KR20200059363A - Composite material layer, structural integrated fuel tank and aircraft comprising same - Google Patents

Abstract

According to an embodiment of the present invention, a composite material layer may comprise: a radio wave absorbing layer formed on a front surface exposed to the outside to absorb external electromagnetic waves; and a high-density metal mesh disposed on a rear surface of the radio wave absorbing layer, reflecting and canceling the electromagnetic waves absorbed by the radio wave absorbing layer, and transmitting electrical energy of lightning to the surroundings when the lightning strikes.

Description

Composite layer and structure-integrated fuel tank and aircraft including the same {COMPOSITE MATERIAL LAYER, STRUCTURAL INTEGRATED FUEL TANK AND AIRCRAFT COMPRISING SAME}

The description below relates to a composite layer and a structure-integrated fuel tank and aircraft comprising the same.

In order to increase survivability, recently developed strategic / tactical aircraft require a stealth function not to be easily exposed to an opponent's detection signal and a lightning protection function to prevent gas loss due to lightning during operation of the aircraft.

The stealth function for radar detection can be implemented by reducing the radar cross section (RCS) of the target aircraft. Research has been conducted to apply a Radar Absorbing Structure (RAS).

The electromagnetic wave absorption structure can implement electromagnetic wave absorption function by applying a resistive sheet or by using materials such as dielectric loss material and magnetic loss material, and in order to impart stealth function to the aircraft, electromagnetic wave is applied to the electromagnetic wave absorption structure. It should be placed on the outermost part of the aircraft, and in the case of lightning protection, high-conductivity materials must be applied to rapidly transmit high electrical energy such as lightning to the grounding area.

Recently, an integrated composite fuel tank structure using a composite material has been applied to the wing of an aircraft to simultaneously reduce the weight of the aircraft fuel tank and mount a large amount of fuel. However, the integrated fuel tank using a composite material has a lower conductivity than a metal material, and thus has a high risk of damage due to direct lightning strike.

Therefore, an additional high-conductivity material should be applied in order to reduce the risk of direct lightning strike of the integral composite fuel tank, but there is a problem that stealth performance may be deteriorated because a problem in which electromagnetic waves are totally reflected by the high-conductivity material may occur. In addition, when a low-conductivity loss material is applied to the outer shell to implement stealth performance, there is a problem that lightning protection cannot be quickly dissipated and thus may be vulnerable to lightning protection.

The above-described background technology is possessed or acquired by the inventor during the derivation process of the present invention, and is not necessarily a known technology disclosed to the public before the filing of the present invention.

The purpose of one embodiment is to provide a composite layer and a structure-integrated fuel tank and aircraft comprising the same.

According to an embodiment, the composite layer may include a radio wave absorbing layer formed on a front surface exposed to the outside to absorb external electromagnetic waves; And a metal mesh disposed on the rear surface of the radio wave absorbing layer to reflect and cancel electromagnetic waves absorbed by the radio wave absorbing layer, transmit electrical energy of the lightning to the surroundings during lightning strike, and have a periodic pattern shape.

The radio wave absorbing layer includes a material capable of transmitting electromagnetic waves, and the length of the side of one cell forming the metal mesh may be within 0.5 mm to 2 mm.

The composite layer may further include a core layer installed on the rear surface of the metal mesh and formed of a material having a density smaller than that of the radio wave absorbing layer and the metal mesh to support the structure of the composite layer and absorb shock when lightning strikes. .

The core layer may include a plurality of holes formed through the composite layer along the stacked direction.

The composite layer may further include a first carbon fiber composite material layer installed on a rear surface of the core layer and formed of a material having a higher density and strength than the core layer and the radio wave absorbing layer to support the structure of the composite layer. .

The composite material layer may further include a second carbon fiber composite material layer provided between the metal mesh and the core layer.

The first carbon fiber composite material layer and the second carbon fiber composite material layer may be formed of carbon fiber reinforced plastic.

