Engine attachment apparatus and method

Abstract

Apparatus for removably suspending a propulsion system externally from a fuselage body of a modular aircraft and along a centre-line of the aircraft, the propulsion system comprising an engine. The apparatus comprises: a support structure; a fuselage mounting arrangement configured to removably suspend the support structure externally from the fuselage body, wherein the support structure is arranged to extend longitudinally below a section of the fuselage body; and an engine mounting arrangement for suspending the engine from the support structure. Also provided is a modular aircraft assembly kit comprising: a plurality of interchangeable support structures arranged to be removably suspended from a fuselage body of a modular aircraft, each support structure being arranged to suspend a respective propulsion system externally from the fuselage body and along a centre-line of the aircraft, and each support structure comprising an engine mounting arrangement for suspending an engine of the respective propulsion system from the support structure. The plurality of support structures comprises: a first support structure from which a first propulsion system is suspended or suspendable, thereby to removably suspend the first propulsion system from the fuselage body; and a second support structure from which a second propulsion system is suspended or suspendable, thereby to removably suspend the second propulsion system from the fuselage body.

Description

[0001] Engine Attachment Apparatus and Method

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to aircraft and apparatus for mounting a propulsion system to an aircraft. In particular, the present invention relates to apparatus and methods for removably suspending a propulsion system from a fuselage body of an aircraft, and a modular aircraft assembly kit for suspending alternative propulsion systems interchangeably from the aircraft.

[0004] BACKGROUND TO THE INVENTION

[0005] The present invention relates to aircraft and airframe structures, and in particular to reconfigurable military training aircraft. Military aircraft pilot training generally requires pilots to train in different aircraft having different capabilities. For example, training may begin with a more basic, relatively low-powered trainer aircraft and may then progress to using one or more different types of more advanced, more powerful trainer aircraft.

[0006] In order to provide trainer aircraft having different capabilities and performance, it is known to provide a modular, reconfigurable jet trainer aircraft which can be reconfigured by fitting different propulsion systems externally to a common fuselage body in order to provide these different types of training aircraft. Such aircraft are disclosed in the present applicant’s granted European Patent No. EP 3 411 293 B1 .

[0007] Advantages of such a modular aircraft system are that a training provider (such as an air force) need not purchase different types of aircraft separately from different manufacturers, but instead a single modular aircraft system can provide all of the required trainer aircraft types, which can have an economic advantage, and also provides continuity and familiarity with the aircraft systems for pilots and engineers.

[0008] In order to provide a conveniently reconfigurable aircraft, there is a need to provide an arrangement to mount a propulsion system externally of a fuselage body of the aircraft,

[0009] P5417PC00

[0010] 05 November 2025 so that propulsion systems can be interchanged without modification to primary, safety- critical airframe structure of the aircraft.

[0011] It is against this background that the present invention is devised. It is an aim of the present invention to overcome at least one problem associated with the prior art, whether referred to herein or otherwise.

[0012] SUMMARY OF THE INVENTION

[0013] According to a first aspect of the invention, there is provided apparatus for removably suspending a propulsion system externally from a fuselage body of a modular aircraft and along a centre-line of the aircraft, the propulsion system comprising an engine, and the apparatus comprising: a support structure; a fuselage mounting arrangement configured to removably suspend the support structure externally from the fuselage body, wherein the support structure is arranged to extend longitudinally below a section of the fuselage body; and an engine mounting arrangement for suspending the engine from the support structure.

[0014] With this arrangement, the apparatus allows convenient mounting and demounting of the propulsion system externally from the fuselage body whilst also providing a support structure which is configured to support an engine of the propulsion system and to transmit thrust from the engine to the fuselage body, and which is external to an airframe structure of the aircraft. Because the support structure is suspended from the fuselage body, and the engine is in turn suspended from the support structure, the engine is indirectly coupled to the fuselage body and the support structure is disposed between the engine and the fuselage body. In this way, the support structure helps to isolate the engine from the airframe structure, which helps to reduce transmission of undesirable forces such as vibrations from the engine to the fuselage body and / or bending forces from the fuselage body to the engine. The apparatus also allows alternative propulsion systems (for example having different engines) to be interchanged for reconfiguration of

[0015] P5417PC00

[0016] 05 November 2025 the aircraft. The support structure may also be referred to as a subframe.

[0017] Also, with these arrangements, the functions of suspending the engine and securing the propulsion system (which comprises the engine and optionally other features) to the aircraft are performed by different structures. Accordingly, the engine mounting arrangement may be optimised for reducing transmission of vibrations to the fuselage body, whilst the fuselage mounting arrangement may be optimised to facilitate convenient removal of the support structure from the fuselage body, to allow removal and / or replacement of the propulsion system. Therefore the apparatus may provide an interface between the fuselage body and the engine and / or propulsion system. Preferably the fuselage mounting arrangement comprises a common interface (e.g., common mounting members) to which a plurality of alternative support structures may be removably secured.

[0018] Preferably the support structure and / or the engine mounting arrangement is configured to reduce transmission of vibrations from the engine to the fuselage body. Preferably the support structure is configured to reduce transmission of bending forces from the fuselage body to the engine.

[0019] The centre-line of the aircraft may also be defined as, or referred to as, a central plane or lateral plane of the aircraft. The central plane or lateral plane extends vertically and longitudinally and may be a plane of symmetry of the aircraft. The apparatus may be arranged to removably suspend the propulsion system along the centre-line of the aircraft such that a central longitudinal axis of the propulsion system is coplanar with, and / or aligned with and / or is parallel to, a longitudinal axis of the aircraft. The support structure may be arranged to be suspended from or secured to part of an airframe structure of the fuselage body. Preferably the centre-line of the aircraft is also a centre-line of the fuselage body.

[0020] According to a second aspect of the invention there is provided a propulsion system assembly comprising a propulsion system and apparatus according to the first aspect of the invention.

[0021] P5417PC00

[0022] 05 November 2025 Also provided is an aircraft comprising apparatus according to the first aspect of the invention.

[0023] According to a third aspect of the invention there is provided a modular aircraft assembly kit comprising: a plurality of interchangeable support structures arranged to be removably suspended from a fuselage body of a modular aircraft, each support structure being arranged to suspend a respective propulsion system externally from the fuselage body and along a centre-line of the aircraft, and each support structure comprising an engine mounting arrangement for suspending an engine of the respective propulsion system from the support structure; the plurality of support structures comprising: a first support structure from which a first propulsion system is suspended or suspendable, thereby to removably suspend the first propulsion system from the fuselage body; and a second support structure from which a second propulsion system is suspended or suspendable, thereby to removably suspend the second propulsion system from the fuselage body.

[0024] In this way the modular aircraft assembly kit enables a single kit to provide different aircraft types for different roles. The modular aircraft assembly kit may comprise the fuselage body. Any or each of the support structures may be according to the first aspect of the invention. Preferably each support structure is configured to suspend a specific respective engine type externally from the fuselage body. Preferably the engine mounting arrangement of each support structure is configured for suspending a specific respective engine type.

[0025] Preferably the modular aircraft assembly kit comprises a fuselage mounting arrangement for removably suspending each support structure from the fuselage body. Preferably the fuselage mounting arrangement is common to (e.g., shared by) each of the support structures so that the support structures can be suspended interchangeably from the fuselage body.

[0026] P5417PC00

[0027] 05 November 2025 According to a fourth aspect of the invention there is provided a method of reconfiguring a modular aircraft, the aircraft comprising a fuselage body, and the method comprising: removing from the fuselage body a first support structure which is arranged to suspend a first propulsion system externally from the fuselage body and along a centreline of the aircraft; suspending from the fuselage body a second support structure which is arranged to suspend a second propulsion system externally from the fuselage body and along a centre-line of the aircraft; wherein each support structure is arranged to be removably suspended externally from the fuselage body and to extend longitudinally below a section of the fuselage body.

