)×the moment of inertia of the fan (23)

(278) In various embodiments, the gearbox support tilt stiffness to moment of inertia product may be greater than or equal to 3.0×10.sup.12 Nm.sup.3 rad.sup.−1 kg (i.e. (Nm/rad).Math.(kg.Math.m.sup.2)), and optionally greater than or equal to 6.0×10.sup.12 Nm.sup.3 rad.sup.−1 kg, and further optionally greater than or equal to 2.5×10.sup.13 Nm.sup.3 rad.sup.−1 kg.

(279) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the gearbox support tilt stiffness to moment of inertia product may be greater than or equal to 2.0×10.sup.13 Nm.sup.3 rad.sup.−1 kg. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the gearbox support tilt stiffness to moment of inertia product may be greater than or equal to 2.5×10.sup.13 Nm.sup.3 rad.sup.−1 kg.

(280) In various embodiments, the gearbox support tilt stiffness to moment of inertia product may be in the range from 3.0×10.sup.12 Nm.sup.3 rad.sup.−1 kg to 9.0×10.sup.15 Nm.sup.3 rad.sup.−1 kg, and optionally in the range from 6.0×10.sup.12 Nm.sup.3 rad.sup.−1 kg to 4.0×10.sup.15 Nm.sup.3 rad.sup.−1 kg, and further optionally in the range from 2.5×10.sup.13 Nm.sup.3 rad.sup.−1 kg to 4.0×10.sup.15 Nm.sup.3 rad.sup.−1 kg.

(281) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the gearbox support tilt stiffness to moment of inertia product may be in the range from 2.0×10.sup.13 Nm.sup.3 rad.sup.−1 kg to 4.0×10.sup.15 Nm.sup.3 rad.sup.−1 kg.

(282) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the gearbox support tilt stiffness to moment of inertia product may be in the range from 2.5×10.sup.13 Nm.sup.3 rad.sup.−1 kg to 9.0×10.sup.15 Nm.sup.3 rad.sup.−1 kg.

(283) In various embodiments, a product of the fan-gearbox axial distance multiplied by the moment of inertia of the fan may be defined.

(284) In various embodiments, the product of the fan-gearbox axial distance and the moment of inertia of the fan may be greater than or equal to 1.9×10.sup.7 kgm.sup.3, and optionally greater than or equal to 2.9×10.sup.7 kgm.sup.3.

(285) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the product of the fan-gearbox axial distance and the moment of inertia of the fan may be greater than or equal to 2.0×10.sup.7 kgm.sup.3. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the product of the fan-gearbox axial distance and the moment of inertia of the fan may be greater than or equal to 1.2×10.sup.8 kgm.sup.3.

(286) In various embodiments, the product of the fan-gearbox axial distance and the moment of inertia of the fan may be in the range from 1.9×10.sup.7 kgm.sup.3 to 6.2×10.sup.8 kgm.sup.3, and optionally in the range from 2.9×10.sup.7 kgm.sup.3 to 3.9×10.sup.8 kgm.sup.3.

(287) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the product of the fan-gearbox axial distance and the moment of inertia of the fan may be in the range from 2.0×10.sup.7 kgm.sup.3 to 8.0×10.sup.7 kgm.sup.3.

(288) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the product of the fan-gearbox axial distance and the moment of inertia of the fan may be in the range from 1.2×10.sup.8 kgm.sup.3 to 6.2×10.sup.8 kgm.sup.3.

(289) In various embodiments, a ratio given by the fan-gearbox axial distance divided by the moment of inertia of the fan may also be defined.

(290) In various embodiments, the fan-gearbox axial distance divided by the moment of inertia of the fan may be less than or equal to 8.8×10.sup.−9 m/kgm.sup.2 (i.e. kg.sup.−1 m.sup.−1), and optionally less than or equal to 6.2×10.sup.−9 m/kgm.sup.2.

(291) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan-gearbox axial distance divided by the moment of inertia of the fan may be less than or equal to 6.5×10.sup.−9 m/kgm.sup.2 or less than or equal to 5.2×10.sup.−9 m/kgm.sup.2. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan-gearbox axial distance divided by the moment of inertia of the fan may be less than or equal to 2.8×10.sup.−9 m/kgm.sup.2 or less than or equal to 1.8×10.sup.−9 m/kgm.sup.2.

