Self-indexing Nut Fastener for Low Clearance Assembly
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Solution Overview
Problem
Aerospace and military applications face challenges in assembling joint elements within limited clearance regions due to difficulties with traditional fasteners, including ergonomic issues, inconsistent torque application, and sub-optimum joint fatigue performance, particularly in wing side-of-body joint assemblies where nut-side torque application is unfeasible and precise tightening is time-consuming.
Innovation Solution
A cylindrical bolt assembly with a threaded stud and cap nut system that allows nut-side torque application without rotating the stud, featuring a spring-loaded stop projection and stop indentations for automatic orientation and a wrenching feature to prevent stud rotation, enabling efficient assembly and reliable joint fatigue performance in reduced clearance regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional bolt assemblies are used in limited clearance regions, then the fastening function is achieved, but the installation becomes difficult and torque application becomes inconsistent
Solution Approach 1:
The fastener is divided into two separate components: a cylindrical stud that passes through the joint elements and a cap nut that threads onto the stud. This segmentation allows the stud to be installed first through the limited clearance region, followed by the cap nut, eliminating the difficulty of maneuvering a complete bolt assembly through tight spaces while enabling consistent nut-side torque application for reliable joint fatigue performance
Solution Approach 2:
The invention inverts the traditional bolt assembly approach by using a cylindrical stud without a head that passes through the joint, followed by a cap nut that threads onto the stud from the opposite side. This inversion enables torque application from the nut side, which is known to deliver consistent optimum joint fatigue performance, rather than the traditional head-side torque application that causes bolt rotation and scoring
2Reliability
If nut-side torque application is implemented, then consistent optimum joint fatigue performance is achieved, but the torque application becomes unfeasible in reduced clearance regions
Solution Approach 1:
By separating the fastener into a cylindrical stud and a cap nut, the invention enables the nut to be accessed from the reduced clearance region after the stud is installed. The stud's cylindrical shape allows it to pass through the tight space, and the cap nut can then be threaded onto the exposed threads and torqued from the accessible side, making nut-side torque application feasible even in reduced clearance regions
3Productivity
If traditional fasteners are used in wing side-of-body joint assembly, then the joint is secured, but the assembly process becomes time-consuming due to trial and error tightening
Solution Approach 1:
The cap nut incorporates a self-indexing mechanism with a stop feature that automatically indexes the nut to the correct orientation as it is threaded onto the cylindrical stud. This self-indexing action eliminates the need for operators to manually adjust and re-tighten the nut multiple times to achieve proper orientation, significantly reducing assembly time and ensuring precise nut orientation in wing side-of-body joint assembly
Data Source
AI summary
According to a preferred embodiment, a multi-piece fastener with self-indexing nut is disclosed. The multi-piece fastener is designed for use in low clearance areas such as aircraft wing side-of-body joint locations. The multi-piece fastener comprises a stud comprising an elongated part extending between a first end face and a second end face, a threaded head fastener, a threaded tail fastener, and a wrenching feature. A self-indexing feature is provided on the stud and head fastener which allows automatic orientation of the head fastener with respect to the stud.