Internal sensor lead sealing structure for aircraft fuel tank pressurizing test

Abstract

The utility model discloses an aircraft fuel tank pressurizing test internal sensor lead sealing structure which comprises a threading taper hole bolt (2), the threading taper hole bolt (2) is in threaded connection with a compression nut (4), a threading hole is formed in the threading taper hole bolt (2) and is composed of a taper hole section and a straight hole section which are sequentially arranged in the axial direction of the threading taper hole bolt (2), and the straight hole section is in threaded connection with the compression nut (4). The straight hole section is located at the small-opening end of the taper hole section. The taper hole section and the straight hole section are filled with curing sealing resin (7) and end sealing resin (8) respectively. The utility model has the characteristics of small and exquisite structure, strong loading capacity, safety and reliability in sealing, good universality and convenience in implementation of sealing.

Description

Technical Field

[0001] This utility model belongs to the field of aircraft structural strength testing technology, specifically relating to a sealing structure for internal sensor leads in an aircraft fuel tank pressurization test. Background Technology

[0002] In recent years, aircraft fuel tanks have adopted a large number of new materials and structures, requiring pressure tests to detect and verify whether the structural strength meets design requirements. To achieve the test objectives, a large number of strain sensors need to be installed inside the test specimen structure. Each strain sensor normally has three signal lines, with dozens to thousands of lead-out signal lines. The sealing of these signal lines becomes one of the key factors for the success of the test. The lead-out sealing structure of the signal lines must withstand test pressures ranging from several thousand Pascals to several megapascals or even higher without leakage to ensure the smooth completion of the test. Due to the special nature of aircraft structural design, the sealing structure cannot have a significant impact on the structural strength of the test specimen. This requires that the openings of the lead-out signal lines be as few and small as possible, which places high demands on the sealing of the lead-out signal lines. Currently, there are many types of internal sensor lead-out sealing structures in China, but their versatility is poor, making it difficult to meet the requirements of aircraft structural pressure tests. Utility Model Content

[0003] The purpose of this invention is to provide a sealing structure for the internal sensor lead wires in aircraft fuel tank pressurization tests. This invention features a compact structure, strong pressure resistance, reliable and safe sealing, good versatility, and ease of implementation.

[0004] The technical solution is as follows: A sealing structure for the internal sensor lead wire of an aircraft fuel tank pressurization test includes a wire-passing tapered hole bolt, which is threadedly connected to a clamping nut. The wire-passing tapered hole bolt is provided with a wire-passing hole, which is composed of a tapered hole section and a straight hole section arranged sequentially along the axial direction of the wire-passing tapered hole bolt. The straight hole section is located at the small end of the tapered hole section. The tapered hole section and the straight hole section are respectively filled with cured sealing resin and end sealing resin.

[0005] In the aforementioned sealing structure for the internal sensor lead wires of the aircraft fuel tank pressurization test, the taper of the conical hole section is 7°.

[0006] In the aforementioned sealing structure for the internal sensor lead wires of the aircraft fuel tank pressurization test, the gap between the threaded tapered hole bolt and the lead wire hole located on the wall plate of the fuel tank test piece is 0.2mm-0.5mm.

[0007] In the aforementioned aircraft fuel tank pressurization test internal sensor lead sealing structure, the thread on the threaded tapered hole bolt is a fine thread.

[0008] In the aforementioned sealing structure for the internal sensor leads of the aircraft fuel tank pressurization test, the diameter of the straight hole section is determined as follows: after all signal harnesses pass through smoothly, the area of ​​the gap retained in the straight hole section accounts for 5%-15% of the total cross-section of all signal harnesses.

[0009] In the aforementioned sealing structure for the internal sensor lead of the aircraft fuel tank pressurization test, the length of the straight hole section is 50% of the diameter of the straight hole section.

[0010] In the aforementioned sealing structure for the internal sensor leads during the aircraft fuel tank pressurization test, the length of the conical bore section is determined as follows:

[0011] L>αFmax / (φz×π×τ)

[0012] In the formula, α is the safety factor; L is the length of the conical hole section; Fmax is the maximum pressure in the test of the projected area of ​​the straight hole section; φz×π is the projected perimeter of the straight hole section; and τ is the shear strength of the cured sealing resin after it has been fully cured.

[0013] The sealing method for the aforementioned internal sensor lead sealing structure in the aircraft fuel tank pressurization test includes the following steps:

[0014] S1. Thread the signal harness through the wire hole;

[0015] S2. Fill the straight hole section with end-sealing resin and allow it to cure;

[0016] S3. Fill the tapered hole section with curing sealant and cure it;

[0017] S4. Apply elastic sealant to the signal harness extending from the large end of the tapered hole section, spread it evenly, and then wrap the sealant-applied area tightly with fiber cloth, and then let it cure.

