Gas turbine engine compression system with core compressor pressure ratio

Abstract

A gas turbine engine has a compression system radius ratio defined as the ratio of the radius of the tip of a fan blade to the radius of the tip of the most downstream compressor blade in the range of from 5 to 9. This results in an optimum balance between installation benefits, operability, maintenance requirements and engine efficiency when the gas turbine engine is installed on an aircraft.

Claims

1. A gas turbine engine for an aircraft, the gas turbine engine comprising: an engine core comprising a turbine, a compressor, and a combustor; a fan comprising a plurality of fan blades; and a gearbox that receives an input from a core shaft that is connected to at least a part of the turbine, the gearbox outputting drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, wherein a compression system speed ratio, defined as a ratio of a rotational speed of a most downstream compressor blade to a rotational speed of the fan at cruise conditions, is in a range of 6 to 8.1; a core compressor pressure ratio, defined as a pressure ratio across the compressor at cruise conditions excluding a pressure rise due to the fan, is in a range from 33 to 60; and a fan pressure ratio, defined as a ratio of a mean total pressure of a flow at a fan exit to a mean total pressure of a flow at a fan inlet, is no greater than 1.45.

2. The gas turbine engine according to claim 1, wherein the compression system speed ratio is in a range of 6 to 8.

3. The gas turbine engine according to claim 1, wherein the compression system speed ratio is in a range of 6.5 to 8.1.

4. The gas turbine engine according to claim 1, wherein a diameter of the fan is in a range of 220 cm to 360 cm.

5. The gas turbine engine according to claim 1, wherein the core compressor pressure ratio is in the range 34 to 52.

6. The gas turbine engine according to claim 1, wherein the compression system speed ratio is in a range of 7.1 to 8.1.

7. The gas turbine engine according to claim 1, wherein, at cruise conditions, a fan tip loading defined as dH/U.sub.tip.sup.2, where dH is an enthalpy rise across the fan and U.sub.tip is a velocity of a fan tip at a leading edge of a tip of a fan blade of the plurality of fan blades, is in a range of 0.28 to 0.30.

8. The gas turbine engine according to claim 1, wherein the compression system speed ratio is in a range of 7.2 to 8.

9. The gas turbine engine according to claim 1, wherein a compression system radius ratio, defined as a ratio of a radius of a tip of a fan blade of the plurality of fan blades to a radius of a tip of the most downstream compressor blade, is in a range of 5.2 to 8.5.

10. The gas turbine engine according to claim 1, wherein the fan pressure ratio is in a range of 1.35 to 1.43.

11. The gas turbine engine according to claim 1, wherein a fan tip pressure ratio, defined as a ratio of a mean total pressure of a flow at the fan exit that subsequently flows through a bypass duct defined radially outside the engine core to the mean total pressure of the flow at the fan inlet, is in a range of 1.30 to 1.45.

12. The gas turbine engine according to claim 1, wherein the gearbox has a reduction ratio in a range of 3.2 to 3.8, such that a rotational speed of the core shaft is in a range of 3.2 to 3.8 times the rotational speed of the fan.

13. The gas turbine engine according to claim 9, wherein a bypass duct is defined radially outside the engine core, with a leading edge of a splitter defining a point at which flow splits into core flow and bypass flow; an engine core radius ratio is defined as a ratio of a radius of a tip of a most downstream turbine blade in the gas turbine engine to a radius of the leading edge of the splitter; and the compression system radius ratio divided by the engine core radius ratio is in a range of 5.5 to 10.

14. The gas turbine engine according to claim 9, wherein a bypass duct is defined radially outside the engine core, with a leading edge of a splitter defining a point at which flow splits into core flow and bypass flow; a core compressor aspect ratio is defined as a ratio of an axial distance between the leading edge of the splitter and a leading edge of the tip of the most downstream compressor blade to a radius of the leading edge of the splitter; and the compression system radius ratio divided by the core compressor aspect ratio is in a range of 1.7 to 4.2.

