Abstract:
The invention relates to a mounting assembly for a rocket nozzle for an engine that may be operable in rocket mode, in which the engine combusts stored oxygen and hydrogen, or in air-breathing mode, in which the engine combusts air from the atmosphere and stored hydrogen. A plurality of ducts and pipes are connected to the nozzle to supply fuel and other fluids. As it is desirable to allow the nozzle to pivot, the mounting assembly may include flexible couplings on the ducts and pipes about selected pivot points allowing the desired freedom of motion. The flexible couplings are designed to withstand various pressure forces in the rocket/aircraft flight environment, and may be composed of spaced annular elements, wherein a partial toroid element connects consecutive pairs of annular elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. §119(a) to the following applications filed in the United Kingdom on Oct. 11, 2013, each of which is incorporated herein by reference: GB 1318105.2 and GB 1318110.2. 
       FIELD 
       [0002]    The present disclosure relates to a mounting assembly for a rocket nozzle for facilitating the control of a rocket trajectory for example in a single stage to orbit (SSTO) vehicle. The present disclosure also relates to a flexible coupling for use in such a mounting assembly. The disclosure also relates to an aircraft or aerospace vehicle including such a mounting assembly. 
       BACKGROUND 
       [0003]    Typically in a rocket engine, a plurality of fluid ducts or pipes are provided in order to supply fuel and air or other oxidant to the rocket combustion chamber. However, with a large number of ducts or connections, the maneuverability of a rocket nozzle associated with the rocket combustion chamber can be hindered. 
         [0004]    The present disclosure seeks to alleviate, at least to a certain degree, the problems and/or address at least to a certain extent, the difficulties associated with the prior art. 
       SUMMARY 
       [0005]    According to a first aspect of the disclosure, there is provided a mounting assembly for mounting a rocket nozzle to allow the nozzle to pivot about a pivot or gimbal point, the assembly comprising a fluid duct for supply of fluid to said nozzle, the duct comprising two or more flexible fluid couplings which substantially intersect a common plane on which said pivot point is arranged. 
         [0006]    Such a mounting can advantageously provide a compact fluid coupling arrangement. The fluid ducts may be formed of substantially rigid ducts to withstand high pressure gases flowing within the ducts. The flexible couplings can be relatively short in length compared with the length of the ducts, minimizing sections of reduced rigidity. The arrangement of the flexible couplings intersecting a common plane can facilitate movement relative to the plane in a direction traverse to the plane, parallel to the plane or in rotation about the gimbal or pivot point in the plane. The flexible fluid couplings may be used to couple consecutive sections of the fluid duct to supply fluids, for example to a combustion chamber attached to or associated with said nozzle. 
         [0007]    The flexible couplings may intersect the common plane by being arranged substantially on or orientated in line with or crossing or traversing the common plane. The flexible couplings may traverse the common plane orthogonally to the surface of the common plane. 
         [0008]    Optionally, the mounting assembly is configured as a rocket nozzle mounting assembly. Optionally, the mounting assembly may be used for non-rocket applications, where fluid couplings are provided to a pivoting body or element. 
         [0009]    The arrangement of the flexible couplings relative to the common plane herein described are generally when the nozzles are at rest, i.e. the longitudinal and/or rotational axis of the nozzle is aligned with a gimbal axis which is perpendicular to the gimbal plane and passes through the gimbal point. 
         [0010]    In this description, reference to a flexible coupling is also intended to cover reference to a portion of a flexible coupling. 
         [0011]    The fluid ducts may be formed of substantially rigid materials. The ducts may be formed as pipes or channels of generally circular cross-section. The ducts may be formed of metals, for example nickel, titanium or alloys, composite materials or any other suitable material. 
         [0012]    Optionally, the fluid duct includes portions on either side of the gimbal point on the common plane. 
         [0013]    The flexible couplings may be formed with a generally circular cross-section. The flexible couplings may be coupled to fluid ducts using welding or other joining techniques. 
