Rear engine mounting structure

Abstract

A rear engine mounting structure 15, for connecting an engine system (fig.1,1) to an aircraft structure 2, has an elongate body 16 having a first end for connection to an aft side of a turbine exhaust case 6; and one or more mounting points 5 for connection to the aircraft structure. The mounting points are on the elongate body spaced apart from the first end in an axial direction, preferably on a surface of the elongate body. The first end may be connected to either an inner ring (fig.3,12) or an outer ring (fig.3,11) of the exhaust casing. The elongate body may have a polygonal cross-section (fig.8b), and include a lattice of beams (fig.10a). Alternatively, the mounting points are located on an annular body (fig.6c,17) with a number of radial struts (fig.6b,18) connecting it to the centrally located elongate body. The struts may be non-parallel and connect via an inner annular part (fig.6c,17b) of the elongate body, located between the elongate and annular bodies, the circumferential spacing of pairs of struts may be different. The struts may be hollow for conveying fluid. The annular portion may have a number of perforations.

Description

FIELD AND BACKGROUND [1] The present invention relates particularly, but not exclusively, to an engine mounting arrangement for connecting an engine system, such as a gas turbine engine, to an aircraft structure. [2] In conventional engine systems for aircraft, such as gas turbine engines, each engine is typically structurally connected to the aircraft wing via a front engine mount, a rear engine mount and a pylon. These mounts (in combination with the pylon) support the weight of each engine and additionally provide a path for thrust to be transmitted from the engine to the aircraft during taxi and flight. Thrust links may also be used which further connect the engine to the pylon. [3] Conventional engine mounting arrangements are extremely reliable and robust and are used in various forms for different engine and aircraft configurations and combinations. Engine mount arrangements are typically statically determinate, and thus provide a simple load pattern between the engine and aircraft, which is not changed significantly from deformations caused by loads or temperature differences. To preserve the statically determinate character, additional mount points cannot be added to an existing mount system, unless they are mechanically inactive or redundant in normal use, for example by means of a clearance between a pin and an oversized hole associated with the mounting point. [4] However, changes to the environmental requirements in the aerospace industry are leading to changes in engine fuels and operating characteristics. In meeting new emissions requirements additional ancillary equipment is needed both within the aircraft structure and within the engine systems themselves, with both engine and aircraft becoming more complex. This in turn has increased the complexity of the interconnections between the aircraft and engines. [5] The inventors have established an alternative approach to engine mounting that allows some of the most complicated emissions technologies to be used in combination with an engine system, such as a gas turbine engine, as described above. More specifically, the inventors have established an engine mounting approach that allows additional ancillary equipment to be conveniently incorporated into an engine system. SUMMARY [6] Particular aspects and embodiments of inventions are set out in the appended claims. [7] Viewed from a first aspect, there is provided a rear engine mounting structure for connecting an engine system to an aircraft structure, the rear engine mounting structure comprising: an elongate body having a first end arranged in use for connection to an aft side of a turbine exhaust case, the elongate body comprising one or more mounting points for connection to the aircraft structure, wherein the one or more mounting points are spaced from the first end in an axial direction. [8] Thus, unconventionally, a rear engine mounting structure described herein provides a support structure with a rear engine mount (or lug) that is moved aft-wards (compared to conventional arrangements) and is positioned aft of the engine in an airflow direction. Such an arrangement would conventionally be highly undesirable owing to the disruption of exhaust gases from the rear or aft of the turbine exhaust case. However, modifying a support structure as described herein provides a number of technical advantages which can be used to allow new emissions technologies to be incorporated into engine systems. [9] For example, an engine mount that is moved further aft-wards (compared to conventional arrangements) allows additional space or volume for ancillary equipment. More specifically such a support structure aft of the turbine allows the incorporation of additional components into the engine system while maintaining a centre of gravity of the engine system between the engine mounts and without adversely affecting the load distribution of the engine system on the engine mounts. For example, the shear and torsional loads on the engine mounts, particularly the rear engine mount, is reduced. This increases the lifespan of the engine mounts and reduces the likelihood of component failure, increasing the overall safety of the aircraft. This also allows a lighter and more compact design of the mounts and attached structures, and preserves the statically determinate character of the engine mount arrangement.

[10] Still further, as described in more detail below, a support structure described herein allows the exhaust gas flow leaving the turbine exhaust case to be controlled and directed in specific ways. For example, the rear engine mounting structure may provide a gas permeable structure through which exhaust gas from the TEC / turbine can flow. Gas flow surfaces arranged within the mounting structure may advantageously allow specific exhaust gas flow paths to be achieved according to the ancillary equipment being used in the engine.

[11] In one example, it is possible to arrange an additional component, such as a heat exchanger, aft of the turbine without adversely affecting the load distribution of the engine system on the engine mounts, and without placing prohibitively large amounts of load on the engine mounts. As discussed above, for example, the shear and torsional loads on the engine mounts, particularly the rear engine mount is reduced.

[12] Furthermore, by providing a rear engine mounting structure to structurally support and bear the weight / load of an additional component, the additional component does not need to provide its own structural and load-bearing support. For example, the additional component may not be suitably stiff or resistant to torsional loads to be load-bearing itself. Thus, the rear engine mounting structure is able to react the loads associated with the additional component rather than the additional component reacting these loads or forces itself.

[13] In this way, the rear engine mounting structure allows for an optimised additional component, as the load-bearing requirements of the additional component are de-coupled from the additional component itself. This increases design flexibility and compatibility of the arrangement, as the requirement for structural modification of additional components is reduced.

[14] The first end of the rear engine mounting structure may be arranged in use for connection to an inner ring portion or outer ring portion of the turbine exhaust case (TEC). In some examples, these may be an inner flange and outer flange, respectively, of the TEC. As a result, the rear engine mounting structure provides a load path between the aircraft structure and structural portions of the TEC. This allows the structure to react the loads of the structure and an additional component that may be coupled or supported by the structure in use.

[15] The elongate body of the rear engine mounting structure may further comprise a surrounding annular portion, the surrounding annular portion providing the one or more mounting points, the surrounding annular portion comprising one or more radially inwardly extending struts that connect the surrounding annular portion to a portion of the elongate body.