(292) In various embodiments, the fan-gearbox axial distance divided by the moment of inertia of the fan may be in the range from 5.3×10.sup.−10 m/kgm.sup.2 to 8.8×10.sup.−9 m/kgm.sup.2, and optionally in the range from 8.8×10.sup.−10 m/kgm.sup.2 to 6.2×10.sup.−9 m/kgm.sup.2.

(293) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the fan-gearbox axial distance divided by the moment of inertia of the fan may be in the range from 2.1×10.sup.−9 m/kgm.sup.2 to 6.5×10.sup.−9 m/kgm.sup.2 and optionally in the range from 4.0×10.sup.−9 m/kgm.sup.2 to 5.2×10.sup.−9 m/kgm.sup.2 (and may be equal to 4.6×10.sup.−9 m/kgm.sup.2).

(294) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the fan-gearbox axial distance divided by the moment of inertia of the fan may be in the range from 5.3×10.sup.−10 m/kgm.sup.2 to 2.8×10.sup.−9 m/kgm.sup.2, and optionally in the range from 8.0×10.sup.−10 m/kgm.sup.2 to 1.8×10.sup.−9 m/kgm.sup.2 (and may be equal to 1.3×10.sup.−9 m/kgm.sup.2).

(295) In various embodiments, a first gearbox support strength ratio may be defined as

(296) $\frac{the torsional strength of the gearbox support (40)}{\begin{matrix} radial bending stiffness of the gearbox support (40) \times \\ the cross sectional area of the gearbox \end{matrix}}$

(297) In various embodiments, the first gearbox support strength ratio may be greater than or equal to 7.0×10.sup.−3, and optionally greater than or equal to 1.0×10.sup.−2 or greater than or equal to 2.0×10.sup.−2.

(298) In various embodiments, the first gearbox support strength ratio may be in the range from 7.0×10.sup.−3 to 2.5×10.sup.−1, and optionally in the range from 1.0×10.sup.−2 to 1.0×10.sup.−1, in the range from 7.0×10.sup.−3 to 2.0×10.sup.−2 or in the range from 2.0×10.sup.−2 to 2.5×10.sup.−1.

(299) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm or in the range from 330 to 380 cm, the first gearbox support strength ratio may be in the range from 1.9×10.sup.−2 to 2.9×10.sup.−2 (and may be equal to 2.4×10.sup.−2).

(300) In various embodiments, a second gearbox support strength may be defined as:

(301) $\frac{the torsional strength of the gearbox support (40)}{\begin{matrix} tilt stiffness of the gearbox support (40) \times \\ the planet gear spacing angle (β) \end{matrix}}$

(302) In various embodiments, the second gearbox support strength ratio may be greater than or equal to 1.0×10.sup.−1, and optionally greater than or equal to 1.5×10.sup.−1, greater than or equal to 1.0×10.sup.−1 or greater than or equal to 2.5×10.sup.−1.

(303) In various embodiments, the second gearbox support strength ratio may be in the range from 1.0×10.sup.−1 to 3.5, and optionally in the range from 1.5×10.sup.−1 to 1.7, in the range from 1.0×10.sup.−1 to 2.5×10.sup.−1 or in the range from 2.5×10.sup.−1 to 3.5.

(304) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm or in the range from 330 to 380 cm, the second gearbox support strength ratio may be in the range from 2.8×10.sup.−1 to 3.8×10.sup.−1 (and may be equal to 3.3×10.sup.−1).

(305) In various embodiments, a first gearbox support shear stress ratio, may be defined as:

(306) $\frac{the torsional shear stress of the gearbox support (40) at MTO}{radial bending stiffness of the gearbox support (40)}$

(307) In various embodiments, the first gearbox support shear stress ratio may be less than or equal to 4.9×10.sup.1 m.sup.−1, and optionally less than or equal to 20 m.sup.−1.

(308) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the first gearbox support shear stress ratio may be less than or equal to 35 m.sup.−1 or less than or equal to 10.0 m.sup.−1. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the first gearbox support shear stress ratio may be less than or equal to 12 m.sup.−1 or less than or equal to 6.0 m.sup.−1.

