Abstract
A fuel tank or bladder-free fuel tank having a reservoir on its inside area, limited to an outside area by a double-walled structure. The double-walled structure has an outer wall and an inner wall. A rib structure includes at least one rib extending inwardly into the inside area of the bladder-free fuel tank from the double-walled structure.
Claims
1. A fuel tank comprising: a reservoir formed on an inside area of the fuel tank, the reservoir being limited to an outside area by a double-walled structure, the double-walled structure comprising: an outer wall; an inner wall; a hollow space configured as a drain and/or venting channel for the fuel tank; and dome-shaped elements on the inner wall or the outer wall; a rib-structure comprising a plurality of ribs extending inwardly into the inside area from the double-walled structure; and fasteners for rigidly connecting the outer wall and the inner wall such that the outer wall and the inner wall cannot move relative to one another and a distance between the outer wall and the inner wall is maintained, wherein the fasteners comprise screwed connections at the dome-shaped elements.
2. The fuel tank according to claim 1, wherein the outer wall is made of a material comprising aluminum and is shaped as a sheet metal part.
3. The fuel tank according to claim 1, wherein the inner wall is a machine-milled component made from a material comprising aluminum.
4. The fuel tank according to claim 1, wherein the rib-structure extending inwardly into the inside area is part of the inner wall or is a separate component fastened to the inner wall by at least one fixture element.
5. The fuel tank according to claim 1, wherein the rib structure is arranged as a cross-link structure pattern, a diagonal or triangular pattern, or a parallel pattern of inwardly extending ribs.
6. The fuel tank according to claim 1, wherein the inwardly extending ribs comprise buckling resistant T-shaped or L-shaped extensions.
7. The fuel tank according to claim 1, wherein the inwardly extending ribs comprise at least one local thickening and/or at least one buckling avoiding expansion.
8. The fuel tank according to claim 1, wherein, within an overlapping region, edge portions of the outer wall overlap each other and are sealingly connected via fixtures.
9. The fuel tank according to claim 1, wherein the inner wall is a milling part having at least one local strengthening portion or comprises a local thickening.
10. The fuel tank according to claim 1, wherein the dome-shaped elements define a width of the hollow space of the double-walled structure and mounting areas for fixture elements.
11. The fuel tank according to claim 10, wherein the dome-shaped elements maintain the width of the hollow space consistently.
12. The fuel tank according to claim 1, wherein adjacent and/or opposite sections of the double-walled structure are interconnected by inner tie rods, the inner tie rods being connected to the inwardly extending ribs at a plurality of force transmission points.
13. The fuel tank according to claim 12, wherein connectors or plate-shaped connectors are fastened to the inwardly extending ribs at the plurality of force transmission points and to additional ribs and/or the inner tie rod, respectively.
14. The fuel tank according to claim 1, wherein the inwardly extending ribs are formed in a height in relation to the double-walled structure or large additional riveted ribs or tie-rods made in a height to prevent excessive sloshing movements of fuel within the fuel tank.
15. The fuel tank according to claim 1, wherein intake equipment including piping, pumps, valve sensors, or slosh valves are directly mounted to the inwardly extending ribs or to the inner wall.
16. The fuel tank according to claim 1, wherein the fuel tank is an additional center tank or a center tank for an aircraft or for an aircraft application.