         [0014]    The internal flow passages or longitudinal axes of the flexible couplings, optionally when unflexed, may optionally be aligned in or with the common plane, or perpendicular thereto or at least in sections or parts of the flexible couplings which traverse the common plane. 
         [0015]    The duct between a consecutive pair or pairs of flexible couplings is optionally rigid or substantially rigid, at least relative to the flexible coupling. The ducts may comprise straight sections and/or curved sections. 
         [0016]    Optionally, a consecutive pair or pairs of said flexible fluid couplings of a fluid duct or sections of the flexible couplings which traverse the common plane, are arranged generally orthogonal to one another about a central axis passing through said pivot point. The duct between a consecutive pair of flexible couplings may be aligned in or parallel to the common plane. 
         [0017]    The flexible couplings may comprise of or be formed as relatively short sections relative to the duct lengths. The flexible couplings may be arranged or configured to prevent strain being imparted by the pivoting to fluid ducts coupled to said flexible couplings. 
         [0018]    The flexible couplings may be aligned with their flow passages in line or in plane with the common plane or perpendicular to or traversing the common plane. The flexible couplings may be configured such that they are unflexed or undeformed when the thrust trajectory of the nozzle is perpendicular to the common plane. 
         [0019]    Additional ducts may also be provided with two or three or more flexible couplings. The flexible couplings of the additional ducts may be spaced or offset from the common plane. 
         [0020]    Optionally, said mounting assembly comprises a further fluid duct comprising a flexible fluid coupling arranged on or traversing said common plane and in line with said pivot point or in line with a gimbal axis which passes through said pivot point and relative to which the rocket nozzle may be angled. 
         [0021]    Optionally, said flexible couplings are configured as bellow-like couplings. The flexible couplings may be provided with an external or internal gimbal arrangement. The internal gimbal arrangement may be coupled to the flexible coupling via internal vanes. 
         [0022]    Optionally, said mounting assembly further comprises a mounting for a rocket nozzle, the mounting being gimbaled or pivotally coupled to allow rotation of the mounting about orthogonal axes on said common plane. 
         [0023]    The mounting may comprise pairs of rotational pivots arranged as a gimbal for multi-directional movement of the nozzle about the gimbal point. 
         [0024]    The mounting may be configured to permit angular adjustment of the nozzle by up to −/+5 degrees or up to +/−3 degrees. 
         [0025]    Optionally, said mounting assembly further comprises one or more actuators for effecting rotation of the mounting about said orthogonal axes. The actuators may comprise hydraulic, electric or electrohydraulic actuators. 
         [0026]    Optionally, said mounting assembly further comprises a rocket nozzle supported on said mounting, the rocket nozzle having its central longitudinal axis substantially concentric with said pivot point. At rest, the longitudinal axis of the nozzle may be aligned with the gimbal axis which passes through said gimbal point. The rocket nozzle may be supported along with an associated rocket combustion chamber or combustion chamber arrangement. 
         [0027]    According to a second aspect of the disclosure, there is provided a rocket engine module comprising a plurality of mounting assemblies according to the first aspect of the disclosure with or without any optional feature thereof. 
         [0028]    The mounting assemblies may be symmetrically arranged. Four mounting assemblies may be provided. The rocket engine module may comprise an air breathing rocket and/or a hybrid air-breathing, liquid oxygen rocket. 
         [0029]    The rocket engine module may comprise an air breathing rocket combustion chamber and an air-breathing combustion chamber. The duct and flexible coupling arrangement can assist with packaging requirements with such a module. 
         [0030]    The rocket engine module may comprise a turbo-compressor for the compression of air and a heat exchanger for cooling said compressed air. 
         [0031]    According to a third aspect of the disclosure, there is provided a flexible coupling, comprising a plurality of spaced annular elements, wherein connecting consecutive pairs of annular elements, a partial toroid element is provided. 
