Electric charge dissipation system for aircraft

A method, apparatus, and composite fuel tank for manufacturing a structure is provided. A first composite layer and a second composite layer are placed on a mold. The second composite layer and the first composite layer are cured. The first composite layer and the second composite layer form the structure. The second composite layer is configured to dissipate an electric charge on a surface of the structure.

BACKGROUND INFORMATION

The present disclosure relates generally to aerospace platforms and, in particular, to structures in aerospace platforms. Still more particularly, the present disclosure relates to a method and apparatus for dissipating electric charges on surfaces in aerospace platforms.

Static electricity is a build-up of electric charge on the surface of an object. The object may be an aerospace platform, such as, for example, an aircraft, a spacecraft, or some other type of aerospace platform. Static electricity may build up on various surfaces on an aircraft. For example, static electricity may build up on a surface of a fuel tank in the aircraft. The dissipation of static electricity may be desirable to reduce the possibility of a discharge of static electricity within a structure.

Many fuel tanks in aircraft are comprised of aluminum. This material often provides a desired level of dissipation of electric charge. If greater dissipation of electric charge is desired, other mechanisms may be used. For example, grounding technologies and materials have been developed to dissipate the electric charge that forms static electricity. Additionally, additives have been placed into liquids, such as fuel, to reduce the formation and aid in the dissipation of static electricity.

With the use of composite materials in place of metals, the manner in which static electricity is handled in structures, such as fuel tanks, changes. With aluminum, these charges may dissipate because of the conductivity of the structure. With composite materials, however, surface conductivity may not be present or as high as with metals. As a result, static electricity may build up more easily on surfaces of fuel tanks using composite materials.

Therefore, it would be advantageous to have a method and apparatus that takes into account at least some of the issues discussed above, as well as possibly other issues.

SUMMARY

In one advantageous embodiment, an apparatus comprises a first composite layer and a second composite layer. The second composite layer is associated with the first composite layer. The first composite layer and the second composite layer form a structure. The second composite layer has a conductivity configured to dissipate an electric charge on a surface of the structure.

In another advantageous embodiment, a composite fuel tank for an aircraft comprises a wall of the composite fuel tank having a first composite layer and a second composite layer located on the first composite layer in an interior of the composite fuel tank. The first composite layer and the second composite layer form a structure. The second composite layer is configured to dissipate an electric charge on a surface in the interior of the composite fuel tank.

In yet another advantageous embodiment, a method for manufacturing a structure is provided. A first composite layer and a second composite layer are placed on a mold. The second composite layer and the first composite layer are cured. The first composite layer and the second composite layer form the structure. The second composite layer is configured to dissipate an electric charge on a surface of the structure.

DETAILED DESCRIPTION

Referring more particularly to the drawings, embodiments of the disclosure may be described in the context of aircraft manufacturing and service method100as shown inFIG. 1and aircraft200as shown inFIG. 2. Turning first toFIG. 1, an illustration of an aircraft manufacturing and service method is depicted in accordance with an advantageous embodiment. During pre-production, aircraft manufacturing and service method100may include specification and design102of aircraft200inFIG. 2and material procurement104.

During production, component and subassembly manufacturing106and system integration108of aircraft200inFIG. 2takes place. Thereafter, aircraft200inFIG. 2may go through certification and delivery110in order to be placed in service112. While in service112by a customer, aircraft200inFIG. 2is scheduled for routine maintenance and service114, which may include modification, reconfiguration, refurbishment, and other maintenance or service.

With reference now toFIG. 2, an illustration of an aircraft is depicted in which an advantageous embodiment may be implemented. In this example, aircraft200is produced by aircraft manufacturing and service method100inFIG. 1and may include airframe202with a plurality of systems204and interior206. Examples of systems204include one or more of propulsion system208, electrical system210, hydraulic system212, and environmental system214. Any number of other systems may be included. Although an aerospace example is shown, different advantageous embodiments may be applied to other industries, such as the automotive industry.

The different advantageous embodiments may be implemented within airframe202in the depicted examples. For example, one or more of the different advantageous embodiments may be implemented in a structure, such as fuel tank216in wing218of airframe202for aircraft200.

In these illustrative examples, fuel tank216in wing218may be comprised of composite materials. These composite materials may include, for example, carbon fiber reinforced composite materials. These components may be comprised partially or entirely of composite materials, depending on the particular implementation. The different advantageous embodiments may be implemented to manage electric charge that may form on the interior surfaces of fuel tank216.

