Lobed Nut Cap Sealing for Fastener Tolerance and Spark Prevention
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Solution Overview
Problem
Lightning strikes on aircraft can cause sparking and ignition risks at metallic fasteners due to high electrical resistance differences between composite and metal components, leading to potential fuel ignition, and existing solutions do not adequately address manufacturing tolerances and sealing effectiveness.
Innovation Solution
A cap with a lobed collar portion that adapts to fastener sizes through deformation, combined with a flexible material like glass fibre reinforced polymers and a sealing system using polysulphide or epoxy-based adhesives, to form a sealed cavity around fasteners, accommodating manufacturing tolerances and ensuring a secure, spark-proof seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional cap with uniform collar cross-section is used, then the sealing structure is simple, but it cannot accommodate manufacturing tolerances in fastener dimensions
Solution Approach 1:
The collar cross-section is designed with asymmetrical lobes and valleys instead of a uniform circular shape. This asymmetrical geometry allows the collar to conform to fastener base portions that vary in diameter due to manufacturing tolerances, providing reliable frictional engagement across a range of fastener sizes without requiring precise dimensional control.
Solution Approach 2:
The collar is designed to be deformable, allowing its cross-sectional shape to dynamically adapt during installation. When installed on a fastener, the collar deforms from its initial lobed configuration to conform to the specific fastener diameter, enabling the same cap design to accommodate varying manufacturing tolerances through elastic deformation.
2Adaptability or versatility
If the collar is made rigid to maintain shape, then manufacturing is easier, but it cannot adapt to varying fastener sizes
Solution Approach 1:
The collar material properties are selected to provide optimal balance between rigidity and flexibility. The material must be rigid enough to maintain the lobed cross-sectional shape during handling and installation, yet flexible enough to deform elastically when installed on fasteners with varying diameters, enabling adaptation to manufacturing tolerances.
Solution Approach 2:
The collar is designed as a thin-walled structure that can flex and deform elastically. This flexible shell design allows the collar to adapt its cross-sectional shape to match the fastener base portion diameter, providing versatility across different fastener sizes while maintaining structural integrity during installation.
3Reliability
If a single-piece cap design is used, then assembly is simpler, but sealing effectiveness around varying fastener sizes is reduced
Solution Approach 1:
The cap is divided into two separate components: a collar portion that interfaces with the fastener and a cap portion that forms the sealed cavity. This segmentation allows the collar to be optimized for frictional engagement and adaptation to fastener variations, while the cap portion provides the sealing function, achieving reliable sealing across varying fastener sizes through coordinated design of separate elements.
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 lobed cap design ensures reliable frictional engagement and sealing across varying manufacturing tolerances, preventing sparking and fuel ingress, while the sealing material provides a strong, rapid-curing bond to contain lightning-induced events and prevent ignition.
Implementation Method 1
a sealing system using polysulphide or epoxy-based adhesives, to form a sealed cavity around fasteners
Implementation Method 2
the collar portion having a lobed shape in cross-section such that an outwardly projecting lobe extends between each neighbouring pair of contact regions... the cap can tolerate relatively large manufacturing tolerances at the fastener end
Implementation Method 3
The lobed shape of the collar portion of the cap body ensures that the contact regions will always provide a good frictional engagement with the nut or fastener head
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The present invention proposes a cap (100) having a collar portion (14) with three or more contact regions arranged to contact the end of a fastener (2, 3, 4) around which the collar portion is provided, the collar portion having a lobed shape in cross-section such that an outwardly projecting lobe extends between each neighbouring pair of contact regions. An advantage of this lobed arrangement is that the cap can tolerate relatively large manufacturing tolerances at the fastener end. For example, the cap may be for fitting over a nut or fastener head, with the contact regions of the cap being arranged to contact corresponding contact regions on a cylindrical collar base portion of the nut or fastener head. The diameter of this cylindrical collar portion may not be well controlled, so that the manufacturing tolerance is high. The lobed shape of the cap base ensures that the contact regions will always provide a good frictional engagement with the nut, whether the cylindrical collar is undersized, oversized, or at its nominal diameter.