[16] Such an arrangement having a surrounding annular portion with radially extending struts increases the strength of the structure and advantageously circumferentially distributes the load. This reduces the load each component or each region of the components may be placed under, increasing the lifetime of the components. The surrounding annular portion also allows turbine exhaust gas to pass through and between the struts, acting to minimise airflow disruption.

[17] The elongate body may further comprise an inner annular portion provided between the elongate body and the surrounding annular portion, wherein the struts connect the surrounding annular portion to the portion of the elongate body via the inner annular portion.

[18] In other words, two concentric annular portions may be centred on the elongate body, and struts may connect the two annular portions to each other, and the inner annular portion to the elongate body. This arrangement further increases the strength of the structure. Vibrational and shear / torque loads may also be decoupled from each other between the struts of the two annular portions.

[19] In some examples, the circumferential spacing between two different pairs may be different. For example, in order to save weight, an increased number of struts may be provided in the top half of the annular portions than the bottom half.

[20] The rear engine mounting structure may further comprise one or more radially spaced and axially extending beams. These beams may extend fore and aft from the surrounding annular portion. By providing axially extending beams, the bending stiffness of the structure is greatly increased.

[21] One or more struts may comprise an internal channel (or conduit) for communicating fluid. In use, the internal channel may be arranged to couple to the additional component, and thus provides an integral and space-efficient way to provide fluid channels that may be required by an additional component.

[22] In some examples, the surrounding annular portion may be in the form of a mesh or grid like structure so as to provide structural rigidity whilst simultaneously allowing exhaust gas to flow through and out of the structure. For example, the structure may comprise one or more perforations, for example cut-outs or holes. These perforations reduce the weight of the surrounding annular portion and allow gas flow. Peripheral flanges may be provided on the surrounding annular portion to further increase stiffness.

[23] In some examples, the elongate body may comprise a surrounding annular portion, the surrounding annular portion providing the one or more mounting points, the surrounding annular portion connected to one or more axially extending beams that connect a portion of the elongate body at its first end to a portion of the elongate body at a second end opposed to its first end.

[24] In this arrangement, struts are omitted and the axially extending beams provide bending stiffness to the structure. This may provide an arrangement with reduced weight, while still providing adequate stiffness and load-bearing properties.

[25] The portions of the elongate body at its first and second ends may be radially extending portions, for example radially extending discs. These portions connect the axially extending beams at fore and aft ends of the elongate member, and provide further strength and stiffness to the structure.

[26] In some examples, the one or more mounting points may be provided on a surface of the elongate body. The mounting points (also known as mounting lugs) may be provided directly on the surface of the elongate body. This allows for an efficient manufacture of the structure.

[27] In some examples, the wherein the elongate body may be tapered or cone-shaped. Such a shape reduces the disruption caused to the turbine exhaust gases, and provides an aerodynamic profile to reduce drag. In some examples, the elongate body may be flared. This directs the airflow from the turbine radially, for example through an additional component in use, which may be advantageous in some arrangements, for example where the additional component is a heat exchanger.

[28] In some examples, the elongate body may comprise a plurality of beams forming a lattice structure. The lattice structure provides stiffness and increased strength to the rear engine mounting structure, while being weight efficient. Optionally, the plurality of beams may comprise axial and transverse beams, for example axial beams and diagonal cross-braces. This elongated cage-like lattice structure allows air to pass through it, thus minimising its disruption to the airflow from the turbine.

[29] In some examples, the elongate body may comprise a plate positioned at a second end opposed to the first end of the elongate body, and a central structure attached to the plate and arranged in use for connection to an inner flange of the turbine exhaust case. By doing so, a second load path is provided through the plate, central structure, and inner flange of the TEC.

[30] By providing multiple load paths, the rear engine mounting structure may distribute load effectively throughout the structure so as to reduce the load experienced by each individual component. This increases the overall lifetime of the mounting structure, and enables the reduction of weight of each individual component as each component is required to withstand a reduced amount of load.

[31] In some examples, the elongate body has a polygonal orannular cross-section. This provides an efficient load carrying structure whose weight can be minimised while fulfilling mechanical requirements. This also provides an aerodynamic profile to minimise the airflow disruption of the turbine exhaust gas.

[32] In some examples, the elongate body is an exhaust cone of a turbine rear structure. This counter-intuitively transforms the cone into a load-bearing structural part that may be used to support the load of additional components.

[33] In some examples, the mounting points may be provided on a mounting ring that circumferentially surrounds the elongate body. By placing the mounting points on a mounting ring, that may be reinforced, the load can be distributed more evenly around the rear engine mounting structure, helping to reduce load 'hot-spots' and increase the lifespan of the structure components.

[34] In some examples, the mounting ring is annular or polygonal. Thus, the mounting ring acts to transfer load to the elongate body. In examples where the mounting ring is polygonal, the mounting points may be provided at vertices of the polygonal mounting ring. These points are typically the strongest points of the polygonal ring and as such are well-suited to be fixing points for the mounting points.

[35] In some examples, the elongate body may comprise a rear ring at a second end opposed from the first end. This rear ring increases the rigidity of the structure.

[36] In some examples, the elongate body is substantially cylindrical. Such an arrangement is aerodynamically efficient and optimised for the shape of the TEC. The internal volume may be utilised in use to house an additional component, or the outer surface may be utilised in use to support the additional component.

[37] To reduce weight of the structure and allow exhaust gas to flow through the surface of the elongate body, in some examples, the elongate body may be provided with perforations on its surface. These perforations may be in the form of circular, triangular, square, hexagonal etc. holes. Advantageously the holes may be triangular with rounded corners, as these may be manufactured using an efficient milling process.

[38] To reduce weight, in some examples, the elongate body may comprise an isogrid arrangement. Such an arrangement reduces weight as material is cut-out from the surface, but still provides strength and stiffness due to the raised lines between cut-out portions.

[39] In some examples, the mounting points are provided on a surface of the elongate body or a mounting ring that circumferentially surrounds the elongate body. By providing mounting points on the surface of the elongate body manufacture is simplified, and by providing the mounting points on the mounting ring, load may be more evenly distributed throughout the structure.