17. The fuel tank according to claim 1, wherein the fuel tank is a bladder-free tank.
18. The fuel tank according to claim 1, wherein the hollow space is disposed between the outer wall and the inner wall.
19. The fuel tank according to claim 1, wherein the screwed connections are disposed in areas in which the inner wall is thickened.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:
(2) FIG. 1 shows a cross section through a double-walled structure having an outer wall and an inner wall with inwardly extending reinforcing ribs;
(3) FIG. 1.1 shows an embodiment of a fixture and a dome present on the inner wall or the inner wall segment;
(4) FIG. 1.2 shows an embodiment of a fixture element, connecting an inner wall and an outer wall of the double-walled structure;
(5) FIG. 2 shows an embodiment of a rib pattern present in the interior of the bladder-free fuel tank according to the present invention;
(6) FIGS. 2a and 2b show details of milled pockets machined in the inwardly extending ribs;
(7) FIG. 3 shows a cross-section of the double-walled structure with overlapping regions present in the inner wall and the outer wall;
(8) FIG. 4 shows the double-walled structure with fixture elements mounted in mounting areas of the fixtures and the resulting and a formed outer wall of the double-walled structure of the bladder-free fuel tank;
(9) FIG. 5 shows a top view of a large additional riveted rib and a part of a tie rod inside the bladder-free fuel tank;
(10) FIG. 6 shows a side view of a fuel tank according to the present invention;
(11) FIG. 7 shows an embodiment of a plurality of force transmission points arranged between the double-walled structure and a part of an inner tie rod;
(12) FIG. 8 shows a rib pattern being arranged substantially triangular;
(13) FIG. 9 shows a parallel rib pattern, the reinforcing ribs having milled pockets;
(14) FIG. 10 shows a substantially parallel rib pattern, the ribs arranged with respect to the respective fixtures in an alternate fashion;
(15) FIG. 11 shows an arch-shaped section of a double-walled structure in a radius with respect to a first axis A; and
(16) FIG. 12 shows a corner design embodiment of the double-walled structure with an internally arranged fixture element for inner wall segments and an externally arranged fixture element within the outer envelope connecting outer wall segments.
DETAILED DESCRIPTION
(17) FIG. 1 shows a cross section through a double-walled structure of the bladder-free fuel tank according to the present invention.
(18) A bladder-free-fuel tank 10 has an inside area 12 which is limited from an outside area 14, i.e. the surrounding, by a double-walled structure 16. The double-walled structure 16 may comprise an outer wall 18 and an inner wall 20 or may comprise—as best shown in FIG. 3—a first inner wall segment 72, a second inner wall segment 74 interconnected to each other. The outer wall 18 may comprise a first outer wall segment 78 and a second outer wall segment 80, likewise best shown in FIG. 3.
(19) As can be derived from the cross-section according to FIG. 1, the double-walled structure 16 of the bladder-free fuel tank 10 according to the present invention comprises a number of fixture elements 22 such as bolts 38 or screws 42, respectively, by means of which the outer wall 18 and the inner wall 20 are fixed to one another. The double-walled structure 16 according to FIG. 1 comprises a hollow space 26 established between the outer wall 18 and the inner wall 20. The hollow space 26, the width 27 of which is defined by a spacer 28 or in the alternative by dome-shaped elements 34 present the inner wall 20, serves as a drain- or vent-channel of the bladder-free fuel tank 10 according to the present invention. Each fixture element 22 being mounted in a mounting region of the double-walled structure 16 may comprise a sealing 30, a sealing ring 32 for instance.
(20) As can be derived from the cross-section according to FIG. 1, inwardly extending ribs 36 are present, which extend from the inner wall 20 of the double-walled structure 16 in direction to the inside area 12 of the bladder-free fuel tank 10 according to the present invention. The inwardly extending ribs 36, which form a rib structure, a rib pattern 56, see FIG. 2, may be part of a machine-milled inner wall 20 or of machine-milled inner wall segments 72, 74, respectively, as best shown in FIG. 3. In the alternative, the inwardly extending ribs 36 shown in FIG. 1 extend into the inside area 12, i.e. the interior of the bladder-free fuel tank 10 according to the present invention enhancing rigidity and mechanical stiffness of the bladder-free fuel tank 10. Instead of a one-part component, i.e. the inner wall 20 and the inwardly extending ribs 36 being a one-part arrangement, the inwardly extending ribs 36 may constitute separate components which are fastened to the inner wall 20 or to machine-milled inner wall segments 72, 74, respectively, of the double-walled structure 16.
(21) In the mounting areas, i.e. in the region where the fixture elements 22, i.e. screws 42 or bolts 38 are present, a threaded connection 40 is established between the outer wall 18 and the inner wall 20. Since the inner wall 20 or respective inner wall segments 72, 74 are machine-milled, the respective threadings for establishing a threaded connection 40 can be milled or drilled upon production of the respective inner wall 20 or the respective inner wall segment 72, 74 respectively, as best shown in FIG. 3.