15. The gas turbine engine according to claim 1, wherein the core compressor comprises twelve or thirteen rotor stages.

16. The gas turbine engine according to claim 1, further comprising an intake that extends upstream of the plurality of fan blades, wherein an intake length L is defined as an axial distance between a leading edge of the intake and a leading edge of a tip of a fan blade of the plurality of fan blades; a fan diameter D is a diameter of the fan at the leading edge of the tip of the fan blade; and a ratio L/D is in a range of 0.25 to 0.4.

17. The gas turbine engine according to claim 9, wherein a product of the compression system radius ratio and the compression system speed ratio is in a range of 35 to 60.

18. The gas turbine engine according to claim 1, wherein a fan root pressure ratio, defined as a ratio of a mean total pressure of a flow at the fan exit that subsequently flows through the engine core to the mean total pressure of the flow at the fan inlet, is no greater than 1.24.

19. The gas turbine engine according to claim 18, wherein a fan tip pressure ratio is defined as a ratio of a mean total pressure of a flow at the fan exit that subsequently flows through a bypass duct defined radially outside the engine core to the mean total pressure of the flow at the fan inlet; and a ratio between the fan root pressure ratio to the fan tip pressure ratio at cruise conditions is in a range of 0.83 to 0.88.

20. The gas turbine engine according to claim 1, wherein the cruise conditions correspond to a forward Mach number of 0.85; and international standard atmospheric conditions at 35000 ft (10668 m).

Description

(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 in accordance with an example of the present disclosure;

(3) FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine in accordance with an example of the present disclosure;

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

(5) FIG. 4 is a schematic of a gas turbine engine in accordance with an example of the present disclosure.

(6) 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.

(7) 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.

(8) Gas turbine engines are susceptible to a phenomenon known as “rotor bow”. As described elsewhere herein, this results from differential cooling of one or more of the shafts 26, 27 when the engine is shut down after use, and can result in the engine being inoperative for an extended period of time after shut down, at least in the absence of time-consuming and/or expensive remedial action. It has been found that this problem may be exacerbated on modern engines, particularly those with a gearbox and/or high compression ratio. As explained elsewhere herein, the gas turbine engines 10 described and/or claimed herein may have a high efficiency (for example in terms of propulsive and/or thermal efficiency) but with a greatly reduced risk of rotor bow affecting the shafts 26, 27.

(9) 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.

(10) 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.

(11) 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.

(12) 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.

(13) 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. 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.

(14) 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.

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

(16) 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.

(17) 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.

(18) It will be appreciated that FIG. 1 is not necessarily to scale in all aspects, and is included merely to aid the description. FIG. 4 is a schematic representation of a gas turbine engine according to the present disclosure, and is provided to illustrate the dimensions referred to herein. Again, FIG. 4 is not necessarily to scale in all aspects. Like reference numerals in the Figures represent like features, and the description provided in relation to one Figure may apply to like features in another Figure.

(19) Referring to FIG. 4, the radius of the fan blade 23 (also referred to as the radius of the tip 231 of the fan blade) is indicated by the dimension ‘Rfan’. The radius of the tip of the most downstream compressor blade 151 is indicated by the dimension ‘Rcomp’. The compression system radius ratio CSRR is thus defined as:

(20) $CSRR=\mathrm{Rfan}\text{/}\mathrm{Rcomp}$

(21) For the gas turbine engine 10, the value of CSRR may be in the ranges defined herein, for example in the range of from 5 to 9, optionally around 5.2 to 8.5, optionally around 5.3 to 7.2, optionally around 5.3 to 6.5.