Apparatus and methods embodied herein may be employed during at least one of the stages of aircraft manufacturing and service method100inFIG. 1. As used herein, the phrase “at least one of”, when used with a list of items, means that different combinations of one or more of the listed items may be used and only one of each item in the list may be needed. For example, “at least one of item A, item B, and item C” may include, for example, without limitation, item A or item A and item B. This example also may include item A, item B, and item C or item B and item C.

In one illustrative example, components or subassemblies produced in component and subassembly manufacturing106inFIG. 1may be fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft200is in service112inFIG. 1. As yet another example, a number of apparatus embodiments, method embodiments, or a combination thereof may be utilized during production stages, such as component and subassembly manufacturing106and system integration108inFIG. 1. A number, when referring to items, means one or more items. For example, a number of apparatus embodiments is one or more apparatus embodiments.

A number of apparatus embodiments, method embodiments, or a combination thereof may be utilized while aircraft200is in service112and/or during maintenance and service114inFIG. 1. The use of a number of the different advantageous embodiments may substantially expedite the assembly of and/or reduce the cost of aircraft200.

The different advantageous embodiments recognize and take into account a number of considerations. For example, the different advantageous embodiments recognize and take into account that primers may be used to manage the dissipation of electric charges on the surfaces of the fuel tank. The different advantageous embodiments recognize and take into account that this mechanism, however, may not provide the desired amount of dissipation of electric charges, such as static electricity.

The different advantageous embodiments recognize and take into account that primers may be formulated to provide increased dissipation of electric charges as compared to currently available primers. Additionally, the application of the primers may be performed to increase dissipation of electric charges. For example, the thickness of the primer placed on the surface of the fuel tank may be selected to increase dissipation of electric charges. Use of these primers, however, may increase the expense of manufacturing structures, such as fuel tanks, from composite materials.

The different advantageous embodiments also recognize and take into account that, with the use of primers and other mechanisms to dissipate electric charges that may build up on the surface of structures, the complexity and weight of the aircraft may increase more than desired. The different advantageous embodiments recognize and take into account that it may be desirable to have a layer that allows electric charge to be dissipated in place of or in addition to the primer. When both the primer and the additional layer that allows electric charge to be dissipated are present, redundant electric charge dissipation is provided.

Time and personnel are needed to apply primers to the interior surfaces of the fuel tank. Applying the appropriate amount of primer to obtain a desired amount of dissipation may require inspections and additional operations to be performed to ensure that the desired amount of primer is present. Additionally, time and personnel may also be needed to add other components to a fuel tank to increase the dissipation of electric charges that may form. As a result, the time needed to manufacture aircraft may be increased.

Thus, the different advantageous embodiments provide a method and apparatus for reducing an electric charge on the surface of a structure. In the different advantageous embodiments, an apparatus may comprise a first composite layer and a second composite layer. The second composite layer is associated with the first composite layer. The first composite layer and the second composite layer form a composite structure. The second composite layer has a conductivity configured to dissipate an electric charge on a surface of the structure.

With reference now toFIG. 3, an illustration of an electric charge management environment is depicted in accordance with an advantageous embodiment. In this illustrative example, electric charge management environment300may be implemented using aircraft200inFIG. 2.

As depicted, structure302may be a structure in aircraft200inFIG. 2. In these illustrative examples, structure302may hold liquids304. In particular, structure302may be a fuel tank, such as fuel tank216inFIG. 2, and liquids304may take the form of fuel306. In particular, structure302may be located within wing218inFIG. 2in these illustrative examples.

Electric charge dissipation system308may be associated with structure302. Electric charge dissipation system308is configured to dissipate electric charge310that may form on surface312of structure302. In these illustrative examples, surface312is located in interior313of structure302. In other words, surface312is located in interior313of the fuel tank.

In these illustrative examples, structure302takes the form of composite structure314. Structure302is formed using first composite layer318. Additionally, electric charge dissipation system308includes second composite layer320. In this illustrative example, second composite layer320is located over first composite layer318.

Second composite layer320in electric charge dissipation system308may be considered part of structure302in these illustrative examples. In other words, second composite layer320may be formed at the same time first composite layer318is formed for structure302. As a result, additional time and expense to add electric charge dissipation system308to structure302after manufacturing of structure302may be avoided.

As depicted, first composite layer318and second composite layer320may be cured at the same time. This type of curing also may be referred to as co-curing.

In these illustrative examples, second composite layer320is configured to dissipate electric charge310that builds up on surface312of structure302. In this example, second composite layer320has conductivity322. Conductivity322allows electric charge310to be dissipated from surface312of structure302.

In this manner, the buildup of electric charge310in second composite layer320may be reduced and/or prevented. In particular, conductivity322of second composite layer320allows electric charge310to be dissipated to reduce undesired electrical discharge from surface312of structure302. This reduction may include substantially preventing undesired electrical discharge to form on surface312of structure302.