(22) As shown in FIG. 1, the double-walled structure 16 is a compound comprising an inwardly arranged inner wall 20 being machine-milled, i.e. a milled component and an outwardly arranged sheet metal part. Both components, i.e. the outer wall 18 and the inner wall 20, are made from a material including aluminum. In the embodiment given in FIG. 1 the inner wall 20 and the outer wall 18 are spaced from one another by spacers 28 establishing a width 27 of the hollow space 26 of the double-walled structure 16.
(23) Both walls, i.e. the outer wall 18 and the inner wall 20 of the double-walled structure 16, are fastened to one another in order to endure tension, pressure, bending and shear forces by being gradually deformable, providing a high mechanical rigidity. The drain and vent channel 24 within the double-wall structure 16 has a width 27 of a few millimeters only.
(24) FIG. 1.1 shows a fixture element of the double-walled structure in greater detail.
(25) According to the exemplary embodiment given in FIG. 1.1 the inner wall 20 comprises a dome element 34 serving as support for the threaded connection 40. As can be derived from FIG. 1.1 the height of the dome element 34 defines the width 27 of the hollow space 26 between the outer wall 18 and the inner wall 20 of the double-walled structure 16 of the bladder-free fuel tank 10. As can be derived from FIG. 1.1 the fixture element 22 is a screw having a washer-type sealing ring 32 performing a sealing function. In inward direction, i.e. in direction of the inside area 12 of the bladder-free fuel tank 10 according to the present invention, the inwardly extending rib 36 is shown having both sides milled.
(26) FIG. 1.2 shows an alternative embodiment of a fixture element of the double-walled structure.
(27) As can be derived from FIG. 1.2 the fixture element 22 is rather a bolt 38 than a screw 42 as shown in FIG. 1.1. In the mounting area of the double-walled structure 16 the bolt 38 fixes the outer wall 18 to the respective inner wall 20 provided with dome-shaped elements 34 defining the width 27 of the hollow space 26 of the double-walled structure 16. As can be derived from FIG. 1.2 in this embodiment, the inner wall 20 of the double-walled structure 16 and the inwardly extending rib 36 constitute a one-piece embodiment. The sealing 30 according to the embodiment given in FIG. 1.2 is achieved by means of a washer-type sealing ring 32.
(28) FIG. 2 shows a rib pattern present in the inside area of the bladder-free fuel tank 10 according to the present invention.
(29) The cross-section given in FIG. 2 shows a section of a rib pattern 56 within which the inwardly extending ribs 36 are arranged in a rectangular pattern. Each of the inwardly extending ribs 36 is orientated in a 90°-degree orientation within the rib pattern 56 as given in FIG. 2. The inwardly extending ribs 36 of the rib pattern may have a first length 50 and a second length 52 which may differ from one another or may be equal with respect to one another. A ratio between the first distance 50 and the second distance 52 as shown with respect to the length of the inwardly extending ribs 36 may vary.
(30) In FIG. 2, the rib pattern 56 nearly is a square-shaped pattern, however, different patterns for instance x-cross pattern, diagonal rib pattern 58 or parallel rib pattern 60 may be feasible as well. In local thickenings 48 quantities of additional material are provided to reduce any stress level during operational material deflection below a crack-propagation level, resulting in an effective crack stop design. The rib pattern 56 given in FIG. 2 is arranged such that a crossing of two ribs 56 corresponds to fixture elements 22. In the top view given in FIG. 2, a section of the interior of the inside area 12 of the bladder-free fuel tank 10 according to the present invention is shown. The inwardly extending ribs 36 may comprise buckling resistant T-shaped extensions preventing expansions 86.
(31) FIGS. 2a and 2b, respectively, show details of machine-milled pockets provided in the inwardly extending ribs 36.
(32) According to the details given in FIGS. 2a and 2b, respectively, the inwardly extending ribs 36 are provided with milled pockets 130. The milled pockets 130 form openings in the inwardly extending ribs 36 to allow for the flow of fuel between different compartments arranged in the interior of the bladder-free fuel tank 10 according to the present invention. By means of the milled pockets 130 a uniform, homogeneous fuel level can be established within all compartments within the interior of the bladder-free fuel tank 10 according to the present invention.
