A wing fuel tank and its manufacturing method

Abstract

This application discloses a wing fuel tank and its manufacturing method. The wing fuel tank includes a beam plate, a skin, and ribs. The ribs are arranged sequentially at intervals along the length of the beam plate. The skin covers the beam plate and ribs, forming a sealed oil cavity between the skin, the beam plate, and the ribs. An energy-absorbing protective layer is disposed on the surface of the skin within the oil cavity. In this application, by providing an energy-absorbing protective layer on the inner surface of the oil cavity, during fuel tank use, static charges within the fuel tank continuously accumulate on the surface of the energy-absorbing protective layer, forming a double electric layer on the upper and lower surfaces of the energy-absorbing protective layer, constituting a capacitor for storing electrical energy. The electric field strength of the energy-absorbing protective layer capacitor is relatively small, insufficient to break down the energy-absorbing protective layer; therefore, the energy-absorbing protective layer can be used normally. The energy stored in the energy-absorbing protective layer capacitor is greater than the minimum ignition energy required by the fuel tank, increasing the energy threshold and achieving electrostatic protection.

Description

Technical Field

[0001] This invention relates to the field of aircraft wing technology, and in particular to a wing fuel tank and its manufacturing method. Background Technology

[0002] Composite material integral fuel tanks have poor electrical conductivity, and aviation kerosene has low conductivity. Composite material integral fuel tanks accumulate charge more easily than metal tanks, resulting in a greater accumulation of charge per unit time, but the static electricity dissipates more slowly. Therefore, composite material integral fuel tanks are more prone to generating electrostatic discharge sparks, leading to catastrophic accidents such as fuel tank explosions. Avoiding the presence of electrostatic ignition sources is a crucial factor in fuel tank electrostatic protection. The formation of an electrostatic ignition source requires three processes: static charge generation, static charge accumulation, and electrostatic discharge. Disrupting any one of these processes can prevent the generation of an electrostatic ignition source. Therefore, fuel tank electrostatic protection design mainly focuses on three aspects: hindering static charge generation, disrupting static charge accumulation, and preventing electrostatic discharge.

[0003] Currently, both domestic and international civil aircraft designs employ various redundant protection measures to prevent shielding failure in these three aspects. However, this also introduces new challenges in terms of R&D costs, maintenance, and reliability. For example, applying antistatic coatings to the inner walls of fuel tanks requires careful consideration. Firstly, besides the coating's inherent properties, research and verification of material system compatibility are necessary. Secondly, because the fuel tank is filled with liquid, anti-corrosion materials must be applied. How to implement this coating, and the interactions between the two materials, are questions that often cannot be thoroughly addressed during model development due to time constraints. Therefore, the domestic and international civil aircraft industry is continuously researching and improving effective electrostatic protection measures. Summary of the Invention

[0004] This invention provides a wing fuel tank and its manufacturing method, which improves electrostatic protection by increasing the energy threshold value.

[0005] To achieve the above-mentioned objectives, this application provides the following technical solution:

[0006] The primary objective of this application is to provide a wing fuel tank, comprising:

[0007] Beams and slabs;

[0008] Ribs, each of which is arranged at intervals along the length of the beam;

[0009] A skin is provided, which covers the beam and rib, and a sealed oil cavity is formed between the skin, the beam and rib.

[0010] The skin has an energy-absorbing protective layer on its surface inside the oil cavity.

[0011] Optionally, the energy-absorbing protective layer includes either fiberglass cloth or carbon nanotube pads.

[0012] Optionally, the fiberglass cloth includes fiberglass and resin, the fiberglass is laid to form a sheet, and the resin fills the sheet to bond and fix the fiberglass.

[0013] Optionally, the skin includes an upper skin and a lower skin, and the upper skin and the lower skin are arranged alternately along the thickness direction of the wing.

[0014] The lower skin is provided with the energy-absorbing protective layer on the surface inside the oil cavity.

