1. Field
The disclosure relates generally to a method and apparatus for dissipating electrical energy in a composite structure and, more particularly, to a method and apparatus for providing an electrical energy dissipation path from an area of a composite structure, such as a composite structure of an aircraft.
2. Background
The use of structures comprised of composite materials has grown in popularity, particularly in such applications as aircraft, where benefits include increased strength and rigidity, reduced weight and reduced parts count. When damaged, however, composite structures often require extensive repair work which may ground an aircraft, thereby adding significantly to the support costs of the aircraft. Maintenance procedures frequently require that the damaged component be removed and replaced before the aircraft can resume flying.
Short commercial domestic flights may have only 30-60 minutes of time at a gate between scheduled flights, while longer and international flights may have 60-90 minutes. The Commercial Airline Composite Repair Committee (CACRC), an international consortium of airlines, OEMs and suppliers has reported, however, that the average composite repair permitted in the Structural Repair Manuals (SRMs) takes approximately 15 hours to complete. In most cases, accordingly, flight cancellations must result when a composite structure repair is performed on an aircraft at the flight line. Removing an aircraft from revenue service in order to repair a damaged composite structure not only requires the operator of the aircraft to adjust its flight schedule in order to make the necessary repairs, but may also result in passenger dissatisfaction.
Recognizing the problems inherent in repairing composite structures, commonly assigned, copending U.S. patent application Ser. No. 11/163,872 filed on Nov. 22, 2005 and entitled FAST LINE MAINTENANCE REPAIR METHOD AND SYSTEM FOR COMPOSITE STRUCTURES, of which the present application is a Continuation-In-Part, describes a method and system for repairing a damaged composite structure quickly by persons having minimal skill using minimal tools and equipment.
Although the repair method and system described in U.S. patent application Ser. No. 11/163,872 is effective in repairing a damaged area of a composite structure; the damaged area may have become electrically isolated from the surrounding structure of the aircraft as a result of the damage, and the repair may not provide a path for dissipating electrical energy from the repaired area. Particularly, when the composite structure is on an aircraft, the repaired area may be electrically isolated from the lightning strike protection system of the aircraft such that there may be no suitable path for dissipating electrical current if the repaired area is struck by lightning. Also, if the repaired area is electrically isolated from the surrounding structure, static electricity may build up in the repaired area; and when the electrical potential becomes great enough, a spark will jump. When this spark occurs on an aircraft, it may cause undesirable “noise” in the communications radio or other electrical systems of the aircraft.
There is, accordingly, a need for a method and apparatus for providing an electrical energy dissipation path from an area of a composite structure, such as a composite structure of an aircraft, for dissipating electrical energy from the area such as electrical current caused by a lightning strike or electrical potential caused by a build up of static electricity.
An embodiment of the disclosure provides a method for providing an electrical energy dissipation path from an area of a composite structure. A bonding site may be prepared on the composite structure that surrounds the area of the composite structure, and an adhesive may be applied to at least a portion of the prepared bonding site. An electrical energy dissipation patch may be placed on the adhesive, a caul plate may be placed over the electrical energy dissipation patch, and a heat pack may be placed over the caul plate. A compaction force may be applied to the heat pack for affixing the electrical energy dissipation patch to the bonding site. The electrical energy dissipation patch includes inner and outer electrically non-conductive layers and an electrically conductive central layer between the inner and outer electrically non-conductive layers. The electrically conductive central layer may include an extended portion that is electrically connected to the composite structure when the electrical energy dissipation patch is affixed to the composite structure for providing a path for dissipating electrical energy from the area.
A further embodiment of the disclosure provides an electrical energy dissipation patch for providing an electrical energy dissipation path from an area of a composite structure. The electrical energy dissipation patch may include an electrically non-conductive inner layer, an electrically non-conductive outer layer, and an electrically conductive central layer between the electrically non-conductive inner and outer layers. The electrically conductive central layer may include an extended portion that extends beyond an outer edge of the electrically non-conductive inner layer for being electrically connected to the composite structure when the electrical energy dissipation patch is affixed to the area of the composite structure.
A further embodiment of the disclosure provides a kit for providing an electrical energy dissipation path from an area of a composite structure. The kit may include an electrical energy dissipation patch. The electrical energy dissipation patch may include inner and outer electrically non-conductive layers and an electrically conductive central layer between the inner and outer electrically non-conductive layers. The electrically conductive central layer may include an extended portion that is electrically connected to the composite structure when the electrical energy dissipation patch is affixed to the composite structure for providing a path for dissipating electrical energy from the area. The kit may further include an adhesive for affixing the electrical energy dissipation patch to the composite structure, and a chemical heat pack for providing heat during curing of the adhesive.
