Spark Containment Cap Sealing Around Aircraft Fasteners
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Solution Overview
Problem
Large passenger aircraft are vulnerable to lightning strikes due to the high electrical resistance of composite materials and low resistance of metallic fasteners, leading to potential sparking and plasma out-gassing at fastener locations, which existing nut caps fail to adequately prevent.
Innovation Solution
A spark prevention cap with an annular base and flange configuration that maximizes contact area with sealant material, allowing for improved retention and sealing around fasteners, combined with a sealing material distribution tool for even sealant application, minimizing air and sealant leakage and enabling closer proximity to other features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nut cap with an annular skirt is provided to form a sealed cavity around the fastener end, then sealing capability is improved, but the skirt impairs location of the nut cap relative to other features
Solution Approach 1:
The nut cap is segmented into distinct functional elements: an annular base for sealing, a locatabase with locating protrusions for positioning, and a central cavity for fastener reception. This segmentation allows each element to perform its specific function optimally without interfering with others.
Solution Approach 2:
The locatabase acts as an intermediary element between the annular base and other structural features. The locating protrusions on the locatabase interface with corresponding features on the aircraft skin, providing precise location while the annular base maintains the seal, thus mediating between sealing requirements and positioning requirements.
2Reliability
If the base rim is in close engagement with the structure surface to minimize leakage, then sealing effectiveness is improved, but the cap cannot be positioned in close proximity to other features
Solution Approach 1:
The locating function is moved to a different dimensional plane by adding locating protrusions that extend radially outward from the base rim. This allows the base rim to maintain close engagement with the surface for sealing while the locating protrusions extend in a different dimension to engage with locating features, enabling close proximity to other features without compromising seal integrity.
3Reliability
If the contact area between cap and sealant is maximized for improved retention, then cap retention is improved, but the cap becomes more complex
Solution Approach 1:
The annular base serves multiple functions simultaneously: it provides the sealing surface against the aircraft skin, provides the bonding surface for sealant application to ensure cap retention, and supports the locatabase structure. This multi-functionality maximizes the utility of each structural element without adding unnecessary complexity.
Data Source
AI summary
A spark prevention cap is disclosed. The cap forms a sealed cavity around an end of a fastener protruding from a surface of a structure, for example, an aircraft structure. The cap has a cap body with an annular base terminating at a rim. The rim surrounds an opening into a central cavity for receiving the end of the fastener. The annular base has an external circumferential surface extending from the base rim, and a mating feature on the external circumferential surface configured to contact a sealant material applied externally to the cap.