         [0032]    Optionally, the annular elements are formed as annular rings. Optionally, the annular elements are formed of round or rounded section wire, for example wire with a substantially square cross-section with rounded corners/edges, or a wire with an oval cross section. 
         [0033]    Optionally, the annular elements are provided as a spiral wall element. 
         [0034]    Optionally, each partial toroid element is part of a single sheet of material. 
         [0035]    Optionally, the wall thickness of said annular elements is greater than the wall thickness of said partial toroid element. 
         [0036]    Optionally, the coupling is formed of a metallic material. The coupling may be formed of nickel, titanium or any suitable alloy. 
         [0037]    Optionally, the coupling comprises fiber reinforcement. 
         [0038]    According to a fourth aspect of the disclosure, there is provided a mounting assembly for mounting a rocket nozzle to allow the nozzle to pivot about a pivot or gimbal point, the assembly comprising a fluid duct for supply of fluid to said nozzle, the duct comprising a flexible fluid coupling arranged on the pivot point and/or traversing a common plane in line with said pivot point. Optionally, the flexible coupling is in line with a gimbal axis which passes through said gimbal point and relative to which the rocket nozzle can be angled. 
         [0039]    According to a fifth aspect of the disclosure, there is provided a vehicle, an aircraft or aerospace vehicle comprising a mounting assembly according to the first or fourth aspect, and/or a rocket engine module according to the second aspect and/or a flexible coupling according to the third aspect with or without any optional feature thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    The present disclosure may be carried out in various ways and embodiments of the disclosure will now be described by way of example with reference to the accompanying drawings, in which: 
           [0041]      FIGS. 1A ,  1 B and  1 C show side, plan and rear elevations respectively of a single stage to orbit (SSTO) aircraft; 
           [0042]      FIG. 2  shows a cross-section through a nacelle containing a rocket engine 
           [0043]      FIG. 3   a  shows a schematic side view of a rocket nozzle with a flexible coupling provided concentric with the axis of the nozzle; 
           [0044]      FIG. 3   b  shows an end on view of the arrangement shown in  FIG. 3   a;    
           [0045]      FIG. 4   a  shows a schematic side view of a rocket nozzle with a fluid conduit provided with two flexible couplings; 
           [0046]      FIG. 4   b  shows an end on view of the arrangement shown in  FIG. 4   a;    
           [0047]      FIG. 5   a  shows a schematic side view of a rocket nozzle with a fluid conduit with three flexible couplings; 
           [0048]      FIG. 5   b  shows an end on view of the arrangement shown in  FIG. 5   a;    
           [0049]      FIG. 6   a  shows a schematic end of a rocket nozzle with a fluid conduit with two flexible couplings; 
           [0050]      FIG. 6   b  shows a side view of the arrangement as shown in  FIG. 6   a;    
           [0051]      FIG. 7   a  shows a schematic end of a rocket nozzle with a fluid conduit with two flexible couplings; 
           [0052]      FIG. 7   b  shows a side view of the arrangement as shown in  FIG. 7   a;    
           [0053]      FIG. 8   a  shows a further example of a rocket engine module comprising two types of combustion chamber; 
           [0054]      FIG. 8   b  shows a view in the longitudinal direction of the rocket nozzle outlet of  FIG. 8   a;    
           [0055]      FIG. 9  shows a cross-section through a flexible fluid coupling; 
           [0056]      FIG. 10  shows a partial cross-section through an alternative flexible fluid coupling; 
           [0057]      FIG. 11   a  shows a schematic view an actuator arrangement for controlling the angle of a rocket nozzle; and 
           [0058]      FIG. 11   b  shows a plan view in the direction of the nozzle outlet of  FIG. 11   a.    