(309) In various embodiments, the first gearbox support shear stress ratio may be in the range from 0.35 m.sup.−1 to 4.9×10.sup.1 m.sup.−1, and optionally in the range from 0.70 m.sup.−1 to 20 m.sup.−1.

(310) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the first gearbox support shear stress ratio may be in the range from 0.70 m.sup.−1 to 35 m.sup.−1 and optionally in the range from 6.0 m.sup.−1 to 10.0 m.sup.−1 (and may be equal to 7.8 m.sup.−1).

(311) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the first gearbox support shear stress ratio may be in the range from 0.50 m.sup.−1 to 12 m.sup.−1, and optionally in the range from 3.0 m.sup.−1 to 6.0 m.sup.−1 (and may be equal to 5.4 m.sup.−1).

(312) In various embodiments a second gearbox support shear stress ratio may be defined as:

(313) 0 $\frac{\begin{matrix} the torsional shear stress of the gearbox \\ support (40) at maximum take off conditions \end{matrix}}{tilt stiffness of the gearbox support (40)}$

(314) In various embodiments, the second gearbox support shear stress ratio may be less than or equal to 4.1×10.sup.3 rad/m.sup.3, and optionally less than or equal to 1.4×10.sup.3 rad/m.sup.3.

(315) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the second gearbox support shear stress ratio may be less than or equal to 2.9×10.sup.3 rad/m.sup.3 or less than or equal to 6.5×10.sup.2 rad/m.sup.3. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the second gearbox support shear stress ratio may be less than or equal to 7.0×10.sup.2 rad/m.sup.3 or less than or equal to 2.5×10.sup.2 rad/m.sup.3.

(316) In various embodiments, the second gearbox support shear stress ratio may be in the range from 6.6 rad/m.sup.3 to 4.1×10.sup.3 rad/m.sup.3, and optionally in the range from 1.25×10.sup.1 rad/m.sup.3 to 1.4×10.sup.3 rad/m.sup.3.

(317) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the second gearbox support shear stress ratio may be in the range from 2.9×10.sup.1 rad/m.sup.3 to 2.9×10.sup.3 rad/m.sup.3 and optionally in the range from 2.5×10.sup.2 rad/m.sup.3 to 6.5×10.sup.2 rad/m.sup.3 (and may be equal to 4.5×10.sup.2 rad/m.sup.3).

(318) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the second gearbox support shear stress ratio may be in the range from 1.0×10.sup.1 rad/m.sup.3 to 7.0×10.sup.2 rad/m.sup.3, and optionally in the range from 50 rad/m.sup.3 to 2.5×10.sup.2 rad/m.sup.3 (and may be equal to 1.5×10.sup.2 rad/m.sup.3).

(319) In various embodiments, a flight cycle ratio may be defined as:

(320) $\frac{\begin{matrix} the torsional shear stress of the gearbox \\ support (40) at maximum take off conditions \end{matrix}}{\begin{matrix} the torsional shear stress of the gearbox \\ support (40) at cruise conditions \end{matrix}}$

(321) In various embodiments, the flight cycle ratio may be less than or equal to 3.20, and optionally less than or equal to 2.95, optionally less than or equal to 2.9 (or 2.90), optionally less than or equal to 2.85, or optionally less than or equal to 2.75.

(322) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the flight cycle ratio may be less than or equal to 3.2 or less than or equal to 3.0. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the flight cycle ratio may be less than or equal to 2.8 or less than or equal to 2.7.

(323) In various embodiments, the flight cycle ratio may be in the range from 2.10 to 3.20, and optionally in the range from 2.3 to 2.9.

(324) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the flight cycle ratio may be in the range from 2.3 to 3.2 and optionally in the range from 2.8 to 3.0 (and may be equal to 2.9).

(325) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the flight cycle ratio may be in the range from 2.1 to 2.8, and optionally in the range from 2.3 to 2.7 (and may be equal to 2.6).

(326) In various embodiments, in addition to or alternatively to the flight cycle ratio, a product of the parameters making up that ratio may be defined. This product (referred to as the flight cycle product) may be defined as:
the torsional shear stress of the gearbox support (40) at maximum take off conditions×the torsional shear stress of the gearbox support (40) at cruise conditions

(327) In various embodiments, the flight cycle product may be greater than or equal to 1.00×10.sup.16 (N/m.sup.2).sup.2, and optionally greater than or equal to 2.05×10.sup.16 (N/m.sup.2).sup.2.

