Vented Fastener Cap Geometry for Aircraft Ignition Isolation
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Solution Overview
Problem
Aircraft fasteners pose an ignition risk during lightning strikes due to non-isotropic electrical conduction in composite materials and potential poor electrical connections, leading to uncontained energy emissions that can ignite fuel tanks, and existing seal solutions are labor-intensive and prone to damage.
Innovation Solution
A cover design with a base and cap configuration that includes holes with specific hydraulic diameters and alignment to prevent straight-line trajectories from the fastener to the exterior, venting gases and particles while maintaining an exclusion zone to prevent ignition, and can be constructed from materials like polymers and ceramics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polysulfide cap seals are used to seal fuel mixtures from arcs and hot gas, then ignition risk is reduced, but installation time and inspection time increase
Solution Approach 1:
The cover is divided into multiple segments or sections, each with specific functions. The base portion provides structural support while the cap portion provides sealing and protection. This segmentation allows for simplified installation of modular components rather than complex seal application processes.
Solution Approach 2:
The cover design uses a simple, inexpensive structure that can be quickly installed and replaced if necessary. Rather than requiring precision-sealed polysulfide caps that need careful installation and inspection, the invention uses a straightforward cover that provides protection through its geometric design and simple sealing mechanism.
2Reliability
If polysulfide cap seals are used to prevent fuel contact with fasteners, then ignition protection is improved, but the seal is prone to damage from environmental exposure and electromagnetic effects
Solution Approach 1:
The cover is constructed from composite materials that combine the benefits of different substances. The base may be made from a rigid material providing structural strength, while the cap incorporates sealing materials resistant to environmental exposure and electromagnetic effects. This composite construction enhances both protection and durability.
Solution Approach 2:
The invention changes the physical and chemical parameters of the sealing system by using materials with higher resistance to thermal cycling and electromagnetic effects. The cap material is selected to maintain its sealing properties across a wide range of temperatures and exposure conditions, rather than relying on polysulfide that degrades under these stresses.
3Stress or pressure
If holes are added to the cap to vent gases and particles, then pressure buildup is prevented, but ignition risk may increase if holes align with fastener
Solution Approach 1:
The holes in the cap are strategically positioned with specific local qualities - they are located in regions where they can effectively vent pressure while their orientation and placement ensure they do not create direct alignment paths with the fastener. The hole geometry and distribution pattern are optimized to provide pressure relief without compromising safety.
Solution Approach 2:
The invention converts the potential harm of holes creating ignition pathways into a benefit by carefully designing the hole pattern to vent harmful pressures and gases while the cover's overall geometry and hole orientation prevent direct lines of sight from holes to the fastener, thus eliminating the ignition risk while maintaining pressure relief.
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 cover effectively prevents ignition by isolating the fastener from the combustible environment, reducing the risk of fuel tank ignition and simplifying the installation process, thereby enhancing safety and reducing production costs.
Implementation Method 1
Each of the holes includes a hydraulic diameter of between 0.1mm - 2.0mm
Implementation Method 2
for each hole a straight line that extends through any point at the second end of the hole and any point at the first end of the hole does not intersect with the at least one fastener
Implementation Method 3
A interior space positioned within the base and cap is sized to extend over at least one fastener
Data Source
Figure 1
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AI summary
A cover that extends over a fastener and methods of installing the cover over the fastener. The cover includes an open end positioned at a member from which the fastener extends. The cover also includes a closed end that extends over the fastener and shields the fastener from the exterior environment that can be combustible. A plurality of holes extend through the cover from the interior space to an exterior environment external to the cap.