       
    
    
     DETAILED DESCRIPTION 
       [0059]      FIGS. 1A ,  1 B, and  1 C show a single stage to orbit (SSTO) aircraft  1  with a retractable undercarriage  2 ,  3 ,  4 , having a fuselage  5  with fuel and oxidant stores  6 ,  7  and a payload region  8 . A tail fin arrangement  9  and canard arrangement  10  are attached to the fuselage  5 . Main wings  13  with ailerons  14  are attached to either side of the fuselage  5  and each wing  13  has an engine module  15  attached to a wing tip  16  thereof. As shown in  FIGS. 1C and 2 , the rear of each engine module  15  is provided with four rocket nozzles  17  surrounded by various bypass burners  18 . 
         [0060]      FIG. 2  shows an engine module contained within a nacelle  20 , which may be attached to an aircraft wing, such as an aircraft wing  13  of an aircraft  1  as shown in  FIGS. 1A ,  1 B and  1 C. 
         [0061]    The engine module  15  includes air inlet  19 , heat exchanger  21 , turbo-compressor  22  and a plurality of fluid flow conduits or channels  23  for the supply of fluid, such as fuel/oxidant to combustion chambers associated with rocket nozzles  17   a,    17   b.    
         [0062]    During operation of the engine module  15 , part of the incoming air passing through the air inlet  19  passes through the heat exchanger  21  to the turbo compressor  22  and another part is bypassed along bypass duct  19   a  to the bypass burners  18 . These bypass burners  18  can provide additional thrust to the thrust provided through the main rocket nozzles  17 . 
         [0063]    The rocket nozzles  17   a,    17   b  may provide thrust through the combustion of fuel with an oxidant in a rocket combustion chamber  52   a,    52   b  associated with each nozzle  17   a,    17   b.  The fuel may, for example, be hydrogen fuel. The oxidant may comprise air which has passed through the turbo-compressor  22  and/or may comprise liquid oxygen from an on-board liquid oxygen store. 
         [0064]    It will be understood that the engine module may be replaced with other types of engine module and that the mounting arrangement described in this disclosure may be equally applied to different engine configurations. 
         [0065]    In the engine module as shown in schematic cross-section in  FIG. 2 , air passes from the turbo compressor  22  through a central main air flow duct  27  which splits into divergent ducts  24   a,    24   b  to deliver air to combustion chambers  52   a,    52   b  associated with each of the rocket nozzles  17   a,    17   b.  Although only two rocket nozzles  17   a,    17   b  are shown in  FIG. 2 , it should be understood that any number of rocket nozzles may be chosen depending on the thrust required and the packaging constraints of the vehicle. 
         [0066]    Each of the divergent air ducts  24   a,    24   b  diverge at an angle to a center line passing through the main inlet air duct  27 . The ducts  24   a,    24   b  extend partially radially and partially axially with the distal end of each duct (i.e. the end furthest from the main air flow duct  27 ) in alignment with the central rotational axis of a respective rocket nozzle  17   a,    17   b.    
         [0067]    The air ducts  24   a,    24   b  are coupled to the combustion chamber  52   a,    52   b  of the respective rocket nozzle  17   a,    17   b.    
         [0068]    Fuel is delivered to the rocket chambers  52   a,    52   b  of the nozzles  17   a,    17   b  via ducts  29   a ,  29   b  using pump  26 . 
         [0069]    The ducts shown in  FIG. 2  may be coupled to the rocket combustion chambers or nozzles using one or more of the coupling arrangements shown in  FIGS. 3   a  to  7   b  and described below. 
         [0070]      FIG. 3   a  shows a side view of a rocket nozzle  17 , which is gimbaled about a pivot or gimbal point  55 . The pivot or gimbal  55  may permit pivoting or rotation of the nozzle about one or more axes. In the embodiment, the nozzle may pivot about two orthogonal axes z, y. 
         [0071]    The degree of movement permitted will depend on application. In the embodiment, the degree of movement or pivoting angle, θ, may be of the order +/−3 degrees relative to the gimbal axis x. Each nozzle may be provided on a mounting which allows for the pivoting or gimballing of each nozzle. 
