Sealed Spark Containment Cap for Aircraft Fastener Plasma Control
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Solution Overview
Problem
Lightning strikes on aircraft pose a risk of sparking and plasma formation at metallic fasteners, which can ignite fuel vapors in composite aircraft structures, leading to potential fires due to the high electrical resistance of composite materials and low resistance of metallic fasteners.
Innovation Solution
A spark containment cap system that includes a cap with an annular sealing volume and a locator tool to securely fasten the cap over the fastener, using a sealing material to prevent outgassing and plasma escape, and a fastening system that minimizes manual torque application by using a locator to align and secure the cap and nut.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a fastener is used in composite aircraft structures, then structural assembly is enabled, but sparking and plasma formation occur during lightning strikes due to electrical resistance differences
Solution Approach 1:
A cap is introduced as an intermediary component between the fastener and the external environment. The cap encloses the fastener and provides a sealing interface with the composite structure, preventing direct exposure of the metallic fastener to fuel vapors and oxygen during lightning strikes, thereby eliminating the harmful sparking and plasma formation while maintaining the structural assembly function
Solution Approach 2:
The cap creates a sealed environment around the fastener that prevents the ingress of oxygen and fuel vapors. By establishing this protected inert atmosphere, the cap eliminates the conditions necessary for combustion even if sparking occurs at the fastener interface, thus resolving the contradiction between structural assembly and prevention of harmful effects
2Object-affected harmful factors
If sealing material is used to prevent outgassing, then fuel ignition risk is reduced, but manufacturing complexity increases
Solution Approach 1:
The sealing material is pre-applied to the sealing surface of the cap or the composite structure before final assembly. This preliminary action ensures that the sealing interface is already prepared with the necessary sealing properties, eliminating the need for complex post-assembly sealing operations and reducing manufacturing complexity while effectively preventing outgassing and fuel ignition risk
3Strength
If manual torque application is required for fastener assembly, then secure fastening is achieved, but ease of operation decreases
Solution Approach 1:
The fastening system is designed so that the cap and fastener components self-align and self-secure during assembly. The cap includes features such as a recessed portion that receives the fastener and a sealing interface that automatically engages with the composite structure, eliminating the need for manual torque application while ensuring secure fastening through precise geometric fitting and elastic deformation of the sealing material
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
Effectively prevents sparking and plasma formation during lightning strikes by creating a sealed environment around the fastener, reducing the risk of fuel ignition and enhancing structural integrity by securely adhering the cap to the structure without requiring manual torque application.
Implementation Method 1
using a sealing material to prevent outgassing and plasma escape
Data Source
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AI summary
The present application relates to a spark containment cap. The cap forms a sealed cavity around an end of a fastener (120) protruding from a structure (110). The cap has a cap body with an annular base terminating at a rim which surrounds an opening into an air cavity arranged to enclose the end of the fastener. An annular sealing volume extends around the rim arranged to receive an annular bead of a curable sealing material (280) around the opening into the cavity to provide a seal between the cap body and the structure to seal a volume of gas within the cavity. An engaging feature is configured to engage with the end of the fastener to prevent rotation of the fastener relative to the cap when the end of the fastener is received by the cap. The present application also relates to a fastening system, a joint, an aircraft and a method of securing a fastener and a spark containment cap to a structure. The present application further relates to a spark prevention rivet.