Insulated Blind Fastener Assembly for Lightning Arc Prevention
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Solution Overview
Problem
Aircraft composite structures are prone to electrical arcing with metal fasteners during lightning strikes, which can ignite fuel in fuel tanks, posing a risk due to the conductive differences between composite and metal materials.
Innovation Solution
A blind fastener design featuring a bolt part, a sleeve part, and a tubular insulating sheath that moves into a post-installation configuration where the sheath is sandwiched between the bolt and sleeve parts, preventing direct contact and thus arcing, eliminating the need for additional coatings and inspections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal fasteners are used to fasten composite structures, then the fastening strength and structural integrity are improved, but the risk of electrical arcing during lightning strikes increases due to conductive differences between composite and metal materials
Solution Approach 1:
An insulating sleeve is introduced as an intermediary component between the metal bolt and the composite structure. This sleeve prevents direct electrical contact between the conductive metal fastener and the composite material, thereby eliminating the arcing pathway while maintaining the mechanical fastening function. The sleeve acts as a mediator that decouples the electrical conductivity issue from the mechanical connection requirement.
Solution Approach 2:
The fastening system employs a composite structure consisting of metal (bolt), insulating material (sleeve), and composite structure. This multi-material approach combines the advantages of metal fasteners (strength, reliability) with the protective benefits of insulating materials (arc prevention), creating a hybrid system that addresses both mechanical and electrical requirements simultaneously.
2Object-affected harmful factors
If insulating coatings are applied to metal fasteners to prevent arcing, then the electrical insulation is improved, but additional manufacturing steps and quality inspections are required
Solution Approach 1:
Instead of coating the entire fastener with insulating material, the insulation function is segmented into a separate, dedicated sleeve component. This segmentation allows the metal bolt to remain simple and uncoated, while the insulating sleeve provides the necessary electrical protection. The separation of functions simplifies both manufacturing and inspection processes compared to applying and verifying coatings on the fastener itself.
Solution Approach 2:
The insulating sleeve serves as a standalone intermediary component that provides electrical isolation without requiring coating processes. This mediator approach eliminates the need for complex coating applications, curing cycles, and subsequent insulation quality inspections that would be necessary if coatings were applied directly to the fastener.
3Reliability
If the sheath is positioned to prevent direct contact between the sleeve part and structure, then the reliability of insulation is improved, but the device complexity increases due to the movable configuration
Solution Approach 1:
The fastener system incorporates a dynamic element - the insulating sheath can move axially relative to the bolt part. During installation, the sheath is positioned to provide insulation; during service, the sleeve deforms and the sheath moves to accommodate this deformation while maintaining the insulating barrier. This dynamic positioning ensures continuous insulation reliability without requiring complex fixed structures.
Solution Approach 2:
The insulating sheath is nested within the sleeve part, creating a compact hierarchical structure. This nesting arrangement allows the sheath to move independently within the sleeve's interior space, providing the necessary insulation function without adding external complexity to the fastener assembly. The nested configuration maximizes space efficiency while maintaining functional independence of the insulating component.
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
Ensures a reliable insulating barrier is maintained between the fastener and structure post-installation, preventing sparking and potential fuel ignition from lightning strikes without requiring additional coating applications or inspections.
Implementation Method 1
A blind fastener according to any one of claims 1 to 6, wherein the sheath is retained on the bolt part such that direct contact between the sleeve part and a structure on which the blind fastener has been installed is prevented by the sheath
Data Source
Figure 1a~2b
Figure 3~4
AI summary
There is provided a blind fastener (1). The blind fastener (1) comprises a bolt part (11), a sleeve part (12), and a tubular insulating sheath (13). The bolt part (11) is at least partially received within the sleeve part (12). A first end (131) of the sheath (13) is retained on the bolt part (11) such that relative axial movement between the first end (131) of the sheath (13) and the bolt part (11) is substantially prevented. The blind fastener (1) is movable between: a pre-installation configuration in which the sleeve part (12) has a first axial position relative to the bolt part (11) and a predetermined section of the sheath (13) is adjacent an outer surface of the sleeve part (12); and a post-installation configuration in which the sleeve part (12) has a second, different axial position relative to the bolt part (11) and the predetermined section of the sheath (13) is adjacent an inner surface of the sleeve part (12).