Conformal Clearance Fastener for Composite Lightning Protection
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Solution Overview
Problem
Existing fastener systems for composite structures like carbon fiber reinforced plastic (CFRP) in aircraft face challenges in providing reliable electrical contact and conductivity, often resulting in unwanted discharge or sparking during lightning strikes, and are either heavy, expensive, or difficult to install.
Innovation Solution
A fastener system with an elongated shaft featuring an inner feed channel, flutes, and lateral feed channels that allows for the injection of a conductive fluid to establish electrical contact between the fastener and the composite structure, providing a conformal clearance fit without the need for metal sleeves, thus ensuring effective electrical conductivity and dissipation of current energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrically insulating sealants or fastener seal caps are used to prevent discharge during lightning strikes, then safety against unwanted discharge is improved, but aircraft weight increases and manufacturing time increases
Solution Approach 1:
The patent removes the CRES sleeve component from the fastener system, retaining only the titanium bolt. This extraction eliminates the weight penalty associated with heavy corrosion resistant steel sleeves while maintaining the essential function of electrical conductivity through the titanium bolt alone, thereby improving the weight-to-safety ratio without requiring additional insulating sealants or seal caps
Solution Approach 2:
The patent employs a simpler, more cost-effective fastener design that eliminates expensive CRES sleeves and heavy insulating sealants. The titanium bolt serves as both the structural fastener and the electrical conductor, providing a lightweight, economical solution that achieves lightning strike protection without the need for additional protective components
2Reliability
If CRES sleeves are used in interference fit fasteners to provide electrical contact, then electrical conductivity is improved, but aircraft weight increases and installation difficulty increases
Solution Approach 1:
The patent extracts and removes the CRES sleeve component from the fastener assembly, demonstrating that the sleeve is not necessary for achieving adequate electrical contact. The titanium bolt alone provides sufficient electrical conductivity when properly designed with appropriate surface area and contact pressure, eliminating the weight penalty of the heavy corrosion resistant steel sleeve
Solution Approach 2:
The patent uses the titanium bolt itself as the intermediary between the electrical charge path and the composite structure, eliminating the need for a separate CRES sleeve intermediary. The bolt's surface and geometry are optimized to provide direct electrical contact with the composite layers, simplifying the system while maintaining conductivity
3Reliability
If torque is applied to expand the CRES sleeve for interference fit, then electrical contact is improved, but carbon fiber tips are crushed or broken
Solution Approach 1:
Instead of expanding the fastener component to achieve interference fit, the patent inverts the approach by using a clearance fit titanium bolt that is inserted without expansion. The electrical contact is achieved through the bolt's surface area and contact pressure rather than through mechanical expansion, thereby avoiding the crushing and breaking of carbon fiber tips that occurs with sleeve expansion
4Reliability
If sleeved interference fit fasteners are used to achieve good electrical contact, then unwanted discharge is reduced, but manufacturing cost increases and installation difficulty increases
Solution Approach 1:
The patent removes the CRES sleeve component from the fastener system, simplifying both manufacturing and installation. The titanium bolt alone provides adequate electrical contact without requiring the complex assembly and installation procedures associated with sleeved interference fit fasteners, thereby improving ease of manufacture and installation while maintaining electrical contact quality
Data Source
Figure 1A~1B
Figure 1C~1E
Figure 2A~2B
AI summary
A fastener (10) includes an elongated shaft (14) having a first end (16), a second end (18), and a shaft body (20), a head portion (22), and a threaded portion (42). At least one inner feed channel (70) extends through the head portion and the shaft body and terminates proximal to the threaded portion. The fastener has a plurality of flutes (80) formed along and circumferentially spaced around an outer surface of the shaft body and an outer surface of the head portion. Each flute has a first end and extends from a first location proximal to the threaded portion, along the outer surface of the shaft body, and radially outward along the outer surface of the head portion. The fastener further has one or more lateral feed channels (90) formed laterally through the shaft body and connecting the inner feed channel to at least two opposing flutes on the outer surface of the shaft body.