[0015] Optionally, the energy-absorbing protective layer is bonded to the surface of the lower skin using an adhesive.

[0016] Optionally, the energy-absorbing protective layer and the lower skin are co-cured to connect and fix them into a single unit.

[0017] Optionally, the energy-absorbing protective layer is fiberglass cloth, which is formed by laying a skin material on the fiberglass cloth and then hot-pressing and curing it into an integral part;

[0018] The skin material includes carbon fiber prepreg.

[0019] The second objective of this application is to provide a method for manufacturing wing fuel tanks, including:

[0020] Step S1: Connect the beams and ribs to form a frame structure;

[0021] Step S2: Install an energy-absorbing protective layer on the skin;

[0022] Step S3: Install the skin onto the frame structure so that the skin, beams, and ribs form a sealed oil cavity, and the energy-absorbing protective layer is located inside the oil cavity.

[0023] Optionally, the energy-absorbing protective layer includes fiberglass cloth;

[0024] In step S2, the fiberglass cloth is bonded to the skin, or the energy-absorbing protective layer and the skin are co-cured to form a single piece.

[0025] Optionally, the step of co-curing the energy-absorbing protective layer and the skin to form a single piece includes:

[0026] Step S21: Determine the shape and size of the fiberglass cloth based on its position on the skin;

[0027] Step S22: Cut the fiberglass cloth using a cutting machine;

[0028] Step S23: Lay the cut glass fiber cloth on the mold;

[0029] Step S24: Lay a skin material on the fiberglass cloth, wherein the skin material includes carbon fiber prepreg;

[0030] Step S25: Place the mold, fiberglass cloth and skin material into an autoclave for curing.

[0031] By adopting the above technical solution, this application has the following beneficial effects:

[0032] In this application, by setting an energy-absorbing protective layer on the inner surface of the fuel tank, during the use of the fuel tank, static charges inside the fuel tank continuously accumulate on the surface of the fiberglass cloth, forming a double electric layer on the upper and lower surfaces of the fiberglass cloth, thus constituting a capacitor for storing electrical energy. The electric field strength of the fiberglass cloth capacitor is relatively small, insufficient to break down the fiberglass cloth; therefore, the fiberglass cloth can be used normally. The energy stored in the fiberglass cloth capacitor is greater than the minimum ignition energy required by the fuel tank, raising the energy threshold and achieving the effect of electrostatic protection. Attached Figure Description

[0033] The accompanying drawings, which form part of this application, are provided to further illustrate the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention but do not constitute an undue limitation thereof. Clearly, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0034] Figure 1 This is a schematic diagram illustrating charge transfer caused by fuel sloshing in a conventional wing fuel tank during refueling.

[0035] Figure 2 A schematic diagram illustrating how the wing fuel tank provided in this embodiment of the application provides electrostatic protection by setting an energy-absorbing protective layer;

[0036] Figure 3 A three-dimensional structural schematic diagram of the wing fuel tank provided in an embodiment of this application;

[0037] Figure 4 A schematic diagram showing the energy-absorbing protective layer and skin of the wing fuel tank provided in this application embodiment being sealed in a vacuum bag.

[0038] In the diagram: 1. Beam plate; 2. Rib plate; 3. Upper skin; 4. Lower skin; 5. Oil cavity; 6. Energy-absorbing protective layer; a. Workpiece; b. Peelable fabric; c. Upper non-porous isolation membrane; d. Lower non-porous isolation membrane; e. Surface breathable felt; f. Vacuum bag; g. Tooling; h. Oil filling pipe; I. Charge; J. Fuel. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0040] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0041] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0042] See Figure 1 As shown, the charge I in the fuel tank mainly originates from the refueling process and the disturbance of the fuel J during aircraft maneuvering, resulting in charge I. These charges I accumulate continuously within the fuel tank, increasing the potential and electric field strength, thus increasing the risk of electrostatic discharge. To prevent electrostatic discharge within the composite material integral fuel tank, see [reference needed]. Figure 2 As shown in the embodiment of this application, an energy-absorbing protective layer 6 is arranged at the bottom of the fuel tank to form a capacitor that can store electrical energy at the bottom of the fuel tank, thereby improving the electrostatic protection effect.

