Double-Shell Fastener Cap With Offset Windows for Ignition Shielding

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Solution Overview

Problem

Aircraft fasteners pose an ignition risk during lightning strikes due to electrical currents passing through composite materials, leading to electromagnetic effects that can interact with fuel vapors, and existing polysulfide cap seals are labor-intensive to install and maintain, increasing production and inspection time.

Innovation Solution

A cover system comprising an inner and outer shell with offset windows and gaps forming a circuitous flow path to prevent direct exposure of fasteners to the exterior environment, dissipating thermal and kinetic energy and preventing ignition.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If polysulfide cap seals are used to seal fuel mixtures from arcs and hot particles, then ignition risk is reduced, but installation and inspection time increase

Engineering Contradiction:

Improveignition risk reductionVSAvoidinstallation and inspection time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The cap seal is divided into an inner shell and an outer shell with distinct functions. The inner shell provides the sealing surface against the fastener, while the outer shell provides the external seal and structural support. This segmentation allows each shell to be optimized independently and simplifies installation procedures.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The inner shell is nested within the outer shell, creating a compact dual-shell structure. The inner shell fits into the outer shell with their respective windows offset, forming an integrated seal assembly that combines both sealing functions in a single unit.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Reliability

If an airtight seal is required to prevent fuel contact with fasteners, then ignition protection is improved, but seal durability under environmental exposure deteriorates

Engineering Contradiction:

Improveignition protectionVSAvoidseal integrity under thermal cycling

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The sealing function is segmented between two shells, each forming seals at different locations. The inner shell seals against the fastener while the outer shell seals externally, creating redundant sealing paths that improve overall seal reliability under thermal and environmental stress.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The inner shell acts as an intermediary barrier between the fastener and the external environment. It provides a first line of defense that protects the fastener directly, while the outer shell provides additional protection and structural support.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If windows in inner and outer shells are aligned, then flow path is simplified, but direct line of sight allows ignition risk

Engineering Contradiction:

Improveflow path configurationVSAvoidignition risk from direct exposure

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The windows of the inner shell and outer shell are deliberately positioned asymmetrically (offset from each other). This asymmetric arrangement blocks direct line-of-sight paths between the exterior environment and the fastener, preventing direct exposure to arcs and hot particles while still allowing necessary flow paths through the offset configuration.

Inventive Principle:

Principle #4Asymmetry

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 system effectively shields fasteners from igniting combustible environments by redirecting energy through circuitous flow paths, reducing the risk of ignition and simplifying the installation and maintenance process, thereby lowering production and inspection costs.

Implementation Method 1

dissipating thermal and kinetic energy and preventing ignition

Methodology Applied

Scientific EffectThermal energy dissipation: Convection

Implementation Method 2

dissipating thermal and kinetic energy and preventing ignition

Methodology Applied

Scientific EffectKinetic energy dissipation: Turbulence

Implementation Method 3

electrical arcs, vaporized materials creating hot gas, and/or heating sufficient to ignite vaporous fuel mixtures

Methodology Applied

Scientific EffectElectrical arc containment: Electric Arc

Implementation Method 4

high electrical current may propagate through conductive paths on the aircraft

Methodology Applied

Scientific EffectElectromagnetic shielding: Faraday Cage

Data Source

PatentUS11022164B2Double shell fastener caps

Publication Date: 2021.06.01 THE BOEING CO

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. The cover includes an outer shell with one or more windows. An inner shell is positioned within the outer shell. The inner shell includes one or more windows that are offset from the windows of the outer shell. One or more flow paths extend through the windows for gas, liquid, and/or some particles to flow through the cover while removing the thermal and/or kinetic energy that may ignite the combustible exterior environment.