[0028] Preferably each support structure is arranged to extend longitudinally below a section of the fuselage body. Preferably the or each support structure defines a mounting plane arranged to locate below the section of the fuselage body and above the engine when the support structure is suspended from the fuselage body and when the engine is suspended from the support structure.

[0029] The or each support structure may define a mounting plane arranged to locate between the fuselage body and the engine when the support structure is suspended from the fuselage body.

[0030] In this way the or each support structure may be arranged to extend in a plane below the fuselage body such that the support structure can be conveniently offered up to a lower side of the fuselage body for mounting the support structure to the fuselage body. Also, this arrangement may allow for a generally planar arrangement of mounting points or mounting members by which the support structure may be secured to the fuselage body, which helps to brace loads acting on the support structure and to distribute loads evenly across the support structure and mounting members.

[0031] Preferably the mounting plane extends horizontally. Preferably the mounting plane

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[0033] 05 November 2025 extends horizontally when the aircraft is at rest. Preferably the mounting plane extends generally horizontally in use. For example, generally parallel to a ground surface when the aircraft is on the ground.

[0034] The or each support structure may comprise a frame. The or each support structure may comprise a frame structure comprising at least one longitudinally extending (elongate) support member and at least one transversely extending (elongate) support member. Preferably the longitudinally extending and transversely extending support members extend parallel to (or extend in) the mounting plane. In this way the or each support structure may comprise a generally planar frame structure which is particularly compact and which helps to brace and / or evenly distribute loads transmitted between the propulsion system and fuselage body.

[0035] Preferably the or each support structure has a longitudinal axis arranged to extend coplanar with, or parallel to, the centre-line of the aircraft or a central plane of the aircraft containing the centre-line. Preferably the longitudinal axis is a central longitudinal axis of the support structure. Preferably the central plane of the aircraft is a vertical plane.

[0036] Preferably each support structure comprises a plurality of first mounting members arranged to be removably secured to second mounting members provided on the fuselage body, thereby to removably secure (suspend) the support structure externally from the fuselage body. Preferably the first mounting members are spaced apart laterally on opposing sides of the longitudinal axis. The fuselage body may comprise the plurality of second mounting members. The fuselage mounting arrangement may comprise the first and second mounting members.

[0037] Preferably the plurality of second mounting members comprises common mounting members and each of the plurality of support structures is arranged to be removably secured to the common mounting members such that the support structures may be suspended interchangeably from the fuselage body.

[0038] In this way, the modular aircraft assembly kit may comprise a common interface for

[0039] P5417PC00

[0040] 05 November 2025 securing the plurality of interchangeable support structures (and thus interchangeable propulsion systems) to the fuselage body.

[0041] The modular aircraft assembly kit may comprise the first and second propulsion systems. Preferably, the second propulsion system is an alternative propulsion system having different propulsion properties to the first propulsion system.

[0042] The modular aircraft assembly kit may comprise a third support structure from which a third propulsion system is suspended or suspendable, thereby to removably suspend the third propulsion system from the fuselage body.

[0043] The modular aircraft assembly kit may comprise at least one pair of removably mountable lateral wing assemblies for securing to a central wing structure of the aircraft. For example to provide wings of the aircraft.

[0044] The modular aircraft assembly kit may comprise a first pair of removably mountable lateral wing assemblies and a second pair of removably mountable lateral wing assemblies. The first pair of removably mountable lateral wing assemblies may be configured for use with the first support structure and first propulsion system to provide a first configuration of the modular aircraft. For example, a basic trainer configuration. The second pair of removably mountable lateral wing assemblies may be configured for use with the second support structure and second propulsion system to provide a second configuration of the modular aircraft. For example, an advanced trainer configuration. The second pair of removably mountable lateral wing assemblies may provide wings having a steeper sweep angle than the first pair of removably mountable lateral wing assemblies.

[0045] The or each propulsion system may be a single or sole propulsion system of the aircraft. That is, preferably only a single propulsion system may be mounted to the aircraft at any time. The or each propulsion system may comprise more than one engine. Preferably at least one of the propulsion systems comprises a twin-engine propulsion system. For example, the first propulsion system may comprise a single-engine propulsion system and the second propulsion system may comprise a twin-engine propulsion system. The

[0046] P5417PC00

[0047] 05 November 2025 third propulsion system may comprise a more powerful engine than the first and / or second propulsion systems. The third propulsion system may comprise an engine having a larger fan diameter than a fan diameter of an engine of the first and / or second propulsion systems.

[0048] According to another aspect of the invention there is provided a propulsion system assembly comprising a propulsion system and apparatus according to the first aspect of the invention.

[0049] When the or each support structure is suspended from the fuselage body, the support structure may be spaced apart below said section of the fuselage body by the fuselage mounting arrangement.

[0050] Preferably the or each support structure is arranged to locate above a central wing structure of the aircraft. Preferably the or each support structure is arranged to locate rearward of the central wing structure. Preferably the or each support structure is arranged to locate rearward of a forward section / front section of the fuselage body. Preferably the aircraft is a low wing aircraft. For example a central wing structure and wings of the aircraft may be disposed on a lower side of the fuselage body. The or each support structure may be arranged to locate below a mid section of the fuselage body. In this way the or each support structure may be arranged to suspend the engine rearward of the central wing structure and / or above the central wing structure.

[0051] The central wing structure may be for securing wing structures thereto to provide wings of the aircraft. For example, the first or second pair of removably mountable lateral wing assemblies may be securable to the central wing structure.

[0052] Preferably the or each engine mounting arrangement comprises vibration isolation mounts arranged to reduce transmission of vibrations from the engine to the support structure.

[0053] Preferably a stiffness of (at least part of) the support structure relative to a stiffness of

[0054] P5417PC00

[0055] 05 November 2025 part of the fuselage body is configured to reduce transmission of forces between the fuselage body and the engine.

[0056] A stiffness of (at least part of) the or each support structure relative to a stiffness of part of the engine mounting arrangement and / or relative to a stiffness of part of the fuselage body may be configured to reduce transmission of ferees between the fuselage body and the engine. In particular, a relative stiffness of parts of the support structure, engine mounting arrangement, and / or fuselage body may be configured to reduce transmission of vibrations from the engine to the fuselage body and / or to reduce transmission of bending or torsional forces from the fuselage body to the engine.

[0057] The or each engine mounting arrangement may be arranged to flex to absorb vibrations from the engine. At least part of the support structure and / or the engine mounting arrangement may be arranged to flex to reduce transmission of bending forces from the fuselage body to the engine. In this way the apparatus may provide isolation between the engine and airframe structure of the aircraft.

[0058] Preferably, the fuselage mounting arrangement comprises a plurality of first mounting members which are provided on the or each support structure and the first mounting members are arranged to be removably secured to second mounting members provided on the fuselage body, thereby to removably suspend the support structure from the fuselage body. The fuselage mounting arrangement may comprise the second mounting members.

[0059] The first and / or second mounting members may comprise brackets. The first or second mounting members may comprise brackets and the other of the first and second mounting members may comprise mounting members arranged to engage with the brackets.

[0060] Preferably the first mounting members are disposed proximate opposing first and second lateral sides of the support structure which are arranged to locate proximate first and second lateral sides of the fuselage body when the support structure is suspended from the fuselage body.

[0061] P5417PC00

[0062] 05 November 2025 This lateral spacing of the mounting members helps to brace loads acting to twist the support structure and helps to evenly distribute transfer of forces from the support structure to the fuselage body.

[0063] The fuselage mounting arrangement may comprise intermediate mounting members (link members) for securing the first mounting members to the second mounting members. Each intermediate mounting member may be arranged to locate between a first mounting member and a second mounting member to secure the first mounting member to the second mounting member. Each link member may be secured to the first mounting member and / or to the second mounting member by a pin (e.g., pinned connection). In this way, the link members may provide a degree of movement or play between the first and second mounting members, which may help the apparatus to absorb transient movements and to prevent binding of the first and second mounting members when removing the support structure.