A further embodiment of the disclosure provides a method for providing an electrical energy dissipation path to a composite structure having an electrically conductive fiber or mesh. An electrical energy dissipation patch that includes electrically non-conductive inner and outer layers and an electrically conductive central layer having an extended portion may be applied to the composite structure, such that the central layer is electrically connected to the electrically conductive fiber, mesh or expanded metal of the composite structure.
The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments in which further details can be seen with reference to the following description and drawings.
The novel features believed characteristic of the embodiments are set forth in the appended claims. The embodiments themselves, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of advantageous embodiments when read in conjunction with the accompanying drawings, wherein:
With reference now to the figures, and, in particular, with reference to
In this illustrative example, aircraft 100 has wings 102 and 104 attached to body 106. Aircraft 100 includes wing mounted engines 108 and 110. Further, aircraft 100 also includes horizontal and vertical stabilizers 112 and 114, respectively.
The use of structures formed of composite materials on aircraft has grown in popularity because such structures provide benefits of increased strength and rigidity, reduced weight and reduced parts count. Aircraft 100 may, for example, include composite structures forming body 106, wings 102 and 104, and horizontal and vertical stabilizers 112 and 114, as well as other structures including movable flight control surfaces and landing gear doors.
When damaged, however, composite structures often require extensive repair work which may ground an aircraft, thereby adding significantly to the support costs of the aircraft. Traditional maintenance procedures frequently require that the damaged component be removed and replaced before the aircraft can resume flying.
Commonly assigned, copending U.S. patent application Ser. No. 11/163,872 filed on Nov. 22, 2005 and entitled FAST LINE MAINTENANCE REPAIR METHOD AND SYSTEM FOR COMPOSITE STRUCTURES, of which the present application is a Continuation-In-Part, describes a method and system for repairing a damaged composite structure quickly by persons having minimal skill using minimal tools and equipment.
Although the repair method and system described in U.S. patent application Ser. No. 11/163,872 is effective in repairing a damaged area of a composite structure, the damaged area may have become electrically isolated from the surrounding structure of the aircraft as a result of the damage, and the repair may not provide a path for dissipating electrical energy from the area. Particularly when the composite structure is on an aircraft, the repaired area may remain electrically isolated from the lightning strike protection system of the aircraft such that there may be no suitable path for dissipating electrical current if the repaired area is struck by lightning. Also, if the repaired area is electrically isolated from the surrounding structure, static electricity may build up in the repaired area, and when the electrical potential becomes great enough, a spark will jump. When this spark occurs on an aircraft, it may cause undesirable “noise” in the communications radio or other electrical systems of the aircraft.
Advantageous embodiments of the disclosure provide a method and apparatus for providing an electrical energy dissipation path from an area of a composite structure, such as a composite structure of an aircraft, for dissipating electrical energy from the area, such as electrical current caused by a lightning strike or electrical potential caused by a build up of static electricity
According to an advantageous embodiment of the disclosure, an electrical energy dissipation patch is provided that may be applied to an area of a composite structure, such as a composite structure of an aircraft, to provide an electrical energy dissipation path from the area to dissipate electrical energy from the area. The area may, for example, be a damaged area of the composite structure, such as an area that has been struck by lightning, or it may be an area that includes a repair but that remains electrically isolated.
Inner and outer fiberglass layers 202 and 204 may have a thickness of about four thousandths of an inch, and metal foil central layer 206 may have a thickness of about four to six thousandths of an inch, although it should also be understood that advantageous embodiments are not limited to an electrical energy dissipation patch having layers of any particular thickness. In this regard, however, it should be recognized that although outer layer 204 is primarily provided to protect the metal foil from the environmental effects of wind and water, it also acts as a dielectric. As a result, the thicker the outer layer 204, the more resistance there will be between a lightning bolt that may strike the outer layer and the metal foil, and the greater the resistance, the greater the amount of electrical energy that will be needed to penetrate the outer layer. As a result, the greater the thickness of the outer layer, the greater the damage that may be incurred if the patch is struck by lightning. Accordingly, it may be desirable for the outer layer to be maintained relatively thin while still providing effective protection for the metal foil.
It should be understood that IWWF and a metal mesh are only examples of a lightning strike protection system. Other types of lightning strike protection systems may also be used including expanded metal. For example, IWWF may be used in graphite composite structures, while expanded metal may be used in fiberglass composite structures.