As conductivity322of second composite layer320increases, the dissipation of electric charge310also increases. Conductivity322may be measured using resistivity. Resistivity is the inverse of conductivity322. As one illustrative example, the resistivity for second composite layer320that allows dissipation of electric charge310may be from about 106ohms-meters to about 109ohms-meters. This range of values for resistivity corresponds to a low range of values for conductivity322.

Additionally, in these depicted examples, second composite layer320is configured to reduce undesired electrical discharge324in interior313of structure302that is caused by external sources. These external sources may be any sources that are not part of structure302. For example, without limitation, an external source, such as lightning, may cause undesired electrical discharge324without the use of second composite layer320.

Further, second composite layer320also may be configured such that number of inconsistencies330in structure302may be reduced. Number of inconsistencies330may include, for example, without limitation, fiber breakouts, tears, and/or other types of inconsistencies. Number of inconsistencies330may form when number of holes332for number of fasteners334is drilled into structure302. As number of inconsistencies330increases, the number of rework procedures that need to be performed to fix number of inconsistencies330may also increase. Second composite layer320is configured to reduce number of inconsistencies330that is formed in structure302to reduce the number of rework procedures that may be needed.

In addition, second composite layer320in electric charge dissipation system308also may reduce an occurrence of galvanic corrosion336. Galvanic corrosion336is an electrical chemical process in which electrical contact occurs between two different types of metals in the presence of liquid which causes corrosion. Galvanic corrosion336may occur where second structure338contacts structure302. In these illustrative examples, second structure338is metal structure340. Second composite layer320separates second structure338from first composite layer318to reduce galvanic corrosion336.

For example, structure302has been described as a structure in aircraft200inFIG. 2. In other advantageous embodiments, structure302may be located in other platforms. For example, without limitation, other advantageous embodiments may be applied to a mobile platform, a stationary platform, a land-based structure, an aquatic-based structure, a space-based structure, and/or some other suitable object. More specifically, the different advantageous embodiments may be applied to, for example, without limitation, a submarine, a bus, a personnel carrier, a tank, a train, an automobile, a spacecraft, a space station, a satellite, a surface ship, a power plant, a dam, a manufacturing facility, a building, and/or some other suitable object.

Still, in other advantageous embodiments, structure302may take other forms other than a fuel tank in which liquids304are in the form of fuel306. For example, without limitation, liquids304may include other volatile and/or non-volatile liquids. Additionally, structure302also may be configured to hold gases in addition to or in place of liquids304.

As another illustrative example, although only first composite layer318is depicted for structure302in electric charge management environment300, other layers may be present in addition to first composite layer318, depending on the particular implementation.

With reference now toFIG. 4, an illustration of an electric charge dissipation system is depicted in accordance with an advantageous embodiment. In this illustrative example, electric charge dissipation system400is an example of one implementation of electric charge dissipation system308inFIG. 3.

In this depicted example, second composite layer401is formed on first composite layer404in wall405of structure406. First composite layer404is a composite layer for structure406. In particular, in this illustrative example, first composite layer404comprises carbon.

As depicted, second composite layer401comprises reinforcement408. Reinforcement408may take the form of fibers412. In these illustrative examples, fibers412may be configured to form fabric415. In other words, reinforcement408may take the form of fabric415containing fibers412. Fabric415may be manufactured through weaving, knitting, spreading, bonding, and/or other mechanisms for associating fibers412with each other.

In these illustrative examples, second composite layer401may also include matrix410. Matrix410may take the form of resin414. Resin414may be infused into fabric415to form second composite layer401.

In these illustrative examples, fibers412may have conductivity416such that electric charge418can be dissipated from surface425of structure406. Additionally, conductivity416may be configured such that undesired electrical discharge420is reduced and/or prevented from occurring.

In these illustrative examples, fibers412may be comprised of a number of different materials. For example, without limitation, fibers412may be comprised by at least one of glass, carbon, ceramic, silica, organic materials, plastic, a polymer, nylon, metal, and other suitable types of materials.

Further, in some illustrative examples, fibers412may be associated with conductive material422. Conductive material422may be, for example, carbon, a metal, or some other suitable type of conductive material. For example, fibers412may be coated with conductive material422. In these illustrative examples, at least a portion of fibers412may be coated with conductive material422. In other words, depending on the amount of conductivity416desired, some or all of fibers412may be coated conductive material422.

In other illustrative examples, resin414may also provide conductivity416in place of or in addition to the conductivity in fibers412. For example, conductivity416may be provided through conductive material424in resin414. Conductive material422and conductive material424may both be present to provide conductivity416for second composite layer401, depending on the particular implementation.