The radio wave absorbing layer can absorb electromagnetic waves of a specific frequency band among frequency bands between 2 GHz and 20 GHz, and the metal mesh has a high density pattern that does not transmit electromagnetic waves of the specific frequency band toward the core layer. Can be.

In a fuel tank having a closed interior space according to an embodiment, a cross section of the fuel tank may be formed of a composite layer according to the above embodiments.

In an aircraft including a fuselage according to an embodiment and a wing portion extending from the fuselage and receiving fuel, a cross section of the wing portion may be formed of a composite layer according to the embodiments.

In an aircraft including a fuselage for receiving fuel according to an embodiment, a cross section of the fuselage may be formed of a composite layer according to the embodiments.

According to the composite layer of one embodiment, it is possible to simultaneously implement a lightning protection function and a radio wave absorption function.

According to the composite layer of one embodiment, since the metal mesh is disposed on the rear surface of the radio wave absorbing layer and can serve as a reflector of the radio wave absorbing structure, cost and weight can be reduced during manufacturing, and the X band band is designed according to the design of the radio wave absorbing layer. In addition, it can absorb a wide range of frequencies.

1 is a perspective view of a fuel tank according to an embodiment.
2 is a cross-sectional view of a composite layer according to an embodiment.
3 is a front view of a metal mesh according to an embodiment.
4 is a cross-sectional view of a composite layer according to another embodiment.
5 is a view showing a cross-sectional structure of one side of an aircraft according to an embodiment.
6 is a view showing a state after the lightning is experimentally applied to the composite layer according to an embodiment.
7 is a view showing a state of a cross section after the lightning is experimentally applied to the composite layer according to an embodiment.
8 is a graph showing the results of analyzing the radio wave absorption performance of a composite layer according to an embodiment.
9 is a graph showing the results of analyzing the radio wave absorption performance of a composite layer having a layered structure different from one embodiment.

Hereinafter, embodiments will be described in detail through exemplary drawings. It should be noted that in adding reference numerals to the components of each drawing, the same components have the same reference numerals as possible even though they are displayed on different drawings. In addition, in describing the embodiments, when it is determined that detailed descriptions of related well-known configurations or functions interfere with understanding of the embodiments, detailed descriptions thereof will be omitted.

In addition, in describing the components of the embodiment, terms such as first, second, A, B, (a), (b), and the like can be used. These terms are only for distinguishing the component from other components, and the nature, order, or order of the component is not limited by the term. When a component is described as being "connected", "coupled" or "connected" to another component, that component may be directly connected to or connected to the other component, but another component between each component It should be understood that may be "connected", "coupled" or "connected".

Components included in any one embodiment and components including a common function will be described using the same name in other embodiments. Unless there is an objection to the contrary, the description described in any one embodiment may be applied to other embodiments, and a detailed description will be omitted in the overlapped range.

1 is a perspective view of a fuel tank according to an embodiment, FIG. 2 is a cross-sectional view of a composite layer according to an embodiment, and FIG. 3 is a front view of a metal mesh according to an embodiment.

1 to 3, the fuel tank 1 according to an embodiment is provided in an aircraft to accommodate fuel of the aircraft.

For example, the fuel tank 1 may include an inner space capable of receiving fuel and a composite layer 11 surrounding the inner space and exposed to the outside.

The composite layer 11 may prevent generation of arcs or sparks formed by concentration of electrical energy as the electrical energy of the lightning is rapidly conducted or transmitted to the periphery during the lightning strike.

In addition, since the composite layer 11 can absorb electromagnetic waves applied to the surface, a radar cross section (RCS) for radar detection can be reduced.

In addition, the composite layer 11 can not only accommodate the structural support of the fuel tank 1, but also can mitigate the physical impact exerted upon lightning strikes.

For example, the composite layer 11 may include a radio wave absorbing layer 111, a metal mesh 112, a core layer 113, and a carbon fiber composite material layer 114.

