FUEL TANK

Abstract

The present disclosure provides a fuel-impermeable structural unit for use as a structural element of a fuel tank, including a multi-plies structure made of one or more composite material and polymers, and, a sealing polymeric film structurally bonded to and coating the entire surface of at least one face of the multi-plied structure. The polymeric film is integrated with an underlying external layer of said multi-plies structure, is impermeable to the fuel, is not reactive with the fuel, and can bind to an adhesive for fixing one or more rigid elements thereto.

Claims

1. A fuel-impermeable structural unit for use as a structural element of a fuel tank, comprising a multi-plies structure made of one or more composite material and polymers, and a sealing polymeric film structurally bonded to and coating the entire surface of at least one face of the multi-plied structure, wherein said polymeric film: is integrated with an underlying external layer of said multi-plies structure, is impermeable to the fuel, is not reactive with the fuel, and can bind to an adhesive for fixing one or more rigid elements thereto.

2. The unit according to claim 1, wherein said multi-plies structure comprises a plurality of composite or polymeric plies, held together by a cured resin.

3. The unit according to claim 1, wherein said multi-plies structure is in the form of a laminate structure.

4. The unit according to claim 1, wherein said multi-plies structure comprises at least one low-density core, encased between solid plies.

5. The unit according to claim 4, wherein said core is in the form of a honeycomb structure.

6. The unit according to claim 4, wherein said core is in the form of a foam core.

7. The unit according to any one of claims 1 to 6, wherein said sealing polymeric film is made of thermoplastic polyurethane.

8. The unit according to any one of claims 1 to 6, wherein said sealing polymeric film is made of a thermosetic nitrile-phenolic copolymer.

9. The unit according to any one of claims 1 to 6, wherein said sealing polymeric film is made of a combination of a thermoplastic polyurethane and a thermosetic nitrile-phenolic.

10. The unit according to any one of claims 1 to 9, wherein said structural element of the fuel tank is a skin.

11. The unit according to any one of claims 1 to 9, wherein said structural element of the fuel tank is a spar.

12. The unit according to any one of claims 1 to 9, wherein said structural element of the fuel tank is a support rib.

13. The unit according to any one of claims 1 to 12, wherein said unit includes at least one designated zone comprising said sealing polymeric film coated and structurally bonded to said at least one face of the multi-plied structure, wherein said at least one designated zone is designated for binding to an adhesive for fixing one or more rigid elements thereto.

14. The unit according to claim 13, wherein the unit is a skin of the fuel tank.

15. The unit according to claim 14, wherein at least one said rigid element is a spar.

16. The unit according to claim 14, wherein at least one said rigid element is a rib.

17. A fuel tank, comprising a skin and one or more rigid elements, wherein said skin is made of one or more fuel-impermeable structural units, each of the one or more said units comprising a multi-plies structure made of one or more composite material and polymers, and a sealing polymeric film structurally bonded to and coating the entire surface of at least one face of the multi-plied structure, wherein said polymeric film is integrated with an underlying external layer of said multi-plies structure, is impermeable to the fuel, is not reactive with the fuel, and can bind to an adhesive for fixing one or more rigid elements thereto; the one or more rigid elements defining at least end walls of the fuel tank, said rigid elements being bonded to respective designated zones of the skin comprising said sealing polymeric film coated and structurally bonded to said at least one face of the multi-plied structure, via said adhesive.

18. The fuel tank according to claim 17, the one or more rigid elements further comprising at least one of one or more support ribs and one or more spars.

19. The fuel tank according to claim 18, the skin being fixed to at least the respective ribs and/or the respective spars by one or more adhesives applied at least between a connecting surface of the respective ribs and/or the respective spars, and the polymeric film of said skin.

20. The fuel tank according to any one of claims 17 to 19, wherein said multi-plies structure is in the form of a sandwich structure comprising a light-weight core encased between dense composite plies.

21. The fuel tank according to claim 20, wherein said core is in the form of a honeycomb structure or in the form of a foam core.

22. The fuel tank according to any one of claims 17 to 19, wherein said multi-plies structure is in the form of a laminate structure.

23. The fuel tank according to any one of claims 17 to 22, wherein the skin is formed out of a single said fuel-impermeable structural unit forming a closed-loop structure.

24. The fuel tank according to any one of claims 17 to 22, wherein said skin comprises two or more said fuel-impermeable structural units.

25. The fuel tank according to any one of claims 18 to 24, wherein at least one of the spars and the support ribs is made of a unit according to any one of claims 1-16.