(22) The gas turbine engine 10 shown in FIG. 4 comprises a splitter 50 having a leading edge at which the flow splits between the bypass flow B and the core flow A. The radius of the leading edge of the splitter is indicated by the dimension ‘Rsplit’. The most downstream turbine blade 191 has a radius indicated by the dimension ‘Rturb’. An engine core radius ratio ECRR is defined as:

(23) $ECRR=\mathrm{Rturb}\text{/}\mathrm{Rsplit}$

(24) For the gas turbine engine 10, the compression system radius ratio (CSRR) divided by the engine core radius ratio (ECRR) may be in the ranges defined herein, for example in the range of from 5.5 to 10, optionally 6 to 8. For the gas turbine engine 10, the compression system blade ratio (defined elsewhere herein) divided by the engine core radius ratio may be in the ranges defined herein, for example in the range of from 50 to 95, optionally 50 to 75. The ECRR itself may be, for example, in the range of from 0.75 to 1, for example 0.8 to 0.95.

(25) The axial distance between the leading edge of the splitter 50 and the leading edge of the tip of the most downstream compressor blade 151 is indicated in FIG. 1 by the dimension ‘Xcomp’. A core compressor aspect ratio CCAR is defined as:

(26) $CCAR=\mathrm{Xcomp}\text{/}\mathrm{Rsplit}$

(27) For the gas turbine engine 10, the compression system radius ratio (CSRR) divided by the core compressor aspect ratio (CCAR) may be in the ranges defined herein, for example in the range of from 1.7 to 4.2, optionally 1.8 to 3.4. For the gas turbine engine 10, the compression system blade ratio (defined elsewhere herein) divided by a core compressor aspect ratio may be in the ranges defined herein, for example in the range of from 15 to 50 The CCAR itself may be in the range of from 2 to 3, for example 2.1 to 2.9, or 2.3 to 2.8.

(28) A compression system speed ratio (CSSR) is defined as the ratio of the rotational speed of the most downstream compressor blade 151 to the rotational speed of the fan 23 at cruise conditions (the rotational speed of the most downstream compressor blade 151 being higher than the rotational speed of the fan 23, of course). For the gas turbine engine 10, the product of the compression system radius ratio and the compression system speed ratio may be in the range of from 25 to 80, for example in the range of from 35 to 65. For the gas turbine engine 10, the product of the compression system blade ratio and the compression system speed ratio may be in the range of from 300 to 800, optionally 320 to 750, optionally 325 to 700. The CSSR itself may be in the range of from 6.0 to 9.5, for example 6.5 to 9.0.

(29) The fan blade has a height hfan. As indicated in FIG. 4 this is defined as the radius of the leading edge 232 at the tip 231 of the blade 23 minus the radius of the point where the leading edge 232 intersects the radially inner gas-washed hub. Similarly, the blade height hcomp of the most downstream compressor blade 151 is defined as the radius of the leading edge at the tip of the blade minus the radius of the point where the leading edge intersects the radially inner gas-washed surface. A compression system blade ratio CSBR is defined as:

(30) $CSBR=\mathrm{hfan}\text{/}\mathrm{hcomp}$

(31) For the gas turbine engine 10, the compression system blade ratio CSBR may be in the ranges defined herein, for example in the range of from 45 to 95, 50 to 75 or 55 to 70.

(32) A core compressor pressure ratio (CCPR) is defined as the pressure (i.e. the mean total pressure) immediately downstream of the final rotor blade 151 in the compressor (for example at the plane perpendicular to the axial direction at the axial position indicated schematically by reference numeral 155 in FIG. 4) divided by the pressure (i.e. the mean total pressure) immediately upstream of the first rotor blade 141 in the core compressor (for example at the plane perpendicular to the axial direction at the axial position indicated schematically by reference numeral 145 in FIG. 4) at cruise conditions. In some arrangements, the core compressor pressure ratio (which is defined at cruise conditions) may be in the range of from 34 to 60, for example 35, 36, 38 or 40 to 55, for example 41 to 52 at cruise conditions.

(33) A ratio of the core compressor aspect ratio divided by the core compressor pressure ratio (i.e. CCAR/CCPR) may be in the ranges defined herein, for example in a range of from 0.03 to 0.09, for example in the range having a lower bound of any of 0.04, 0.045 or 0.05, and an upper bound of any of 0.06, 0.07, 0.08 or 0.085.