[0064] Preferably the plurality of first mounting members comprises at least one front first mounting member and at least one rear first mounting member spaced apart longitudinally from the at least one front first mounting member. Preferably the plurality of first mounting members comprises at least two front first mounting members and at least two rear first mounting members spaced apart longitudinally from the at least one front first mounting member.

[0065] The at least one front first mounting member may comprise a pair of front first mounting members. The pair of front first mounting members may be spaced apart laterally from one another. The at least one rear first mounting member may comprise a pair of rear first mounting members. The pair of rear first mounting members may be spaced apart laterally from one another.

[0066] Preferably the fuselage mounting arrangement comprises a front mounting arrangement and a rear mounting arrangement spaced longitudinally from the front mounting arrangement along the longitudinal axis. Preferably the front mounting arrangement

[0067] P5417PC00

[0068] 05 November 2025 comprises the at least one front first mounting member. Preferably the rear mounting arrangement comprises the at least one rear first mounting member. Preferably the front and rear mounting arrangements intersect the mounting plane.

[0069] The apparatus may comprise the second mounting members. The second mounting members may be arranged to be secured to the fuselage body. The second mounting members may be permanently secured to and / or integrally formed with the fuselage body.

[0070] The fuselage mounting arrangement may comprise a mounting interface comprising the second mounting members. Preferably the second mounting members are secured to part of an airframe structure of the fuselage body.

[0071] The second mounting members may comprise front second mounting members and rear second mounting members. The front mounting arrangement may comprise the front second mounting members. The rear mounting arrangement may comprise the rear second mounting members.

[0072] The first mounting members may intersect the mounting plane. The first mounting members may be aligned with or arranged on the mounting plane. The first mounting members may be disposed below the mounting plane. The first mounting members may be disposed between the mounting plane and the engine.

[0073] Preferably, a (central) longitudinal axis of the or each support structure is arranged to extend parallel to the centre-line (or a central plane) of the aircraft when the support structure is suspended from the fuselage body and preferably (at least some of) the first mounting members are spaced apart laterally on opposing sides of the longitudinal axis.

[0074] Preferably the or each support structure comprises first and second lateral support members arranged on either side of the longitudinal axis and which are elongate to extend parallel to the longitudinal axis. Preferably the first mounting members are provided on the first and second lateral support members. The at least one longitudinally extending support member may comprise the first and second lateral support members.

[0075] P5417PC00

[0076] 05 November 2025 The at least one transversely extending support member may comprise front and rear transverse members which are spaced apart from each other longitudinally along the longitudinal axis and which extend laterally between the lateral support members.

[0077] A first lateral support member may at least partially define a first lateral side of the or each support structure. A second lateral support member may at least partially define a second lateral side of the or each support structure. The first mounting members may be disposed inboard of the first and second lateral sides of the or each support structure. The fuselage mounting arrangement may be disposed inboard of the first and second lateral sides of the or each support structure.

[0078] The or each support structure may comprise front and rear transverse members which are spaced apart from each other longitudinally along the longitudinal axis and which extend laterally between the lateral support members. The at least one transverse support member comprises the front and / or rear transverse members.

[0079] Preferably the first and second lateral support members and the front and rear transverse members are disposed in a generally rectangular arrangement. Preferably the or each support structure is generally rectangular. Preferably the or each support structure comprises a generally rectangular frame. Preferably the or each support structure comprises a support frame structure. The or each support structure may be a unitary body. The or each support frame structure may be a unitary body.

[0080] Preferably the or each engine mounting arrangement comprises a front engine mount for securing to a front portion of the engine. Preferably the or each engine mounting arrangement comprises a rear engine mount for securing to a rear portion of the engine. The engine may be spaced apart below the support structure, and / or below the mounting plane, by the engine mounting arrangement. The rear engine mount may be spaced apart rearwardly from the front engine mount along the longitudinal axis.

[0081] The front engine mount may be disposed proximate the front first mounting members and

[0082] P5417PC00

[0083] 05 November 2025 the rear engine mount may be disposed proximate the rear first mounting members. The or each support structure may comprise the engine mounting arrangement.

[0084] The front engine mount may be disposed proximate the front mounting arrangement. The rear engine mount may be disposed proximate the rear mounting arrangement. The front engine mount may be disposed rearwardly of the front mounting arrangement. The rear engine mount may be disposed forward of the rear mounting arrangement.

[0085] The or each engine mounting arrangement may be disposed between the front and rear mounting arrangements (of the fuselage mounting arrangement). The front engine mount may be disposed between the front and rear mounting arrangements. The rear engine mount may be disposed between the front and rear mounting arrangements.

[0086] The or each engine mounting arrangement may comprise at least one elongate bracing member or linkage which extends between the front engine mount and the rear engine mount. The bracing member may extend from the front engine mount in a direction towards the mounting plane and towards the rear engine mount.

[0087] The front engine mount may comprise a bracket. The front engine mount may comprise a pair of laterally spaced arms arranged to extend downward away from the mounting plane on opposing sides of an engine.

[0088] The first mounting members may be disposed proximate peripheral edges of the support structure. The first mounting members may be disposed around a periphery of the support structure. The first mounting members may be disposed between the longitudinal axis and the first and second lateral sides of the support structure. The first mounting members may be disposed inboard of the first and second lateral sides of the support structure.

[0089] In this way the first mounting members may be arranged to locate on either side of the centre-line of the fuselage body. The first mounting members may be arranged to be spaced apart laterally from the centre-line. These arrangements help to brace loads acting on the support structure, such as load from the engine.

[0090] P5417PC00

[0091] 05 November 2025 An aerodynamic housing may be secured to the or each support structure. The or each propulsion system may comprise an aerodynamic housing. The aerodynamic housing may comprise a nacelle. The apparatus may comprise a peripheral (lateral) structure for securing part of an aerodynamic housing or nacelle of the propulsion system thereto.

[0092] The support structure may comprise the peripheral structure. The support structure may comprise a peripheral structure which extends at least part way around a periphery of the support structure for securing part of an aerodynamic housing of the propulsion system to the support structure. The first and second lateral support members may comprise at least part of the peripheral structure.

[0093] In this way, the nacelle may be secured to the support structure, rather than directly to parts of the engine or to a housing or casing of the engine, so that the nacelle is at least partially isolated from engine vibrations. This arrangement helps to prevent the nacelle from colliding or impacting with other parts of the aircraft such as parts of the fuselage body or other airframe structure as a result of engine vibrations and / or relative movements of the engine with respect to other parts of the aircraft.

[0094] With these arrangements, the aerodynamic housing (e.g., nacelle, cowling, or fairings) may be secured to the support structure, rather than directly to the engine or engine mounting arrangement, which helps to isolate the aerodynamic housing from movements and / or vibrations of the engine, which could otherwise damage the aerodynamic housing.

[0095] Preferred features of each embodiment and aspect of the invention may be used, alone or in appropriate combination, in the other embodiments and aspects also.