(33) FIG. 3 shows a cross-section through a double-walled structure 16 in the region of a 90°-degree bow 76.
(34) According to FIG. 3, the double-walled structure 16 of the bladder-free fuel tank 10 according to the present invention comprises overlapping regions 70. To prevent mechanical stress, the overlapping regions 70 are arranged not directly within a 90°-degree bow 76 but rather in straight portion of the double-walled structure 16. As can be derived from the top view given in FIG. 3, the double-walled structure 16 with respect to the outer wall 18 and the inner wall 20, respectively, comprise the overlapping regions 70 within which either inner wall segments 72, 74 contact one another and/or outer wall segments 78, 80, respectively, are interconnected with one another. Within the overlapping regions 70 respective edge portions 82, 84 of the first inner wall segment 72 and the second inner wall segment 74 are interconnected with one another by means of a fixture element 22. The overlapping regions 70 may comprise the first outer wall segment 78 and the second outer wall segment 80 overlapping each other or as likewise shown in FIG. 3 may comprise an overlapping region 70 within which one edge portion 82 of a first inner wall segment 72 is embedded in a recess 88 of a corresponding edge portion 84 of the second inner wall segment 74, respectively. In the second alternative, a flat surface of the inner wall 20 towards the hollow space 26 present within the double-wall structure 16 is achieved.
(35) Within the overlapping regions 70 the edge portions 82, 84, respectively, may be interconnected either via fixture elements 22 such as bolts 38 or screws 42 having a sealing 30 such as a sealing ring 32. In the alternative, within the overlapping regions 70 the edge portions 82, 84, respectively, may be sealingly interconnected with each other by means of automatically performed laser welding or the like.
(36) Within the overlapping regions 70 likewise edge portions of outer wall segments 78, 80, respectively, may be interconnected either via fixture elements 22 such as bolts 38 or screws 42 having a sealing 30 such as a washer-type sealing ring 32. In the alternative, within the overlapping regions 70 the edge portions may be sealingly connected with each other by means of automatically performed laser welding or the like.
(37) Within the 90°-degree-bow 76 according to FIG. 3, a local strengthening of the milled component is achieved. As can be seen in the cross-section view given in FIG. 3, the inwardly extending ribs 36 may comprise broader buckling resistant T-shaped or L-shaped extensions 86 fastened or not fastened to a ground plate 44 onto which the double-walled structure 16 of the bladder-free fuel tank 10 sealingly is mounted.
(38) According to an exemplary embodiment of the present invention the ground plate 44 is sealingly fixed to the double-walled structure 16 of the bladder-free fuel tank 10 according to the present invention. Thus, a continuous interruption-free circumferentially extending double-walled structure 16 is established thereby maximizing the capacity of the reservoir in the interior of the bladder-free fuel tank 10 according to the present invention. Still further—however not shown in the embodiments given in FIG. 3—inner tie rods 106 or compression struds 110 may be present, preferably arranged between neighbouring or oppositely arranged sections 112 of the double-walled structure 16. By means of the inner tie rods 106 an inner pressure imposing a local mechanical load on the double-walled structure 16 is reduced significantly. The inner tie rods 106 may be connected to the inwardly extending ribs 36 by means of bolts 38 or screws 42. Plate-shaped connectors 96 as best shown in connection with FIG. 7 are arranged between the inwardly extending ribs 36 and the inner tie rods 106 (shown in FIGS. 5 and 7), thus allowing for a connection of oppositely arranged sections 112 of the double-walled structure 16 providing a plurality of force transmission points 108, as best shown in FIGS. 5 and 7, respectively.