(34) No compressor rotor blades other than the most upstream row of rotor blades 141 of the low pressure compressor 14 and the most downstream row of compressor blades 151 of the high pressure compressor 15 are shown in FIG. 4. However, it will be appreciated that this is merely to assist in the explanations provided herein, and that the low pressure compressor 14 and the high pressure compressor 15 each comprise more than one rotor stage, each of which may have an associated stator stage. The total number of rotor stages in the low pressure compressor 14 and the high pressure compressor 15 combined may be, for example, twelve, thirteen, or fourteen.

(35) In a first arrangement of gas turbine engine 10, any one or more of the following may apply: the radius of the fan blade Rfan is 160 cm to 190 cm, the radius of the tip of the most downstream compressor blade 151 is 27 cm to 31 cm, and the CSRR in the range of from 5.3 to 7.7; by way of non-limitative example, the radius of the fan blade Rfan is 175 cm and the radius of the tip of the most downstream compressor blade 151 is 29 cm, giving a CSRR of 6.0 the radius of the most downstream turbine blade 191 is 65 cm to 80 cm, the radius of the leading edge of the splitter 50 is 70 cm to 90 cm, and the ECRR in the range of from 0.8 to 1; by way of non-limitative example, the radius of the most downstream turbine blade 191 is 75 cm and the radius of the leading edge of the splitter 50 is 80 cm, giving an ECRR of 0.93 the axial distance between the leading edge of the splitter 50 and the leading edge of the tip of the most downstream compressor blade 151 Xcomp is 180 cm to 225 cm, and the CCAR is in the range of from 1.7 to 3.4; by way of non-limitative example, the axial distance between the leading edge of the splitter 50 and the leading edge of the tip of the most downstream compressor blade 151 Xcomp is 195 cm, giving a CCAR of 2.4 the fan blade height is 115 cm to 150 cm, the height of the most downstream compressor blade is 1.9 cm to 2.3 cm, and the CSBR is 50 to 90; by way of non-limitative example, the fan blade height is 125 cm, and the height of the most downstream compressor blade is 2.1 cm, giving a CSBR of 60 at cruise conditions, the rotational speed of the fan 23 is 1300 rpm to 1800 rpm and the rotational speed of the most downstream compressor blade 151 is 11000 rpm to 12000 rpm, and the CSSR is in the range of from 6.5 to 9; by way of non-limitative example, at cruise conditions, the rotational speed of the fan 23 is 1650 rpm and the rotational speed of the most downstream compressor blade 151 is 12000 rpm, giving a CSSR of 7.3 at cruise conditions, the fan pressure ratio is 1.30 to 1.45, the fan root pressure ratio is 1.18 to 1.30, the fan tip pressure ratio is 1.30 to 1.45, and the core compressor pressure ratio is 35 to 55; by way of non-limitative example, at cruise conditions, the fan pressure ratio is 1.4, the fan root pressure ratio is 1.25, the fan tip pressure ratio is 1.42, and the core compressor pressure ratio is 44 at cruise conditions, the CCPR is 40 to 60, the ratio CCAR/CCPR is 0.03 to 0.08, and the number of compressor rotor stages is 12 to 14; by way of non-limitative example, at cruise conditions, the CCPR is 44, the ratio CCAR/CCPR is 0.055, and the number of compressor rotor stages is 12.

(36) Purely by way of example, the non-limitative examples referred to in each of the bullets points above relating to a first arrangement may relate to the same engine.

