Injectable Cap for Fastener Lightning Protection
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Solution Overview
Problem
Existing methods for providing spark suppression around fasteners, such as those during lightning strikes, are inadequate in ensuring a sealed and reliable seal to prevent fuel leakage and maintain a stable air cavity, particularly in aircraft structures where composite materials and metal fasteners are used.
Innovation Solution
A cap system comprising an inner and outer cap member with a snap-fit joint and an annular sealing cavity, where curable sealing material is injected to form a strong, reliable bond and seal, utilizing a sealing material inlet for even distribution and quick curing, ensuring a secure seal around the fastener.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cap system with snap-fit joint is used to enclose the fastener end, then the reliability of spark suppression is improved, but the device complexity increases due to multiple cap members and locking features
Solution Approach 1:
The cap is divided into an inner cap member and an outer cap member that can be assembled separately. The inner cap member encloses the fastener end while the outer cap member provides additional sealing and locking features. This segmentation allows for improved reliability through layered protection while managing complexity through modular design.
Solution Approach 2:
The inner cap member is nested within the outer cap member, with the inner cap's flange fitting into the outer cap's recess. This nesting arrangement creates a compact, reliable structure where the inner component provides primary enclosure and the outer component adds sealing and mechanical locking, achieving high reliability without excessive complexity.
2Reliability
If curable sealing material is injected into the annular sealing cavity, then the seal reliability is improved to prevent fuel leakage, but the manufacturing complexity increases due to injection process requirements
Solution Approach 1:
The sealing cavity is pre-formed between the inner and outer cap members during assembly, creating a dedicated space for the curable sealing material. The injection ports are integrated into the cap design, allowing sealing material to be injected after assembly. This preliminary preparation of the sealing cavity ensures reliable fuel leakage prevention while simplifying the manufacturing process by eliminating the need for separate sealing operations.
Solution Approach 2:
The curable sealing material acts as an intermediary substance that fills the annular sealing cavity and bonds the inner and outer cap members together. This sealing material provides the necessary seal reliability to prevent fuel leakage while the injection process integrates seamlessly into the manufacturing workflow, balancing reliability with ease of manufacture.
3Strength
If multiple locking features are provided between cap members, then the bond strength is improved to withstand accidental knocks, but the device complexity increases
Solution Approach 1:
The locking features utilize asymmetrical geometry with ramps and undercuts that provide strong mechanical interlocking. The inner cap member has a flange with specific profile that mates with the outer cap member's recess, creating asymmetric locking points that resist forces from accidental knocks. This asymmetrical design achieves high bond strength through optimized geometry rather than adding numerous symmetric locking features, thereby managing device complexity.
4Volume of stationary object
If the outer cap member extends radially outwardly with an annular flange, then the sealing cavity volume is increased for better sealing, but the area occupied by the cap increases
Solution Approach 1:
The outer cap member extends radially outwardly in the radial dimension, creating an annular flange that increases the sealing cavity volume without significantly increasing the axial height. This dimensional approach allows the sealing cavity to expand in the radial direction, providing adequate volume for effective sealing while minimizing the increase in overall cap footprint area, thus balancing sealing performance with space constraints.
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 effectively prevents fuel leakage and maintains a sealed air cavity, providing a strong and reliable bond that can withstand accidental knocks and lightning-induced sparking, with quick curing times ensuring the seal is robust within a short timeframe.
Implementation Method 1
injecting curable sealing material into the annular sealing cavity via the sealing material inlet so that the curable sealing material contacts the structure; and curing the curable sealing material to seal the air cavity
Implementation Method 2
The outer cap member has an inner surface formed with a first locking feature, and the inner cap member has an outer surface formed with a second locking feature which forms a snap-fit joint with the first locking feature
Data Source
Figure 1~3
Figure 3a
Figure 4
AI summary
The present invention proposes a cap (100) for forming a sealed cavity (12) around one end of a fastener (2-4) to thereby contain out-gassing and sparking events in the event of a lightning strike to the fastener (2-4). The invention also proposes a joint comprising such a cap (100), and a kit of parts and method for installing such a cap (100). A cap (100) according to the invention comprises: an inner cap member (10) having an annular base (11) terminating at an edge (18) which surrounds an opening into an air cavity (12) for enclosing the one end of a fastener (2-4); and an outer cap member (20) having an annular skirt or flange (40) which extends radially outwardly away from the annular base (11), the annular skirt or flange (40) and annular base (11) between them defining an annular sealing cavity (34a-c). The cap (100) also comprises a sealing material inlet (44) comprising an opening (22) in the outer cap member (20) that is in fluid communication with the annular sealing cavity (34a-c), the opening (22) being arranged to interconnect with a sealing material injection device (80) to provide a flow of curable sealing material (81) from the sealing material inlet (44) into the annular sealing cavity (34a-c). The outer cap member (20) has an inner surface formed with a first locking feature (95,96), and the inner cap member (10) has an outer surface formed with a second locking feature (97) which forms a snap-fit joint with the first locking feature (95,96).