         [0072]    The orientation of each nozzle may be adjusted in order to control the trajectory of the aircraft to which the engine module is attached. Actuators (not shown) may be provided in order to control the degree of movement of the nozzles. 
         [0073]    In the embodiment, the rocket combustion chamber/nozzle  17  is supplied with air or other fluid via duct  56 . A flexible coupling  57  is provided to couple the duct  56  to the combustion chamber/nozzle arrangement  17 . The flexible coupling  57  intersects a common or gimbal plane  36 , by crossing or traversing said gimbal plane  36 , which is a plane passing through the pivot or gimbal point  55  and perpendicular to gimbal axis x relative to which the nozzle can be angled. 
         [0074]    The flexible coupling  57  is arranged concentric on the gimbal axis x at the point the coupling traverses the gimbal plane. The gimbal axis is an axis passing through the gimbal point and perpendicular to the gimbal plane  36 . 
         [0075]    The flexible coupling  57  provides a compliant coupling to permit pivoting of the nozzle/combustion chamber assembly  17  about the pivot point  55 . With such an arrangement with the coupling  57  on the gimbal axis, x, only a single flexible coupling  57  is required. The flexible coupling may be a bellow type connection. 
         [0076]    The arrangement as shown in  FIG. 3   a ,  3   b  has the advantage that the axial thrust load on the gimbal  55  is reduced as it is offset by the axial air or fluid pressure load in the flexible coupling  57 . In addition, the arrangement is also more compact than the arrangements shown in  4   a,    4   b,    5   a,    5   b  and is therefore most suited to the largest diameter pipe crossing the gimbal plane. 
         [0077]      FIG. 4   a  shows a side view of a rocket combustion chamber/nozzle assembly  17  which is supplied with fluid from duct  58 . The duct  58  may, for example, supply cooling medium to the rocket nozzle skirt. The duct  58  may be provided in additional to the duct  56  shown in  FIG. 3   a , for example where multiple fluid connections to the rocket nozzle/chamber are required. 
         [0078]    As shown in  FIG. 4   b , the duct  58  is provided with two flexible couplings  59   a,    59   b  which intersect the gimbal plane by being aligned in the gimbal plane  36 . The two flexible couplings  59   a,    59   b  or at least a portion thereof are positioned or arranged orthogonal to one another about the gimbal point  55 . 
         [0079]    The flexible couplings  59   a,    59   b  are arranged substantially in alignment on the common plane  36 , which, when the nozzles  17  are at rest, i.e. with no pivoting, is perpendicular to the gimbal axis, x. In the embodiment, the gimbal axis, x, is also the longitudinal rotational axis of the rocket nozzle  17 , when the nozzle is at rest. 
         [0080]    By providing each of the fluid ducts with a flexible coupling substantially intersecting, in the embodiment, by being aligned on or traversing the common plane  36 , any possible strain imparted on the fluid supply ducts  24   a,    24   b,    28   a,    28   b  as the nozzles pivot can be better controlled or reduced. 
         [0081]      FIG. 5   a  shows how ducts can be coupled to the combustion chamber/rocket nozzle assembly  17  if the flexible couplings cannot be provided on the gimbal plane  36 . Here, the duct  60  comprises three flexible couplings  63   a,    63   b,    63   c  as shown in  FIG. 5   b . The flexible couplings  63   a,    63   b,    63   c  are offset from the gimbal plane  36 . The duct  60  can cope with fore/aft movement, b, of the duct pipe work. The ghost line  64  shows the movement of the duct  60 , such that flexible coupling  63   c  is offset to position  62   b  at a distance, b, from its original position  62   a , while flexible coupling  63   a  remains substantially in its original position  61   a.    
         [0082]      FIG. 6   a  shows an end view of a rocket combustion chamber/nozzle assembly  17  which is supplied with fluid from a propellant source represented by cylinder  71 . 