The radio wave absorbing layer 111 may be located on the outside exposed to the outside, that is, on the front surface, and absorb electromagnetic waves transmitted from the outside. For example, the radio wave absorbing layer 111 may be formed of a material having low electrical conductivity. For example, the radio wave absorbing layer 111 may include a resistance sheet, a dielectric loss material, or a magnetic loss material formed in a periodic pattern or a fine pattern. The radio wave absorbing layer can be designed to absorb a specific frequency domain by theoretically combining the shape of the periodic pattern, dielectric thickness, dielectric constant, and permeability.

The metal mesh 112 may be a member of metal having a mesh shape of a periodic pattern disposed on the rear surface of the radio wave absorbing layer 111. The metal mesh 112 may function as a photoelectric reflector of electromagnetic waves that pass through the radio wave absorbing layer 111, and may form a transmission path for rapidly conducting or dissipating electrical energy of the lightning to a peripheral portion or a grounding area when lightning strikes. have.

For example, the metal mesh 112 may be formed of a material having high electrical conductivity, and when the lightning strikes, the electrical energy of the lightning is quickly conducted to a peripheral portion or a grounding point, and the composite layer 11 is damaged due to the lightning and The risk of fuel ignition can be effectively reduced.

In addition, the metal mesh 112 reflects the electromagnetic wave absorbed by the radio wave absorbing layer 111 in an inverted phase, interferes with and counteracts the electromagnetic wave passing through the radio wave absorbing layer 111, resulting in the composite layer 11 being removed. It is possible to perform the radio wave absorption function through, which means that the radar reflection area of the fuel tank 1 can be reduced.

For example, the metal mesh 112 may have a high-density mesh shape in order to transmit or dissipate high electrical energy of a lightning strike upon lightning strike. In other words, the size and spacing of the pattern of the metal mesh 112 may be very small. For example, the length of the side of one cell forming the grid pattern of the metal mesh 112 may be within 0.2 mm.

According to the structure of the radio wave absorbing layer 111 and the metal mesh 112 installed on the rear surface of the radio wave absorbing layer 111, the radio wave absorbing layer 111 is formed of a material having low conductivity and disposed at the outermost side of the composite layer 11 It is possible to form a radio wave absorbing structure (Radar Absorbing Structure) capable of absorbing electromagnetic waves transmitted to the.

In addition, in order to quickly conduct and dissipate the electrical energy of the lightning during lightning strike, a metal mesh 112 having high conductivity is disposed on the rear surface of the electromagnetic wave absorbing layer 111 to compensate for the low conductivity of the electromagnetic wave absorbing layer 111. It can play the role of an energy transmission path.

For example, the radio wave absorbing layer 111 may absorb electromagnetic waves of a specific frequency band in a frequency band between 2 GHz and 20 GHz, such as frequency bands such as C band, X band, and KU band, depending on the design. In this case, the metal mesh 112 may reflect the electromagnetic wave that is in phase with the incident electromagnetic wave toward the electromagnetic wave absorption layer 111.

For example, when the radio wave absorbing layer 111 is designed to absorb electromagnetic waves in the C band, the X band, and the KU band, the length of the side of one cell forming the metal mesh 112 may be 0.5 mm to 2 mm. have.

On the other hand, unlike one embodiment, when the metal mesh 112 is disposed on the front side of the radio wave absorbing layer 111, when the shape of the metal mesh is determined to allow the transmission of electromagnetic waves, the density of the metal mesh is low to perform a function for lightning protection. This is difficult, and it is difficult to absorb electromagnetic waves because electromagnetic waves are totally reflected when the mesh is designed with a metal film for lightning protection. Therefore, it is physically impossible for a metal mesh to be placed on the front side to perform two functions simultaneously. Therefore, through the structure in which the metal mesh 112 is disposed on the front surface of the radio wave absorbing layer 111, it is revealed that it is difficult to achieve the intended radio wave absorbing performance.