Conductive material422and conductive material424may be comprised of at least one of, for example, without limitation, a metal, a metal alloy, nickel, carbon, and other suitable types of materials that may provide a desired level of conductivity416. In some illustrative examples, fibers412and/or resin414may be doped or treated to provide conductivity416.

In this illustrative example, second composite layer401is located on first composite layer404. Of course, second composite layer401may be in direct contact with first composite layer404. In other illustrative examples, second composite layer401may be connected to first composite layer404through other composite layers, such as number of additional layers426. Number of additional layers426may comprise a number of conductive layers.

Number of additional layers426may provide other desirable features. For example, number of additional layers426may provide for isolation of structure406from another structure in a manner that reduces galvanic corrosion.

With reference now toFIG. 5, an illustration of a manufacturing environment for a structure is depicted in accordance with an advantageous embodiment. In this illustrative example, manufacturing environment500is an example of an environment that may be used to manufacture structure302inFIG. 3or structure406inFIG. 4.

In these illustrative examples, number of composite layers502and number of composite layers504may be laid up on mold506. Mold506may take a number of different forms. For example, mold506may be an inner-line mold or an outer-line mold in these examples.

Number of composite layers502forms composite layers for the wall of a fuel tank in this example. Number of composite layers504includes composite layers for an electric charge dissipation system in these depicted examples. For example, number of composite layers502may comprise first composite layer404inFIG. 4. Number of composite layers504may include second composite layer401inFIG. 4. Additionally, number of additional layers426inFIG. 4also may be present in number of composite layers504.

Number of composite layers504may take the form of prepreg507. In other words, number of composite layers504may be ready for curing without requiring infusion of resin when placed onto number of composite layers502in these illustrative examples.

After number of composite layers504and number of composite layers502have been laid up on mold506, structure508has shape510and is ready for curing. Mold506with structure508may be cured using heating system514. Heating system514may provide both heat and a vacuum, depending on the particular implementation. Heating system514may include, for example, without limitation, an autoclave, an oven, a heating blanket, and/or some other suitable type of heating device. Of course, any heat source suitable for curing composite materials may be employed.

In these illustrative examples, structure508may be a fuel tank in a wing of an aircraft. After curing structure508, cured structure512is formed. Thereafter, primer518, sealant520, and/or other suitable layers may be added to cured structure512, depending on the particular implementation.

With reference now toFIG. 6, an illustration of an aircraft with fuel tanks is depicted in accordance with an advantageous embodiment. In this depicted example, aircraft600is an example of one implementation of aircraft200inFIG. 2. In this example, fuel tanks602,604,606,608,610,612,614,616, and618are located in aircraft600.

Fuel tanks602,604, and606are located in wing620; while fuel tanks610,612, and614are located in wing622. Fuel tank608is located in fuselage624. Fuel tanks616and618are located in horizontal stabilizers626and628, respectively.

In these illustrative examples, electric charge dissipation system308inFIG. 3and electric charge dissipation system400inFIG. 4may be implemented in at least one of fuel tanks602,604,606,608,610,612,614,616, and618.

With reference now toFIG. 7, an illustration of a cross section of a structure is depicted in accordance with an advantageous embodiment. In this illustrative example, cross section700is a cross section from a fuel tank, such as fuel tank602in FIG.6. Of course, cross section700may be employed in any fuel tank illustrated for aircraft600inFIG. 6.

In this illustrative example, structure702in cross section700is a portion of fuel tank602inFIG. 6. In this illustrative example, composite layer704forms wall706of fuel tank602.

As depicted, composite layer708comprises a portion of electric charge dissipation system710. Electric charge dissipation system710is an example of one implementation for electric charge dissipation system308inFIG. 3and electric charge dissipation system400inFIG. 4.

In this depicted example, composite layer708is in contact with composite layer704. Primer712also may be part of electric charge dissipation system710. In this example, primer712may be comprised of a material that may also aid in dissipating electric charges. Sealant714is formed on primer712in these illustrative examples.

In these illustrative examples, composite layer708may be configured to have conductivity such that electric charge that forms on surface716of fuel tank602may be dissipated. Additionally, composite layer708also may be configured to reduce or prevent undesired electrical discharge caused by electrical current generated by external sources. Composite layer708also may be configured to reduce and/or prevent undesired electrical discharge in fuel tank interior718that may occur in or travel through composite layer704. Also, composite layer708may be configured to reduce galvanic corrosion from occurring from other structures that may contact fuel tank602.