[0043] For details, see Figure 3As shown in the illustration, this application provides a wing fuel tank, comprising: a beam plate 1, a skin, and ribs 2. There can be two beam plates 1, spaced apart. There can also be two ribs 2, each spaced apart along the length of the beam plate 1. The skin covers the beam plate 1 and the ribs 2, forming a sealed oil cavity 5 between the skin, the beam plate 1, and the ribs 2. An energy-absorbing protective layer 6 is disposed on the surface of the skin within the oil cavity 5. In this application, by providing the energy-absorbing protective layer 6 on the inner surface of the oil cavity 5, during fuel tank use, the static charge I within the fuel tank continuously accumulates on the surface of the energy-absorbing protective layer 6, forming a double electric layer on the upper and lower surfaces of the energy-absorbing protective layer 6, constituting a capacitor for storing electrical energy. The electric field strength of the capacitor in the energy-absorbing protective layer 6 is relatively small, insufficient to break down the energy-absorbing protective layer 6; therefore, the energy-absorbing protective layer 6 can be used normally. The energy stored in the capacitor in the energy-absorbing protective layer 6 is greater than the minimum ignition energy required by the fuel tank, increasing the energy threshold and achieving electrostatic protection.

[0044] Optionally, the energy-absorbing protective layer 6 includes either fiberglass cloth or carbon nanotube pads. Carbon nanotube pads have strong energy absorption properties and can provide some electromagnetic shielding, making them suitable for protecting fuel tank ignition sources. Fiberglass cloth is suitable for raising the energy threshold. According to airworthiness regulations 25.981, 25.899, and related advisory circulars, the minimum ignition energy in the fuel tank is 0.2 MJ. The fiberglass cloth capacitor stores a relatively large amount of energy, approximately 0.36 mJ, which is far greater than the maximum electrostatic discharge energy required by the FAA (0.2 mJ). Since the surface of the fiberglass cloth is completely covered by the fuel J and does not come into contact with combustibles or oxidizers, electrostatic discharge will not occur inside the fuel tank.

[0045] During the use of the composite material integral fuel tank, the static charge I inside the fuel tank continuously accumulates on the surface of the glass fiber cloth, forming a double electric layer on the upper and lower surfaces of the glass fiber cloth, which constitutes a capacitor for storing electrical energy. The performance parameters of the glass fiber cloth capacitor can be calculated by the following formulas.

[0046] (1) ε=ε r ·ε0;

[0047] (2) C = ε·A / d;

[0048] (3) U = Q / C;

[0049] (4) E = U / d;

[0050]

[0051] (6) R = d / (Aδ);

[0052] (7)τ γ =RC;

[0053] Where ε·0 is the vacuum permittivity (F / m), ε γ ε is the relative permittivity of the glass fiber (F / m), ε is the dielectric constant of the glass fiber (F / m), and A is the surface area of ​​the glass fiber cloth (m²). 2 ), d is the thickness of the fiberglass cloth (m), C is the capacitance of the fiberglass cloth (F), U is the voltage between the fiberglass cloth and the CFRP (V), Q is the charge of the fiberglass cloth (C), E is the electric field strength between the fiberglass cloth and the CFRP (V / m), W is the energy stored in the fiberglass cloth (J), R is the resistance of the fiberglass cloth (Ω), δ is the conductivity of the fiberglass cloth (S / m), τ γ denoted as dielectric relaxation time (s) of the glass fiber cloth.