         [0083]    The fluid is supplied via a duct comprising three sections  72   a,    72   b,    72   c.  Between the first section  72   a  and the second section  72   b  of the duct, a flexible coupling  73   a  is provided. Between the second section  72   b  and the third section  72   c  of the duct, a further flexible coupling  73   b  is provided. The duct sections are substantially rigid. 
         [0084]    As shown in  FIG. 6   a , the flexible couplings or at least a portion thereof are arranged or positioned orthogonal to one another about a gimbal point  55  which is in alignment with the central longitudinal axis X of the rocket nozzle. The second section  72   b  of duct follows a curve with its center of curvature on the gimbal point  55 . In the embodiment, the flexible couplings  73   a,    73   b  are arranged offset and substantially equidistant from the gimbal axis x in directions perpendicular therefrom. 
         [0085]    As shown in  FIG. 6   b , the first and the second flexible couplings  73   a,    73   b  are aligned so as to intersect the plane  36  by crossing or traversing the gimbal plane  36 . The propellant source, in the embodiment, is arranged offset from the gimbal plane  36  in the direction of the open end of the nozzle  17 . 
         [0086]    The flexible couplings  73   a,    73   b  are arranged crossing or traversing the common plane  36 , which, when the nozzle  17  is at rest, i.e. with no pivoting, is perpendicular to the gimbal axis, x. In the embodiment, the gimbal axis, x, is also the longitudinal rotational axis of the rocket nozzle  17 . 
         [0087]    By providing the fluid duct with flexible couplings substantially aligned on or traversing the common plane  36 , any possible strain imparted on the fluid supply ducts  72   a,    72   b,    72   c  as the nozzles pivot can be better controlled or reduced. 
         [0088]      FIG. 7   a  shows an end view of a rocket combustion chamber/nozzle assembly  17  which is supplied with fluid from a propellant source represented by cylinder  71 . 
         [0089]    The fluid is supplied via a duct comprising three sections  74   a,    74   b,    74   c.  Between the first section  74   a  and the second section  74   b  of the duct, a flexible coupling  75   a  is provided. Between the second section  74   b  and the third section  74   c  of the duct, a further flexible coupling  75   b  is provided. 
         [0090]    As shown in  FIG. 7   a , the flexible couplings or at least a portion thereof are arranged or positioned orthogonal to one another about a gimbal point  55  which is in alignment with the central longitudinal axis X of the rocket nozzle. The second section  74   b  of the duct has a main straight section arranged substantially parallel to the gimbal plane  36  and slopes or leans towards the gimbal axis X away from the propellant source  71 . The first and second flexible couplings are thus arranged at different distances from the gimbal point  55  or axis X. 
         [0091]    As shown in  FIG. 7   b , the first and the second flexible couplings  75   a,    75   b  are aligned so as to cross or traverse the gimbal plane  36 . The propellant source, in the embodiment, is arranged offset from the gimbal plane  36  in the direction of the open end of the nozzle  17 . 
         [0092]    The flexible couplings  75   a,    75   b  are arranged substantially to cross or traverse the gimbal plane  36 , which, when the nozzle  17  is at rest, i.e. with no pivoting, is perpendicular to the gimbal axis, x. In the embodiment, the gimbal axis, x, is also the longitudinal rotational axis of the rocket nozzle  17 . 
         [0093]    By providing the fluid duct with flexible couplings substantially aligned on or traversing the common plane  36 , any possible strain imparted on the fluid supply ducts  74   a,    74   b,    74   c  as the nozzles pivot can be better controlled or reduced. 
         [0094]      FIG. 8   a  shows in schematic cross-section, a possible implementation of the arrangements shown in  FIGS. 3   a  through  5   b  in an aircraft rocket engine. The rocket engine as shown in  FIG. 8   a  includes four rocket nozzles of which only two rocket nozzles  17   a,    17   b  are shown. Associated with each of the rocket nozzles  17   a,    17   b  are two types of combustion chamber for the combustion of oxidant and fuel. In the embodiment, the two types of combustion chamber are an air-breathing combustion chamber and a rocket combustion chamber. Three air-breathing combustion chambers  30  may be provided around a central rocket combustion chamber  31  with both the rocket combustion chamber and the air breathing combustions chambers sharing a common nozzle. 