(39) The inwardly extending ribs 36 as shown in FIGS. 1, 2 and 3 are made in a height 90, 92 corresponding to the height of the double-walled structure 16, and/or large additional e.g. riveted ribs 102 as best shown in FIG. 6 and/or tie rods made in a height, so that the inside area 12 of the bladder-free fuel tank 10 according to the present invention as precautionary measure is protected against excessive sloshing of fuel. According to the present invention the fixture elements 22 may be realized by the bolts 38 or the screws 42 establishing the threaded connection 40 between the outer wall 18 and the inner wall 20 of the double-walled structure 16. Alternatively, the fixture elements 22 may be realized as shear-sleeves including a threaded connection. By means of local deepened drawing of the sheet metal part, i.e. the outer wall 18, a forming of a flat-shaped deepening is performed, followed by a subsequent connection with the shear sleeves and/or a spacer such as a washer.
(40) FIG. 4 shows a top view of a cross-section through the double-walled structure 16, fixture elements 22 mounted in mounting areas 46 thereof. As can be derived from embodiment given in FIG. 4, the outer wall 18 of the double-walled structure 16 is bulged by arrangements of fixture elements 22 in the region of the respective mounting areas 46 against the inner wall 20 of the respective double-walled structure 16. Thus within the bulging regions 100 of the outer wall 18 the hollow space 26 defining the drain- or vent channel 24 is locally interrupted.
(41) In the embodiment given in FIG. 4 the fixture elements 22 are screws 42 which establish a threaded connection 40 to respective threadings arranged in local thickenings 48 of the inner wall 20. In the embodiment given in FIG. 4 the inner wall 20 of the double-walled structure 16 and the inwardly extending ribs 36 are a one-part-embodiment. The inwardly extending ribs 36 may have one milled side or may have both sides milled.
(42) The sealing of the double-walled structure 16 is achieved by the machine-milled inner wall 20, which in the overlapping regions 70 as best shown in FIG. 3 has a sealing 30 such as sealing paste or the like. Still further, the sealing 30 of the inside area 12 of the bladder-free fuel tank 10 according to the present invention is established by interconnected edge portions 82, 84, respectively, of first and second inner wall segments 72, 74, respectively. A sealing 30 between the ground plate 44 and the double-walled structure 16 of the bladder-free fuel tank 10 is likewise realized by circumferentially extending sealing means. The connection of the ground plate 44 and the double-walled structure 16 of the bladder-free fuel tank 10 according to the present invention is performed likewise to the connection between according to FIG. 3 or 13, respectively.
(43) The bladder-free fuel tank 10 according to the present invention comprises a rigid connection of the outer wall 18 or outer wall segments 78, 80, respectively with the inner wall 20 or inner wall segments 72, 74 forming a rigid shear resistant structure which is subject to pressure differences between i.e. the inside area 12 and the outside area 14 of the bladder-free fuel tank 10. By means of the inwardly extending reinforcing ribs 36 and the inner tie rods 106 or compression struds 110, respectively, the bladder-free fuel tank 10 according to the present invention has a lower weight as compared to fuel tank arrangements having a bladder arranged within the interior.
(44) The double-walled structure 16 as given in FIGS. 1, 3 and 4, respectively, may comprise openings for fittings allowing for double-walled openings for piping and electrical connections or openings for maintenance personnel for reasons of inspection. Still further, in the double-walled structure 16 openings may be present allowing for the installation of drain valves or the like. Still further, in the double-walled structure 16 elements may be integrated for the connection of fuel valves and the like without outer parts arranged within the outer space envelope of the bladder-free fuel tank 10. Still further, in-fuel-tank equipment such as valves, piping, sensors, pumps is arranged and can be fastened directly to the inwardly extending ribs 36 or the rib pattern arranged in the inside area 12 of the bladder-free tank 10.
(45) FIG. 5 shows a top view of the double-walled structure 16 with assigned thereto large additional riveted ribs and a combination of large additional riveted ribs with tie rods connected thereto.