[0096] P5417PC00

[0097] 05 November 2025 BRIEF DESCRIPTION OF THE DRAWINGS

[0098] Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which like reference numerals indicate like features and in which:

[0099] Figure 1 is a perspective view of apparatus according to a first embodiment of the invention, in use to mount an engine to a fuselage body of an aircraft;

[0100] Figures 2 and 3 are perspective views showing parts of the apparatus of Figure 1 on a lower side of the fuselage body;

[0101] Figure 4A is an upper side perspective view of a support structure of the apparatus of Figure 1 ;

[0102] Figure 4B is a lower side perspective view of the support structure of Figure 4A;

[0103] Figure 5 shows the support structure of Figures 4A and 4B, mounted to the lower side of the fuselage body;

[0104] Figure 6 is an upper perspective view of the support structure of Figures 4A and 4B together with an engine suspended from the support structure and also showing mounting members for securing the support structure to the fuselage body;

[0105] Figure 7 is an upper side perspective view of the support structure and engine of Figure 6;

[0106] Figure 8 is a lower side perspective view of an alternative support structure and engine mounted to a lower side of the fuselage body;

[0107] Figure 9 is a lower side perspective view of another alternative support structure and engine mounted to a lower side of the fuselage body;

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[0109] 05 November 2025 Figure 10A is a lower side perspective view of the support structure of Figure 9;

[0110] Figure 10B is an upper side perspective view of the support structure of Figure 9;

[0111] Figure 11 shows a variant of the support structure of Figure 9, mounted to the lower side of a fuselage body;

[0112] Figures 12A and 12B are perspective views of the variant of the support structure of Figure 11 ;

[0113] Figure 13 is a perspective view of the support structure of Figure 9 superimposed on the variant support structure of Figure 11 , showing shared positioning of mounting members of the support structures;

[0114] Figure 14A is a perspective view of another alternative support structure; and

[0115] Figure 14B is a perspective view of the support structure of Figure 14A, together with engines which the support structure is arranged to suspend from the fuselage body.

[0116] DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0117] The present invention provides apparatus for removably suspending a propulsion system or propulsion unit from a fuselage body of a jet aircraft. In particular the present invention provides a convenient arrangement for releasably mounting a propulsion system to the fuselage body, to support the propulsion system and to transfer thrust from the propulsion system to the fuselage body, whilst also isolating the propulsion system from the fuselage body to prevent undesirable transfer of certain forces and motion (e.g., vibrations) from the propulsion system to the fuselage body. The apparatus of the present invention also helps to prevent parts of the propulsion system from being subjected to unwanted loads transmitted from the fuselage body to the propulsion system, for example resulting from flexing of the fuselage and airframe structure.

[0118] P5417PC00

[0119] 05 November 2025 The present invention also provides a kit comprising a plurality of common (i.e. shared) mounting points or mounting members on the fuselage body, and a plurality of different support structures provided with mounting members which can be releasably mounted to the common mounting points, in order to allow interchanging of the different support structures. Each of the different support structures is configured to carry a different type of propulsion system and in this way, different types of propulsion systems may be mounted interchangeably to the fuselage body via the common mounting points, without the need to modify the fuselage body or other airframe structure.

[0120] In this specification, the terms “front”, “forward” and related terms refer to a position or direction towards a forward end or nose end of the aircraft (e.g. generally towards the left in Figures 1 and 2). Similarly, the terms “rear”, “rearward”, “aft” and related terms refer to a position or direction towards an aft end or tail end of the aircraft (e.g. generally towards the right in Figures 1 and 2).

[0121] Apparatus 100 according to a first embodiment of the invention is shown in Figures 1 to 7. Figure 1 shows the apparatus 100 in use to mount a propulsion system 10 to a fuselage body 12 of an aircraft. The propulsion system comprises an engine 32. Parts of the propulsion system 10 and fuselage body 12 are omitted to show the apparatus 100 more clearly.

[0122] In this example, the fuselage body 12 comprises a forward fuselage section 14 a central or mid fuselage section 16, and an aft fuselage section 18. The fuselage body 12 is at least partly constructed of a conventional arrangement of frames and stringers having an aerodynamic outer skin (not shown). As can be seen in Figure 1 , the propulsion system is mounted below the mid fuselage section 16 and immediately aft of the forward fuselage section 14. Figures 1 , 2 and 3 show parts of the mid and aft fuselage sections 16, 18 and in particular the mid fuselage section 16 to which the apparatus 100 is mountable. The fuselage body 12 has a centre-line X corresponding to a centre-line or midline of the aircraft and which extends longitudinally between a nose end and a tail end of the aircraft. In this embodiment, the modular aircraft comprises a central wing structure 20 which

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[0124] 05 November 2025 extends rearwardly from a lower portion of the forward fuselage section 14. The apparatus 100 and propulsion system 10 are disposed above the central wing structure 20 and rearwardly of the central wing structure 20. The central wing structure 20 is configured for modular lateral wing structures (not shown) to be secured to the central wing structure 20, to provide wings of the aircraft. In this embodiment the aircraft is a low-wing aircraft, in which the wings are arranged proximate a lower side of the aircraft and the propulsion system is mounted at least partially above the wings.

[0125] The mid fuselage section 16 comprises frame members which form part of an airframe structure of the mid fuselage section 16. Referring to Figure 2, the mid fuselage section 16 is elongate and extends between a forward end 28 of the mid fuselage section 16 proximate the forward fuselage section 14 and an aft end 30 of the mid fuselage section 16 proximate the aft fuselage section 18. The mid fuselage section extends laterally between first and second lateral sides 25a, 25b (i.e. , port and starboard sides).

[0126] Referring also to Figures 4A and 4B, the apparatus 100 comprises a support structure which in this embodiment comprises a support frame or support sub-frame 102 from which the propulsion system 10 is suspendable. The support frame 102 is arranged to locate between the fuselage body 12 and the propulsion system 10. The support frame 102 is arranged to be releasably or removably mounted to the fuselage body 12. Accordingly, the apparatus 100 comprises a fuselage mounting arrangement for removably mounting the support frame 102 to the fuselage body 12.

[0127] The fuselage mounting arrangement comprises first, support frame mounting members 104, 106 provided on the support frame 102 (as described further below) and second, fuselage mounting members 108, 110. The fuselage mounting members 108, 110 are arranged to be secured to the fuselage body 12 and in this embodiment are shown secured to (and thus provided on) the fuselage body 12. The support frame mounting members 104, 106 are arranged to engage with the fuselage mounting members 108, 110 to mount the support frame 102 to the fuselage body 12.

[0128] Referring again to Figure 2, in this embodiment, the fuselage mounting members 108,

[0129] P5417PC00

[0130] 05 November 2025 110 comprise a pair of fuselage front mounting members 108a, 108b and a pair of fuselage rear mounting members 110a, 110b. In this example, each of the fuselage front mounting members 108a, 108b is provided by a clevis bracket 108a, 108b and each of the rear fuselage mounting members 110a, 110b is provided by a clevis bracket 110a, 110b. Each clevis bracket 108a, 108b, 110a, 110b comprises a base 112 for securing to the fuselage body 12 and a pair of arms 114 which extend away from the base 112 and are spaced from one another to define a slot 116 therebetween. An aperture 118 extends through each arm 114 proximate an end of the arm furthest from the base 112, and the apertures 118 of the arms 114 are aligned to receive a fastener (such as bolt or pin; not shown) therethrough to extend between the arms 114 across the slot 116.

[0131] As can be seen most clearly in Figure 2, the base 112 of each clevis bracket 108a, 108b, 110a, 110b is secured to a lower side 24 of the mid fuselage section 16, with the arms 114 extending downwardly away from the lower side 24. The slot 116 of each bracket 108a, 108b, 110a, 110b opens downwardly and extends between the arms 114 in a direction parallel to the centre-line X. In this example the fuselage front mounting members (brackets) 108a, 108b are disposed proximate opposing lateral sides 25a, 25b of the mid fuselage section 16. The brackets 108a, 108b are spaced rearwardly from the forward end 28 of the mid fuselage section 16. The fuselage rear mounting members 110a, 110b are longitudinally spaced rearwardly from the fuselage front mounting members 108a, 108b and are disposed proximate opposing lateral sides 25a, 25b of the mid fuselage section 16. With this arrangement, each fuselage rear mounting member 110a, 110b is aligned with, and spaced rearwardly from, a respective fuselage front mounting member 108a, 108b. The slot 116 of each bracket 108a, 108b, 110a, 110b is arranged to receive part of a link member for securing the support structure 102 to the fuselage body 12, as described further below.

