Towbar Shear Pin with Adjustable Positioning and Retention
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Solution Overview
Problem
Current tow bar systems require manual tool-based conversion between aircraft types, are prone to errors, and suffer from shear pin breakage issues that can result in parts falling and causing damage, especially in adverse weather conditions.
Innovation Solution
A tow bar design that allows adjustment of shear pins in the longitudinal direction using shear notches and a positioning device, eliminating the need for tools and ensuring no parts fall during breakage, with a catch bolt to maintain connection integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple shear pins with different dimensions are used to accommodate different aircraft types, then the tow bar can be used for different aircraft types, but the conversion process requires manual tool-based removal and installation of shear pins, which is time-consuming and error-prone
Solution Approach 1:
The shear pin is designed with a movable adjustable element that can be positioned at different locations along the pin's length. By moving the adjustable element to different positions, the effective shear strength is changed, allowing the same shear pin to accommodate different aircraft types with different load requirements. This eliminates the need to physically replace the entire shear pin during conversion.
Solution Approach 2:
The invention changes the effective parameters of the shear pin by varying the position of the adjustable element along the pin's length. Different positions create different lever arms or effective shear areas, thereby changing the shear strength parameter. This allows a single shear pin design to provide multiple shear strength values suitable for different aircraft types without requiring physical replacement.
2Reliability
If shear pins are secured with self-locking nuts, then the shear pins are prevented from falling out, but the nuts can be overtightened and prestress the shear pin, which changes the shearing force and may cause premature failure
Solution Approach 1:
A resilient element (such as a spring or elastomeric component) is introduced as an intermediary between the shear pin and the securing mechanism. This resilient element provides the necessary retention force to prevent drop-out while being compliant enough to avoid transmitting excessive clamping forces to the shear pin. The resilient element absorbs the preload, ensuring that the shear pin is retained securely without being prestressed to the point of premature failure.
3Strength
If shear pins break at the predetermined breaking points, then the breaking force is limited to protect the aircraft, but the broken parts fall out and scatter on the apron, causing safety hazards and requiring time-consuming search and recovery operations
Solution Approach 1:
The invention captures the potentially harmful broken parts and converts them into a contained, non-hazardous state. The retention mechanism is designed to capture the broken segments of the shear pin after failure and hold them securely within the assembly. This prevents the broken parts from scattering on the apron, eliminating the safety hazard and the need for time-consuming search and recovery operations while maintaining the beneficial controlled breaking force.
4Ease of operation
If the shear pin is made adjustable in the longitudinal direction, then tool-free conversion between aircraft types is enabled, but the positioning device adds complexity to the shear pin structure
Solution Approach 1:
The shear pin is segmented into distinct functional zones: a fixed head portion, an adjustable intermediate portion with positioning features, and a shank portion. The positioning device is segmented into discrete elements such as notches, ridges, or detent features that can be engaged with corresponding elements in the towing head. This segmentation allows for simple, tool-free adjustment while keeping each individual feature geometrically simple, thereby limiting the overall complexity increase.
Data Source
Figure 1a
Figure 1b
Figure 1c
AI summary
The bar (23) has a towing head fastened to a base body by a shear pin. A form-fitting positioning device positions the shear pin in a pin direction in the towing head. The shear pin includes multiple break areas with different shearing values, where the break areas are spaced in the pin direction. The shear pin possesses a round cross-section contour and a widened head. The shear pin exhibits two pairs of shear notches that exhibit a distance for contact areas of a projecting component. A shaft of the pin is larger than a passage hole by a base body and the head.