[40] In some examples, the number of mounting points is three. The present inventors have identified three to be the optimal number for sharing load throughout the structure, and for providing redundancy in case of component failure.

[41] In some examples, one of the mounting points comprises an oversized hole. This hole is oversized relative to the pin or bolt the hole is configured to receive in use. Thus, this mounting point is only active in transferring load if one or more of the other mounting points / links fail. This arrangement provides redundancy and increases safety in the event of component failure.

[42] In some examples, the mounting ring may comprise one or more perforations, for example cut-outs or holes. These perforations facilitate the radial outward flow of air from the turbine.. Peripheral flanges may be provided on the mounting ring to further increase stiffness.

[43] It will be recognised from the description above and the teaching herein that the rear engine mounting structure provides a gas permeable structure through which exhaust gas from the TEC can flow. Gas flow surfaces arranged within the mounting structure may advantageously allow specific exhaust gas flow paths to be achieved according to the ancillary equipment being used in the engine. For example, one or more heat exchangers may be incorporated within or around the engine mounting structure and the exhaust gas directing into, around or through such a heat exchanger(s). Thus, the mounting structure may provide a structural support for the heat exchanger in combination with a means to direct the exhaust gas towards and through the heat exchanger(s). Other configurations could equally be achieved with the mounting structures described herein.

[44] In some examples, the engine system may be a gas turbine engine.

[45] Viewed from a second aspect, there is provided a rear engine mounting structure for connecting an engine system to an aircraft structure, the rear engine mounting structure comprising: an annular body comprising one or more mounting points for connection to the aircraft structure; and one or more radially inwardly extending struts that connect the annular body to an elongate central body, a first end of the elongate central body arranged in use for connection to an aft side of a turbine exhaust case of the engine system.

[46] Thus, in a similar way to the first aspect, it is possible to arrange an additional component, such as a heat exchanger, aft of the turbine without adversely affecting the load distribution of the engine system on the engine mounts, and without placing prohibitively large amounts of load on the engine mounts. For example, the shear and torsional loads on the engine mounts, particularly the rear engine mount is reduced. This increases the lifespan of the engine mounts and reduces the likelihood of component failure, increasing the overall safety of the aircraft.

[47] Viewed from a third aspect, there is provided a method for connecting an engine system to an aircraft structure, the method comprising: providing the rear engine mounting structure of any of the present examples; connecting the first end to an aft side of a turbine exhaust casing of the engine system; and connecting the one or more mounting points to the aircraft structure.

[48] Thus, an engine system may be connected to an aircraft structure in a way to allow the incorporation of an additional component aft of the turbine and without adversely affecting the load distribution of the engine system on the engine mounts or placing prohibitively high amounts of load on the engine system components.

[49] View from a fourth aspect, there is provided an aircraft comprising the rear engine mounting structure of any of the present examples.

[50] Other aspects will also become apparent upon review of the present disclosure, in particular upon review of the Brief Description of the Drawings, Detailed Description and Claims sections. BRIEF DESCRIPTION OF THE DRAWINGS

[51] Examples of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[52] Figure 1 shows an engine system and a conventional arrangement for connecting the engine system to an aircraft structure.

[53] Figure 2 shows an engine system arrangement like that of figure 1, but with an additional component located aft of the TEC.

[54] Figure 3 shows a rear engine mounting structure according to an invention described herein.

[55] Figures 4a and 4b illustrate a side-on cross-sectional view and end-on (rear) view of a rear engine mounting structure according to an invention described herein.

[56] Figures 5a and 5b show end-on (rear) views of rear engine mounting structures according to an invention described herein.

[57] Figures 6a, 6b, and 6c illustrate a side-on cross-sectional view, end-on (rear) view, and end- on (rear view), respectively, of rear engine mounting structures according to an invention described herein.

[58] Figure 7 shows a rear engine mounting structure according to an invention described herein.

[59] Figures 8a and 8b illustrate a side-on cross-sectional view and end-on (rear) view of a rear engine mounting structure according to an invention described herein.

[60] Figure 9 shows a rear engine mounting structure according to an invention described herein.

[61] Figures 10a and 10b illustrate a side-on cross-sectional view and end-on (rear) view of a rear engine mounting structure according to an invention described herein.

[62] Figures Ila and lib illustrate a side-on cross-sectional view and end-on (rear) view of a rear engine mounting structure according to an invention described herein.

[63] Figures 12a and 12b illustrate a side-on cross-sectional view and end-on (rear) view of a rear engine mounting structure according to an invention described herein.

[64] Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known orforms part of the common general knowledge in the field. As used in this specification, the words "comprises", "comprising", and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to". The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

[65] The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc, other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future. DETAILED DESCRIPTION

[66] Figure 1 shows an engine system 1 and a conventional arrangement for connecting the engine system 1 to an aircraft structure 2. In this example, the engine system 1 is a gas turbine engine, having components conventionally associated with a gas turbine engine. Engine system 1 includes a fan case 4 and a turbine exhaust case (TEC) 6. The TEC 6 forms the outer casing of a turbine rear structure (TRS).

[67] As shown in figure 1, engine system 1 is attached to aircraft structure 2, for example a wing pylon, via front engine mount(s) 3, rear engine mount(s) 5 and thrust link(s) 7. Aircraft structure 2 may instead be a portion of the aircraft fuselage itself, for example the rear fuselage or in a blended wing body arrangement. These mounts (also known as lugs) and links distribute and transfer the load of the engine system 1 to the aircraft structure 2. More particularly, in conventional arrangements, the engine system 1 is connected to the aircraft structure 2 via a front engine mount 3 provided on the fan case 4, and via the rear engine mount 5 provided on the TEC 6.

[68] The TEC 6 comprises an inner ring 9 having an inner flange 12 or inner ring portion 12, and an outer ring 10 having an outer flange 11 or outer ring portion 11. In some arrangements, a cone may be centrally provided at the TEC.