[0018] S5. After installing the sealing ring on the threading tapered bolt, pass it through the lead hole on the oil tank test piece wall panel, connect the threading tapered bolt with the clamping nut, tighten it, and the installation is complete.

[0019] In the aforementioned sealing method for the internal sensor lead sealing structure of the aircraft fuel tank pressurization test, the curing sealing resin is epoxy resin.

[0020] Beneficial Effects: To meet the pressure testing requirements of a certain type of aircraft's sealed structure, after multiple optimizations and improvements, this utility model designs a sealing structure for the internal sensor lead wires in an aircraft fuel tank pressure test. This structure has been successfully applied to the test, resulting in a compact, high-pressure-bearing, reliable, versatile, easy-to-implement, easy-to-manufacture, and low-cost sealing structure suitable for various signal lines with different structures. Application in pressure testing of sealed structures for multiple aircraft models proves that this utility model fully meets the test requirements. This utility model has good versatility and can be applied to other similar tests and structures, possessing strong promotional value. Specifically, the following technical effects have been achieved:

[0021] 1. After the internal sensor leads of the sealed structure are assembled, they can withstand the test pressure during the pressure test and ensure no liquid or gas leakage.

[0022] 2. It will not damage the sensor signal line, will not affect the acquisition and transmission of sensor signals, and can ensure the correct acquisition of test data;

[0023] 3. The lead wire sealing connector has a small and circular opening on the test piece, which has little impact on the strength of the test piece and allows for a large number of signal lines to pass through (the φ40mm lead wire hole in the test piece can accommodate 500-600 signal lines with a diameter of 1 mm).

[0024] 4. The lead wire sealing structure has good versatility and can be applied to pressure tests of various aircraft sealed structures and signal lines of various specifications;

[0025] 5. Lead wire sealing is easy to implement, and sealing joints are easy to install;

[0026] 6. The sealed structure offers good production economy;

[0027] 7. The sealed structure is recyclable. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a threading tapered hole bolt structure;

[0029] Figure 2 This is a schematic diagram of the sealing structure of the internal sensor leads for the pressure test. Detailed Implementation

[0030] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0031] Example 1. A sealing structure for the internal sensor leads in an aircraft fuel tank pressurization test, the overall design concept of which is as follows:

[0032] A circular lead-in hole is made at the lead-in section of the test specimen wall panel 1. The lead-in sealing structure is divided into two parts by a tapered bolt 2. The first part is a tapered elongated hole through which the sensor lead is threaded. Epoxy resin is used to seal and fix the sensor lead to the bolt. Elastic sealant is applied to the pressure end of the sensor lead to ensure reliable sealing between the sensor lead and the inner hole of the tapered bolt. The second part of the seal involves installing a rubber gasket around the opening of the test specimen wall panel where the tapered bolt is located. The signal wire and the tapered bolt pass through the opening in the test specimen, with the rubber gasket between the tapered bolt and the test specimen. Nuts are installed on the outside of the wall panel and tightened to form a reliable sealing structure.

[0033] The key design considerations for the sealing structure of the internal sensor leads during the pressure test are as follows:

[0034] 1. Determining the outer diameter of the external thread of the threaded tapered hole bolt:

[0035] The outer diameter of the thread should be 0.2mm-0.5mm smaller than the diameter of the hole at the lead wire part of the tank test piece wall panel. Fine threads should be used as much as possible to reduce the thread depth, thereby making the wall of the tapered bolt hole thinner and allowing more signal lines to pass through.

[0036] 2. Determining the nominal diameter of the straight section of the threading hole for the threading tapered bolt:

[0037] The size of the hole should be determined based on the number and thickness of the sensor leads inside the test piece, with all the leads passing through smoothly and the gaps retaining 5%-15% of the total cross-section of all the leads.

[0038] 3. Determining the length of the straight section of the threading hole for the threading tapered bolt.

[0039] The wire hole has two sections: a straight section and a tapered section. After the tapered section is filled with glue, it becomes the main pressure-bearing structure to prevent the signal wire and glue from failing under test pressure. Through multiple tests and optimizations, the length of the straight section should be about 50% of the nominal diameter.

[0040] 4. Method for determining the length of the tapered hole section:

[0041] L>αFmax / (φz×π×τ)

[0042] The safety factor α in the above formula is 4. If the test requires a larger safety factor, the factor can be increased accordingly.

[0043] L is the length of the tapered hole section;

[0044] Fmax is the maximum pressure during the test of the projected area of ​​the straight section;

[0045] φz×π is the projected perimeter of the straight hole segment;

[0046] τ is the shear strength of the filled resin after it has fully cured.