[0132] Referring in particular to Figure 3, in this embodiment the fuselage mounting arrangement further comprises intermediate mounting members or link members (which may also be referred to as drop links) which are arranged to secure the support frame 102 to the fuselage mounting members 108a, 108b, 110a, 110b. The link members comprise a pair of front link members 115 and a pair of rear link members 117. Each of the front and rear

[0133] P5417PC00

[0134] 05 November 2025 link members 115, 117 has a generally Y-shaped profile and comprises an upwardly extending lug portion which is arranged to be secured in the slot 116 of a respective front or rear clevis bracket 108a, 108b, 110a, 110b, and a downwardly extending clevis portion comprising a pair of arms defining a slot 119, 121 therebetween. Each slot 119, 121 opens generally downward and is sized to receive part of a support frame mounting member as described below. In this example, the front link members 115 are bulkier than the rear link members 117 and are configured to support a greater load than the rear link members 117.

[0135] Referring in particular to Figures 4A, 4B and 5, in this embodiment the support frame 102 comprises a generally rectangular frame 102 which is elongate and extends between a forward end 122 and a rear end 124. The support frame 102 comprises a generally rectangular plate 105 having an elongate stadium shaped central aperture 107 which extends along the plate 105. In this way, portions of the plate 105 extend around the central aperture 107 and along edges of the generally rectangular plate to define support members of the support frame 102. A flange 109 depends downwardly from a peripheral edge of the plate 105, perpendicular to a plane of the plate 105. This flanged edge 109 helps to provide structural rigidity and stiffness to the support frame 102.

[0136] The support frame 102 comprises first and second lateral support members 126a, 126b which each extend longitudinally between the forward end 122 and the rear end 124 of the support frame 102. The first and second lateral support members 126a, 126b extend generally parallel to one another and generally parallel to a central longitudinal axis A of the support frame 102. The lateral support members 126a, 126b are spaced apart from each other on either side of the longitudinal axis A of the support frame 102. The first and second lateral support members 126a, 126b define first and second (port and starboard) lateral sides 125a, 125b, respectively, of the support frame 102. The first and second lateral support members 126a, 126b converge slightly towards the rear end 124.

[0137] The support frame 102 comprises transverse support members 128, 130 which extend transversely between the lateral support members 126a, 126b. A first, forward transverse support member 128 extends between the first and second lateral support members

[0138] P5417PC00

[0139] 05 November 2025 126a, 126b at the forward end 122 of the support frame 102. A second, rear transverse support member 130 extends between the first and second lateral support members 126a, 126b at the rear end 124 of the support frame 102. The first and second lateral support members 126a, 126b and the front and rear transverse support members 128, 130 are therefore disposed in a generally rectangular arrangement to provide the generally rectangular support frame 102.

[0140] When mounted to the fuselage body 12, the front end 122 of the support frame 102 is arranged to locate proximate the forward end 28 of the mid fuselage section 16 and the rear end 124 of the support frame is arranged to locate below the aft end 30 of the mid fuselage section 16, as can be seen in Figures 1 and 5. The longitudinal axis A is arranged to extend parallel to and below the centre-line X of the fuselage body 12, parallel to a central plane (centre-line) of the aircraft.

[0141] In this embodiment, the first and second lateral support members 126a, 126b and the front and rear transverse support members 128, 130 extend generally in the same plane and together define a mounting plane of the apparatus 100. In this embodiment the mounting plane is arranged to extend generally horizontally below the mid section 16 of the fuselage body 12 when the support frame 102 is suspended from the fuselage body 12. In other embodiments, the mounting plane may be defined by an upper surface of the support frame, or by a lower surface of the support frame, or by a plane intermediate the upper and lower surfaces of the support frame.

[0142] As mentioned above, the support frame 102 comprises the support frame mounting members 104, 106 which form part of the fuselage mounting arrangement for releasably mounting the support frame 102 to the fuselage body 12. In this embodiment, the support frame mounting members 104, 106 comprise a pair of support frame front mounting members 104a, 104b and a pair of support frame rear mounting members 106a, 106b. Each support frame front mounting member 104a, 104b is arranged to be secured to a front fuselage mounting member 108a. 108b. Each support frame rear mounting member 106a, 106b is arranged to be secured to a fuselage rear mounting member 110a, 110b, as described in more detail below.

[0143] P5417PC00

[0144] 05 November 2025 Referring again to Figures 4A and 4B, each support frame front mounting member 104a, 104b projects downwardly from a lower side surface 103 of the plate 105. Each support frame front mounting member 104a, 104b comprises a generally V-shaped member having arm portions and a base. The arm portions extend downward from the lower side surface 103 of the plate 105 and meet at the base of the V-shaped member to provide a lug portion 111 of the front mounting member 104a, 104b which is spaced below the support frame plate 105. In this embodiment therefore, the support frame front mounting members 104a, 104b are arranged below the mounting plane.

[0145] Each support frame front mounting member 104a, 104b is disposed proximate, and rearward of, the forward transverse support member 128. With this arrangement, each support frame front mounting member 104a, 104b is disposed proximate a respective opposing lateral side 125a, 125b of the support frame 102. The support frame front mounting members 104a, 104b are disposed towards the forward end 122 of the support frame 102. An edge of the central aperture 107 is recessed to provide an opening or cutout in the plate 105 above each front mounting member 104a, 104b. A thickness of each lug portion 111 is sized to fit in the slot 119 of one of the forward link members 115. An aperture 136 extends through each lug portion 111 and is arranged to align with corresponding apertures in the clevis portion of a respective forward link member 115.

[0146] In this embodiment, each support frame rear mounting member 106a, 106b projects downwardly from a lower side surface 103 of the plate 105. Each support frame rear mounting member 106a, 106b comprises a generally V-shaped member having arm portions and a base. The arm portions extend downward from the lower side surface 103 of the plate 105 and meet at the base of the V-shaped member to provide a lug portion 113 of the rear mounting member 106a, 106b which is spaced below the support frame plate 105. In this embodiment therefore, the support frame rear mounting members 104a, 104b are arranged below the mounting plane.

[0147] Each of the support frame rear mounting members 106a, 106b is disposed proximate a respective opposing lateral side 125a, 125b of the support frame 102. The support frame

[0148] P5417PC00

[0149] 05 November 2025 rear mounting members 106a, 106b are disposed proximate the rear end 124 of the support frame 102. The support frame rear mounting members 106a, 106b are therefore spaced rearwardly from the support frame front mounting members 104a, 104b. A thickness of each lug portion 113 is sized to fit in the slot 121 of one of the rear link members 117. An aperture 138 extends through each support frame rear mounting member 106a, 106b and is arranged to align with corresponding apertures of a respective one of the rear link members 117. An opening is provided in the plate 105 above each rear mounting member 106a, 106b.

[0150] With the arrangements described above, in the present embodiment, the fuselage mounting arrangement comprises a front mounting arrangement comprising the fuselage front mounting members 108a, 108b, front link members 115 and the support frame front mounting members 104a, 104b, and a rear mounting arrangement comprising the fuselage rear mounting members 110a, 110b, rear link members 117 and the support frame rear mounting members 106a, 106b. In this way the front mounting arrangement is spaced apart longitudinally from the rear mounting arrangement along the longitudinal axis A of the support frame 102. The front and rear mounting arrangements are arranged to intersect the mounting plane. These arrangements help to distribute and brace forces from the propulsion system over several points of connection (four in this example) between the support frame 102 and the fuselage body 12.

[0151] In use, and referring in particular to Figures 3 and 5, to secure the support frame 102 to the fuselage body 12, the support frame 102 is offered up to the lower side 24 of the mid fuselage section 16 so that each support frame front mounting member 104a, 104b is aligned with the slot 119 of a respective front link member 115 secured to a respective fuselage front mounting member 108a, 108b. Each support frame rear mounting member 106a, 106b is aligned with the slot 121 of a respective rear link member 117 secured to a respective fuselage rear mounting member 110a, 110b. Each lug portion 111 is inserted into the slot 119 of a respective front link member 115 and the aperture 136 in the lug portion 111 is aligned with apertures of the front link member 115. Each support frame front mounting member 104a, 104b is secured to its respective front link member 115 by insertion of a pin or other fastener (not shown) through the respective aligned apertures

[0152] P5417PC00

[0153] 05 November 2025 118, 136 of the link member and front mounting member 104a, 104b.

