Telescoping Arm Restraint for Ejection Seat
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Solution Overview
Problem
Ejection seats fail to effectively restrain a pilot's arms during high-speed ejection from an aircraft, leading to potential injury due to extreme pressure-induced forces causing arm flailing.
Innovation Solution
The ejection seat features a telescoping arm restraint system with lower and upper support arms that deploy laterally to form a forward-facing surface, utilizing a pressure source to telescope the arms outward and a ratcheting or non-ratcheting hinge system to secure them, along with a plurality of shrouds to provide a safe arrest for the occupant's arms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the backstop uses fixed support arms, then the structure is simple, but the lateral extension area is insufficient to effectively restrain arms during high-speed ejection
Solution Approach 1:
The support arms transition from a fixed static structure to a dynamic telescoping structure that can extend and retract. The telescoping mechanism allows the support arms to increase their lateral extension area when needed during ejection while maintaining a compact form when not in use, effectively resolving the contradiction between area and complexity.
Solution Approach 2:
The support arms are divided into multiple telescoping segments that can extend relative to each other. This segmentation allows the structure to achieve greater lateral extension area through the coordinated extension of multiple segments, while the modular nature of segmentation keeps the overall system manageable in terms of complexity.
2Reliability
If the support arms are extended to increase restraint surface area, then arm restraint effectiveness improves, but the mechanism complexity increases due to telescoping components
Solution Approach 1:
The telescoping mechanism is designed to be self-actuating through the force dynamics of ejection itself. The support arms automatically extend to the required length during the ejection process without requiring external control systems, sensors, or active actuation mechanisms, thereby maintaining reliability while minimizing added complexity.
Solution Approach 2:
The telescoping mechanism is pre-configured with shear pins positioned at specific locations that determine the extension length. During ejection, the shear pins automatically fail at the predetermined moment, allowing the support arms to extend to the pre-calculated optimal length for arm restraint, ensuring reliability without complex real-time control.
3Manufacturing precision
If shear pins are used to control telescoping extension, then the extension length is precisely controlled, but the manufacturing precision requirements increase
Solution Approach 1:
The shear pins are designed as disposable, low-cost components that are intentionally made simple and robust rather than precision-critical. Their function is to fail at a predetermined load, so they are manufactured with tolerances suitable for their sacrificial role, not for precise positioning. This approach prioritizes ease of manufacture over high precision, as the pins are replaced after use anyway.
Solution Approach 2:
The design incorporates built-in tolerance compensation through the telescoping mechanism structure itself. The shear pins are positioned to account for manufacturing variations, and the telescoping segments are designed with clearance tolerances that accommodate pin position variations. This beforehand cushioning of potential precision errors allows use of simpler, easier-to-manufacture shear pins without compromising extension length control.
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 telescoping arm restraint system effectively increases the lateral extension of the backstop, providing a larger surface area to safely arrest the occupant's arms, reducing the risk of injury from windblast forces and allowing for more effective arm restraint during ejection.
Implementation Method 1
a pressure source, the pressure source configured to telescope the first lower telescoping member from the lower base member in response to deployment of the ejection seat
Data Source
AI summary
An ejection seat is disclosed. In various embodiments, the ejection seat includes a seat frame having a seat-back and a seat-pan adapted to support an occupant, the ejection seat further comprising a propulsion system configured to propel the ejection seat from an aircraft; and a backstop configured to deploy laterally outward from the seat-back to form a forward-facing surface, the backstop including a lower support arm and an upper support arm, the lower support arm and the upper support arm configured to telescope upon deployment of the ejection seat.