External Lightning Protection Appliques for Composite Aircraft Structures
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Solution Overview
Problem
Composite materials used in aircraft structures are prone to electrical breakdown during lightning strikes due to their low conductivity, and existing lightning protection methods often cause damage and hazards by forcing high electrical currents into the composite structure or buried networks.
Innovation Solution
An external current return network using dielectric polymer-based appliqués and metal foils to isolate and conduct lightning currents, allowing for a deterministic and flexible protection scheme that keeps energy out of the composite structure, replacing traditional methods like Inter Woven Wire Fabric, Copper grid, and expanded aluminum foil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional buried current return networks are used, then lightning protection is provided, but high currents damage composite structures and create hot spots
Solution Approach 1:
The current return network is extracted from the buried position inside the composite structure and placed on the external surface. This allows the network to carry lightning currents without forcing them into the composite structure, eliminating the damage to fasteners, joints, and fiber interfaces while still providing effective lightning protection.
Solution Approach 2:
A dielectric layer is introduced as an intermediary between the current return network and the composite structure. This dielectric barrier prevents direct electrical contact, isolating the composite structure from high currents while allowing the network to function as intended. The dielectric layer acts as a mediator that protects the composite from electrical damage.
2Weight of moving object
If composite materials are used for structural components, then mass is reduced and structural rigidity is improved, but conductivity decreases and lightning dissipation capability is worsened
Solution Approach 1:
The solution uses a composite protection system combining a conductive metal foil layer for current conduction with a dielectric polymer layer for isolation. This composite structure provides both the electrical conductivity needed for lightning dissipation and the electrical insulation needed to protect the underlying composite aircraft structure, allowing lightweight composite materials to be used while maintaining lightning strike resistance.
3Reliability
If high currents are driven into composite structure, then current return path is established, but electrical discontinuities cause damage and hot spots
Solution Approach 1:
The current return path is extracted from the composite structure and relocated to the external surface. This eliminates the need to drive high currents through electrical discontinuities within the composite, preventing the generation of hot spots and sparks that could ignite fuel or damage structural components.
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
This solution improves flight safety, reduces weight, enhances repairability, and eliminates hazards by providing a predictable current path, effectively managing lightning strikes without damaging composite structures.
Implementation Method 1
appliqués that have a dielectric polymer to isolate the return current from the structure
Implementation Method 2
a metal foil for conducting the current
Data Source
AI summary
A method and apparatus for implementing a return current network that is external to a composite structure, which directs a current along a known path to the aircraft grounding system using appliqués. The appliqués have a dielectric polymer to isolate the return current from the structure, and a metal foil for conducting the current