(328) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the flight cycle product may be greater than or equal to 2.0×10.sup.16 (N/m.sup.2).sup.2. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the flight cycle product may be greater than or equal to 2.2×10.sup.16 (N/m.sup.2).sup.2.

(329) In various embodiments, the flight cycle product may be in the range from 1.00×10.sup.16 (N/m.sup.2).sup.2 to 7.50×10.sup.16 (N/m.sup.2).sup.2, and optionally in the range from 2.05×10.sup.16 (N/m.sup.2).sup.2 to 4.9×10.sup.16 (N/m.sup.2).sup.2.

(330) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the flight cycle product may be in the range from 2.0×10.sup.16 (N/m.sup.2).sup.2 to 4.9×10.sup.16 (N/m.sup.2).sup.2.

(331) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the flight cycle product may be in the range from 2.2×10.sup.16 (N/m.sup.2).sup.2 to 6.2×10.sup.16 (N/m.sup.2).sup.2.

(332) In various embodiments, a first torque transmission ratio may be defined as:

(333) $\frac{\begin{matrix} the torque transmitted through the \\ gearbox (30) at maximum takeoff conditions \end{matrix}}{\begin{matrix} the torque transmitted through \\ the gearbox (30) at cruise conditions \end{matrix}}$

(334) In various embodiments, the first torque transmission ratio may be less than or equal to 3.2, and optionally less than or equal to 2.95, optionally less than or equal to 2.9 (or 2.90), optionally less than or equal to 2.85 or optionally less than or equal to 2.75.

(335) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the first torque transmission ratio may be less than or equal to 3.2 or less than or equal to 3.0. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the first torque transmission ratio may be less than or equal to 2.8 or less than or equal to 2.7.

(336) In various embodiments, the first torque transmission ratio may be in the range from 2.1 to 3.2, and optionally in the range from 2.3 to 2.9.

(337) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the first torque transmission ratio may be in the range from 2.3 to 3.2 and optionally in the range from 2.8 to 3.0 (and may be equal to 2.9).

(338) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the first torque transmission ratio may be in the range from 2.1 to 2.8, and optionally in the range from 2.5 to 2.7 (and may be equal to 2.6).

(339) In various embodiments, in addition to or alternatively to the first torque transmission ratio, a product of the parameters making up that ratio may be defined. This product (referred to as the first torque transmission product) may be defined as:
the torque transmitted through the gearbox (30) at maximum take off conditions×the torque transmitted through the gearbox (30) at cruise conditions

(340) In various embodiments, the first torque transmission product may be greater than or equal to 2.1×10.sup.9 (Nm).sup.2, and optionally greater than or equal to 3.5×10.sup.9 (Nm).sup.2.

(341) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the first torque transmission product may be greater than or equal to 4.0×10.sup.9 (Nm).sup.2. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the first torque transmission product may be greater than or equal to 9.0×10.sup.9 (Nm).sup.2.

(342) In various embodiments, the first torque transmission product may be in the range from 2.1×10.sup.9 (Nm).sup.2 to 9.0×10.sup.10 (Nm).sup.2, and optionally in the range from 3.5×10.sup.9 (Nm).sup.2 to 5.2×10.sup.10 (Nm).sup.2.

(343) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the first torque transmission product may be in the range from 4.0×10.sup.9 (Nm).sup.2 to 9.0×10.sup.9 (Nm).sup.2.

(344) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the first torque transmission product may be in the range from 9.0×10.sup.9 (Nm).sup.2 to 9.0×10.sup.10 (Nm).sup.2.

(345) In various embodiments, a second torque transmission ratio may be defined as:

(346) $\frac{\begin{matrix} the torque transmitted through the \\ gearbox support (40) at maximum take off conditions \end{matrix}}{\begin{matrix} the torque transmitted through \\ the gearbox support (40) at cruise conditions \end{matrix}}$

(347) In various embodiments, the second torque transmission ratio may be less than or equal to 3.2, and optionally less than or equal to 2.95, or optionally less than or equal to 2.9 (or 2.90), optionally less than or equal to 2.85, or optionally less than or equal to 2.75.

