Copper Grid Repair for Lightning Strike Protection
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Solution Overview
Problem
Current methods for protecting composite aircraft skin panels from lightning strikes are expensive, difficult to maintain, and lack an effective, cost-efficient way to repair damaged copper grid systems, which are crucial for diverting lightning currents away from fuel tank substructures.
Innovation Solution
A method involving a copper patch and specialized adhesive is used to repair damaged copper foil grids by removing surfacers, fasteners, and a portion of the conductive layer, applying a copper patch with an unsupported film adhesive, and re-curing it with resin-impregnated fiberglass fabric, allowing for reinstallation of fasteners and reapplication of surfacers to maintain electrical continuity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flame spraying or plating is used to apply a conductive layer to the outer surface of skin panels, then lightning strike protection is improved, but manufacturing complexity and cost increase, and the protective layer adds mass without contributing to structural strength
Solution Approach 1:
The copper foil grid is embedded within the composite skin panel during the initial manufacturing process, before the panel is assembled into the aircraft structure. This preliminary integration eliminates the need for secondary operations like flame spraying or plating, reducing manufacturing complexity while maintaining lightning strike protection
Solution Approach 2:
The conductive copper foil grid is merged with the composite skin panel structure itself, becoming an integral part of the panel rather than a separate protective coating. This combination eliminates the need for additional protective layers while providing both structural integrity and lightning strike protection
2Reliability
If a conductive woven screen or foil is installed to the outer surface of skin panels, then lightning strike protection is improved, but additional weight is added due to required fiberglass isolation layers
Solution Approach 1:
The copper foil grid is merged directly with the carbon fiber composite plies during manufacturing, eliminating the need for separate fiberglass isolation layers that would be required if a woven screen or foil were installed on the outer surface. This integration reduces overall weight while maintaining electrical isolation and lightning protection
3Reliability
If special designed fasteners are employed to transmit electric current safely to the substructure, then arcing prevention is improved, but manufacturing cost increases
Solution Approach 1:
The copper foil grid itself serves the dual function of providing structural support and transmitting electric current safely to the substructure through standard fasteners. The grid's inherent electrical conductivity eliminates the need for specially designed fasteners, reducing manufacturing cost while maintaining arcing prevention
Solution Approach 2:
The copper foil grid performs multiple functions: it provides structural reinforcement, establishes electrical continuity, and safely conducts lightning current to the substructure. This multi-functionality eliminates the need for separate specialized components, reducing overall system cost
4Reliability
If the copper grid system is damaged by lightning strike or mechanical damage, then structural integrity is compromised, but repair capability is needed to restore electrical continuity and maintain lightning protection
Solution Approach 1:
The copper foil grid is designed as a segmented system where damaged sections can be individually identified and repaired without requiring complete replacement of the entire grid. This segmentation enables localized repairs, reducing repair complexity and maintaining lightning protection integrity
Solution Approach 2:
When the copper foil grid is damaged, the damaged section is removed and replaced with a new copper foil section that is bonded to the composite panel using the same manufacturing techniques. This recovery process restores electrical continuity and maintains lightning protection without requiring complex repair procedures
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides a cost-effective and quick repair that maintains the integrity of the lightning prevention system by creating a lower resistance path for lightning currents, reducing current density at fasteners, and allowing aircraft to return to service with minimal downtime and expense.
Implementation Method 1
bonded to the skin panel 14 by an unsupported film adhesive 60
Implementation Method 2
one ply of resin-impregnated fiberglass fabric 62 is wet-layed over the copper patch 53
Implementation Method 3
The copper foil grid 32 is formed from a plurality of strips 33... providing a lower resistance path along the wing's surface
Data Source
Figure 1~3
Figure 4
Figure 5~7
AI summary
A method for re-establishing the electrical continuity of an electrically conductive layer of a composite aircraft wing damaged by a lightning strike or other mechanical event is disclosed in which a copper patch (32) replaced the damaged section (50) of the electrically conductive layer contained. The repair is performed by first removing any surfacers (36), fasteners (12), and damaged electrically conductive layer (33) to expose a portion of the underlying composite skin (14). A copper patch having a copper foil section (52) coupled to an unsupported film adhesive (60) is then introduced onto an underlying composite skin opening contained within an undamaged section of a copper foil grid and covered with resin-impregnated fiberglass material (34). The film adhesive (60) and resin-impregnated fiberglass material (34) are then cured and fasteners (12) are then reinserted within the fiberglass material, copper patch (32) and underlying composite skin. The surface of the composite wing is then reprimed and repainted to complete the repair.