The core layer 113 is installed on the back surface of the metal mesh 112 and may be formed of a material having a small density. For example, the core layer 113 may have a smaller density than the radio wave absorbing layer 111 and the metal mesh 112. For example, the core layer 113 may be formed of a material such as a fabric, clay urethane, epoxy or sponge, which is lightweight but has a certain level of stiffness.

According to the core layer 113, it is possible to increase the stiffness of the composite layer 11 at a level that minimizes the increase in the weight of the composite layer 11, and it is possible to absorb a physical shock that occurs during a lightning strike.

For example, the core layer 113 may include an arrangement of a plurality of holes formed through the composite layer 11 along the stacked direction, thereby reducing the weight of the core layer 113, Insulating performance can be enhanced. For example, the core layer 113 is a honeycomb core in which hexagonal columnar holes are periodically arranged. Or it may be a foam core such as a sponge.

The carbon fiber composite material layer 114 may be formed of carbon fiber reinforced plastic made of a high-strength and lightweight plastic material using carbon fiber as a reinforcement material.

For example, the carbon fiber composite material layer 114 may be installed on the rear surface of the core layer 113 and may form an inner wall of the inner space of the fuel tank 1. For example, since it serves as a high-strength member of the carbon fiber composite material layer 114 and plays a role of high rigidity of the core layer 113, as a result, the core layer 113 and the carbon fiber composite material layer 114 The silver composite layer 11 may serve as a high-rigidity and high-strength member that enhances structural stability.

The carbon fiber composite material layer 114 can support the structure of the inner space of the fuel tank 1 and the load of the fuel tank 1 and can withstand the physical impact that occurs during a lightning strike.

According to the core layer 113 and the carbon fiber composite material layer 114, it supports the structural load of the fuel tank 1 and absorbs the impact due to the lightning during a lightning strike to prevent structural damage of the fuel tank 1 Can be.

For example, the thickness of each of the core layer 113 and the carbon fiber composite material layer 114 may be designed according to the load and shape structure of the fuel tank 1.

For example, each of the radio wave absorbing layer 111, the metal mesh 112, the core layer 113, and the carbon fiber composite material layer 114 may be combined through a bonding fastening method using an adhesive. For example, the carbon fiber composite material layer 114 may be applied as a fuel primer to prevent corrosion and strength from being reduced due to fuel accommodated in the interior space.

4 is a cross-sectional view of a composite layer according to another embodiment.

Referring to FIG. 4, an embodiment of the composite layer 2 including the additional carbon fiber composite material layer 114 in the structure of the composite layer 11 illustrated in FIGS. 1 to 3 may be confirmed.

According to the composite material layer 2 according to an embodiment, the carbon fiber composite material layer 114 is installed not only on the rear surface of the core layer 113 but also on the front surface of the core layer 113 and the back surface of the metal mesh 112. Can be installed on.

By further adding a carbon fiber composite material layer 114 between the core layer 113 and the metal mesh 112, the structural stability of the fuel tank 1 can be further increased, and in addition, the impact generated during a lightning strike is the core layer. Since it can be primarily absorbed before being transferred to 113, it is possible to effectively reinforce the structural stability of the core layer 113.

For example, since the carbon fiber composite material layer 114 installed on the front surface of the core layer 113 has a property capable of totally reflecting incident electromagnetic waves, it reinforces the role of the metal mesh 112 serving as a reflector. can do.

Meanwhile, the carbon fiber composite material layer 114 installed on the rear surface of the core layer 113 is referred to as a “first carbon fiber composite material layer”, and is installed on the front surface of the core layer 113 and the back surface of the metal mesh 112. The carbon fiber composite material layer 114 may be referred to as a “second carbon fiber composite material layer”.

5 is a view showing a cross-sectional structure of one side of an aircraft according to an embodiment.

Referring to FIG. 5, the aircraft 3 according to an embodiment may include a fuselage 31 and a wing 32.