(348) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the second torque transmission ratio may be less than or equal to 3.2 or less than or equal to 3.0. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the second torque transmission ratio may be greater than or equal to 2.8 or less than or equal to 2.7.

(349) In various embodiments, the second torque transmission ratio may be in the range from 2.1 to 3.2, and optionally in the range from 2.3 to 2.9.

(350) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the second torque transmission ratio may be in the range from 2.3 to 3.2 and optionally in the range from 2.8 to 3.0 (and may be equal to 2.9).

(351) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the second torque transmission ratio may be in the range from 2.1 to 2.8, and optionally in the range from 2.3 to 2.7 (and may be equal to 2.6).

(352) In various embodiments, in addition to or alternatively to the second torque transmission ratio, a product of the parameters making up that ratio may be defined. This product (referred to as the second torque transmission product) may be defined as:
the torque transmitted through the gearbox support (40) at maximum take off conditions×the torque transmitted through the gearbox support (40) at cruise conditions

(353) In various embodiments, the second torque transmission product may be greater than or equal to 4.1×10.sup.9 (Nm).sup.2, and optionally greater than or equal to 6.1×10.sup.9 (Nm).sup.2.

(354) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the second torque transmission product may be greater than or equal to 4.1×10.sup.9 (Nm).sup.2. In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the second torque transmission product may be greater than or equal to 1.1×10.sup.10 (Nm).sup.2.

(355) In various embodiments, the second torque transmission product may be in the range from 4.1×10.sup.9 (Nm).sup.2 to 9.0×10.sup.10 (Nm).sup.2, and optionally in the range from 6.1×10.sup.9 (Nm).sup.2 to 8.0×10.sup.10 (Nm).sup.2.

(356) In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the second torque transmission product may be in the range from 4.1×10.sup.9 (Nm).sup.2 to 3.9×10.sup.10.

(357) In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the second torque transmission product may be in the range from 1.1×10.sup.10 (Nm).sup.2 to 9.0×10.sup.10 (Nm).sup.2.

(358) In the ratios defined above the maximum take-off and cruise conditions are as defined anywhere herein.

(359) FIG. 19 illustrates an example aircraft 1000 having a gas turbine engine 10 attached to each wing 1002a, 1002b thereof. Each gas turbine engine 10 is attached via a respective pylon 1004a, 1004b. The gas turbines 10 may be that of any embodiment described herein. The aircraft shown in FIG. 19 is to be understood as the aircraft for which the gas turbine engine 10 of any embodiment or aspect disclosed herein has been designed to be attached. The aircraft 1000 has a cruise condition corresponding to the cruise conditions defined elsewhere herein and a max take-off condition corresponding to the MTO conditions defined elsewhere herein.

(360) The present disclosure also relates to a method 2000 of operating a gas turbine engine on an aircraft (e.g. the aircraft of FIG. 19). The method 2000 is illustrated in FIG. 20. The method 2000 comprises operating 2010 the gas turbine engine 10 described elsewhere herein to provide propulsion for the aircraft to which it is mounted under maximum take-off conditions. The method further comprises operating 2020 the gas turbine engine to provide propulsion during cruise conditions. The gas turbine engine is operated such that any of the parameters or ratios defined herein are within the specified ranges. Cruise conditions and max-take off conditions are as defined elsewhere herein.

(361) The torque on the core shaft 26 may be referred to as the input torque, as this is the torque which is input to the gearbox 30. The torque supplied by the turbine 19 to the core shaft (i.e. the torque on the core shaft) at cruise conditions may be greater than or equal to 10,000 Nm, and optionally greater than or equal to 11,000 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque on the core shaft 26 at cruise conditions may be greater than or equal to 10,000 or 11,000 Nm (and optionally may be equal to 12,760 Nm). In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torque on the core shaft 26 at cruise conditions may be greater than or equal to 25,000 Nm, and optionally greater than or equal to 30,000 Nm (and optionally may be equal to 34,000 Nm).

