Dual Load Path Fastener Anti-Rotation Locking Plate
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Solution Overview
Problem
Existing dual load path fastener systems, such as those used in horizontal stabiliser assemblies, are not reliable as the secondary mechanical locking device can lead to shearing and loosening of the nut due to free spinning of the outer pin, compromising safety in case of failure.
Innovation Solution
A dual load path fastener assembly with an outer male fastener featuring a threaded section with axial slots, an inner male fastener, a female fastener with notches, and a locking plate with projections that engage with the slots and notches, preventing free spinning and ensuring load transfer to the inner fastener in case of outer fastener failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cotter pin is used as the secondary mechanical locking device, then the locking arrangement meets regulatory requirements, but the outer pin can still spin freely upon failure leading to shearing of the cotter pin and loosening of the nut
Solution Approach 1:
A locking plate is introduced as an intermediary component between the outer and inner fasteners. The locking plate includes a projection that engages with a slot in the outer fastener and a notch in the female fastener, preventing free spinning. This intermediary element transfers the anti-rotation function from the cotter pin to the locking plate, eliminating the harmful free spinning effect while maintaining the dual load path structure.
2Strength
If a castellated nut with cotter pin is used for mechanical locking, then the primary friction lock is secured, but the cotter pin may shear and fall out during operation compromising the locking arrangement
Solution Approach 1:
The anti-rotation function is extracted from the cotter pin and transferred to the locking plate with its projection-slot-notch engagement mechanism. The locking plate provides a more robust mechanical interlock that prevents shearing and loosening, while the cotter pin is eliminated or reduced to a secondary element. This extraction of the critical locking function to a dedicated component resolves the shearing and loosening problems.
3Reliability
If the outer fastener is designed as a sleeve receiving the inner fastener, then separate and independent load paths are established, but the outer fastener lacks rotational constraint leading to free spinning upon failure
Solution Approach 1:
The locking plate merges multiple functions: it provides rotational constraint on the outer fastener through projection-slot engagement, engages with the female fastener through the notch, and sandwiches between the inner and outer fasteners. This combination of functions in a single component simultaneously provides rotational constraint while maintaining the independent load path structure, resolving the contradiction between reliability and operational constraint.
Data Source
AI summary
A dual load path assembly includes an outer pin, which has an axial through bore and at least one end that includes a threaded section. The threaded section includes at least one slot orientated from the end and extends axially along at least part of the threaded section. The assembly also includes an inner pin, which is receivable in the through bore of the outer fastener. A female fastener comprising at least one notch is receivable on the threaded end of the outer pin. A locking plate comprises a through hole via which it is receivable on the shank of the inner pin and at least one projection. The locking plate is arranged such that the projection is receivable in both the notch and the slot. A locking member engages with the end of the inner pin and abuts a face of the locking plate thereby sandwiching the locking plate between the locking member and the female fastener.