[69] The engine system 1 has a central axis shown by dotted line 13 in figure 1, extending axially through the centre of the engine system 1. As also shown in figure 1, the centre of gravity of the engine system 1, labelled by CoG, is located axially between the front engine mount 3 and the rear engine mount 5. As also labelled, an aft-wise direction refers to components located further downstream in an, in use, airflow direction. For example, air enters the fore side of the engine system 1, and exits via the turbine at the aft side of the engine system 1.

[70] Figure 2 shows an engine system arrangement 1 like that of figure 1, but with an additional component 14 located aft (or downstream in an airflow direction in use) of the TEC 6. As discussed herein, in some engine system arrangements it can be beneficial to arrange an additional component aft of the TEC 6, for example a heat exchanger. If an additional component, for example a heat exchanger, is located aft or downstream in an exhaust gas direction of the TEC 6 or turbine, the load distribution of the engine system 1 on the engine mounts 3, 5 can be significantly changed.

[71] This is shown by the centre of gravity, CoG, having previously been located between the front and rear engine mounts 3, 5, now being located aft or rearwards of the rear engine mount 5. As identified by the present inventors, this changed load distribution of the engine system on the engine mounts places significant and varied loads on the engine mounts. This increased load, particularly on the rear engine mount, can result in uneven or increased wear on the engine mounts, thus reducing the 11 lifespan of the components. Furthermore, such increased and aft-distributed loads increases the shear and torsional load on components of the engine system 1 which may increase the likelihood of component failure. This reduces the overall safety of the aircraft.

[72] Turning to figure 3, a rear engine mounting structure 15 according to an invention described herein is shown.

[73] As shown, the rear engine mounting structure 15 comprises an elongate body 16. The elongate body 16 of the rear engine mounting structure 15 is arranged in use for connection to an aft side of the TEC 6 (or TRS) at a first end. For readability, the remainder of the engine system 1 fore of the TEC 6 is not shown. The elongate body 16 may be arranged to connect in use to an inner flange 12, outer flange 11, or both, or other portion, of the TEC 6 at the first end of the elongate body 16. Alternatively, the elongate body 16 may be arranged in use to connect to a radially inner or radially outer surface or portion of the TEC 6 or TRS. By arranging the first end to connect to portions of the TEC 6, the rear engine mounting structure 15 footprint is minimised and so aerodynamic disruption is reduced.

[74] The elongate body 16 is arranged in use to house, directly or indirectly connect with, or otherwise support the additional component 14, which in some examples is a heat exchanger. For example, the elongate body 16 may be provided with one or more connection points for connecting the additional component 14. The additional component 14 may in use be housed by the elongate body 16, or it may be structurally supported by the elongate body 16.

[75] The rear engine mounting structure 15 comprises one or more mounting points 5 (corresponding to the rear engine mount(s)) provided on the elongate body 16. The mounting points 5 described herein may be lugs or portions provided with a through-hole for receiving a bolt or a pin, although it will be appreciated that other techniques may be used. As shown, the mounting point 5 connects to the aircraft structure 2 via a link and pin arrangement. The mounting points 5 may be integrally formed with the elongate body 16.

[76] In comparison to figures 1 and 2, the mounting point 5 is moved from the TEC 6 to instead be provided on the elongate body 16 of the rear engine mounting structure 15. In other words, the rear mounting point 5 is moved aft of the TEC 6, and is spaced in an axial aft-wise direction from the rear of the TEC 6 or TRS. In this way, the mounting points 5 and the TEC 6 are provided on different and axially separated planes that perpendicularly intersect with the axial direction of the engine system 1.

[77] As a result of the changed rear engine mount 5 positon, the centre of gravity, CoG, of the engine system 1 (including the additional component 14) is located between the front engine mount 3 (not shown) and the rear engine mount / mounting point 5. Accordingly, the adverse effects caused by the changed load distribution of the engine system on the engine mounts and the centre of gravity being aft of the rear engine mounting point are reduced. For example, the varied loads on the engine mounts are reduced. In particular, as a result of the arrangement, the shear and torsional loads on the engine mounts, particularly the rear engine mount is reduced. This increases the lifespan of the engine mounts and reduces the likelihood of component failure, increasing the overall safety of the aircraft. In addition, the structure provides a light and compact way for this to be achieved.

[78] Furthermore, by providing a rear engine mounting structure 15 to structurally support and bear the weight / load of the additional component 14, the additional component 14 does not need to provide its own structural and load-bearing support. Indeed, in some examples where the additional component 14 is a heat exchanger, rather than providing structural supports within the heat exchanger which reduces the functional volume of the heat exchanger, the rear engine mounting structure 15 can provide the structural support required. In this way, the rear engine mounting structure 15 allows for an optimised additional component, as the load-bearing requirements of the additional component are decoupled from the additional component itself. This increases flexibility and compatibility of the arrangement, as the requirement for structural modification of additional components is reduced.

[79] Further, in some examples, the additional component 14 may not be suitably stiff or resistant to torsional loads to be load-bearing itself. Thus, the rear engine mounting structure 15 reacts the loads associated with the additional component 14 rather than the additional component 14 reacting these loads or forces itself. This further allows the additional component 14 to be optimised for its intended purpose, such as heat exchanging, without needing to meet structural and strength requirements to support its own load.

[80] As shown in figure 3, the one or mounting points 5 are provided on a surface of the elongate body. A mounting ring may instead be provided that circumferentially surrounds the elongate body and provides a reinforced ring where the mounting points 5 may be located. This provides increased strength and further distributes the load throughout the rear engine mounting structure 15. For example, the mounting ring circumferentially distributes the load throughout the elongate body 16.

[81] Turning to figures 4a and 4b, these show further rear engine mounting structures according to an invention described herein.

[82] As shown, the rear engine mounting structure 15 comprises an elongate body 16, in this example a cone-shaped or tapered elongate body. The elongate body 16 may alternatively be substantially cylindrical or flared. The elongate body 16 is centred on the axis of the engine system (previously shown by dotted line 13), and extends axially aft of the TEC 6 or TRS.

