Arm Restraint Latch Shear Pin Deployment Mechanism
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Solution Overview
Problem
Current ejection seat arm restraint systems fail to effectively limit arm movement during ejection, leading to potential limb flail injuries due to inadequate deployment mechanisms.
Innovation Solution
The arm restraint assembly includes a primary arm, latch, primary shear pin, and secondary shear pins, which deploy to restrict arm movement by shearing at specific loads, ensuring the arms are secured before entering the wind stream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the arm restraint system uses a simple latch mechanism, then the device complexity is reduced, but the reliability of limiting arm movement during ejection is insufficient
Solution Approach 1:
The latch mechanism is divided into multiple independent components including a latch body, latch arm, shear pins (primary and secondary), and spring elements. Each component performs a specific function: the shear pins provide staged failure modes at different load levels, the spring elements provide biasing forces, and the latch arm provides the mechanical linkage. This segmentation allows the system to achieve high reliability through distributed functionality while managing complexity through modular design.
Solution Approach 2:
The system is pre-configured with shear pins at predetermined locations and spring elements pre-loaded to provide biasing forces. The latch mechanism is designed to automatically engage and disengage at specific load thresholds without requiring active control systems. This preliminary configuration ensures that the arm restraint deploys reliably at the moment of ejection when windblast forces exceed the shear pin strength, while avoiding the need for complex electronic controls or manual operations during the critical ejection sequence.
2Reliability
If the arm restraint assembly includes multiple shear pins and latch components, then the reliability of deployment is improved, but the ease of manufacture decreases
Solution Approach 1:
The latch mechanism is divided into modular components (latch body, latch arm, shear pins, springs) that can be manufactured separately using standard fabrication processes and then assembled. This segmentation allows each component to be optimized for its specific manufacturing requirements while simplifying quality control and assembly procedures, thereby reducing overall manufacturing complexity despite the multi-component design.
Solution Approach 2:
The system incorporates movable components such as the latch arm that pivots about a pivot joint, and spring elements that provide dynamic biasing forces. These dynamic elements are designed to move through defined ranges of motion and engage/disengage at predetermined positions, which simplifies the manufacturing requirements compared to fully rigid mechanisms while maintaining high deployment reliability through controlled mechanical behavior.
3Ease of operation
If the latch mechanism uses pinned connections for movement, then the ease of operation is improved, but the strength of the connection during high-load ejection decreases
Solution Approach 1:
The shear pins are pre-installed at predetermined locations within the latch mechanism, positioned to fail at specific load thresholds during ejection. This preliminary placement ensures that the pinned connections provide sufficient strength and smooth operation during normal conditions and deployment initiation, while the pre-positioned shear pins automatically fail at the appropriate moment to allow latch arm rotation and full deployment under high windblast loads.
Solution Approach 2:
The latch mechanism transitions from a rigid pinned connection state during normal operation to a rotated deployed state during ejection. The pivot joint allows the latch arm to rotate smoothly when the shear pins fail, providing ease of operation during the deployment sequence. The dynamic behavior of the system adapts to the loading conditions: pinned connections maintain strength during low-load operation, while the pivot joint enables free rotation during high-load ejection after shear pin failure.
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 deployment mechanism effectively limits arm movement, reducing the risk of limb flail injuries by ensuring the arms are restrained before exposure to windblast, enhancing pilot safety during ejection.
Implementation Method 1
The secondary shear pin may be designed to shear at a first minimum shear load, and the primary shear pin may be designed to shear at a second minimum shear load.
Data Source
AI summary
An arm restraint assembly for an ejection seat may comprise a primary arm configured to pivot about a primary arm pivot joint. A latch may be coupled to the primary arm. The latch may comprise a first pair of lugs and may be configured to pivot relative to the primary arm. A primary shear pin may extend between the first pair of lugs. A lanyard may be coupled to the primary shear pin.