26. The fuel tank according to any one of claims 18 to 24, wherein both the spars and the support ribs are made of a unit according to any one of claims 1-16.

27. The fuel tank according to any one of claims 17 to 26, wherein said sealing polymeric film is made of thermoplastic polyurethane.

28. The fuel tank according to any one of claims 17 to 26, wherein said sealing polymeric film is made of a thermosetic nitrile-phenolic copolymer.

29. The fuel tank according to any one of claims 17 to 26, wherein said sealing polymeric film is made combination of a thermoplastic polyurethane and a thermosetic nitrile-phenolic.

30. A method for producing a fuel-impermeable structural unit for use as a structural element of a fuel tank, comprising: preparing a multi-layer structure comprising a multi-plies sub-structure of one or more plies of composite materials and/or polymers impregnated with one or more polymeric resin, and a sealing polymeric film applied over the entire surface of at least one face of the multi-plies sub-structure, wherein said polymeric film is impermeable to the fuel, is not reactive with the fuel, and can bind to an adhesive; and curing the multi-layer structure under heat and/or pressure to obtain a multi-plies structure wherein the polymeric film is structurally bonded to and integrated with an underlying external ply of said multi-plies structure, thereby obtaining the unit.

31. The method according to claim 30, wherein the multi-plies sub-structure is prepared by stacking a plurality of plies of composite material and/or polymers, each ply being pre-impregnated with a thermosetic resin.

32. The method according to claim 30, wherein the multi-plies sub-structure is prepared by stacking a plurality of dry plies of composite material and/or polymers, and impregnating the plies with a thermosetic resin.

33. The method according to claim 30, wherein the multi-plies sub-structure is prepared by resin transform molding.

34. The method according to claim 30, wherein the multi-plies sub-structure is prepared by liquid resin infusion.

35. The method according to any one of claims 30 to 34, wherein curing is carried out in an autoclave, an oven, or at ambient temperature.

36. The method according to any one of claims 30 to 35, wherein the structural element is a skin, a spar, or a support rib.

37. The method according to any one of claims 30 to 36, wherein said sealing polymeric film is made of thermoplastic polyurethane.

38. The method according to any one of claims 30 to 36, wherein said sealing polymeric film is made of a thermosetic nitrile-phenolic copolymer.

39. The method according to any one of claims 30 to 36, wherein said sealing polymeric film is made combination of a thermoplastic polyurethane and a thermosetic nitrile-phenolic.

40. A method of producing a fuel tank, comprising: preparing one or more rigid elements defining at least end walls of the fuel tank; and fixing one or more skin segments to the one or more rigid elements, the skin segments being made out of a fuel-impermeable structural unit as defined in any one of claims 1 to 16.

41. The method according to claim 40, comprising bonding said rigid elements to respective designated zones of the skin segments comprising said sealing polymeric film coated and structurally bonded to said at least one face of the multi-plied structure, via said adhesive.

42. The method according to any one of claims 40 to 41, the one or more rigid elements further comprising at least one of one or more support ribs and one or more spars.

43. The method according to claim 42, the skin segments being fixed to at least the respective ribs and/or the respective spars by one or more adhesives applied at least between a connecting surface of the respective ribs and/or the respective spars, and the polymeric film of said skin segments.

44. The method according to any one of claims 40 to 43, wherein said support ribs and said spars are adhered onto the polymeric film of the skin segments during said fixing.

45. The method according to claims 40 to 44, comprising applying one or more additional sealing materials at locations of contact between the rigid elements and the skin.

46. The method according to any one of claims 40 to 45, comprising applying one or more reinforcing elements over locations where the rigid elements are adhered to the skin.

47. The method according to claim 46, comprising applying a said polymeric film over the reinforcing elements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0174] In order to better understand the subject matter that is disclosed herein and to exemplify how it can be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0175] FIGS. 1A and 1B show schematic representations of a section of a fuel tank according to the prior art (FIG. 1A) and according to the present disclosure (FIG. 1B).

[0176] FIG. 2A shows perspective isometric view of a schematic fuel tank according to an embodiment of this disclosure.

[0177] FIG. 2B shows a side view cross-section through a support rib of the fuel tank schematically represented in FIG. 2A.

[0178] FIG. 2C shows side view cross-section through a support rib of a fuel tank according to another embodiment of this disclosure.

[0179] FIG. 3 shows a test set-up for evaluating the fuel-impermeability of the polymeric film.

