Self-Sealing Fixing Element for Aircraft Lightning Protection
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Solution Overview
Problem
Current lightning strike protection for fasteners on metallic aircraft requires additional measures beyond conventional insulating coatings and over-sealants, as existing solutions do not adequately ensure a liquid-tight seal and protection against electrical discharges.
Innovation Solution
A self-sealing fixing element with a curable sealant layer and a barrier layer that exposes the sealant to atmosphere upon installation, allowing it to cure and form a seal, combined with a deformable sealing ring to ensure electrical isolation and prevent moisture ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional insulating coatings and over-sealants are used for lightning strike protection, then electrical isolation is provided, but a reliable liquid-tight seal and adequate protection against electrical discharges are not achieved
Solution Approach 1:
The patent combines the insulating coating and sealing functions into a single integrated fixing element. The fixing element incorporates both the curable sealant layer for liquid-tight sealing and the barrier layer for electrical isolation, eliminating the need for separate over-sealant applications and insulating coatings.
Solution Approach 2:
The fixing element uses composite material structure with a curable sealant layer (moisture-curing polymer) combined with a barrier layer (insulating material). This composite structure provides both sealing and electrical isolation properties within a single component, achieving reliable lightning strike protection.
2Reliability
If a curable sealant layer is used to form a liquid-tight seal, then sealing reliability is improved, but the sealant requires exposure to atmosphere to cure which complicates the installation process
Solution Approach 1:
The sealant is pre-applied to the fixing element in a uncured state before installation. The barrier layer is pre-positioned to protect the sealant during handling and installation. Upon installation, the barrier layer is removed or broken away, automatically exposing the sealant to atmosphere to initiate curing, thus simplifying the installation process.
Solution Approach 2:
The barrier layer acts as an intermediary that protects the curable sealant layer during storage and installation, preventing premature exposure to atmosphere. During installation, the barrier layer is removed or broken away, allowing the sealant to cure. This intermediary mechanism simplifies installation by eliminating the need for separate sealing operations.
3Reliability
If the barrier layer is designed to slide off during installation, then the sealant is exposed to atmosphere for curing, but the barrier layer must be sufficiently thick to provide electrical isolation which conflicts with ease of removal
Solution Approach 1:
The barrier layer has different thicknesses at different locations: it is thicker at the outer diameter to provide adequate electrical isolation and lightning strike protection, and thinner at the inner diameter or edge portions to facilitate easy removal or breaking away during installation. This local quality variation resolves the conflict between electrical isolation requirements and ease of removal.
Solution Approach 2:
The barrier layer can be designed as segmented or with a frangible structure that allows it to break into separate pieces during installation. This segmentation enables the barrier layer to provide adequate thickness for electrical isolation while allowing easy removal or breaking away to expose the sealant for curing.
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
The solution provides a reliable, liquid-tight seal and electrical isolation, protecting against lightning strikes and preventing galvanic corrosion, while ensuring the fastener assembly remains functional and secure.
Implementation Method 1
a curable sealant layer which is carried by the bearing surface and encircles the opening in the bearing surface, wherein the curable sealant layer is formed from a sealant material which cures when exposed to atmosphere
Data Source
AI summary
A self-sealing fixing element is disclosed having a body with a bearing surface, and a bore with an opening in the bearing surface. A curable sealant layer is carried by the bearing surface and encircles the opening in the bearing surface. The curable sealant layer is formed from a sealant material which cures when exposed to atmosphere. A barrier layer overlays the curable sealant layer and can break apart when the fixing element is installed in order to expose the sealant layer to atmosphere. The curable sealant layer has a thickness which decreases away from the bore, and the barrier layer has a thickness which increases away from the bore.