[0154] Each support frame rear mounting member 106a, 106b is positioned to insert into the slot of a respective rear link member 117 and to align the aperture 138 of the support frame rear mounting member 106a, 106b with the aperture 120 of the rear link member 117. The support frame rear mounting member 106a, 106b is secured to the rear link member 117 by insertion of a pin or other fastener (not shown) through the respective aligned apertures 120, 138, of the rear link member 117 and the respective support frame rear mounting member 106a, 106b. With these arrangements, the support frame 102 can be conveniently and releasably secured to the fuselage body 12, to secure releasably the propulsion system 10 to the fuselage body 12, as described further below. Figure 6 shows from above the support frame 102 suspended from the fuselage mounting members 108a, 108b, 110a, 110b by the link members 115, 117, with the fuselage body hidden so that the arrangement of the fuselage mounting members 108a, 108b, 110a, 110b can be seen clearly.

[0155] In the present example, the pinned connections between the first and second mounting members and the link members provide a degree of movement or play between the first and second mounting members and the link members. This arrangement helps to prevent binding or jamming of the first and second mounting members and helps to ensure that the support frame can be conveniently mounted and demounted from the fuselage body. This arrangement also helps to prevent transmission of transient movements such as vibrations from the support frame to the fuselage body. The use in some embodiments of intermediate link members between the fuselage mounting members and the support frame mounting members may additionally provide flexibility in how the aircraft may be reconfigured, for example by use of alternative link members for use with different support frames. In this way the link members may function as adaptors to couple different support frames to the common fuselage mounting members. It will be appreciated that other suitable mounting arrangements and / or fasteners may be used to releasably secure the support structure to the fuselage body.

[0156] Referring again to Figures 4A, 4B and 5, and also to Figures 6 and 7, the apparatus 100

[0157] P5417PC00

[0158] 05 November 2025 further comprises an engine mounting arrangement for suspending the engine 32 from the support frame 102. In this embodiment, the engine mounting arrangement comprises a front engine mount 144 and rear engine mount 146. The front engine mount 144 is arranged to be secured to a front portion of the engine 144. The rear engine mount 146 is arranged to be secured to a rear portion of the engine 32.

[0159] In this embodiment, the front engine mount 144 comprises a generally U-shaped bracket 144 comprising a base portion 148 secured to the support frame 102 and a pair of laterally spaced arms 150 which extend downwardly from the base portion 148 proximate opposing lateral sides 125a, 125b of the support frame 102. The base portion 148 comprises a downwardly facing arcuate surface which extends between the arms 150 and which is shaped to match the curvature of a cylindrical outer surface of the engine 32. The front engine mount 144 is secured to the support frame 102 proximate a rear side of the support frame front mounting members 104a, 104b. Although not shown or described in detail herein, the arms 150 and / or the base portion 148 are provided with means for securing the engine 32 to the bracket 144, in order to secure the engine 32 to the support frame 102.

[0160] The rear engine mount 146 comprises elongate mounting members which extend transversely between the lateral support members 126a, 126b across the central aperture 107, adjacent the rear end 124 of the support frame 102. The rear engine mount defines an elongate transverse slot 154 which opens downwards through the central aperture 107. The slot 154 is elongate to extend generally perpendicular to the longitudinal axis of the support frame 102. The slot 154 is sized to receive a mounting projection 34 provided on the rear portion of the engine 32, to secure the rear portion of the engine 32 to the rear engine mount 146 and thus to secure the engine 32 to the support frame 102.

[0161] In the present embodiment, the engine mounting arrangement comprises a pair of elongate linkages 164 which extend rearwardly from the front engine mount 144 towards the rear engine mount 146. Each linkage 164 extends from a lower end portion of one of the arms 150 in a direction rearward and upward, towards the plate 105. Each linkage 164 is connected by a pin to a bracket provided on the lower side surface of the plate,

[0162] P5417PC00

[0163] 05 November 2025 proximate a front side of a respective support frame rear mounting member 106a, 106b. Each linkage 164 may be secured by a pin to its respective arm 150. The linkages 164 help to transfer loads (for example loads applied by the engine) between the front and rear engine mounts 144, 146, to help distribute load more evenly between the front and rear mounting arrangements 144, 146. In preferred embodiments, the engine mounting arrangement comprises vibration isolation mounts (not shown) comprising one or more resilient elements configured to reduce transmission of vibrations from the engine to support frame. The front and / or rear engine mounts may comprise vibration isolation mounts.

[0164] The support structure and engine mounting arrangement illustrated in Figures 1 , 4A, 4B, 5, 6 and 7 are configured to support a specific engine. As mentioned above however, the present invention also provides a plurality of alternative support structures, each configured to support a different engine type. Accordingly, each support structure may comprise a different engine mounting arrangement for securing a specific engine to the support structure. Examples of such alternative support structures are described further below. It will be appreciated that substantially any suitable engine mounting arrangement may be used, to suit a particular engine.

[0165] With the arrangements described above, the apparatus 100 is configured to removably suspend a propulsion system from the fuselage body 12 so that the propulsion system can be conveniently removed and replaced (for example with an alternative propulsion system) without requiring disassembly of any primary airframe structure of the aircraft. The apparatus 100 is arranged such that useful forces (e.g., thrust) are transmitted between the propulsion system and the fuselage body 12 (for example during flight, takeoff and / or landing) whilst reducing transfer of unwanted forces or movements (e.g., vibrations) from the engine 32 to the fuselage body 12 and other airframe structure.

[0166] Because the support frame 102 is suspended from the fuselage body 12, and the engine is suspended from the support frame 102, the propulsion system is indirectly coupled to the fuselage body and so the apparatus 100 acts to isolate the propulsion system 10, and in particular the engine 32, from the fuselage body 12. The link members help further to

[0167] P5417PC00

[0168] 05 November 2025 isolate the support frame from the fuselage body. In this way, certain forces such as vibrations or transient forces resulting from sudden movements from the engine 32 are absorbed and / or dampened by the apparatus 100 and thus at least partially prevented from being transmitted to the fuselage body 12 and airframe structure of the aircraft. For instance, the engine 32 may produce vibrations or other behaviours, which can cause unwanted forces to act on other parts of the aircraft such as the fuselage body 12 or other parts of the airframe structure, which may cause wear and damage. Similarly, if there is a sudden change in thrust from the engine 32, the apparatus 100 may allow a limited degree of movement of the engine 32 relative to the fuselage body 12, to limit the magnitude of ferees transmitted to the fuselage body 12.

[0169] Moreover, the apparatus 100 also functions to isolate parts of the propulsion system 10 such as the engine 32 from forces which act on the fuselage body 12 during flight. For instance, flexing or bending of parts of the fuselage body 12 may occur during flight as a result of loads acting on wings of the aircraft and / or torsion between the wings and empennage (not shown) may act to twist or flex the fuselage body 12. The apparatus 100 acts to reduce the transmission of these forces from the fuselage body 12 to the propulsion system 10, to prevent undesirable loads being transferred to parts of the engine 32 (such as a casing of the engine), which could cause damage or failure. In this way, the apparatus 100 can be considered to act as an adapter between the fuselage body 12 and the propulsion system 10 which reduces transmission of certain forces between the fuselage 12 and parts of the propulsion system 10.

[0170] As can be seen most clearly in Figures 4B and 6, in this embodiment the support structure also comprises a bracing arrangement comprising front and rear bracing members or struts 166, 168. A first end 170 of the front bracing member 166 is secured by a pinned connection to the first lateral support member 126a proximate the front end 122 of the support frame 102. The front bracing member 166 is arranged to extend across the central aperture proximate the forward transverse support member 128. A second end 172 of the front bracing member 166 is arranged to be mounted to a front bracket 174 provided on the lower side 24 of the fuselage body 12.