For example, the wing portion 32 may include an inner space that protrudes from the body 31 and accommodates fuel, and a composite layer 321 that surrounds the inner space and is exposed to the outside. For example, the wing portion 32 may be understood that the fuel tank 1 according to the embodiments disclosed in FIGS. 1 to 3 is structurally formed integrally.

As another example, the fuselage 31 may also be formed by structurally integrating the fuel tank 1 disclosed in FIGS. 1 to 3, and in this case, the surface of the fuselage 31 may be formed of a composite layer 321. .

For example, the composite layer 321 may include a radio wave absorbing layer 3211, a metal mesh 3212, a core layer 3213, and a carbon fiber composite material layer 3214.

The radio wave absorbing layer 3211 may form an outer surface of the wing portion 32 and absorb electromagnetic waves incident from the outside.

The metal mesh 3212 may be installed on the rear surface of the radio wave absorbing layer 3211.

The core layer 3213 and the carbon fiber composite material layer 3214 are installed on the rear surface of the metal mesh 3212 to add structural strength of the wing portion 32 to support the shape structure and load of the wing portion 32. Can be.

For example, the thickness of each of the core layer 3213 and the carbon fiber composite material layer 3214 can be freely designed according to the load of the wing portion 32, aerodynamic load during flight, or shape structure.

For example, an additional carbon fiber composite material layer 3214 may be installed on the front surface of the core layer 3213, such as the composite layer 21 shown in FIG. 4.

6 is a view showing a state after the lightning is experimentally applied to the composite layer according to an embodiment, and FIG. 7 is a view showing a cross section after the lightning is experimentally applied to the composite layer according to an embodiment to be.

6 and 7, the metal mesh 112, the carbon fiber composite material layer 114, the core layer 113, and the carbon fiber composite material layer 114 are sequentially stacked from the upper surface of the composite layer from the top surface. The result of the test in which electric discharge with conditions similar to the lightning was applied can be confirmed.

Specifically, when looking at the cross section of the composite layer shown in FIG. 7, it can be seen that damage occurred only in the upper metal mesh 112 and the carbon fiber composite material layer 114, and the core layer 113 and the core layer ( It can be seen that damage did not occur in the carbon fiber composite material layer 114 at the bottom of 113).

Therefore, the fuel tank 1 and the aircraft 3 including the composite layers 11, 21, and 321 according to an embodiment are part of the outer shell during a lightning strike, that is, a portion of the radio wave absorbing layer 111 or the metal mesh 112. Since the damage can be intensively formed, the core layer 113, as well as the carbon fiber composite material layer 114 on the back of the core layer 113 can absorb the impact of the lightning strike, the fuel tank 1 It is possible to prevent the fire due to the ignition of , it is possible to ensure the structural stability of the fuel tank 1 and the wing (32).

8 is a graph showing the results of analyzing the radio wave absorption performance of the composite layer according to an embodiment, and FIG. 9 is a graph showing the results of analyzing the radio wave absorption performance of the composite layer having a different layer structure from the composite layer of one embodiment to be.

Specifically, the graph of FIG. 8 shows the performance of absorbing radio waves in the X-band frequency domain of the composite layer 11 in which the metal mesh 112 is installed on the rear surface of the radio wave absorbing layer 111, as shown in FIGS. 1 to 4. The results of the analysis are shown, and the graph of FIG. 9 absorbs radio waves in the X-band frequency domain of the composite layer installed on the front surface of the radio wave absorbing layer 111, unlike the composite layer 11 of one embodiment. The results of performance analysis are shown.

Comparing the results of the two graphs, it can be seen that the radio wave absorption performance of the composite layer 11 of one embodiment is superior to the radio wave absorption performance of the composite layer having a different layered structure from the one embodiment.

Specifically, in the case of the composite layer in which the metal mesh 112 is disposed on the front surface of the radio wave absorbing layer 111, in the X-band frequency region, reflection loss near 0 dB is recorded, whereas the composite layer according to an embodiment (11, 21, 321) recorded a return loss of less than -10 dB in most of the X-band frequency domain, and in particular, it was confirmed that the return loss increased to -50 dB in the 10 Ghz frequency domain.

