Captive Nut Sleeve Interference Fit for Rivet-Free Fuel Tank Assembly
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Solution Overview
Problem
Existing fastener systems for aircraft structures, such as those described in GB-A-2212580, weaken the substructural member and complicate the assembly process due to the use of rivets to hold captive nuts in place.
Innovation Solution
A fastener system utilizing a captive nut with a sleeve that achieves an interference fit within a hole, eliminating the need for rivets by using a metallic sleeve with a cylindrical interface, which allows for quick and easy installation without compromising the structural integrity of the substructural member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rivets are used to hold the captive nut in place, then the captive nut is securely attached to the substructural member, but the substructural member is weakened and the assembly process becomes complicated
Solution Approach 1:
The invention extracts the rivet from the assembly, eliminating the need for separate fastening elements. The captive nut is designed with an integrated sleeve that directly interfaces with the substructural member through an interference fit, removing the rivet and its associated weakening effect while maintaining secure attachment
Solution Approach 2:
The captive nut and sleeve are merged into a single integrated component. The sleeve is an integral part of the captive nut assembly, combining the functions of the nut and the fastening element into one unified structure that achieves secure attachment without compromising the substructural member
2Reliability
If rivets are used to hold the captive nut, then the captive nut is securely attached, but the assembly process is complicated
Solution Approach 1:
The rivet and its associated installation steps are extracted from the assembly process. The interference fit design allows the captive nut to be installed directly into the substructural member without requiring separate riveting operations, simplifying the overall assembly process
Solution Approach 2:
The sleeve is pre-configured with interference fit dimensions that enable direct installation into the substructural member. This preliminary design of the interference fit interface eliminates the need for complex assembly steps, allowing the captive nut to be securely attached in a single operation
3Productivity
If an interference fit is used between the sleeve and hole, then the captive nut can be installed quickly and easily, but the fit must be precisely controlled
Solution Approach 1:
The invention specifies precise dimensional parameters for the sleeve outer surface and hole inner surface to achieve the desired interference fit. By carefully controlling these geometric parameters, the design enables both quick installation and reliable attachment, balancing productivity with manufacturing precision requirements
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 enables rapid and straightforward assembly of secondary structures to primary structures like aircraft fuel tanks, enhancing assembly efficiency and maintaining structural strength without the weaknesses introduced by rivets, while also being applicable to other vehicle fuel tanks and structures.
Implementation Method 1
The interference fit between an outer surface of the sleeve and an inner surface of a wall of the hole
Data Source
AI summary
An assembly with an aircraft fuel tank is disclosed having a captive nut with an internal thread, a secondary structure, and a fastener which secures the secondary structure to the fuel tank. The fastener has a shaft which passes through the secondary structure and has an external thread coupled to the internal thread of the captive nut. The fuel tank has a fuel tank element with a hole, and the captive nut has a sleeve which is located in the hole with an interference fit between an outer surface of the sleeve and an inner surface of the wall of the hole.