         [0095]    A liquid oxygen pump  33  is provided to supply oxidant to the rocket combustion chambers  30 ,  31  along fluid ducts  24   a,    24   b.  A liquid hydrogen pump  34  is also provided to supply fuel to the rocket combustion chambers along fluid ducts  29   a,    29   b.  A plurality of fuel or oxidant ducts may be provided to deliver fuel to required stages or sections of each combustion chamber. 
         [0096]    The rocket engine includes a turbo compressor  22  for supplying compressed cooled air to the rocket combustion chambers. 
         [0097]    The rocket combustion chambers and nozzles  17   a,    17   b  are coupled indirectly to a box beam  32  which is connected to the aircraft in order to transfer thrust to the aircraft space frame. A triangulated spaceframe could also be used or any other suitable connection to aircraft. 
         [0098]    The nozzles  17   a,    17   b  are mounted on a mounting which allows them to pivot or gimbal relative to a common plane  36  about pivot or gimbal points  55   a,    55   b.    
         [0099]    The rocket combustion chambers  30  may be fluidly coupled using the arrangements as shown in  FIG. 3   a  with a single flexible coupling which traverses the gimbal plane  36 . The common gimbal plane  36  is perpendicular to a longitudinal axis  53 . At rest when the nozzles are not pivoted, the rotational axes of the rocket nozzles  17   a,    17   b  are parallel to the longitudinal axis  53 . 
         [0100]    To supply fluids to the air-breathing combustion chambers  31 , the duct and flexible coupling arrangement as shown in  FIGS. 4   a  to  7   b  may be provided. 
         [0101]    In the example, the fluid ducts are typically rigid, with the flexible couplings providing a compliant join between consecutive sections of fluid duct. 
         [0102]    Each rocket nozzle and chamber may be supported on a mounting which can be pivoted or gimbaled to adjust the relative angle of nozzle relative to the gimbal plane  36  in order to adjust/control the trajectory of the aircraft. The maximum relative angle will depend on the particular engine and nozzle arrangement, but could typically be around +/−3 degrees to an axis perpendicular to the common gimbal plane. 
         [0103]    By providing the supply ducts with flexible coupling arrangements as shown in  FIGS. 3   a  to  7   b , each rocket nozzle may rotate about a respective gimbal point on the gimbal plane  36 . 
         [0104]      FIG. 8   b  shows a plan view of the rocket nozzles as shown in  FIG. 8   a . As shown in  FIG. 8   b , the engine comprises four rocket engines each with a mounting arrangement  41   a ,  41   b,    41   c,    41   b.  The rocket engines are arranged symmetric about planes AA and BB. Although only one of these rocket nozzles will be described, each rocket nozzle is provided with similar fluid connections in the form of ducts  37 ,  38 ,  39  and  40 . As described above, some of the ducts comprise flexible couplings which intersect a common plane, for example by being aligned in or traversing a common gimbal plane  36  as shown in  FIG. 8   a . In the example, a total of seven such ducts are provided to each combustion chamber/nozzle arrangement. 
         [0105]    As viewed in  FIG. 8   b , some of the ducts are provided in line with or traversing the gimbal plane (plane  36  as shown in  FIG. 8   a ). Such ducts are provided with pairs or orthogonally arranged or positioned flexible couplings (or parts thereof). The orthogonal angles between the pairs of flexible couplings are represented by angles alpha, beta, gamma and delta in four of these ducts. Typically, each duct is provided with two flexible couplings in alignment with the common gimbal plane  36 . 