[0171] P5417PC00

[0172] 05 November 2025 A first end 176 of the rear bracing member 168 is secured by a pinned connection to the second lateral support 126b member adjacent the rear end 124 of the support frame 102. A second end 178 of the rear bracing member 168 is arranged to be pivotally mounted to a rear bracket 180 provided on the lower side 24 of the fuselage body 12. In this way, the front and rear bracing members 166, 168 extend from opposing lateral sides 125a, 125b of the support frame 102. This arrangement helps to prevent sway and torsional movement of the support frame 102 with respect to the fuselage body 12.

[0173] Although not illustrated, the support frame 102 also provides a supporting structure to which at least part of an aerodynamic housing or nacelle (not shown) of the propulsion system is secured. In particular, parts of the nacelle are secured to the first and second lateral support members 126a, 126b on the first and second lateral sides 125a, 125b of the support frame 102. In this way the support frame 102 comprises a peripheral structure to which parts of the nacelle are attached. Accordingly, the apparatus 100 may be arranged to suspend from the fuselage body a propulsion system or engine pod comprising an engine and nacelle, so that the engine and nacelle may be suspended from the fuselage body 12 as a single integrated unit.

[0174] In this way, the nacelle is mounted to the support frame 102, rather than being directly mounted to the engine 32. This arrangement helps to reduce the transmission of vibrations or other transient movements from the engine to the nacelle, which could otherwise cause the nacelle to collide with other parts of the aircraft such as the fuselage body 12.

[0175] Also, as the fuselage body flexes under in-flight loads, and causes the support frame 102 to flex slightly, the nacelle also flexes sufficiently that edges of the nacelle remain close to an outer surface of the fuselage body 12, to prevent gaps forming between the nacelle and fuselage 12 which may otherwise disrupt the aerodynamic integrity of the aircraft.

[0176] As mentioned above, the present invention also provides a modular aircraft assembly kit configured to allow a modular aircraft to be conveniently fitted with different propulsion systems having different engines. For example, the kit may comprise a plurality of

[0177] P5417PC00

[0178] 05 November 2025 different propulsion systems which may be of different types, each propulsion system being suspended from a corresponding support frame configured to support a specific engine. Different support frames (for example each having different engine mounting arrangements) may be used for different propulsion system types, but the support frame mounting members of each of the support frames are arranged to be secured to the fuselage mounting members, which provide common mounting points on the fuselage body.

[0179] For example, a second support frame 202 is shown in Figure 8, together with an alternative, second engine 232 which the second support frame is configured to secure to the fuselage body. The support frame 202 is substantially similar to the support frame 102 of the first embodiment and features of the support frame 202 of Figures 8 that correspond to features of the support frame 102 of Figures 1 , 4A, 4B and 5 to 7 are provided with corresponding reference numerals incremented by 100. The support frame 202 comprises support frame front mounting members 204a, 204b and rear mounting members 206a, 206b which are arranged to be secured to the fuselage mounting members 108, 110 by link members 215, 217. In this example, the rear link members 217 are bulkier than the front link members 215 and are configured to support greater loads than the front link members 215. This arrangement is used in this example since the second engine has a higher mass towards the rear of the engine.

[0180] A third variant of support frame 302 is shown in Figures 9, 10A and 10B. This variant of the support frame 302 is substantially similar to the support frame described above, except that the engine mounting arrangement is configured for mounting a different, third engine type 332, as can be seen in Figure 9. The variant of the support frame is therefore configured to suspend a second, different type of propulsion system and accordingly comprises a different engine mounting arrangement. The position on the variant support frame 302 of the support frame mounting members 304a, 304b, 306a, 306b also differs from the support frames 102, 202 described previously. In this third support frame 302, the support frame mounting members 304, 306 are provided on the first and second lateral support members 326a, 326b.

[0181] P5417PC00

[0182] 05 November 2025 Each support frame front mounting member 304a, 304b is provided by a portion of a respective one of the first and second lateral support members 326a, 326b which is recessed so as to be offset inwardly (i.e. towards the longitudinal axis A) from a respective lateral side 325a, 325b of the support frame 302. Each support frame front mounting member 304a, 304b is disposed proximate, and rearward of, the forward transverse support member 328. With this arrangement, each support frame front mounting member 304a, 304b is disposed proximate a respective opposing lateral side 325a, 325b of the support frame 302. The support frame front mounting members 304a, 304b are arranged on, and intersect, the mounting plane.

[0183] A thickness of each support frame front mounting member 304a, 304b is sized to fit in the slot 116 of a respective one of the clevis brackets 108a 108b. An aperture 336 extends through each front support frame mounting member 304a, 304b and is arranged to align with corresponding apertures 118 of a respective one of the clevis brackets 108a, 108b.

[0184] Each support frame rear mounting member 306a, 306b is provided by a portion of a respective one of the first and second lateral support members 326a, 326b which is recessed inwardly from a respective lateral side 325a, 325b of the support frame 302. With this arrangement, each of the support frame rear mounting members 306a, 306b is disposed proximate a respective opposing lateral side 325a, 325b of the support frame 302. Each support frame rear mounting member 306, 306b is aligned with the rearward transverse support member 330. The support frame rear mounting members 306a, 306b are spaced rearwardly from the support frame front mounting members 304a, 304b. An aperture 338 extends through each support frame rear mounting member 306a, 306b and is arranged to align with a corresponding aperture 120 of a respective one of the brackets 110a, 110b. The support frame rear mounting members 306a, 306b are arranged on, and intersect, the mounting plane. With this third support frame 302, the link members are not used, and each support frame front and rear mounting member is arranged to be secured directly to a respective one of the brackets 108, 110.

[0185] A fourth support frame 402, for mounting a fourth engine type (not shown) is shown in Figures 11 , 12A and 12B. The fourth support frame 402 is substantially similar to the third

[0186] P5417PC00

[0187] 05 November 2025 support frame 302, except that the engine mounting arrangement is configured for suspending the fourth engine type from the support frame 402. Figure 13 shows the third and fourth support frames 302, 402 superimposed on one another to show the common positioning of the support frame front mounting members 304a, 304b, 404a, 404b and rear mounting members, 306a, 306b, 406a, 406b.

[0188] A fifth support frame 502, for mounting a fifth engine type 532 is shown in Figures 14A and 14B. The fifth support frame 502 is substantially similar to the third support frame 302, except that the engine mounting arrangement is configured for suspending the fifth engine type 532 from the support frame 502. In this example, the fifth engine type 532 is a twin engine arrangement. The front engine mount 544 comprises a pair of adjacent generally U-shaped brackets 544 secured to the support frame 502 and which extend downwardly from the support frame 502. Each bracket 544 comprises a downwardly facing arcuate surface which is shaped to match the curvature of a cylindrical outer surface of one of the engines of the twin engine arrangement 532. The rear engine mount 546 comprises a pair of laterally spaced brackets, each arranged to receive a projecting lug extending from a respective engine 532. A generally Y-shaped linkage or bracing member 564 extends between the front and rear engine mounts 544, 546. A tail of the Y- shaped bracing member 564 is secured to the front engine mount and arms of the bracing member are secured to the rear engine mount.

[0189] A modular aircraft assembly kit according to an embodiment of the invention is illustrated generally by Figures 1 to 8 and comprises the fuselage front mounting members 108a, 108b, fuselage rear mounting members 110a, 110b, the first support frame 102, and the second support frame 202. The kit may also comprise a first propulsion system in the form of the propulsion system 10 for use with the support frame 102, and a second propulsion system (not shown) for use with the variant support frame 202. The kit may also comprise further additional support frames, such as the support frames 302, 402 and 502 of Figures 9 to 14B, each configured to be mounted to the common mounting members 108a, 108b, 110a, 110b, and each configured to suspend a respective propulsion system.

