Lightning-Protection Washer Seal for Composite Fasteners
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Solution Overview
Problem
Metallic fasteners in composite structures, such as those in aircraft, cause sparking and arcing during lightning strikes, leading to material breakdown and potential ignition due to unmitigated electromagnetic effects, and existing solutions like pre-molded caps and conductive coatings are costly and labor-intensive.
Innovation Solution
A washer assembly comprising a metallic washer with a high-strength polymer seal, featuring a lower seal portion engaging the fastener and an upper seal portion engaging a counter-bored nut, to reduce the escape of energized particles and prevent arcing, fabricated using injection molding or insertion molding techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-molded caps are used to guard fastener heads, nuts, and washers, then sparking and arcing are reduced, but installation cost and labor time increase substantially
Solution Approach 1:
The patent extracts the protective function from separate pre-molded caps and integrates it into a single polymer seal that is molded directly onto the washer. This eliminates the need for separate protective components while maintaining the lightning protection function, thereby reducing installation complexity and labor costs.
Solution Approach 2:
The patent combines multiple protective functions (sealing against hot gases, preventing arcing, and protecting fastener elements) into a single integrated polymer seal component. This merging of functions reduces the number of parts and simplifies installation while maintaining comprehensive protection against electromagnetic effects.
2Reliability
If conductive coatings and interference fits are used to reduce contact resistance, then sparking is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies local quality by creating a polymer seal with specific material properties (conductive or dissipative) only where needed - in the sealing portions that contact the fastener elements. This localized application of functional properties achieves contact resistance control without requiring complex coatings on entire components, simplifying the manufacturing process.
3Strength
If metallic fasteners are used to join structures, then structural strength is achieved, but electromagnetic effects cause material breakdown and hot particle ejection
Solution Approach 1:
The patent introduces a polymer seal as an intermediary material between the metallic fastener elements and the surrounding environment. This polymer layer acts as a mediator that suppresses electromagnetic effects and prevents hot particle ejection while allowing the metallic fastener to maintain its structural joining function. The polymer seal absorbs and dissipates the electromagnetic energy, protecting the surrounding structures.
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 seals voids between fasteners and conjoined structures, reducing the escape of hot gases and plasma, preventing arcing, and simplifying installation while being more cost-effective and efficient than existing solutions.
Implementation Method 1
The lower seal portion is configured to engage, at the counter-bore, a fastener to form a seal to reduce escape of energized particles
Implementation Method 2
A polymer seal, made from a high-strength polymer material, is attached to the metallic washer to reduce sparking and arcing that may occur around the fastener due to lightning strikes
Data Source
AI summary
A method of protecting an air vehicle against lightning strikes includes inserting a fastener through a hole in conjoined structures, the fastener defining an axis along its length and having a threaded end and a sleeve, and installing a washer assembly over the threaded end and the sleeve, the washer assembly having a metallic washer and a polymer seal radially inward of the metallic washer. The seal includes a lower seal portion defining a counter-bore, and an upper seal portion extending axially from the lower seal portion. The method includes installing a counter-bored nut on the threaded end, and applying torque to the nut to compress the lower seal portion against a surface of the conjoined structures and around the sleeve at the counter-bore of the seal, and to compress the upper seal portion of the seal into a counter-bore of the nut and around the threaded end.