According to the above results, the fuel tank 1 and the aircraft 3 including the composite layers 11, 21, and 321 according to an embodiment have excellent radio wave absorption performance over the X-band frequency domain, and thus the X-band radar. Excellent stealth performance can be guaranteed.

In addition, since the reflection loss can be maximized in a specific area according to the design of the radio wave absorbing layer, it may be possible to appropriately adjust the radio wave absorbing performance according to the frequency characteristics of the radar to be detected.

In addition, by placing the metal mesh 112 on the back of the radio wave absorbing layer 111, the metal mesh 112 not only functions as a transmission path for dissipating lightning, but also serves as a reflector of the radio wave absorbing layer 111 at the same time. It can be advantageous for cost and weight reduction in manufacturing.

In addition, by disposing the metal mesh 112 on the back surface of the radio wave absorbing layer 111, not only a periodic pattern type radio wave absorbing structure using a resistance sheet, but also a dielectric, magnetic material, radio wave absorbing structure printed with a fine pattern, and reinforced fibers coated with metal Since it can be applied to various types of radio wave absorbing structures such as composite radio wave absorbing structures and thick sandwich type radio wave absorbing structures, it has a high design scalability effect.

Although the embodiments have been described by the limited drawings as described above, a person skilled in the art can make various modifications and variations from the above description. For example, the described techniques may be performed in a different order than the described method, and / or components such as the structure, device, etc. described may be combined or combined in a different form from the described method, or may be applied to other components or equivalents. Even if replaced or substituted by, appropriate results can be achieved.

Claims (11)

A radio wave absorbing layer formed on a front surface exposed to the outside to absorb external electromagnetic waves; And
A composite layer comprising a metal mesh disposed on the rear surface of the radio wave absorbing layer and reflecting and canceling electromagnetic waves absorbed by the radio wave absorbing layer, transmitting electrical energy of the lightning to the surroundings when lightning strikes, and having a periodic pattern shape.
According to claim 1,
The radio wave absorbing layer includes a material capable of transmitting electromagnetic waves,
The length of the side of one cell forming the metal mesh is a composite layer within 0.5 mm to 2 mm.
According to claim 1,
The composite layer further includes a core layer installed on the rear surface of the metal mesh and formed of a material having a density smaller than that of the radio wave absorbing layer and the metal mesh to support the structure of the composite layer and absorb shock during a lightning strike.
The method of claim 3,
The core layer is a composite layer including a plurality of holes formed through the direction in which the composite layer is stacked.
The method of claim 3,
A composite layer further comprising a first carbon fiber composite material layer installed on the rear surface of the core layer and formed of a material having a higher density and strength than the core layer and the radio wave absorbing layer to support the structure of the composite layer.
The method of claim 5,
A composite material layer further comprising a second carbon fiber composite material layer provided between the metal mesh and the core layer.
The method of claim 6,
The first carbon fiber composite material layer and the second carbon fiber composite material layer is a composite material layer formed of carbon fiber reinforced plastic (Carbon Fiber Reinforced Plastic).
The method of claim 3,
The radio wave absorbing layer can absorb electromagnetic waves in a specific frequency band among frequency bands between 2 GHz and 20 GHz,
The metal mesh has a high density pattern that does not transmit electromagnetic waves in the specific frequency band toward the core layer.

In the fuel tank having a closed interior space,
A cross section of the fuel tank is a fuel tank formed of a composite layer according to any one of claims 1 to 8.
In the aircraft comprising a fuselage and a wing portion extending from the fuselage and receiving fuel,
The aircraft section is formed of a composite layer according to any one of claims 1 to 8.
In the aircraft comprising a fuselage for receiving fuel,
The cross section of the fuselage is formed of a composite layer according to any one of claims 1 to 8.

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