(37) In a second arrangement, any one or more of the following may apply: the radius of the fan blade Rfan is 120 cm to 140 cm, the radius of the tip of the most downstream compressor blade 151 is 20 cm to 25 cm, and the CSRR is in the range of from 5.2 to 6.6; by way of non-limitative example, the radius of the fan blade Rfan is 130 cm and the radius of the tip of the most downstream compressor blade 151 is 23 cm, giving a CSRR of 5.7 the radius of the most downstream turbine blade 191 Rturb is 40 cm to 60 cm, the radius of the leading edge of the splitter 50 Rsplit is 50 cm to 70 cm, and the ECRR is in the range of from 0.75 to 1.0; by way of non-limitative example, the radius of the most downstream turbine blade 191 Rturb is 45 cm and the radius of the leading edge of the splitter 50 Rsplit is 56 cm, giving an ECRR of 0.80 the axial distance between the leading edge of the splitter 50 and the leading edge of the tip of the most downstream compressor blade 151 Xcomp is 150 cm to 190 cm, and the CCAR is in the range of from 2.2 to 3.8; by way of non-limitative example, the axial distance between the leading edge of the splitter 50 and the leading edge of the tip of the most downstream compressor blade 151 Xcomp is 159 cm, giving a CCAR of 2.8 the fan blade height is 75 cm to 100 cm, the height of the most downstream compressor blade is 1.5 cm to 2.0 cm, and the CSBR is 45 to 75; by way of non-limitative example, the fan blade height is 85 cm, and the height of the most downstream compressor blade is 1.7 cm, giving a CSBR of 50 at cruise conditions, the rotational speed of the fan 23 is 2200 rpm to 2700 rpm, the rotational speed of the most downstream compressor blade 151 is 14000 rpm to 17000 rpm, and the CSSR is in the range of from 6 to 8; by way of non-limitative example, at cruise conditions, the rotational speed of the fan 23 is 2500 rpm and the rotational speed of the most downstream compressor blade 151 is 16000 rpm, giving a CSSR of 6.4 at cruise conditions, the fan pressure ratio is 1.30 to 1.45, the fan root pressure ratio is 1.18 to 1.30, the fan tip pressure ratio is 1.30 to 1.45, and the core compressor pressure ratio is 35 to 55; by way of non-limitative example, at cruise conditions, the fan pressure ratio is 1.4, the fan root pressure ratio is 1.25, the fan tip pressure ratio is 1.42, and the core compressor pressure ratio is 35 at cruise conditions, the CCPR is 34 to 50, the ratio CCAR/CCPR is 0.05 to 0.09, and the number of compressor rotor stages is 12 to 14; by way of non-limitative example, at cruise conditions, the CCPR is 35, the ratio CCAR/CCPR is 0.08, and the number of compressor rotor stages is 12.

(38) Purely by way of example, the non-limitative examples referred to in each of the bullets points above relating to a second arrangement may relate to the same engine.

(39) A further example of a feature that may be better optimized for gas turbine engines 10 according to the present disclosure compared with conventional gas turbine engines is the intake region, for example the ratio between the intake length L and the fan diameter D. Referring to FIG. 1, the intake length L is defined as the axial distance between the leading edge of the intake and the leading edge 232 of the tip 231 of the fan blades, and the diameter D of the fan 23 is defined at the leading edge of the fan 23 (i.e. D=2×Rfan). Gas turbine engines 10 according to the present disclosure, such as that shown by way of example in FIG. 1, may have values of the ratio L/D as defined herein, for example less than or equal to 0.45, for example 0.2 to 0.45. This may lead to further advantages, such as installation and/or aerodynamic benefits.

(40) The gas turbine engine 10 shown by way of example in the Figures may comprise any one or more of the features described and/or claimed herein. For example, where compatible, such a gas turbine engine 10 may have any one or more of the features or values described herein of: CSRR; CCAR; ECRR; CSSR; CSBR; core compressor pressure ratio; CCAR/(core compressor pressure ratio); CSRR/ECRR; CSRR/CCAR; CSRR*CSSR; CSBR/ECRR; CSBR/CCAR; CSBR*CSSR; number of compressor rotor stages; specific thrust; maximum thrust, turbine entry temperature; overall pressure ratio; bypass ratio; fan diameter; fan rotational speed; fan hub to tip ratio; fan pressure ratio; fan root pressure ratio; ratio between the fan root pressure ratio to the fan tip pressure ratio; fan tip loading; number of fan blades; construction of fan blades; and/or gear ratio.

(41) 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.