(46) The cross-section according to FIG. 5 shows a double-walled structure 16, comprising the outer wall 18 and the inner wall 20. Within mounting area 46 fixtures elements 22, such as screws 42 or bolts 38 are connecting the outer wall 18 and the inner wall 20. As can be derived from the cross-section according to FIG. 5, the outer wall 18 has a somewhat bulged or buckled shape, limiting the drain- or vent-channel 24 within the hollow space 26 of the double-walled structure 16. The fixture elements 22, such as screws or bolts, are fixed to respective threadings, i.e. constituting a threaded connection 40. The corresponding threading is manufactured within local thickenings 48 of the inner wall 20. From the inner side of the inner wall 20 of the double-walled structure 16 the inwardly extending, reinforcing ribs 36 extend in direction to the inside area 12 of the bladder-free fuel tank 10 according to the present invention. As can be derived from FIG. 5, additional riveted ribs 102 are fastened to the inwardly extending ribs 36 extending into inward direction in the inside area 12 of the bladder-free fuel tank 10. The large additional riveted ribs 102 are connected via a rivet connection 104 for example, to an upright or to a horizontally extending portion of the inwardly extending ribs 36.
(47) Still further, by means of a further riveted connection 104, a part or an entire tie rod 106 can be connected to the inwardly extending rib 36. The tie rod 106, a portion thereof given in FIG. 5, extends to an oppositely arranged double-walled structure 16 of the respective bladder-free fuel tank 10 as schematically shown in FIG. 6.
(48) As can be seen in FIG. 5, e.g. every third of the inwardly extending reinforcing ribs is provided with a large additional rib 102 connected via a rivet connection 104.
(49) FIG. 6 shows a bladder-free fuel tank 10 according to the present invention not to scale with an example of an inner tie rod.
(50) As can be derived from this schematic view according to FIG. 6, two oppositely arranged double-walled structures 16 comprising inner walls 20 or first and second inner walls 72, 74, respectively. To each of the inner walls 20 a respective large additional e.g. riveted rib 102 is assigned. Via e.g. riveted connections 104 a tie rod 106 is fastened to both of the oppositely arranged large additional e.g. riveted ribs 102 at several force transmission points 108, which may be embodied likewise as e.g. riveted connections 104 as sketched in the schematic view according to FIG. 6. The inner tie rod 106 enhances mechanical rigidity of the bladder-free fuel tank 10 according to the present invention.
(51) The fuel contained in the interior of the bladder-free fuel tank 10 is conveyed to a respective main tank of a fuel supply of an aircraft by means of a pressure difference. The pressure difference may result from the pressure difference between the outside air pressure of an aircraft when operated at flight level about 10 km and the cabin air pressure amounting to approximately 0.75 bar to 0.9 bar. By means of this pressure difference Δp the fuel contained in the interior i.e. in the inside area 12 of the bladder-free fuel tank 10 is conveyed to the main fuel supply system for the engines of the respective aircraft. Thus, the interior, i.e. the inside area 12 of the bladder-free fuel tank 10 according to the present invention is pressure-loaded by the pressure provided e.g. by the cabin air and has to be designed such that the pressure for conveying the fuel present in the bladder-free fuel tank 10 according to the present invention imposes a load on the double-walled structure 16 of the bladder-free fuel tank 10. By means of the at least one tie rod 106 connecting opposingly arranged sections 112 of the double-walled structure 16, the mechanical rigidity of the bladder-free fuel tank 10 according to the present invention is enhanced significantly.
(52) The tie rod 106 connecting the large additional riveted ribs 102 to one another may be made from sheet metal or another material. The fuel capacity of the bladder-free fuel tank 10 according to the present invention is typically at least ca. 1500 l and may of course contain larger volumes of aircraft fuel.
(53) FIG. 7 shows a schematic view of an inner tie rod connected to a plate-shaped connector which internally is connected to inwardly extending ribs of the double-walled structure.
(54) As can be derived from the schematic view given in FIG. 7, the inwardly extending reinforcing ribs 36 which are a part of the inner wall 20 of the double-walled structure 16, extend into the interior, i.e. the inside area 12 of the bladder-free fuel tank 10 according to the present invention. The inwardly extending reinforcing ribs 36 may have the same lengths or may have different lengths as shown in FIG. 7.
