Welded Cap System for Aircraft Fastener Lightning Protection
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Solution Overview
Problem
Existing methods for providing spark suppression around fasteners during lightning strikes are inadequate, as they fail to ensure a reliable seal and prevent fuel leakage, especially in aircraft structures where composite materials and metal fasteners are used.
Innovation Solution
A cap system comprising an inner and outer cap member with an annular sealing cavity, where the cap members are welded together and filled with a curable sealing material to form a strong, reliable bond, preventing air gaps and ensuring a sealed cavity to contain sparking and out-gassing events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the cap members are not welded together, then the assembly process is simpler, but the outer cap member becomes dislodged by the pressure of the sealing material
Solution Approach 1:
The inner cap member and outer cap member are merged together through welding to form a unified structure. This welding process creates a permanent bond that prevents the outer cap member from becoming dislodged during sealing material injection, while maintaining manufacturing efficiency through a straightforward welding operation.
2Productivity
If sealing material is injected before cap positioning, then the sealing process is faster, but the material may not be applied during its working life
Solution Approach 1:
The cap is positioned on the fastener before the sealing material is injected. This preliminary positioning ensures that the cap is correctly located and secured, allowing the sealing material to be injected afterward during its full working life, ensuring proper application and curing without rushing the positioning step.
3Ease of manufacture
If air gaps are present in the sealing material, then the application process is less stringent, but the seal is compromised and fuel leakage occurs
Solution Approach 1:
The sealing material forms a continuous, gap-free film or shell around the fastener within the air cavity. This continuous sealing film prevents fuel leakage by eliminating air gaps that would compromise the seal, ensuring complete coverage and integrity of the sealing barrier.
4Area of stationary object
If the annular sealing cavity has small contact area, then the cap footprint is smaller, but the bond strength is reduced
Solution Approach 1:
The sealing material is concentrated in the annular sealing cavity where it provides localized bonding strength. The cavity geometry and material distribution are optimized to achieve maximum bond strength in this specific region, ensuring reliable sealing and bonding without requiring a large overall cap footprint.
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 cap system provides a strong, reliable seal around fasteners, preventing fuel leakage and ensuring the containment of sparking and out-gassing events during lightning strikes, while withstanding accidental knocks and maintaining a stable bond quickly, even in aircraft structures.
Implementation Method 1
The sealing material can be mixed in the sealing material injection device on application, thus ensuring that the material is applied during its working life and before it has started to cure. Quick cure sealing materials have the advantage of providing a stable bond very quickly.
Implementation Method 2
The inner cap member and outer cap member are welded together by one or more welds. Welding the cap members together prevents the outer cap member from becoming dislodged by the pressure of the sealing material.
Data Source
AI summary
The present invention proposes a cap for forming a sealed cavity around one end of a fastener to thereby contain out-gassing and sparking events in the event of a lightning strike to the fastener. The invention also proposes a joint comprising such a cap, and a kit of parts and method for installing such a cap. A cap according to the invention comprises: an inner cap member having an annular base terminating at an edge which surrounds an opening into an air cavity for enclosing the one end of a fastener; and an outer cap member having an annular skirt or flange which extends radially outwardly away from the annular base, the annular skirt or flange and annular base between them defining an annular sealing cavity. The cap also comprises a sealing material inlet comprising an opening in the outer cap member that is in fluid communication with the annular sealing cavity, the opening being arranged to interconnect with a sealing material injection device to provide a flow of curable sealing material from the sealing material inlet into the annular sealing cavity. The inner cap member and outer cap member are welded together.