Double-Shell Lightning Arrester Cap Assembly Without Angular Play
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Solution Overview
Problem
Existing lightning protection caps for aircraft fastening elements face issues such as angular play, material stress, breakage, complex manufacturing, and difficult assembly, which increase the risk of fuel leaks and fire due to lightning strikes.
Innovation Solution
A dual-shell lightning cap design with complementary fixing means, including a ramp and protrusion forming a housing, allows for angular and axial locking of the outer shell relative to the inner shell, ensuring reliable assembly and preventing deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the outer shell is snapped onto the inner shell with gripping means, then the assembly is simplified, but angular play between the shells occurs and assembly stresses may exceed material elastic limits
Solution Approach 1:
The fixing means is divided into two distinct functional elements: a ramp structure that guides initial engagement and a separate protrusion that provides final locking. This segmentation allows the assembly process to occur in controlled stages, reducing stress while ensuring precise angular alignment without play.
Solution Approach 2:
The ramp structure performs a preliminary guiding action during assembly, directing the protrusion into the correct position before final engagement. This preliminary alignment prevents misalignment stresses and ensures that the shells engage smoothly without exceeding material elastic limits.
2Reliability
If welding or gluing is used to join the shells before filling, then angular play is eliminated, but the manufacturing process becomes more complex with additional steps
Solution Approach 1:
The protrusion and ramp structure enable the shells to self-align and self-lock during assembly without requiring external welding or gluing operations. The mechanical interlocking mechanism automatically eliminates angular play while maintaining manufacturing simplicity.
3Reliability
If friction-based locking with multiple contact zones is used, then rotational locking is achieved, but assembly becomes difficult and requires precise adjustment
Solution Approach 1:
The friction-based mechanical locking system is replaced with a geometric locking mechanism using the ramp and protrusion. This substitution transforms the assembly from a friction-dependent process requiring precise adjustment to a geometry-driven process that is more tolerant of variations and easier to assemble.
Data Source
Figure 1
Figure 2a~2b
Figure 3
AI summary
The invention relates to a lightning arrester cap (1) for sealing a fastener attached to the structure of an aircraft, the lightning arrester cap (1) comprising an inner shell (10) defining an internal volume for receiving the fastener and an outer shell (20) configured to cover the inner shell (10), said inner and outer shells (10, 20) comprising first and second fastening means (14, 15, 16, 16a, 23, 23a), complementary, adapted to cooperate so as to allow the engagement of the outer shell (20) with the inner shell (10), said lightning arrester cap (1) being characterized in that the first and second fastening means (14, 15, 16, 16a, 23, 23a) are configured so as to angularly lock the outer shell (20) relative to the inner shell (10) when the outer shell (20) is rotation relative to the inner shell (10).