[83] Having a cone-shaped or tapered elongate body 16 reduces the aerodynamic footprint of the rear engine mounting structure 15 and helps to direct airflow being exhausted from the rear of the turbine. Further, having a cone-shaped or tapered elongate body 16 reduces airflow disruption of the turbine exhaust gas thus resulting in increased thrust. Having a flared elongate body 16 may be help radially direct the airflow of the turbine exhaust gas.

[84] Furthermore, in some examples, the present inventors have established that an exhaust cone of the TRS may be counter-intuitively adapted to be the cone-shaped elongate body of the present arrangement.

[85] For example, in some engine systems, it is known to provide an exhaust cone centred on the TEC 6. However, conventionally, these exhaust cones have not performed a load-bearing purpose but are rather based on airflow considerations. Indeed, it is counterintuitive to modify an exhaust cone or structure aft of the TEC 6 so as to disrupt the airflow by including mounting points 5 for connecting the cone or structure to the aircraft structure 2.

[86] Further, as shown, the elongate body 16 is arranged in use to be substantially circumferentially surrounded by additional component 14. This can aid with further reducing the overall footprint of the rear engine mounting structure 15. This can also help direct airflow through the additional component 14, which in examples where the additional component 14 is a heat exchanger, can be particularly advantageous.

[87] The elongate body 16 may be configured in use to connect to or otherwise support the additional component 14. For example, one or more struts may be provided that radially protrude outwards from the elongate body 16. These struts, or indeed the surface of the elongate body 16 itself may be arranged for connection to the additional component 14 or segments thereof.

[88] The aircraft structure 2 may be a wing pylon or may be part of the aircraft fuselage itself. In use, the elongate body 16 of the rear engine mounting structure 15 connects to an aft side of the turbine exhaust casing (TEC) 6 at a first end (the fore end of the rear engine mounting structure 15). This connection may be made through one or more bolts to secure the elongate body 16 to an inner portion, for example inner flange or engine outlet inner flange, of the TEC 6, as discussed above. The elongate body 16 may comprise a flange at its first end to aid in the connection to the TEC 6 and to provide an additional surface through which the connection may be made. Other connection arrangements are possible. In some examples, the elongate body may be welded to the TEC inner casing / inner ring, or the elongate body may be integrally formed with the TEC hub / inner case / inner ring, and thus manufactured as one piece.

[89] The rear engine mounting structure 15 includes one or more mounting points 5 for connection to the aircraft structure 2 as discussed above. For example, the elongate body 16 comprises mounting points 5. The connection is illustrated as being made via a link and a pin inserted through an end of the link and a hole in the mounting point 5. It will be appreciated that other forms of linking arrangements may be used.

[90] As illustrated in figure 4a, the mounting point 5 is spaced from the first end (the end that is arranged to connect to the TEC 6 in use) in an axial direction of the elongate body 16. In some examples, the mounting point 5 may be placed at a central region, for example an axially central region, of the elongate body 16, while the elongate body 16 of the rear engine mounting structure 15 connects to the TEC 6 at its end.

[91] The mounting point 5 in this arrangement transfers vertical force. Thus, in addition to the transferred lateral, vertical and thrust forces, the front engine mount (not shown) also transfers torque around the vertical axis and lateral load. A link for attachment to the mounting point 5 may include a spherical bushing to minimise the transferral of torque, thereby increasing the lifespan of the component. A second mounting point may be added for redundancy, where the second mounting point may comprise an oversized hole (relative to the pin it is configured to receive). This arrangement provides redundancy and increases safety in the event of component failure.

[92] As further shown in figure 4a, the additional component 14, for example a heat exchanger, may be arranged aft of the TEC 6. Although not shown, the rear engine mounting structure may support the weight and load of the additional component 14. This weight or load may be transferred via a variety of connections, for example one or more connecting struts, or the additional component 14 may be attached directly to the elongate body 16 of the rear engine mounting structure, as discussed above. In this way, the rear engine mounting structure 15 may be configured in use to connect to a heat exchanger or configured in use to support the weight of the heat exchanger.

[93] Although the additional component 14 is shown as being provided radially around the elongate body 16, it will be appreciated that the additional component 14 may extend to various amounts of the length of the rear engine mounting structure 15 and elongate body 16. In some examples, the additional component 14 may extend the entire length of the elongate body 16 of the rear engine mounting structure 15.

[94] A load path of this arrangement will now be described. In conventional systems, the rear engine mount is provided on the TEC 6, as discussed above. However, in the present arrangement, the rear engine mount (the mounting point 5) is moved aft of the TEC 6. A load path from the aircraft structure 2 passes through the link to the mounting point 5 of the rear engine mounting structure 15. The mounting point 5 load is reacted in the rear engine mounting structure 15. The load path continues through and along the elongate body 16 of the rear engine mounting structure and then connects with an aft side of the TEC 6. Thus, the elongate body 6, for example the cone or an exhaust cone of the TRS, is a load carrying structure.

[95] Turning to figure 4b, this illustrates an end-on view of the arrangement of figure 4a, taken from the rear. As shown, the rear engine mounting structure 15 and the additional component 14 that it is configured in use to support / connect to are arranged concentrically around a centre axis of the rear engine mounting structure 15 (shown previously by dotted line 13), the TEC 6 and the engine system 1 itself. This concentric arrangement aids in uniform load distribution around the rear engine mounting structure 15 and acts to minimise airflow disruption thus resulting in increased thrust.

[96] As shown in this figure, the additional component 14, which may be a heat exchanger, is provided with a cut-out region surrounding the link that connects the rear engine mounting structure 15 to the aircraft structure 2.

[97] Figure 5a illustrates the rear engine mounting structure 15 having a plurality of mounting points 5, in this example three. In this example, the three mounting points 5 are arranged co-linearly around a circumference of the elongate body 16. As a result of the increased number of mounting points 5, the rear engine mounting structure is able to transfer vertical and lateral forces around the engine axis. It will be appreciated that any of the arrangements described herein may advantageously be provided with three mounting points.

[98] In some examples, one of the mounting points 5, for example the middle of three, has an oversized hole (relative to the pin the hole is shaped to receive), and thus is only active in transferring load if one or more of the other mounting points / links fail.