(55) As schematically given in FIG. 7, a substantially plate-shaped connector 96 is connected to each of the inwardly extending reinforcing ribs 36 at a number of force transmission points 108. On the other hand, the plate-shaped connector 96 according to FIG. 7 is fastened at a further force transmission point 108 to a part of an inner tie rod 106 which internally is fastened to an oppositely arranged plate-shaped connector 96 fastened to an opposite section of the respective double-walled structure 16, however not shown in FIG. 7, of the bladder-free fuel tank 10 according to the present invention. The plate-shaped connector 96 may likewise be a sheet metal component made of aluminum or aluminum alloy, similar to the tie rod 106.
(56) As an alternative to the tie rod arrangements shown in FIGS. 5, 6 and 7, respectively, at the interior, i.e. the inside area 12 of the bladder-free fuel tank 10 according to the present invention, may comprise compression struds 110 extending between sections of the double-walled structure 16 orientated opposite to one another.
(57) FIG. 8 shows a rib pattern of inwardly extending ribs, the rib pattern having a substantially triangular shape.
(58) According to FIG. 8 a first the ribs 36 in the interior, i.e. the inside area 12 of the bladder-free fuel tank 10, are spaced from one another horizontally by the first distance 50. Fixture elements 22 are spaced from one another by the second distance 52. The first distance 50 and the second distance 52 may be equal or may vary with respect to one another. The triangular rib pattern 62 according to FIG. 8 is further characterized by an angle 64 (α) which is chosen between 30° and 60° particularly 45° but may as well vary, e.g. up to 90° or up to 120°. In dashed-dotted lines, milled pockets 130 are shown. The milled pockets are milled portions at the bottom of the ribs, perpendicular to the drawing plane. The milled pockets 130 are arranged close to the ground plate 44 and to the top plate of the bladder-free fuel tank 10 according to the present invention to allow for a flow of fuel and air between the compartments—in this case triangular shaped compartments—limited by the reinforcing ribs 36 in the inside area 12 of the bladder-free fuel tank 10. By means of the milled pockets, an exchange of fuel and air between neighboring compartments in the inside area 12 of the bladder-free fuel tank 10 according to the present invention is feasible.
(59) FIG. 9 shows a part of a parallel rib pattern.
(60) As can be derived from the schematical view according to FIG. 9, the inwardly extending ribs 36 are arranged in a parallel rib pattern 60 inside the interior, i.e. the inside area 12 of the bladder-free fuel tank 10 according to the present invention. As can be derived from FIG. 9 the inwardly extending ribs 36 likewise are equipped with milled pockets 130 connecting neighboring compartments, limited by the inwardly extending ribs 36 to allow for an exchange of fuel or air between neighboring compartments in the inside area 12 of the bladder-free fuel tank 10. The fixture elements 22 are spaced apart from one another by the first distance 50. The parallel rib pattern 60 is further characterized by the second distance 52 between each of the in parallel orientated inwardly extending ribs 36.
(61) FIG. 10 shows a parallel rib pattern similar to the embodiment given in FIG. 9, however, the fixture element being alternately arranged with respect to neighboring, in parallel orientated inwardly extending ribs.
(62) As is shown in FIG. 10, each inwardly extending rib 36 comprises fixture elements 22 spaced with respect to one another by the first distance 50. Similar to the embodiment of the parallel rib pattern 60 given in FIG. 9, the in parallel orientated inwardly extending ribs 36 are spaced from one another by the second distance 52.
(63) Contrary to the embodiment given in FIG. 9, fixture elements 22 may alternate with respect to one another by the alternate fixture points design 66 as schematically shown in FIG. 10. However, similar to the embodiments given in FIG. 9, the parallel rib pattern 60 according to the embodiment given in FIG. 10 comprises inwardly extending ribs 36, each having a number of milled pockets 130 arranged at the bottom of the inwardly extending ribs 36. By means of the milled pockets 130 arranged at the bottom of each of the inwardly extending ribs 36 an exchange of fuel or air between neighboring compartments separated by the inwardly extending ribs 36 from one another is feasible. The milled pockets 130 allow for a collection of fuel to be conveyed into a main tank of an area, the collection being in an integrated sump or a deepening 132 in the bottom of the bladder-free fuel tank 10, i.e. the integrated sump/deepening 132 being manufactured in the ground plate 44 of the bladder-free fuel tank 10 according to the present invention (see FIG. 6).