[0047] 5. The outer diameter of the threading tapered bolt φA should be at least 6mm larger than ΦD. The mating position of ΦD with the test piece hole should be smooth, and the mating clearance should not exceed 0.5mm.

[0048] 6. Design of the clamping nut

[0049] This ensures a reliable connection and fixation between the threaded tapered bolt and the test piece. Sufficient compression of the sealing ring is sufficient. See illustration. Figure 2 The inner hole of the clamping nut 4 has a section without threads near the test piece. This is to improve the versatility and reliability of the sealing structure. It can be applied to test piece mounting plates of different thicknesses, and the nut can be reliably tightened even for thin test piece plates.

[0050] Based on the above overall concept and design points, this embodiment describes a sealing structure for the internal sensor lead of an aircraft fuel tank pressurization test, see [link / reference]. Figures 1-2 It includes a wire-passing tapered hole bolt 2, which is threadedly connected to a clamping nut 4. The wire-passing tapered hole bolt 2 is provided with a wire-passing hole, which is composed of a tapered hole section and a straight hole section arranged sequentially along the axial direction of the wire-passing tapered hole bolt 2. The straight hole section is located at the small end of the tapered hole section. The tapered hole section and the straight hole section are respectively filled with cured sealing resin 7 and end sealing resin 8.

[0051] The taper of the aforementioned tapered hole section is 7°.

[0052] The gap between the aforementioned threading tapered bolt 2 and the lead hole located on the wall plate 1 of the oil tank test piece is 0.2mm-0.5mm.

[0053] The thread on the aforementioned threaded tapered bolt 2 is a fine thread.

[0054] The diameter of the aforementioned straight hole section is determined as follows: after all signal harnesses 5 pass through smoothly, the area of ​​the gap left by the straight hole section accounts for 5%-15% of the total cross-section of all signal harnesses 5.

[0055] The length of the aforementioned straight hole section is 50% of the diameter of the straight hole section.

[0056] The length of the aforementioned tapered section is determined as follows:

[0057] L>αFmax / (φz×π×τ)

[0058] In the formula, α is the safety factor; L is the length of the conical hole section; Fmax is the maximum pressure in the test of the projected area of ​​the straight hole section; φz×π is the projected perimeter of the straight hole section; and τ is the shear strength of the cured sealing resin 7 after complete curing.

[0059] The sealing method for the aforementioned internal sensor lead sealing structure in the aircraft fuel tank pressurization test includes the following steps:

[0060] S1. Insert the signal harness 5 into the wire hole; before threading, clean the inner and outer surfaces of the wire threading taper bolt 2; when threading, if the gap is too large, insert other cables to reduce the gap;

[0061] S2. Fill the straight hole section with end sealing resin 8 and cure it; use a resin with a fast curing speed to complete the filling of end sealing resin 8 to prevent resin from flowing out during the filling of the curing sealing resin 7 below;

[0062] S3. Fill the tapered hole section with curing sealant 7 and cure it; select a resin with good fluidity (preferably epoxy resin) and pour it into the inner hole of the wire-passing tapered bolt 2 from the tapered direction to complete the filling of the curing sealant 7, ensuring that the signal wire is well adhered to the inner hole. The purpose is firstly to fix the signal wire during the pressure test and prevent it from being pressed out. Secondly, it serves a sealing function.

[0063] S4. Apply elastic sealant 6 (rubber or silicone sealant can be used) to the signal wire harness 5 extending from the large end of the tapered hole section. After spreading evenly, wrap the coated area of ​​the signal wire harness 5 tightly with fiber cloth and then allow it to cure. When applying the sealant, ensure that each wire is coated, and the coating length should be more than 3cm. Then wrap the coated signal wire area with fiber cloth, tighten the fiber cloth to squeeze out the air in the elastic sealant, and proceed to the next step after curing. The purpose is to prevent the signal wire from shrinking in diameter under high pressure, peeling off between the signal wire and the resin, and leakage of liquid or gas.

[0064] S5. After installing the sealing ring 3 on the threading tapered bolt 2, pass it through the lead hole on the oil tank test piece wall panel 1, connect the threading tapered bolt 2 with the clamping nut 4, tighten it, and the installation is complete.

[0065] This invention was first applied to aircraft fuel tank pressurization tests with good results. Through extensive testing, application, and optimization, it was extended to other sealed structure pressurization tests, achieving the same results. After the test, the lead-wire sealing structure was cleaned and applied to other tests.

