Lightning-Protective Fastener Insulating Cover Design
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Solution Overview
Problem
Conventional lightning-protective fasteners for aircraft fail to achieve sufficient fastening force and tactile feedback due to deformation of insulating washers and spacers, leading to impaired work stability and increased risk of arc occurrence and ignition in fuel tank environments.
Innovation Solution
A lightning-protective fastener design featuring a pin-shaped fastener body with a fastening member and an insulating cover having step parts on its tip surface, where the insulating cover includes outer-circumferential and inner-circumferential cylindrical parts that fit into corresponding step parts, providing enhanced insulation and maintaining fastening strength while preventing deformation and arc occurrence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If insulating washers and spacers made of resin-based material are interposed between the fastening member and the structural member, then the occurrence of arc is suppressed by interrupting current, but the fastening force cannot be sufficiently achieved due to deformation and crushing of the washers and spacers
Solution Approach 1:
The insulating cover is divided into multiple functional segments: a tip covering part for arc suppression at the interface, and outer-circumferential and inner-circumferential cylindrical parts for maintaining fastening strength. This segmentation allows each part to perform its specific function optimally without compromising the other.
Solution Approach 2:
Different parts of the insulating cover have different thicknesses and geometries tailored to their specific functions. The tip covering part has a thickness designed for arc suppression, while the cylindrical parts have greater thickness to prevent deformation under fastening load. This local differentiation resolves the contradiction between arc suppression and fastening force.
2Reliability
If insulating washers and spacers are interposed between the fastening member and the structural member, then lightning-protective effect is enhanced by interrupting current, but work stability is impaired due to deformation of the insulating components
Solution Approach 1:
The insulating cover is segmented into a tip covering part and cylindrical parts with different functions. The cylindrical parts with larger thickness provide structural support and prevent deformation during fastening operations, thereby maintaining work stability while the tip covering part provides lightning protection.
Solution Approach 2:
The insulating cover is pre-installed on the fastening member before assembly, ensuring proper positioning and preventing any deformation or misalignment during the fastening operation. This preliminary action ensures both lightning protection and work stability.
3Ease of manufacture
If the insulating cover has uniform thickness, then manufacturing is simplified, but arc suppression effectiveness is reduced due to insufficient insulation distance from the member surface
Solution Approach 1:
The insulating cover has non-uniform thickness with the outer-circumferential and inner-circumferential cylindrical parts having larger thickness than the tip covering part. This local quality differentiation ensures sufficient insulation distance for effective arc suppression while maintaining manufacturing feasibility through a single-mold injection process.
Solution Approach 2:
The insulating cover extends in the radial dimension with cylindrical parts that protrude from the tip covering part. This dimensional extension creates the necessary insulation distance from the member surface without complicating the manufacturing process, as the multi-level structure can be formed in a single mold.
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 ensures reliable fastening force and improved work stability by preventing insulation breakdown and surface discharge, while effectively suppressing arc occurrence and enhancing lightning protection in aircraft fuel tank environments.
Implementation Method 1
an insulating cover made of insulating material covers a tip surface of the fastening member facing at least the member
Implementation Method 2
the outer-circumferential-side cylindrical part and the inner-circumferential-side cylindrical part have dimensions rising from the tip covering part in a thickness direction larger than a dimension of the tip covering part in the thickness direction. Thus, it is possible to ensure a distance from the member on an outer circumferential side and an inner circumferential side of the fastening member, thereby preventing occurrence of surface discharge and insulation breakdown
Data Source
AI summary
In an insulating cover 50A according to the present invention, a dimension of each of an outer-circumferential-side cylindrical part 50c and an inner-circumferential-side cylindrical part 50b fitting in step parts 40 and 41 in an axial direction of a fastener body 25 is set large with respect to a tip covering part 50a covering a tip surface 26a of a fastening member 26. As a result, on an outer circumferential side and an inner circumferential side of the fastening member 26, a distance from a member 22 is sufficiently ensured by the cylindrical part 50b and 50c. The tip covering part 50a is thinner than the cylindrical part 50B and 50c. Therefore, when the fastener body 25 and the fastening member 26 are fastened together, the amount of deformation of the tip covering part 50a in a thickness direction can be made small.