DETAILED DESCRIPTION

[0180] Turning first to FIG. 1A, shown is a schematic representation of a section of a typical integral fuel tank according to the prior art. Section 100 of the fuel tank comprises a multilayer structure 102 forming a skin of the fuel tank, with a support rib 104 adhered thereto by adhesive 106. Reinforcement patches 108, typically made of composite layers are laid-up or applied over the regions joining the ribs and the skin for providing mechanical reinforcement to the structure. Additional sealing elements (sheets and/or pastes) 110, 112, 114, 118 are then applied to sections of the surface of the rib and the skin. As common sealing sheets are limited in their ability to be adhered to other surfaces, they are applied as patches or pre-cut sections over the surface of the skins, ribs and spars, resulting in discontinuities and imperfect sealing. Thus, an additional sealing paste 116 needs to be applied in addition to sealant paste 118. As appreciated, such a production process has multiple steps, which both elongates and complicates the construction of the fuel tank. Further, the use of a large variety and number of different layers and sealing means significantly increases the overall weight of the fuel tank.

[0181] Shown in FIG. 1B is a section of a fuel tank, for example an integral fuel tank, according to an example of the presently disclosed subject matter. As can be seen a section of fuel tank 200 comprises a tank skin 202 with a support rib 204 attached thereto. However, according to aspects of the presently disclosed subject matter the skin 202 is formed from one or more fuel-impermeable structural unit 209, each of which comprises a respective multi-plies structure 203 and a respective sealing polymeric film 205 structurally bonded to the multi-plies structure 203.

[0182] The multi-plies structure 203 can be made from any suitable materials, for example as provided above in the section “General Description”.

[0183] While in this example the multi-plied structure 203 is in the form of a sandwich structure that comprises a light-weight core (for example in the form of a honeycomb structure or in the form of a foam core) encased between dense composite plies, in alternative variations of this example, the multi-plied structure 203 can instead be in the from a laminate structure, for example.

[0184] The sealing polymeric film 205 can be made from any suitable materials, for example as provided above in the section “General Description”. In at least this example, the sealing polymeric film 205 is made of thermoplastic polyurethane, or from a thermosetic nitrile-phenolic copolymer, or from a combination of a thermoplastic polyurethane and a thermosetic nitrile-phenolic.

[0185] The polymeric film 205 is structurally bonded to the surface of at least one face of the multi-plied structure 203, thereby causing the polymeric film 205 to be integrated with an underlying external layer of the multi-plies structure 203.

[0186] Furthermore, the polymeric film 205 coats at least a portion of the surface, or alternatively a majority of the surface, or alternatively the entire surface, of at least one face of the multi-plied structure 203.

[0187] The polymeric film 205 is configured to be impermeable to the fuel that it is desired to accommodate in the fuel tank.

[0188] The polymeric film 205 is configured to be non-reactive with the fuel that it is desired to accommodate in the fuel tank.

[0189] For example, such fuel can be aviation fuel.

[0190] The polymeric film 205 is configured with the capability to bind to a suitable adhesive for fixing one or more rigid elements thereto. For example, such rigid elements can include rib 204 and/or rigid spars 230, as will become clearer herein.

[0191] Although polymeric film 205 is shown for visualization purposes as a separate layer, it is to be understood that polymeric film 205 forms an integral part of the unit 209 that constitutes skin 202, and the polymeric film 205 is structurally bonded to the multi-plies structure 203. As the polymeric film 205 is configured to be fuel-impermeable, the polymeric film 205 forms a continuous, uninterrupted barrier between the fuel and the multi-plies structure 203. It is noted that the rib 204 can be similarly covered by a polymeric film 220 to prevent leakage of fuel into the structure of the rib. The rib 204 is adhered at location 206 to the polymeric film 205 via suitable adhesive 207, and reinforcing patches 208 are optionally placed thereon (optionally comprising a respective polymeric film). Optionally, a sealing paste 216 can be applied, however this is not mandatory.

[0192] Such a skin 202, and the respective one or more fuel-impermeable structural unit 209 corresponding thereto, includes at least one such location 206, which is essentially a designated zone comprising the sealing polymeric film 205 coated and structurally bonded with respect to at least one face of the multi-plied structure 203. It is readily evident that such a designated zone is designated for binding to an adhesive for fixing one or more rigid elements thereto, for example for fixing end walls of the tank, a rib or spar to the designated zone via the adhesive.

