Sealed Spark Containment Cap for Aircraft Fastener Cavities
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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 is designed to form a sealed cavity around fastener ends, using an annular base with a rim and an annular sealing volume filled with curable material, along with an engaging feature to prevent fastener rotation and a locating tool for precise alignment, thereby reducing the risk of sparking and fuel ignition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fastener is used to join composite or metallic panels in aircraft structures, then structural assembly is enabled, but sparking and plasma formation may 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. This cap encloses the fastener within a sealed cavity, acting as a mediator that prevents direct exposure of the fastener to lightning strikes and fuel atmosphere, thereby eliminating the harmful sparking effect while maintaining the structural function of the fastener
Solution Approach 2:
The fastener is extracted from the direct exposure environment by enclosing it within a sealed cavity formed by the cap. This separation removes the fastener from the harmful interaction zone between lightning strikes and fuel atmosphere, allowing the fastener to perform its structural function without being a target for lightning attachment
2Reliability
If a sealed cavity is formed around the fastener to prevent sparking, then spark containment is improved, but device complexity increases due to additional components and installation steps
Solution Approach 1:
The cap is designed to perform multiple functions simultaneously: it provides spark containment by enclosing the fastener, seals the cavity to prevent fuel vapor ingress, and facilitates installation through integrated locating features. This multi-functionality reduces the need for separate components, thereby managing device complexity while maintaining reliability
Solution Approach 2:
The cap incorporates self-aligning locating features that automatically position the cap correctly on the fastener during installation. This self-service mechanism eliminates the need for complex alignment procedures or additional positioning components, reducing installation complexity while ensuring proper spark containment
3Manufacturing precision
If access is required to both sides of the structure for fastener installation, then proper fastening can be achieved, but manufacturing productivity decreases due to increased assembly time and complexity
Solution Approach 1:
The fastening system is segmented into two functional parts: the fastener itself and the cap. The cap can be pre-installed on the fastener from one side of the structure, while the fastener is then inserted through the structure from the opposite side. This segmentation allows the cap to provide its spark containment function during installation from a single side, improving productivity while maintaining installation precision
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 effectively seals the fastener area, preventing out-gassing and plasma formation during lightning strikes, ensuring the structural integrity and safety of aircraft fuel tanks by enhancing spark containment and reducing the risk of ignition.
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.