Spring-Loaded Fingers for Low Impedance Aircraft Interfaces
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Solution Overview
Problem
Aircraft components on the exterior are susceptible to lightning strikes, leading to charge buildup and destructive arcing due to high impedance gaps, which traditional screw-based mounting and coatings fail to adequately address, as coatings degrade over time.
Innovation Solution
A low impedance interface using spring-loaded fingers mechanically connected to the component, providing a parallel electrical connection and interference fit with the aircraft body, maintaining a low impedance path without the need for coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If screw-based mounting is used to hold components in place, then mechanical connection is achieved, but the electrical connection impedance increases over time due to coating degradation
Solution Approach 1:
The electrical connection is segmented into multiple parallel paths through the use of multiple conductive fingers (typically 3-5 fingers) instead of relying on a single screw connection. This segmentation distributes the electrical current across multiple pathways, reducing the overall impedance and providing redundancy if one finger degrades.
Solution Approach 2:
The conductive fingers are made spring-loaded to provide continuous pressure against the component housing, maintaining optimal electrical contact over time. The spring mechanism compensates for thermal expansion, vibration, and manufacturing tolerances, ensuring consistent low-impedance connection without relying on degradable coatings.
2Reliability
If coatings are applied to reduce impedance, then initial impedance is reduced, but impedance increases over time as coatings degrade
Solution Approach 1:
The spring-loaded fingers automatically self-adjust to maintain optimal contact pressure and electrical connection. The elastic deformation of the spring fingers compensates for wear, thermal cycling, and vibration without requiring external maintenance or re-coating, making the system self-regulating over its service life.
Solution Approach 2:
The interface combines multiple materials with complementary properties: spring-loaded fingers made of conductive metal (such as beryllium copper or phosphor bronze) that provide both mechanical compliance and electrical conductivity, paired with hardened contact surfaces to prevent wear. This composite approach eliminates the need for separate protective coatings.
3Reliability
If a single electrical connection path is used, then mechanical simplicity is achieved, but impedance is too high preventing compliance with safety standards
Solution Approach 1:
The electrical connection is segmented into multiple parallel conductive fingers (typically 3-5 fingers) that collectively provide the low-impedance path required for lightning strike protection. This segmentation reduces overall impedance by creating parallel electrical pathways, complying with safety standards while maintaining a relatively simple overall structure.
Solution Approach 2:
The spring-loaded conductive fingers serve multiple functions simultaneously: they provide mechanical retention of the component, establish electrical connection, maintain low impedance through parallel paths, and compensate for misalignment or wear. This multi-functionality reduces the need for separate retention and electrical connection mechanisms.
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 reduces impedance between the component and the aircraft body to below 2.5 milliohms, preventing arcing and ensuring compliance with safety standards by maintaining a consistent low impedance path over time.
Implementation Method 1
The plurality of conductive fingers are spring-loaded and provide an interference fit with the body
Implementation Method 2
each second end is electrically connected with an inner surface of the body to provide a low impedance path between the component and the body
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An assembly mounted to a surface (37) includes a component (10) and a plurality of fingers (37) connected to the component (10) and in contact with the surface (37) to provide a low impedance path between the component (10) and the surface (37).