[0190] P5417PC00

[0191] 05 November 2025 In some examples, the first propulsion system may comprise a single-engine propulsion system for a basic training configuration of the modular aircraft, whilst the second propulsion system may comprise a twin-engine propulsion system for an advanced training configuration of the aircraft. The kit may comprise a third propulsion system comprising a more highly powered engine than the engine of the first or second propulsion systems, for a combat configuration of the aircraft.

[0192] It will also be appreciated therefore that the present invention provides a method of reconfiguring a modular aircraft, for instance to allow the interchanging of alternative propulsion systems for different aircraft roles. For example, in one embodiment, the method may comprise removing the support frame 102 (and propulsion system 10 suspended therefrom) from the fuselage body of the aircraft and mounting the second support frame 202 from the mounting members 108a, 108b, 110a, 110b, (in this example via the link members 115, 117) to enable the second propulsion system to be suspended from the fuselage body 12. In this case each support frame 102, 202 comprises a plurality of first mounting members 104a, 104b, 106a, 106b arranged to be removably secured to second (fuselage) mounting members 108a, 108b, 110a, 110b provided on the fuselage body 12, thereby to removably secure each support frame 102, 202 externally from the fuselage body 12. When mounted to the fuselage body, the longitudinal axis A of each support frame 102, 202 is arranged to extend parallel to the centre-line X of the fuselage body 12, or to a central plane of the fuselage body containing the centre-line X.

[0193] With the arrangements described above, the present invention provides a system which allows alternative propulsion systems to be suspended and easily removed from the same fuselage body. Each propulsion system is mounted externally of the fuselage body and other airframe structure of the aircraft, such that the different propulsion systems may be interchanged without modification or disturbance to the airframe structure of the aircraft. In this way, a modular aircraft may be conveniently and safely reconfigured for different roles.

[0194] P5417PC00

[0195] 05 November 2025

Claims

CLAIMS1. Apparatus for removably suspending a propulsion system externally from a fuselage body of a modular aircraft and along a centre-line of the aircraft, the propulsion system comprising an engine, and the apparatus comprising: a support structure; a fuselage mounting arrangement configured to removably suspend the support structure externally from the fuselage body, wherein the support structure is arranged to extend longitudinally below a section of the fuselage body; and an engine mounting arrangement for suspending the engine from the support structure.

2. Apparatus according to Claim 1 , in which the support structure defines a mounting plane arranged to locate below the section of the fuselage body and above the engine when the support structure is suspended from the fuselage body and the engine is suspended from the support structure.

3. Apparatus according to Claim 1 or Claim 2, in which the support structure comprises a frame structure comprising at least one longitudinally extending support member and at least one transversely extending support member and in which said support members extend parallel to the mounting plane.

4. Apparatus according to any preceding claim, in which the support structure is arranged to locate above a central wing structure of the aircraft and rearward of the central wing structure.

5. Apparatus according to any preceding claim, in which the engine mounting arrangement comprises vibration isolation mounts arranged to reduce transmission of vibrations from the engine to the support structure.

6. Apparatus according to any preceding claim, in which a stiffness of the support structure relative to a stiffness of part of the fuselage body is configured to reduceP5417PC0005 November 2025transmission of ferees between the fuselage body and the engine.

7. Apparatus according to any preceding claim, in which the fuselage mounting arrangement comprises a plurality of first mounting members which are provided on the support structure and the first mounting members are arranged to be removably secured to second mounting members provided on the fuselage body, thereby to removably suspend the support structure from the fuselage body.

8. Apparatus according to Claim 7, in which the first mounting members are disposed proximate opposing first and second lateral sides of the support structure which are arranged to locate proximate first and second lateral sides of the fuselage body when the support structure is suspended from the fuselage body.

9. Apparatus according to Claim 7 or Claim 8, in which a longitudinal axis of the support structure is arranged to extend parallel to the centre-line of the aircraft when the support structure is suspended from the fuselage body and in which the first mounting members are spaced apart laterally on opposing sides of the longitudinal axis.

10. Apparatus according to Claim 9, in which the support structure comprises first and second lateral support members arranged on either side of the longitudinal axis and which are elongate to extend parallel to the longitudinal axis, and in which the first mounting members are provided on the first and second lateral support members.11 . Apparatus according to any of Claims 7 to 10, in which the plurality of first mounting members comprises at least one front first mounting member and at least one rear first mounting member spaced apart longitudinally from the at least one front first mounting member.

12. Apparatus according to any of Claims 7 to 11 when dependent on Claim 2 or when dependent on any of Claims 3 to 6 when dependent on Claim 2, in which the first mounting members intersect the mounting plane.P5417PC0005 November 202513. Apparatus according to any preceding claim, in which the engine mounting arrangement comprises a front engine mount for securing to a front portion of the engine and a rear engine mount for securing to a rear portion of the engine.

14. Apparatus according to Claim 13 when dependent on any of Claims 7 to 12, in which the front engine mount is disposed proximate the front first mounting members and the rear engine mount is disposed proximate the rear first mounting members.

15. Apparatus according to any preceding claim, in which the support structure comprises a peripheral structure which extends at least part way around a periphery of the support structure for securing part of an aerodynamic housing of the propulsion system to the support structure.

16. A propulsion system assembly comprising a propulsion system and apparatus according to any preceding claim.

17. A modular aircraft assembly kit comprising: a plurality of interchangeable support structures arranged to be removably suspended from a fuselage body of a modular aircraft, each support structure being arranged to suspend a respective propulsion system externally from the fuselage body and along a centre-line of the aircraft, and each support structure comprising an engine mounting arrangement for suspending an engine of the respective propulsion system from the support structure; the plurality of support structures comprising: a first support structure from which a first propulsion system is suspended or suspendable, thereby to removably suspend the first propulsion system from the fuselage body; and a second support structure from which a second propulsion system is suspended or suspendable, thereby to removably suspend the second propulsion system from the fuselage body.

18. A modular aircraft assembly kit according to any of Claim 17, in which each support structure comprises a plurality of first mounting members and the fuselage bodyP5417PC0005 November 2025comprises a plurality of second mounting members arranged to be secured to the first mounting members to removably suspend the support structure from the fuselage body.

19. A modular aircraft assembly kit according to Claim 18, in which the plurality of second mounting members comprises common mounting members and each of the plurality of support structures is arranged to be removably secured to the common mounting members such that the support structures may be suspended interchangeably from the fuselage body.

20. A modular aircraft assembly kit according to Claim 18 or Claim 19, in which each support structure is arranged to extend longitudinally below a section of the fuselage body when the support structure is suspended from the fuselage body.21 . A modular aircraft assembly kit according to any of Claims 17 to 20, in which each support structure defines a mounting plane arranged to locate below the section of the fuselage body and above the engine when the support structure is suspended from the fuselage body and when the engine is suspended from the support structure.

22. A modular aircraft assembly kit according to any of Claims 17 to 21 , comprising the first and second propulsion systems, and in which the second propulsion system is an alternative propulsion system having different propulsion properties to the first propulsion system.

23. A modular aircraft assembly kit according to any of Claims 17 to 22, comprising a third support structure from which a third propulsion system is suspended or suspendable, thereby to removably suspend the third propulsion system from the fuselage body.

24. A modular aircraft assembly kit according to any of Claims 17 to 23, comprising at least one pair of removably mountable lateral wing assemblies for securing to a central wing structure of the aircraft.

25. A method of reconfiguring a modular aircraft, the aircraft comprising a fuselageP5417PC0005 November 2025body, and the method comprising: removing from the fuselage body a first support structure which is arranged to suspend a first propulsion system externally from the fuselage body and along a centreline of the aircraft; suspending from the fuselage body a second support structure which is arranged to suspend a second propulsion system externally from the fuselage body and along a centre-line of the aircraft; wherein each support structure is arranged to be removably suspended externally from the fuselage body and to extend longitudinally below a section of the fuselage body.P5417PC0005 November 2025

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