In the advantageous embodiment illustrated in
As shown in
Initially, a bonding site 456 that includes and surrounds area 452 of composite structure 450 is prepared to receive patch 200. The preparation may include removing any material that may protrude from composite structure 450, as well as removing any paint or other covering material that may be present on the bonding site such as by sanding. The sanding should not remove the lightning strike protection system 454 from the composite structure. The prepared bonding surface may then be abraded, for example, by an appropriate abrading pad, to remove any glossy areas that may remain on bonding site 452, and the bonding site is also cleaned using, for example, pre-saturated solvent wipes.
A layer 402 of adhesive may then be applied to bonding site 456. The adhesive may be a multi-component paste adhesive that has a short working life and can cure quickly when a low temperature heat is applied. The adhesive may be applied to bonding site 456 using a notched trowel or similar tool to control the thickness of layer 402.
An adhesive layer 404 may also be applied to bonding surfaces of electrical energy dissipation patch 200. Adhesive layer 404 may be applied to both bonding surface 210 of inner fiberglass layer 202 and bonding surface 212 of protruding portion 208 of electrically conductive central layer 206 such that the central layer will be substantially coextensive with the adhesive. A notched trowel or the like may also be used to apply adhesive layer 404 to bonding surfaces 210 and 212.
After adhesive layers 402 and 404 have been applied, electrical energy dissipation patch 200 may be placed on bonding site 456 of composite structure 400. Release film 406 may then be placed over patch 200, and caul plate 408 may be placed over the release film 406. Release film 406 assists in preventing any adhesive from sticking to caul plate 408 and also provides a smooth outer surface on the caul plate. The release film may, for example, comprise a fluorinated ethylene propylene film or equivalent.
Caul plate 408 may be formed of a flexible material capable of conducting heat. For example, caul plate 408 may be a copper or aluminum caul plate having a thickness of about 0.020-0.030 inch.
Chemical heat pack 410 may then be activated and placed over caul plate 408. A variety of off-the-shelf chemical heat packs may be used. Such heat packs may have a “gel” like consistency when activated/mixed. The gelling of the heating medium of the heat pack allows the heat pack to be deployed in any orientation without adversely affecting heat transfer. This allows the heat pack to perform equally well in horizontal, vertical and inverted applications.
Heat pack 410 may, for example, comprise a sodium-acetate heat pack which provides a reliable, repeatable and uniform heat source for 30-60 minutes at about 120-130° F. For higher temperatures, a potassium permanganate heat pack may be used, for example, a heat pack that is available from Tempra Technologies Inc. of Bradenton, Fla. and that is described in U.S. Pat. No. 5,035,230. Such a heat pack provides a temperature of approximately 140-160° F. for approximately 35 minutes.
Compaction mechanism 412 may then be placed over heat pack 410 to apply a compaction force to patch 200 during curing of adhesive layers 402 and 404. The compaction mechanism 412 may comprise the manual application of pressure during the cure time (e.g., about 35 minutes), or it may comprise a compaction tool such as a vacuum bag as is illustrated in
Once the time for curing adhesive layers 402 and 404 has elapsed, compaction mechanism 412, heat pack 410, caul plate 408 and release film 406 are removed.
As illustrated in
An electrical energy dissipation patch according to advantageous embodiments permits an electrical energy dissipation path to be provided to a area of a composite structure, such as a composite structure of an aircraft, quickly by persons having minimal skills, using minimal tools and equipment.
An electrical energy dissipation patch according to advantageous embodiments may not provide a permanent electrical energy dissipation path for an area of a composite structure of an aircraft. The patch will, however, normally provide a reliable electrical energy dissipation path until the next regularly scheduled maintenance for the aircraft, thus making it unnecessary to remove the aircraft from regularly scheduled service.
According to an advantageous embodiment, the electrical energy dissipation patch can be incorporated in a kit that contains the patch and all items necessary or useful for affixing the patch to a composite structure. An exemplary kit may include, for example, electrical energy dissipation patch 200, and all components illustrated in
Following expiration of the time needed to fully cure the adhesive, the compaction force, the heat pack, the caul plate and the release film are removed (Step 618) and the method ends.
The description of the different advantageous embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous embodiments may provide different advantages as compared to other advantageous embodiments. The embodiment or embodiments selected are chosen and described in order to best explain features and practical applications, and to enable others of ordinary skill in the art to understand various embodiments with various modifications as are suited to the particular uses that are contemplated.
This application is a Continuation-In-Part of copending U.S. patent application Ser. No. 11/163,872 filed on Nov. 22, 2005 and entitled FAST LINE MAINTENANCE REPAIR METHOD AND SYSTEM FOR COMPOSITE STRUCTURES.
Number | Date | Country | |
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Parent | 11163872 | Nov 2005 | US |
Child | 11840643 | Aug 2007 | US |