[0066] In the initial research of this invention, only the curing and sealing resin 7 was used to cure and seal the signal lines and connectors. During its application in aircraft fuel tank pressurization tests, it was found that while the initial sealing effect basically met the test requirements, as the pressurization time increased and the test was repeated intermittently, air, water, and oil leaks occurred at the connector seals. Through dissection of the connectors and extensive analysis, two reasons were identified: 1. The signal lines consist of multi-strand soft wires. The epoxy resin, after curing, has a high hardness. Although the epoxy resin can provide a sealing effect, the long-term pressure applied to the signal lines during the test causes slight compression of the signal line diameter, which over time leads to peeling between the signal lines and the epoxy resin; 2. Analysis of used connectors revealed that the sealing resin 7, which had been used to cure hundreds of signal lines through the conical bolt, contained defects such as air bubbles and voids. While these defects may not necessarily cause air or water leaks, they still pose a potential risk. To solve the above two problems, after the curing and sealing resin 7 is filled, sealed and fixed, this utility model adds elastic sealant 6 to the pressure end. The elastic sealant will not peel off after it is combined with the signal line. In addition, the elastic sealant will seal the defects and achieve a good sealing effect.

[0067] Furthermore, the initial design of this invention used a straight hole for the wire threading. However, two problems were discovered during use: 1. The curing of the sealing resin 7 and the signal wire relied entirely on the adhesive force between the cured resin 7 and the inner wall of the wire threading hole to withstand the forces during testing. This resulted in poor reliability, and the resin might loosen under the influence of oil and water during prolonged testing. 2. The wire threading hole was too small, making it difficult to thread with many wires and easily damaging the signal wire. Based on the above analysis, this invention changed the pressure-bearing end to a tapered hole. The advantage is that the cured epoxy resin forms a cone shape, so the pressure is no longer primarily transmitted through adhesive force, but rather the tapered epoxy resin bears the shear force. Additionally, because the wire threading opening is larger when using a tapered hole, threading becomes easier and smoother.

[0068] In summary, extensive testing has demonstrated that, compared to conventional aircraft fuel tank pressurization test lead flange installation methods, this invention offers the following advantages: 1. This invention requires fewer and smaller openings on the test piece, minimizing the impact on the fuel tank structure and strength, resulting in more reliable test conclusions. 2. Implementation is easier and simpler, with better sealing reliability and safety; no water or oil leakage occurred during long-term testing. 3. The sealing structure is recyclable after use and can be reused after cleaning.

[0069] The above description is merely a specific embodiment of this utility model, providing a detailed description of the utility model. Parts not covered in detail are conventional techniques. However, the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this utility model should be included within the protection scope of this utility model. The protection scope of this utility model should be determined by the scope of the claims.

Claims

1. A sealing structure for internal sensor leads in an aircraft fuel tank pressurization test, characterized in that, It includes a wire-passing tapered hole bolt (2), which is threadedly connected to a clamping nut (4). The wire-passing tapered hole bolt (2) is provided with a wire-passing hole, which is composed of a tapered hole section and a straight hole section arranged sequentially along the axial direction of the wire-passing tapered hole bolt (2). The straight hole section is located at the small end of the tapered hole section. The tapered hole section and the straight hole section are respectively filled with curing sealant (7) and end sealant (8).

2. The sealing structure for the internal sensor lead of the aircraft fuel tank pressurization test according to claim 1, characterized in that, The taper of the tapered hole section is 7°.

3. The sealing structure for the internal sensor lead of the aircraft fuel tank pressurization test according to claim 1, characterized in that, The gap between the threading tapered bolt (2) and the lead hole located on the wall plate (1) of the oil tank test piece is 0.2mm-0.5mm.

4. The sealing structure for the internal sensor lead of the aircraft fuel tank pressurization test according to claim 1, characterized in that, The thread on the threaded tapered bolt (2) is a fine thread.

5. The sealing structure for the internal sensor lead of the aircraft fuel tank pressurization test according to claim 1, characterized in that, The diameter of the straight hole section is determined as follows: after all signal harnesses (5) pass through smoothly, the area of ​​the gap left by the straight hole section accounts for 5%-15% of the total cross-section of all signal harnesses (5).

6. The sealing structure for the internal sensor lead of the aircraft fuel tank pressurization test according to claim 1, characterized in that, The length of the straight hole section is 50% of the diameter of the straight hole section.

7. The sealing structure for the internal sensor lead of the aircraft fuel tank pressurization test according to claim 1, characterized in that, The length of the tapered section is determined as follows: L>αFmax / (φz×π×τ) In the formula, α is the safety factor; L is the length of the conical hole section; Fmax is the maximum pressure in the test of the projected area of ​​the straight hole section; φz×π is the projected perimeter of the straight hole section; and τ is the shear strength of the cured sealing resin (7) after it is fully cured.

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