Sealed Spark Containment Cap for Lightning-Safe Aircraft Fasteners
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Solution Overview
Problem
Large passenger aircraft are vulnerable to lightning strikes, which can cause sparking and ignition of fuel due to the high electrical resistance of composite materials and low resistance of metallic fasteners, leading to potential fuel tank hazards.
Innovation Solution
A spark containment cap and fastening system that forms a sealed cavity around fasteners, using a cap body with an annular base and engaging feature to prevent rotation and a curable sealing material to create a secure seal, along with a locating tool for precise alignment and installation, reducing the need for access from both sides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional fastener assembly is used in composite aircraft structures, then the fastener provides mechanical fastening function, but it creates sparking hazards during lightning strikes due to electrical resistance differences between composite materials and metallic fasteners
Solution Approach 1:
The patent introduces a spark containment cap as an intermediary component between the metallic fastener and the composite structure. This cap is made of electrically conductive material and creates a controlled pathway for electrical current during lightning strikes, preventing direct arcing at the fastener interface where fuel vapor could be ignited. The cap acts as a mediator that manages the electrical energy safely.
Solution Approach 2:
The patent converts the harmful electrical energy from lightning strikes into a controlled phenomenon. By designing the cap with specific electrical properties and geometry, the harmful high-current lightning strike is transformed into a controlled electrical discharge through a defined path that does not reach fuel vapor, thereby converting a potentially catastrophic event into a manageable one.
2Reliability
If a spark containment cap with curable sealing material is used, then the seal provides spark suppression and secure fastening, but the installation requires access from both sides of the structure
Solution Approach 1:
The patent divides the fastening system into separate functional components: a spark containment cap that provides electrical protection and a sealing system that creates the gas-tight seal. This segmentation allows each component to be optimized independently and facilitates installation from one side, as the sealing material can be applied and cured without requiring access to both sides of the structure.
Solution Approach 2:
The patent employs preliminary action by pre-positioning the spark containment cap and applying the curable sealing material before final fastening. The sealing material is applied in advance, allowed to cure partially or fully, and then the cap is secured, enabling the sealing function to be established before the fastening operation is complete, thus eliminating the need for dual-side access.
3Strength
If a blind rivet fastener is used in fuel tank boundaries, then the fastener provides secure mechanical attachment, but sparking may occur at the interface of the collar and shaft during lightning strikes
Solution Approach 1:
The patent introduces a spark containment cap as an intermediary component that fits over the blind rivet assembly. This cap is made of electrically conductive material and creates a controlled pathway for electrical current during lightning strikes, preventing direct arcing at the collar-shaft interface where fuel vapor could be ignited. The cap manages the electrical energy safely while preserving the mechanical fastening function.
4Productivity
If conventional fastening methods are used, then the fastening process is simple and quick, but precise alignment and secure installation require access from both sides of the structure
Solution Approach 1:
The patent employs self-service principles by designing the spark containment cap with integrated alignment features and self-retaining mechanisms. The cap includes locating features that automatically align with the fastener and structure, and the curable sealing material provides self-retaining properties that secure the cap in position without requiring secondary operations from the other side of the structure. This enables complete installation from one side while maintaining precise alignment.
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 system effectively prevents sparking and ignition by sealing the fastener area, ensuring secure fastening and reducing the risk of fuel tank hazards during lightning strikes, while allowing for one-sided access and efficient installation.
Implementation Method 1
an annular sealing volume extending around the rim arranged to receive a annular bead of a curable sealing material 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
Data Source
AI summary
A spark containment cap for forming a sealed cavity around an end of a fastener protruding from a structure is disclosed having 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 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. A fastening system, a joint, an aircraft and a method of securing a fastener and a spark containment cap to a structure are also disclosed.