[0054] Table 1 below shows the various input parameters, and Table 2 shows the calculation results:

[0055] Table 1 Input Parameter Table

[0056]

[0057] Table 2 Calculation Data Table

[0058]

[0059] As shown in Table 2, the relaxation time of the fiberglass cloth is very short (τγ = 177 ms), which prevents excessive charge I from accumulating on the surface of the fiberglass cloth. The electric field strength of the fiberglass cloth capacitor is relatively small (E = 565 kV / m), which is insufficient to break down the fiberglass cloth; therefore, the fiberglass cloth can be used normally. The energy stored in the fiberglass cloth capacitor is relatively large (W = 0.36 mJ), which is greater than the maximum electrostatic discharge energy required by the FAA (0.2 mJ). However, since the surface of the fiberglass cloth is completely covered by fuel J and does not come into contact with combustibles or oxidizers, no electrostatic discharge will occur inside the fuel tank.

[0060] The fiberglass cloth comprises fiberglass and resin. The fiberglass is laid out to form a sheet, and the resin fills the sheet to bond and fix the fiberglass. Fiberglass cloth has the advantages of good insulation, strong heat resistance, and good corrosion resistance.

[0061] The skin includes an upper skin 3 and a lower skin 4. The upper skin 3 and the lower skin 4 are arranged alternately along the thickness direction of the wing. The energy-absorbing protective layer 6 is disposed on the surface of the lower skin 4 inside the oil cavity 5.

[0062] The lower skin 4 is located at the bottom of the fuel tank. An energy-absorbing protective layer 6 is provided on the lower skin 4, which allows the energy-absorbing protective layer 6 to be covered by fuel J and not to come into contact with combustibles and combustion accelerants. Therefore, no electrostatic discharge will occur inside the fuel tank.

[0063] In one possible implementation, the energy-absorbing protective layer 6 is bonded to the surface of the lower skin 4 by an adhesive.

[0064] Taking fiberglass cloth as an example, a two-stage bonding method can be used to connect the fiberglass cloth and the skin. First, the skin is cured and machined to its net dimensions. The position and dimensions of the fiberglass cloth are designed according to the positions of the tank beam ribs. The fiberglass cloth sheet is cut using a cutting machine. The bonding surface of the skin is manually sanded until there are no protrusions, taking care not to damage the fibers during sanding. Adhesive is applied to the bonding surface as needed, and the fiberglass cloth is then adhered to the skin surface. To avoid secondary tank loading of the composite material, it is cured at room temperature under vacuum pressure (the resin system must meet room temperature curing requirements). Specifically, a non-porous release membrane and a surface breathable felt (e) are laid on the surface of the test piece (skin and fiberglass), and then a vacuum bag (f) is applied. A vacuum is drawn to -0.08 MPa (according to material requirements), and curing is performed at room temperature under vacuum pressure.

[0065] In another possible implementation, the energy-absorbing protective layer 6 and the lower skin 4 are co-cured to connect and fix them into a single unit. Taking fiberglass cloth as an example, the single unit is formed by laying the skin material on the fiberglass cloth and then hot-pressing and curing it. The skin material includes carbon fiber prepreg.

[0066] The performance of co-cured bonding structures is far superior to that of co-bonding. Adhesive bonding involves first curing the skin and fiberglass cloth, then bonding them together. Co-curing differs from adhesive bonding in that the skin and fiberglass cloth are not cured after being laid out; instead, they are combined into a sandwich structure and cured simultaneously. The performance of co-cured pre-formed adhesive bonding is far superior to that of co-bonding.

[0067] This application also provides a method for producing wing fuel tanks, including:

[0068] Step S1: Connect beam 1 and rib 2 to form a frame structure;

[0069] Step S2: Install an energy-absorbing protective layer 6 on the skin;

[0070] Step S3: Install the skin onto the frame structure so that the skin, beam plate 1 and rib plate 2 form a sealed oil cavity 5, and the energy-absorbing protective layer 6 is located inside the oil cavity 5.

[0071] The energy-absorbing protective layer 6 includes fiberglass cloth;

[0072] In step S2, the fiberglass cloth is bonded to the skin, or the energy-absorbing protective layer 6 and the skin are co-cured to form an integral part.