[99] Figure 5b illustrates the same arrangement as figure 5a, with the difference that the links for connecting the mounting points 5 to the aircraft structure 2 are serpentine. This allows the cut-out region of the additional component 14, for example a heat exchanger, to be reduced in size as the footprint of the links is reduced, due to the links overlapping in the axial direction of the rear engine mounting structure 15 / elongate body 16.

[100] Figures 6a and 6b illustrate another arrangement of the rear engine mounting structure 15. As shown, the elongate body 16 further comprises a surrounding annular portion 17, for example a mounting ring, where the mounting points 5 are provided. The surrounding annular portion 17 circumferentially surrounds and extends around the elongate body 16 of the rear engine mounting structure 15, for example around a central region of the elongate body 16. The surrounding annular portion 17 increases the strength of the rear engine mounting structure 15 and advantageously distributes 16 the load. This reduces the load each component of the arrangement may individually experience, thus increasing the lifetime of the components. The surrounding annular portion 17 may comprise a flange to further increase rigidity.

[101] Further, the use of an annular portion 17, such as a surrounding ring, allows for radial airflow throughout the rear engine mounting structure 15. This is particularly advantageous for arrangements where the additional component 13, such as a heat exchanger, is reliant on the flow of air. This also reduces disruption to the airflow exiting the turbine, thus resulting in increased thrust.

[102] The surrounding annular portion 17 is connected to the elongate body 16 via one or more struts 18. The struts 18 extend radially inwardly from the surrounding annular portion 17 to the elongate body 16. As shown, the surrounding annular portion 17 may have a circular cross-section, and may be cylindrical. The struts assist in the transferral of load from the annular portion 17 to the elongate body 16, and then to the TEC 6. Thus, the struts help to radially distribute the load evenly in the rear engine mounting structure 16.

[103] Advantageously, the one or more mounting points 5 may be provided at regions where a strut 18 connects to the surrounding annular portion 17, so as to aid in the transferral of load. As described previously, one or more (in particular one of three) of the mounting points 5 may comprise an oversized hole.

[104] The additional component 14 may be supported or connected in use to one or more of the struts 18, elongate body 16 or surrounding annular portion 17. As a result, the weight of the additional component 14 is distributed between components of the rear engine mounting structure 15.

[105] In some arrangements (not shown), there may be provided an inner annular portion between the surrounding annular portion 17 and the elongate body 16 that circumferentially surrounds the elongate body 16. The struts 18 may pass through this inner annular portion. This inner annular portion further increases the strength of the arrangement and provides additional connections for the additional component 14 to be connected to in use. The struts 18 above and below the inner ring may be non-parallel, in other words angled with respect to each other. This can advantageously direct the air throughout the arrangement. One or more struts may be provided with an internal channel or cavity for the communication of fluid, for example for use with the additional component 14.

[106] A load path of the arrangement of figures 6a and 6b will now be described. As before, the load is transferred between the aircraft structure 2 and the mounting points 5. The load is then transferred to the mounting ring 17 and the struts 18 to the elongate body 16 and along the elongate body 16, to the aft side of the TEC 6. Thus, this arrangement advantageously provides multiple load paths from the mounting points 5 to the TEC 6 along the different struts 18.

[107] By providing multiple load paths, the rear engine mounting structure may distribute load effectively throughout the structure so as to reduce the load experienced by each individual component. This increases the overall lifetime of the mounting structure, and enables the reduction of weight of each individual component as each component is required to withstand a reduced amount of load.

[108] As shown, the surrounding annular portion 17 only extends along part of the axial extent of the elongate body 16. In other examples, the surrounding annular portion 17 may be a surrounding cylinder that extends along the whole radial extent of the elongate body 16.

[109] While the circumferential spacing of struts 18 is shown as being substantially uniform in this figure, in some cases it may be advantageous to vary this spacing. For example, in order to save weight, an increased number of struts 18 may be provided in the top half of the surrounding annular portion 17 than the bottom half.

[110] The elongate body 16 is this arrangement may be cone-shaped, tapered or flared. This may help promote airflow throughout the structure and the radial movement of the turbine exhaust gas. Further, the elongate body 16 may have perforations on its surface to further allow air to flow throughout the structure and to reduce weight. In some arrangements, the elongate body 16 may be substantially cylindrical. [Ill] Figure 6c shows a similar arrangement to figures 6a and 6b, but with an additional inner annular portion 17b. This inner annular portion 17b provides an additional ring located between the elongate body 16 and surrounding annular portion 17. As shown, struts 18a connect the elongate body 16 with the inner annular portion 17b, and struts 18b connect the inner annular portion 17b with the surrounding annular portion 17. These struts 18a, 18b may advantageously be non-parallel or angled with respect to each other to reduce the thermal mechanical stresses in the component. The addition of this inner annular portion 17b provides further locations to attach ancillary or additional equipment or components.

[112] Turning to figure 7, this shows a similar arrangement to figures 6a and 6b, with the addition of a plurality of axially or longitudinally extending beams 19. These beams are radially spaced around the mounting ring 17 / surrounding annular portion 17 and these beams 19 extend fore and aft from the mounting ring 17 and provide increased bending stiffness to the rear engine mounting structure 15. Furthermore, these beams 19 help to separate the load from the additional component 14 in use. As shown, the beams 19 extend the entire axial length of the rear engine mounting structure 15. This serves to further increase the bending stiffness. The beams 19 may be provided with a plurality of connection points which are configured in use to connect to the additional component 14.

[113] As with all of the described arrangements, the mounting ring 17 (or surrounding annular portion) may be provided with one or more perforations or cut-outs to reduce weight.

[114] The rear engine mounting structure 15 of this figure also comprises a rear plate at the end opposed to the first end, where the elongate body 16 is arranged in use to connect with the TEC 6. As also shown, a first end of the plurality of beams 19 is arranged in use to connect to an outer circumferential portion or ring of the TEC 6, whereas the elongate body 16 is arranged in use to connect to an inner ring of the TEC 6. This arrangement thus advantageously provides multiple load paths from the mounting points 5 to the TEC 6.

