Bulkhead Fitting Thermal Shell Air Pocket Electrical Path
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Solution Overview
Problem
Existing bulkhead fittings in composite structure aircraft face challenges in providing both thermal insulation and electrical conductivity, while also ensuring safety against spark propagation and compliance with Federal Aviation Regulation (FAR) 25.981, which requires a redundant system to prevent ignition sources within fuel tanks.
Innovation Solution
The bulkhead fitting assembly includes a thermal shell with an air pocket between the tube and the shell, a mounting flange, and a plurality of bushings and nuts that create a continuous metal path for electrical conductivity and thermal insulation, along with an O-ring for sealing, to reduce heat transfer and prevent fluid leakage, while providing a spark-resistant connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If thermal insulating materials are used to resist heat flow, then thermal insulation is improved, but electrical conductivity deteriorates
Solution Approach 1:
The bulkhead fitting is segmented into distinct functional zones: a thermal shell providing thermal insulation, and a separate all-metal pathway (flange, studs, nuts, bushings) providing electrical conductivity. This segmentation allows each component to optimize its specific function without compromise.
Solution Approach 2:
The thermal shell acts as an intermediary element that selectively blocks thermal energy while allowing electrical current to pass through dedicated metal pathways. It mediates between the thermal management requirements and electrical conductivity requirements of the system.
2Reliability
If additional components are added to protect against spark propagation, then safety is improved, but device complexity increases
Solution Approach 1:
The fitting combines multiple functions into a single integrated assembly: thermal insulation, electrical conductivity, mechanical mounting, and spark protection all work together in one unified structure rather than requiring separate components for each function.
Solution Approach 2:
The all-metal pathway serves multiple purposes simultaneously: it provides electrical conductivity for spark protection, structural support for mounting, and a sealed pathway for the conduit. This multi-functionality reduces the need for additional specialized components.
3Object-affected harmful factors
If thermal insulation is increased to prevent heat damage, then thermal protection is improved, but heat dissipation deteriorates
Solution Approach 1:
Different regions of the fitting have different thermal properties: the thermal shell provides insulation where needed to protect the bulkhead, while the all-metal pathway provides thermal conduction where heat dissipation is required. This local differentiation of thermal quality optimizes both protection and dissipation.
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 design effectively reduces heat transfer to the bulkhead, maintains structural integrity, and ensures electrical conductivity, thereby protecting against thermal damage and electrical discharges, while meeting safety regulations by providing a redundant spark-resistant path.
Implementation Method 1
a thermal shell joining the mounting flange and the tube, the thermal shell having a portion spaced away from the tube forming an air pocket between the tube and the thermal shell
Implementation Method 2
a plurality of bushings positioned between the plurality of mounting studs and the bulkhead, the plurality of bushings each shaped to complete a current path from the tube to the plurality of mounting studs, from the plurality of mounting studs to the plurality of bushings, and from the plurality of bushings to the bulkhead
Implementation Method 3
an O-ring for sealing
Data Source
AI summary
A bulkhead fitting assembly that includes a tube, a mounting flange attachable to a bulkhead, a thermal shell joining the mounting flange and the tube and having a portion spaced away from the tube forming an air pocket between the tube and the thermal shell, a plurality of mounting studs extending from the mounting flange away from the thermal shell, and a plurality of bushings positioned between the mounting studs and the bulkhead. The plurality of bushings are each shaped to complete a current path from the tube to the plurality of mounting studs, from the plurality of mounting studs to the plurality of bushings, and from the plurality of bushings to the bulkhead. Nuts are threaded on the studs to secure the fitting assembly by sandwiching the bulkhead between the mounting flange and the bushings, which are retained by the nuts.