(362) The torque on the core shaft at cruise conditions may be in the range from 10,000 to 50,000 Nm, and optionally from 11,000 to 45,000 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque on the core shaft 26 at cruise conditions may be in the range from 10,000 to 15,000 Nm, and optionally from 11,000 to 14,000 Nm (and optionally may be equal to 12,760 Nm). In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torque on the core shaft 26 at cruise conditions may be in the range from 25,000 Nm to 50,000 Nm, and optionally from 30,000 to 40,000 Nm (and optionally may be equal to 34,000 Nm).

(363) Under maximum take-off (MTO) conditions, the torque on the core shaft 26 may be greater than or equal to 28,000 Nm, and optionally greater than or equal to 30,000 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque on the core shaft 26 under MTO conditions may be greater than or equal to 28,000, and optionally greater than or equal to 35,000 Nm (and optionally may be equal to 36,300 Nm). In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torque on the core shaft 26 under MTO conditions may greater than or equal to 70,000 Nm, and optionally greater than or equal to 80,000 or 82,000 Nm (and optionally may be equal to 87,000 Nm).

(364) Under maximum take-off (MTO) conditions, the torque on the core shaft 26 may be in the range from 28,000 Nm to 135,000 Nm, and optionally in the range from 30,000 to 110,000 Nm. In some embodiments, for example in embodiments in which the fan diameter is in the range from 240 to 280 cm, the torque on the core shaft 26 under MTO conditions may be in the range from 28,000 to 50,000 Nm, and optionally from 35,000 to 38,000 Nm (and optionally may be equal to 36,300 Nm). In some embodiments, for example in embodiments in which the fan diameter is in the range from 330 to 380 cm, the torque on the core shaft 26 under MTO conditions may be in the range from 70,000 Nm to 135,000 Nm, and optionally from 80,000 to 90,000 Nm or 82,000 to 92,000 Nm (and optionally may be equal to 87,000 Nm).

(365) Torque has units of [force]×[distance] and may be expressed in units of Newton metres (N.Math.m), and is defined in the usual way as would be understood by the skilled person.

(366) FIG. 21 illustrates how the stiffnesses defined herein may be measured. FIG. 21 shows a plot of the displacement δ resulting from the application of a load L (e.g. a force, moment or torque) applied to a component for which the stiffness is being measured. At levels of load from zero to L.sub.R there is a non-linear region in which displacement is caused by motion of the component (or relative motion of separate parts of the component) as it is loaded, rather than deformation of the component; for example moving within clearance between parts. At levels of load above L.sub.S the elastic limit of the component has been exceeded and the applied load no longer causes elastic deformation—plastic deformation or failure of the component may occur instead. Between points R and S the applied load and resulting displacement have a linear relationship. The stiffnesses defined herein may be determined by measuring the gradient of the linear region between points R and S (with the stiffness being the inverse of that gradient). The gradient may be found for as large a region of the linear region as possible to increase the accuracy of the measurement by providing a larger displacement to measure. For example, the gradient may be found by applying a load equal to or just greater than L.sub.R and equal to or just less than L.sub.S. Although the displacement is referred to as δ in this description, the skilled person would appreciate that equivalent principles would apply to a linear or angular displacement.

(367) The stiffnesses defined herein, unless otherwise stated, are for the corresponding component(s) when the engine is off (i.e. at zero speed/on the bench). The stiffness generally does not vary over the operating range of the engine; the stiffness at cruise conditions of the aircraft to which the engine is used (those cruise conditions being as defined elsewhere herein) may therefore be the same as for when the engine is not in use. However, where the stiffness varies over the operating range of the engine, the stiffnesses defined herein are to be understood as being values for when the engine is at room temperature and unmoving. Values for component strength (e.g. the torsional strength of the gearbox support) as given herein are also at room temperature unless otherwise stated.

(368) Anything described herein with reference to a planetary type gearbox can apply equally to a star type gearbox unless otherwise stated or where it is apparent that a feature is specific to a particular gearbox type.

(369) It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Gas turbine engine having gearbox support shear stress ratio

Assignee

Inventors

Cpc classification

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F02C7/36

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F16H57/025

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F02C3/113

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

F16H1/2809

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

F02K3/06

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

F05D2260/941

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

F02C7/20

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

F16H57/082

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

Y02T50/60

GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

Classification Explorer

F05D2260/40311

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

International classification

Classification Explorer

F02C7/36

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F02C3/113

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Abstract

Claims

Description