(64) FIG. 11 shows an arch-shaped section of the double-walled structure 16 of the bladder-free fuel tank 10 according to the present invention.
(65) As can be derived from FIG. 11, the double-walled structure 16 may have an arch-shaped section given in part in FIG. 11. The arch-shaped section of the double-walled structure 16 according to FIG. 11 is manufactured in a radius 114 about a first axis 116. Perpendicular to the drawing plane according to FIG. 11, the arch-shaped section of the double-walled structure 16 as shown in FIG. 11 may additionally be arch-shaped with respect to a second axis 118, i.e. the bladder-free fuel tank 10 according to the present invention in this embodiment having a spherical or semi-spherical shape, for instance when arranged within a tail section of an aircraft.
(66) The arch-shaped section of the double-walled structure 16 according to the embodiment in FIG. 11 comprises the outer wall 18 and the inner wall 20 defining the hollow space 26. The width 27 of the hollow space 26 is defined by the height of dome-shaped elements 34 of the inner wall 20 or inner wall segments 72, 74, respectively. The arch-shaped section according to FIG. 11 describes a 90°-bow within mounting area 46, the outer wall 18 and the inner wall 20 are connected with one another by fixture elements 22 the heads of which define an outer envelope 122 as shown in FIG. 11.
(67) Threadings for the fixture elements 22 are manufactured in local thickenings 48 constituting a mounting area 46 of the fixture elements 22, i.e. screws 42 or bolts 38. From the local thickenings 48 of the inner wall 20 of the double-walled structure 16 inwardly extending ribs 36 extend into the inside area 12 of the bladder-free fuel tank 10 according to the present invention. The inwardly extending ribs 36 may comprise buckling-resistant T-shaped extensions 86 fastened to the ground plate 44 of the bladder-free fuel tank 10 according to the present invention.
(68) FIG. 12 finally shows a corner design of the double-walled structure of the bladder-free fuel tank 10 according to the present invention.
(69) In the embodiment according to FIG. 12, a corner design 120 of the double-walled structure 16 is shown. The double-walled structure 16 comprises the outer wall 18 and the inner wall 20, or may comprise first and second inner wall segments 72, 74, respectively, and/or first and second outer wall segments 78, 80, respectively. From the interior of the inner wall 20 or inner wall segments 72, 74, respectively, the inwardly extending ribs 36 extend into the inside area 12, i.e. the interior of the bladder-free fuel tank 10 according to the present invention. The inwardly extending ribs 36 further may comprise buckling-resistant T-shaped or L-shaped extensions 86, respectively.
(70) The width 27 of the hollow space 26 of the double-walled structure 16 depends on the height of domes 34 present on the surface of the inner wall 20 or inner wall segments 72, 74, respectively, facing the outer wall 18. The outer wall 18 and the inner wall 20 are connected to each other within mounting areas by fixture elements 22 such as bolts 38 or screws 42.
(71) As can be derived from FIG. 12, the inner wall segments 72, 74, respectively, of the inner wall 20 of the double-walled structure are fastened to each other by an inward arrangement 126 of a fixture element 22. This means that the fixture element 22 connecting the inner wall segments 72, 74, respectively, is arranged within the hollow space 26 having a width 27.
(72) Contrary, outer wall segment 78, 80, respectively, are connected with each other by a fixture element 22 which is arranged within an outer corner recess 124. The fixture element 22 in the outer corner recess 24 is arranged as not to interfere with the outer envelope 122. Which is defined by the head of the fixture elements 22 as best shown in FIG. 12.
(73) The double-walled structure 16, a ground plate 44 of the bladder-free fuel tank 10 according to the present invention may be made of metal materials such as aluminum or aluminum alloys, CFK, GFK or honeycomb materials with respect to the outer wall 18. The space which is occupied by the bladder-free fuel tank 10 according to the present invention is about 6 m.sup.2 to 8 m.sup.2 and the usable tank capacity is in a magnitude between 1000 and 1500 l per minimum.
(74) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.
