Captive Nut Interference Fit for Rivet-Free Fuel Tank Assembly
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Solution Overview
Problem
Existing fastener systems for aircraft structures, such as those disclosed in GB-A-2212580, weaken the substructural member and complicate the assembly process due to the use of rivets, and lack efficient methods for securing secondary structures to primary structures like aircraft fuel tanks without compromising structural integrity or ease of assembly.
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 and allowing for quick and easy installation, with a cylindrical interface providing a frictional force to prevent rotation and secure the nut in place, suitable for various aircraft components including fuel tanks, wings, and other vehicle structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rivets are used to hold the captive nut as in GB-A-2212580, then the captive nut is secured to the substructural member, but the substructural member is weakened and the assembly process is complicated
Solution Approach 1:
The invention extracts the rivet from the fastening system and replaces it with a direct interference fit between the sleeve and the hole in the substructural member. The sleeve is press-fitted into the hole with an interference fit that provides sufficient securing force without requiring additional rivets, thereby eliminating the weakening effect on the substructural member while maintaining reliable captive nut attachment.
2Reliability
If rivets are used to hold the captive nut as in GB-A-2212580, then the captive nut is secured to the substructural member, but the assembly process is complicated
Solution Approach 1:
The invention removes the rivet installation step from the assembly process. The sleeve is designed to be directly press-fitted into the pre-drilled hole in the substructural member, eliminating the need for separate rivet installation operations. This simplifies the assembly process while maintaining reliable securing of the captive nut through the interference fit between the sleeve and hole.
3Productivity
If an interference fit is used between the sleeve and hole, then the captive nut can be installed quickly and easily without rivets, but the manufacturing precision requirements increase
Solution Approach 1:
The invention optimizes the interference fit parameters by selecting appropriate interference values and material properties. The sleeve and hole are designed with specific dimensional tolerances and interference fit magnitudes that balance the need for quick installation with manufacturing capability. The interference fit is engineered to provide sufficient securing force while accommodating normal manufacturing variations, enabling rapid installation without excessive 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
The solution enables secure and efficient attachment of secondary structures to primary structures without the need for rivets, enhancing assembly ease and structural integrity while providing a liquid-tight seal and resisting high torque and tensile loads, applicable to aircraft fuel tanks and other vehicles.
Implementation Method 1
a sleeve which is located in a hole with an interference fit between an outer surface of the sleeve and an inner surface of a wall of the hole
Implementation Method 2
The interference fit between the two abutting surfaces enables the captive nut to be installed quickly and easily... The cylindrical interface providing a frictional force to prevent rotation
Data Source
Figure 1~3
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Figure 6~7
AI summary
An assembly with an aircraft fuel tank; 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, wherein the fuel tank comprises a fuel tank wall, the fuel tank element is a fitting which is inside the fuel tank and carried by the fuel tank wall, and the shaft passes through the secondary structure and the fuel tank wall.