Fail-safe Push-pull Rod with Dual Load Paths
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Solution Overview
Problem
Aircraft push-pull rods require fault-free and fail-safe designs with automatic damage detection and repair, as frequent maintenance and replacement are costly and inefficient due to material fatigue and overloading.
Innovation Solution
A double-wall push-pull rod design with two load paths, where one path is initially used for load transmission, and the second path automatically takes over in case of failure, featuring diagonally positioned holes and bolts for force-fitting contact, allowing for external detection of failures through inspection holes and test mandrels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If push-pull rods are routinely replaced or removed for testing at frequent maintenance intervals, then reliability and safety are ensured, but maintenance cost and time consumption increase significantly
Solution Approach 1:
The push-pull rod is segmented into two separate load paths (first and second layers), each capable of independently carrying the load. This segmentation allows the system to maintain functionality even when one load path fails, eliminating the need for frequent routine replacements and enabling targeted maintenance only when failure occurs.
Solution Approach 2:
The inspection hole is pre-formed during manufacturing with a specific diameter that allows test mandrels to detect failures. This preliminary action enables failure detection during routine inspections without requiring complete disassembly or extensive testing, significantly reducing maintenance time while ensuring reliability.
2Reliability
If push-pull rods are routinely removed and tested at frequent maintenance intervals, then damage is detected, but maintenance cost and effort increase considerably
Solution Approach 1:
The inspection hole extracts the complexity of failure detection from the overall maintenance process. By providing direct visual access to the critical connection area, it allows maintenance personnel to detect failures through simple inspection rather than requiring complete disassembly and comprehensive testing procedures.
Solution Approach 2:
The double-load-path design makes the system self-diagnosing through the inspection hole. When the primary load path fails, the stress redistribution becomes visible through the inspection hole, automatically indicating the need for maintenance without requiring complex diagnostic procedures.
3Device complexity
If a single load path is used in push-pull rods, then structural simplicity is maintained, but fail-safe capability is compromised
Solution Approach 1:
The load transmission function is segmented into two independent layers, each forming a complete load path from yoke to tubular body. This segmentation provides fail-safe capability while maintaining relative structural simplicity, as each layer follows a straightforward load path without complex mechanisms.
Solution Approach 2:
The first and second load paths are nested within each other in the wall thickness direction, with the first layer forming the outer wall and the second layer forming the inner wall. This nesting arrangement provides redundant load paths without significantly increasing the overall structural complexity or external dimensions.
Data Source
AI summary
A fail-safe push-pull rod has two load paths that are separated from each other, of which always only one takes up the load transmission and which automatically detects possible damage to or functional failure of the first load path so that in such a case then the second load path takes over the load transmission, whereby the functional change from the first to the second load path can be determined during the routine maintenance inspection by an inspection hole irreversibly showing the damage or the failure of the first load path.