         [0106]    In the example of  FIG. 8   b , each rocket nozzle  17   a,    17   b  is provided with an oxidant carrying duct, which is provided in alignment with the gimbal point  55  or axis itself. In the example, for this central air duct, a single flexible coupling is provided which traverses the common gimbal plane  36 . 
         [0107]    The arrangement of flexible couplings which intersect the gimbal plane, for example by alignment with or traversing the gimbal plane  36 , which is orthogonal to the gimbal point, can serve to allow a more compact arrangement and facilitate rocket nozzle movement control. 
         [0108]      FIG. 9  shows a cross-section of a flexible coupling in the form of a bellows-like connection  42 . The cross section comprises a plurality of spaced annular sections  51  or rings of radius R. Consecutive or successive pairs of annular sections  51  are joined via split or partial toroid sections  43  which extend radially from the edges of the annular sections  49 ,  51  with the toroid center of each toroid section being spaced a distance, a, from the rotational centerline (CL) of the coupling. Each partial toroid  43  is formed of radius, b, about said toroid center. The wall thickness, t w  of the split toroid parts is less than the wall thickness, t p  of the narrow annular sections. 
         [0109]    The pipe pressure hoop loads are carried by the narrow annular sections  49 ,  51  in the flexible coupling. These annular sections are resistant to flex when the bellow connection is bent. Annular sections could be formed of a metal material, such as nickel or titanium or any suitable alloys, and could be additionally fiber reinforced or formed of composite materials. The flexible couplings can be configured to withstand the high fluid pressures being carried in the ducts to the rocket combustion chambers. 
         [0110]    Bending of the flexible connection is enabled by the split toroids  43 , which elastically deform. The split toroid sections  43  can be manufactured in extremely thin material due to their small internal radius. This construction means that the pressure load (pipe hoop) carrying material and the bending material have distinct separate roles, and can be formed of suitable, possibly distinct and different, materials accordingly. 
         [0111]    The pipe axial loads are carried by an external or internal gimbal arrangement  65  coupled to the pipe walls via vanes  66   a,    66   b,    66   c,    66   d.    
         [0112]    As an alternative to the annular rings  51 , a thick walled spiral could be used instead. The spiral may carry the pipe hoop burst loads, but may have greater stiffness to carry its own weight and prevent flow induced vibrations. The partial toroids could be formed substantially the same as shown in  FIG. 9 . 
         [0113]    A further embodiment of a flexible coupling is shown in  FIG. 10 . Instead of the annular rings, round section wire  70  may be used to reinforce the coupling. The partial toroids  43 , which are thin walled, may be hydroformed from a single sheet of material. This can serve to reduce the difficulty in effecting a pressure-tight join with the annular rings as shown in  FIG. 9 . 
         [0114]      FIG. 11   a  shows a schematic representation of a rocket nozzle  17  and actuator  44  which includes actuator piston  45 . The actuator may be provided as a hydraulic, electric or electro-hydraulic unit that can be used to vary the degree of movement of the rocket nozzle about the gimbal point  47 , which lies on the gimbal plane  36  as shown in  FIGS. 3   a  to  5   b.    
         [0115]    The gimbal point  47  is a point about which the rocket nozzle  17  may pivot. The actuator  44  is connected via the piston  45  to a mounting  46  which is used to support the nozzle  17 . 
         [0116]    In the example, each nozzle is provided with two actuators, acting parallel to the rocket chamber axis, but positioned orthogonally to one another. This gives rotation about both Y and Z axes as shown in  FIG. 11   b . As shown in  FIG. 11   b , a first actuator is shown in line with axis ZZ and second actuator  48  is provided in line with axis YY. 
         [0117]    The arrangement of ducts and flexible connections can provide for a compact design of the mounting assembly and can facilitate the movement of the rocket nozzles in order to control the trajectory of a rocket powered vehicle. 
         [0118]    Various modifications may be made to the described embodiments without departing from the scope of the invention as defined in the accompanying claims.