[115] By providing multiple load paths, the rear engine mounting structure may distribute load effectively throughout the structure so as to reduce the load experienced by each individual component. This increases the overall lifetime of the mounting structure, and enables the reduction of weight of each individual component as each component is required to withstand a reduced amount of load.

[116] A further arrangement described herein is as shown in figure 7, with the omission of the struts 19. When the rear engine mounting structure 15 comprises one or more axially extending beams (such as beams 19), the structure may have enough stiffness to dispense with the struts 19 to save weight. In this arrangement, the axially extending beams connect a portion of the elongate body 16 at its first end to a portion of the elongate body 16 at a second end opposite to its first end. These portions at the first and second ends may be radially extending portions, for example discs that extend radially from the elongate body 16 at the first and second ends, which are connected by the axially extending beams.

[117] Figures 8a and 8b show another arrangement of the rear engine mounting structure 15.

[118] In this arrangement, the elongate body 16 comprises a plurality of beams forming a lattice structure, for example a cylindrical or polygonal elongate lattice structure. The beams provide strength to the structure and help to spread the load of the additional component 14 throughout the structure. The lattice structure also ensures that air may flow radially outward from the exhaust of the turbine and thus acts to minimise airflow disruption thus resulting in increased thrust.

[119] The plurality of beams may comprise axial and transverse beams, or longitudinal beams and diagonal cross braces, which may be straight or curved to increase the internal space for the additional component 14. Four or more, for example six as shown, longitudinal / axial beams may be used. A hexagonal cross-sectional lattice structure provides substantial internal room while providing structural stiffness.

[120] In this arrangement, the one or more mounting points 5, for example three, are provided at vertices of the polygonal elongate lattice structure. The mounting points 5 transfer load to the elongate lattice structure of the elongate body 16. Further, the elongate body 16 is configured in use to connect to an aft side of the TEC 6, for example an outer flange, such as an engine outlet outer flange or circumferential portion of the TEC 6, as discussed above.

[121] Thus, in contrast to some previous arrangements, the load path of the rear engine mounting structure 15 connects to an outer portion of the TEC 6 rather than an inner flange or inner portion of the TEC 6. In this arrangement, a cone, if present, does not form part of the structure and does not act to carry part of the load of the additional component 14. This can be advantageous for certain arrangements where a cone is not present or where the cone cannot be modified without adversely affecting the engine performance.

[122] The rear engine mounting structure 15, as shown, may comprise a support ring 8 provided at an end opposed to the end that connects in use to the aft side of the TEC 6. This support ring 8 may further provide stiffness to the arrangement.

[123] Figure 9 shows a similar arrangement to figures 8a and 8b. The arrangement of figure 9 additionally comprises a mounting ring 20 that circumferentially surrounds the elongate body 16 and provides the mounting points 5. In other words, the mounting points 5 are provided on the mounting ring 20. The mounting ring 20 increases the strength and stiffness of the rear engine mounting structure 15. The mounting ring 20 also acts to evenly transfer the load circumferentially throughout the rear engine mounting structure 16.

[124] Figures 10a and 10b show a similar arrangement to figures 8a, 8b, and 9. The arrangement of figure 10 additionally or alternatively comprises a plate 22 positioned at the second end opposed from the first end, i.e. at the aft end of the rear engine mounting structure 15. Attached to the plate 22 is a central structure 21. The central structure 21 may be cone-shaped or tapered or flared. This plate 22 and central structure 21 together form a second load path from the mounting points 5 to an inner portion of the TEC 6, for example the inner flange or engine outlet inner flange.

[125] By providing a cone-shaped or tapered central structure 21, the disruption to the airflow exiting the turbine is minimised. A flared central structure 21 may also help to radially direct airflow.

[126] By providing a second load path, the rear engine mounting structure may distribute load effectively throughout the structure so as to reduce the load experienced by each individual component. This increases the overall lifetime of the mounting structure, and enables the reduction of weight of each individual component as each component is required to withstand a reduced amount of load.

[127] Figures Ila and lib show another arrangement of the rear engine mounting structure 15.

[128] As shown, the elongate body 16 in this arrangement is substantially cylindrical. As further shown, the elongate body 16 is provided with perforations on its surface. These perforations may take the form of a plurality of holes, for example circular, triangular, rectangular or hexagonal holes. Preferably the perforations in the form of a plurality of triangular shaped holes having rounded corners, as these are efficient to create with a milling machine. By providing perforations on the elongate body 16, the overall weight of the rear engine mounting structure 16 is reduced, and air may flow between the internal volume of the rear engine mounting structure 16 and the external vicinity. This helps to minimise the airflow disruption of the rear engine mounting structure 16 and allows turbine exhaust gas to pass through the rear engine mounting structure 16. This increases thrust. The perforations may be made by milling sheet metal.

[129] Alternatively, the elongate body 16 comprises an isogrid arrangement. Such an arrangement can increase the strength of the elongate body while reducing its weight.

[130] As shown, a cross-section of the elongate body is circular. It will be appreciated that this may instead be polygonal, with perforated sheets joining longitudinal / axial beams at the vertices of the polygon (as shown for figures 8a, 8b, 9,10a, and 10b).

[131] Figures 12a and 12b show a similar arrangement to figures Ila and lib.

[132] The arrangement of figures 12a and 12b additionally comprise a mounting ring 20 that substantially circumferentially surrounds the elongate body 16. The mounting ring 20 provides the mounting points 5 and increases the strength and stiffness of the rear engine mounting structure 16. The elongate body 16 may be provided with multiple circumferentially surrounding rings spaced apart in an axial direction so as to further increase the strength of the structure.

[133] As with all of the arrangements described herein, the mounting ring 20 may be provided with one or more perforations or cut-outs to reduce its weight.

[134] As shown, air is able to flow through the perforations in the A-A cross section. It will be appreciated that any of the arrangements described herein may be provided with perforations, for example perforations on a surface of the elongate body 16. This reduces weight of the arrangement and allows turbine exhaust gas to flow through the rear engine mounting structure 16, thus minimising its effect on the airflow path.