Turning next toFIG. 8, an illustration of a cross-sectional view of a portion of a fuel tank is depicted in accordance with an advantageous embodiment. Structure800in cross section802is for a portion of fuel tank602inFIG. 6in this illustrative example. Composite layer804forms wall806of fuel tank602inFIG. 6.

As depicted, composite layer808is located on composite layer804. Additionally, composite layer810also may be located between composite layer808and composite layer804. Composite layer808and composite layer810may form electric charge dissipation system812in this particular example. Electric charge dissipation system812may be an example of an implementation of electric charge dissipation system308inFIG. 3and electric charge dissipation system400inFIG. 4.

As illustrated, sealant814may be applied to surface816of composite layer808. In this particular example, a primer is not present. Composite layer808is configured to dissipate electric charge that may form on surface818of structure800for fuel tank602. Additionally, composite layer808also may be configured to reduce and/or prevent undesired electrical discharge in fuel tank interior820that may occur in or travel through composite layer804.

The illustration of different components in fuel tank602inFIG. 7andFIG. 8are presented for purposes of showing one implementation of an electric charge dissipation system. Of course, other electric charge dissipation systems may have other configurations. For example, in some illustrative examples, sealant714and primer712may be unnecessary. In still yet other illustrative examples, other layers may be present between composite layer808and composite layer804. For example, another composite layer or another material, such as fiberglass, may be located between composite layer708and composite layer704.

As another example, additional composite layers may be present in structure800in electric charge dissipation system812in addition to the ones illustrated. In addition, in some illustrative examples, paint or primer also may be present on surface816of composite layer808.

In these depicted examples, composite layer804and composite layer808are laid up on a mold. These composite layers are cured to form fuel tank602. As a result, additional operations are unneeded to add electric charge dissipation system812to fuel tank602at a later time, as compared to currently available electric charge dissipation systems.

With reference now toFIG. 9, a flowchart of a process for manufacturing a structure with an electric charge dissipation system is depicted in accordance with an advantageous embodiment. The process illustrated inFIG. 9may be implemented to manufacture a structure, such as structure302inFIG. 3and/or structure406inFIG. 4, in accordance with an advantageous embodiment. The process illustrated in this figure may be implemented using manufacturing environment500inFIG. 5.

The process begins by laying up a number of composite materials on a mold to form a first composite layer (operation900). This number of composite materials may be the composite materials for a composite layer, such as first composite layer318inFIG. 3. Thereafter, composite materials are laid up on the mold to form a second composite layer (operation902). This second composite layer is second composite layer320inFIG. 3.

Thereafter, the composite materials are cured (operation904). The process then adds a number of coatings to the surface of the structures (operation906), with the process terminating thereafter. These coatings may include, for example, without limitation, a primer, a sealant, paint, and other suitable types of coatings.

The flowchart and block diagrams in the different depicted embodiments illustrate the architecture, functionality, and operation of some possible implementations of apparatus and methods in different advantageous embodiments. In this regard, each block in the flowchart or block diagrams may represent a module, segment, function, and/or a portion of an operation or step.

In some alternative implementations, the function or functions noted in the block may occur out of the order noted in the figures. For example, in some cases, two blocks shown in succession may be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Also, other blocks may be added in addition to the illustrated blocks in a flowchart or block diagram.

For example, in some illustrative examples, operation906may not be performed to add coatings to the structures, depending on the particular implementation. In still yet other advantageous embodiments, additional layers may be included in addition to the composite layer performing the structure and the composite layer for the electric charge dissipation system.

Thus, the different advantageous embodiments provide a method and apparatus for managing electric charge. In one advantageous embodiment, an apparatus comprises a composite layer and a fabric layer. The composite layer is located on the fabric layer. The composite layer and the fabric layer form a structure. The fabric layer is configured to dissipate an electric charge on the surface of the structure.

In addition, the fabric layer may be configured to reduce or prevent a flow of an electric charge that may occur in response to different events. Further, the fabric layer also may be configured to reduce galvanic corrosion that may occur from the structure contacting another structure.

In this manner, the different advantageous embodiments may provide dissipation of electric charges in a manner that may require less expense, less complexity, and less time to implement, as compared to currently available systems.

For example, by forming the electric charge dissipation system at the same time as the structure, additional operations to add the electric charge dissipation system may be avoided.

Further, with the use of one or more composite layers configured to dissipate an electric charge, the different advantageous embodiments may have a reduced weight and complexity, as compared to other types of electric charge dissipation systems. For example, the electric charge dissipation system in the different illustrative examples may be integrated as part of the structure itself. The addition of coatings, such as primers or other materials to the surface of the structure, may be avoided using the different advantageous embodiments.