[0193] In some examples, the sealing polymeric film 205 in one such designated zone can be made of thermoplastic polyurethane, for example where the respective rigid element that is to be affixed thereat is expected to be a non-structural element or semi-structural element, and/or for example where such a rigid element is a rib.

[0194] In some examples, the sealing polymeric film 205 in one such designated zone can be made of thermosetic nitrile-phenolic copolymer, for example where the respective rigid element that is to be affixed thereat is expected to be a structural element, and/or for example where such a rigid element is a spar.

[0195] As can be seen, by utilizing a continuous, structurally integrated polymeric film, the production process of the fuel tank can be simplified, and the overall weight of the fuel tank can be significantly reduced.

[0196] Sealing paste can also be added, if required or desired.

[0197] A perspective isometric view of a schematic representation of an exemplary integral fuel tank constructed using fuel-impermeable structural units according to this disclosure is shown in FIG. 2A. The fuel tank 200A is constructed out of skin 202 being constituted by fuel-impermeable structural units as described herein. Although skin 202 is shown in this example to have a curvature (e.g., for fitting into a wing section of an aircraft), it is to be understood that the skin can be planar or assume any other desired 3-dimensional configuration. The end walls of the tank can be made from suitable such rigid members, for example spars and/or ribs. In order to form the tank, rigid spars 230 are fixed to the skin 202, e.g., by means of adhering at locations 232. Rigid support ribs 204 are fixed within the tank by adhering them to the spars and the skin at respective said designated zones, thus increasing the strength of the tank and creating compartmentalization of the tank's volume. As can be seen, the polymeric film that is part of the skin 202 forms a continuous fuel-impermeable barrier, lining the entire internal (fuel-facing) surface of the skin.

[0198] A side cross-sectional view through a support rib 204 of the tank of FIG. 2A is shown in FIG. 2B. As can be seen, support rib 204 is adhered to the polymeric film of the skin at locations or designated zones 236—hence adherence of the rib to the skin, similar to the adherence of the spars to the skin, does not form discontinuities or non-continuities in the skin, as all rigid elements that are adhered to the skin 202 are not adhered directly to the multi-plies structure 203, but rather to the polymer film 205, which forms a continuous fuel-impermeable barrier. Optionally, rib 204 can include cut-outs or openings 234, that permit free flow of fuel between the compartments formed between two adjacent ribs.

[0199] Another exemplary integral fuel tank is shown in FIG. 2C, in which similar functional elements to that of FIG. 2A were designated similar numerals, however marked by a “‘” sign. In the example of FIG. 2C, the spars 230’ can be made from a unit similar to the unit constituting the skin 202′, hence also including a structurally bonded polymeric film on their surface that faces the inside of the tank. Thus, ribs 204′ are adhered to the polymeric film coating the spar 230′ at locations or designated zones 236′, via suitable adhesive.

EXAMPLES

Example 1: Fuel-Impermeability by Vacuum Test

[0200] The polymeric film's impermeability to fuel was assessed as follows: a sandwich panel was coated by a nitrile-phenolic polymeric film or by a polyurethane film. A control sample was prepared from the same sandwich panel, however without a polymeric film. An open-bottomed container filled with fuel was adhered to the polymeric film. The panel was placed in a vacuum bag and vacuum was applied for 7 days. Pressure within the bag was measured throughout the test. The test set-up is shown in FIG. 3, and the results are shown in Table 1.

TABLE-US-00001 TABLE 1 vacuum test results: Thickness Sample Polymeric film of film Results 1 nitrile-phenolic 0.254 mm Vacuum was maintained for over 7 days 2 nitrile-phenolic 0.152 mm Vacuum was maintained for over 7 days 3 polyurethane 0.150 mm Vacuum was maintained for over 7 days 4 — — Vacuum was not maintained

[0201] As can be seen, vacuum was not maintained for the reference sample, while the samples in which the respective panel was structurally bonded to a nitrile-phenolic or polyurethane polymeric films maintained vacuum for over 7 days, indicating that the polymeric films are fuel impermeable.

[0202] In the method claims that follow, alphanumeric characters and Roman numerals used to designate claim steps are provided for convenience only and do not imply any particular order of performing the steps.

[0203] Finally, it should be noted that the word “comprising” as used throughout the appended claims is to be interpreted to mean “including but not limited to”.

[0204] While there has been shown and disclosed examples in accordance with the presently disclosed subject matter, it will be appreciated that many changes may be made therein without departing from the scope of the presently disclosed subject matter as set out in the claims.