[135] The components of the rear engine mounting structure 16 described herein may be formed from Nickel alloys. Alternatively, the components may be formed from alloy steel (ferritic or austenitic).

[136] The arrangements described herein may be manufactured using any suitable technique such as forging, pressing, sheet forming, chemical milling, casting, conventional machining or 21 hydroforming. These techniques allow the aerodynamic shapes to be formed to define the desired geometry which is itself defined by the particular engine. The components of the described arrangements may be joined by various techniques such as welding, brazing, and mechanical joints such as bolts, rivets, and pins.

[137] Additive manufacturing technique may also be conveniently used to form either components of the rear engine mounting structure 16 or the rear engine mounting structure 16 itself. Additive manufacturing technique involve building up a 3 dimensional shape as a series or layers, for example using a powder bed technique such as laser beam melting or the like. Intricate geometries may be conveniently formed with minimal material wastage.

[138] Additive manufacturing techniques that may be used to form all or part of an invention described herein include but are not limited to: Powder bed fusion methods; Direct metal laser sintering (DMLS); Electron beam melting (EBM); Selective laser melting (SLM); Selective laser sintering (SLS); Direct metal wire deposition; and Direct metal powder deposition.

Claims

1. A rear engine mounting structure for connecting an engine system to an aircraft structure, the rear engine mounting structure comprising:an elongate body having a first end arranged in use for connection to an aft side of a turbine exhaust case, the elongate body comprising one or more mounting points for connection to the aircraft structure, wherein the one or more mounting points are spaced from the first end in an axial direction.

2. The rear engine mounting structure of claim 1, wherein the first end is arranged in use for connection to an inner ring portion of the turbine exhaust case.

3. The rear engine mounting structure of claim 1, wherein the first end is arranged in use for connection to an outer ring portion of the turbine exhaust case.

4. The rear engine mounting structure of any preceding claim, wherein the elongate body further comprises a surrounding annular portion, the surrounding annular portion providing the one or more mounting points, the surrounding annular portion comprising one or more radially inwardly extending struts that connect the surrounding annular portion to a portion of the elongate body.

5. The rear engine mounting structure of claim 4, wherein the elongate body further comprises an inner annular portion provided between the elongate body and the surrounding annular portion, wherein the struts connect the surrounding annular portion to the portion of the elongate body via the inner annular portion.

6. The rear engine mounting structure of claim 5, wherein an upper portion of the strut that connects the surrounding annular portion to the inner annular portion and a lower portion of the strut that connects the inner annular portion to the portion of the elongate body are non-parallel.

7. The rear engine mounting structure of any of claims 4 to 6, wherein the circumferential spacing between two different pairs of struts is different.

8. The rear engine mounting structure of any of claims 4 to 7, further comprising one or more radiallyspaced and axially extending beams.

9. The rear engine mounting structure of any of claims 4 to 8, wherein one or more struts comprise an internal channel for communicating fluid, and / or optionally wherein the surrounding annular portion comprises one or more perforations.

10. The rear engine mounting structure of any of claims 1 to 3, wherein the elongate body further comprises a surrounding annular portion, the surrounding annular portion providing the one or moremounting points, the surrounding annular portion connected to one or more axially extending beams that connect a portion of the elongate body at its first end to a portion of the elongate body at a second end opposed to its first end.

11. The rear engine mounting structure of claim 10, wherein the portions of the elongate body at its first and second ends are radially extending portions, and / or the surrounding annular portion comprises one or more perforations.

12. The rear engine mounting structure of claims 1 or 2, wherein the one or more mounting points are provided on a surface of the elongate body.

13. The rear engine mounting structure of any preceding claim, wherein the elongate body is tapered, cone-shaped, or flared.

14. The rear engine mounting structure of claims 1 or 3, wherein the elongate body comprises a plurality of beams forming a lattice structure, wherein optionally the plurality of beams comprise axial and transverse beams.

15. The rear engine mounting structure of claims 1, 3 or 14, wherein the elongate body comprises a plate positioned at a second end opposed to the first end, and a central structure attached to the plate and arranged in use for connection to an inner flange of the turbine exhaust case.

16. The rear engine mounting structure of claims 14 to 15, wherein the elongate body has a polygonal or annular cross-section.

17. The rear engine mounting structure of claims 14 to 16, wherein the mounting points are provided on a mounting ring that circumferentially surrounds the elongate body.

18. The rear engine mounting structure of claim 17, wherein the mounting ring is annular or polygonal.

19. The rear engine mounting structure of claim 18, wherein the mounting ring is polygonal and the mounting points are provided at vertices of the polygonal mounting ring.

20. The rear engine mounting structure of claims 14 to 19, wherein the elongate body comprises a rear ring at a second end opposed from the first end.

21. The rear engine mounting structure of claims 1 or 3, wherein the elongate body is substantially cylindrical.

22. The rear engine mounting structure of claim 21, wherein the elongate body is provided with perforations on its surface.

23. The rear engine mounting structure of claim 21, wherein the elongate body comprises an isogrid arrangement.

24. The rear engine mounting structure of claims 21 to 23, wherein the mounting points are provided on a surface of the elongate body or a mounting ring that circumferentially surrounds the elongate body.

25. The rear engine mounting structure of any preceding claim, wherein the number of mounting points is three.

26. The rear engine mounting structure of any preceding claim, wherein one of the mounting points comprises an oversized hole.

27. The rear engine mounting structure of any of claims 17 to 20, and 24, wherein the mounting ring provides one or more perforations.

28. A rear engine mounting structure for connecting an engine system to an aircraft structure, the rear engine mounting structure comprising:an annular body comprising one or more mounting points for connection to the aircraft structure; andone or more radially inwardly extending struts that connect the annular body to an elongate central body, a first end of the elongate central body arranged in use for connection to an aft side of a turbine exhaust case of the engine system.

29. A method for connecting an engine system to an aircraft structure, the method comprising: providing the rear engine mounting structure of any of claims 1 to 28;connecting the first end to an aft side of a turbine exhaust casing of the engine system; and connecting the one or more mounting points to the aircraft structure.

30. An aircraft comprising the rear engine mounting structure of any of claims 1 to 28.

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