[0073] Optionally, the step of co-curing the energy-absorbing protective layer 6 and the skin to form a single piece includes:

[0074] Step S21: Determine the shape and size of the fiberglass cloth based on its position on the skin;

[0075] Step S22: Cut the fiberglass cloth using a cutting machine;

[0076] Step S23: Lay the cut glass fiber cloth on the mold;

[0077] In this step, laser projection can be used to project onto the mold to form a projection area, which makes it convenient to lay fiberglass cloth (fiberglass prepreg) on ​​the mold.

[0078] Step S24: Lay a skin material on the fiberglass cloth, wherein the skin material includes carbon fiber prepreg;

[0079] Step S25: The mold, fiberglass cloth, and skin material are placed in an autoclave for curing. Both the glass fiber prepreg and the carbon fiber prepreg contain resin, and the resins of the two are melt-bonded, allowing the fiberglass cloth and the skin to be co-cured to form a single piece.

[0080] See Figure 4 As shown, step S24 also includes encapsulating workpiece a (formed by laying a skinning material on glass fiber cloth). Peelable fabric b can be laid on both sides of workpiece a in the thickness direction. On the side of peelable fabric b away from fixture g, an upper non-porous release film c and a surface breathable felt e are sequentially bonded. On the side of peelable fabric b close to fixture g, a lower non-porous release film d, a release cloth, etc., are bonded. Finally, each layer of the structure is supported on fixture g and wrapped by a vacuum bag f, with the vacuum bag f and fixture g sealed together. After the process is completed, a curing process is performed for a certain time under set pressure and temperature according to the material system requirements.

[0081] The preferred embodiments disclosed above are merely illustrative of this application. These preferred embodiments do not exhaustively describe all details, nor do they limit the application to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of this application, thereby enabling those skilled in the art to better understand and utilize this application. This application is limited only by the claims and their full scope and equivalents.

Claims

1. A method of producing a wing tank, characterized by, The wing fuel tank includes: a beam, ribs, and a skin. The ribs are spaced apart sequentially along the length of the beam. The skin covers the beam and ribs, forming a sealed fuel cavity between them. The skin includes an upper skin and a lower skin, which are spaced apart sequentially along the thickness of the wing. An energy-absorbing protective layer is disposed on the surface of the lower skin inside the fuel cavity. This energy-absorbing protective layer is located at the bottom of the fuel tank to form a capacitor at the bottom of the fuel cavity capable of storing electrical energy. The minimum ignition energy required by the wing fuel tank is greater than that required by the fuel tank. During the use of the fuel tank, the static charge in the fuel tank accumulates on the surface of the energy-absorbing protective layer, forming a double electric layer on the upper and lower surfaces of the energy-absorbing protective layer, which constitutes a capacitor for storing electrical energy. The electric field strength of the capacitor formed by the energy-absorbing protective layer is insufficient to break down the energy-absorbing protective layer. The energy-absorbing protective layer includes glass fiber cloth, which includes glass fiber and resin. The glass fiber is laid to form a sheet, and the resin fills the sheet to bond and fix the glass fiber. The energy-absorbing protective layer and the skin are co-cured to form an integral part. The production methods include: Step S1: Connect the beams and ribs to form a frame structure; Step S2: Install an energy-absorbing protective layer on the skin; Step S3: Install the skin onto the frame structure so that the skin, beams, and ribs form a sealed oil cavity, and the energy-absorbing protective layer is located inside the oil cavity; Step S2 includes: Step S21: Determine the shape and size of the fiberglass cloth based on its position on the skin; Step S22: Cut the fiberglass cloth using a cutting machine; Step S23: Lay the cut glass fiber cloth on the mold; Step S24: Lay a skin material on the fiberglass cloth, wherein the skin material includes carbon fiber prepreg; Step S25: Place the mold, fiberglass cloth and skin material into an autoclave for curing.

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