Shear Cap Cable Break-away Safety Device
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Solution Overview
Problem
Rescue hoists for aircraft face damage risks due to excessive loads when cables become entangled with objects on the ground, as existing securing methods rely on torque and friction that can fail to release the cable effectively, leading to potential damage to the hoist and aircraft.
Innovation Solution
A shear cap device is integrated into the cable drum system, featuring a head, neck, and attachment portion, where the neck is designed to fracture at a predetermined load, allowing the cable to break free and prevent damage by transmitting tensile forces until the fracture point is reached, eliminating the need for set screws and simplifying installation and maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If set screws are torqued to secure the cable to the cable drum, then the cable can resist pull-out forces, but the cable cannot release effectively when overloaded
Solution Approach 1:
The cable securing system is segmented into two distinct functional components: a shear cap that provides overload protection and a cable drum that provides secure mounting. The shear cap acts as a sacrificial element that segments the load path, allowing the cable to be securely mounted while enabling automatic release when the shear cap fractures under excessive load.
Solution Approach 2:
The shear cap serves as an intermediary element between the cable and the cable drum. It mediates the force transmission, normally allowing the cable to be securely held while providing a fracture point that enables automatic release when overloaded, thus resolving the contradiction between secure holding and easy release.
2Strength
If set screws are used to secure the cable, then the cable can be firmly attached, but the installation and maintenance become more complex
Solution Approach 1:
The complex set screw mechanism is extracted and replaced with a simpler shear cap design. The shear cap can be installed by simply inserting it into a slot on the cable drum, eliminating the need for torque tools and complex adjustment procedures, while still providing secure cable attachment through its structural design.
Solution Approach 2:
The shear cap is designed as a sacrificial, disposable component that can be easily replaced. Instead of maintaining complex set screw mechanisms, the system uses inexpensive shear caps that fracture under overload and are simply replaced, significantly simplifying maintenance procedures.
3Reliability
If the cable is securely secured to prevent pull-out, then the hoist can handle normal loads, but the cable cannot break free to prevent damage during overload
Solution Approach 1:
The shear cap provides beforehand cushioning by acting as a predetermined fracture point. It is designed to fracture at a specific load threshold, cushioning the system against excessive forces by breaking rather than allowing the cable to snap or the hoist to be damaged. This protective function is built into the design before any overload event occurs.
Solution Approach 2:
The system uses parameter changes in the shear cap design (material properties, dimensions, geometry) to create a component with a specific fracture load. By carefully controlling these parameters, the shear cap can be designed to fracture at precisely the right moment - when the load exceeds safe limits but before damage can occur to the hoist or cable.
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 shear cap effectively prevents damage to the rescue hoist and aircraft by ensuring the cable detaches at a predetermined overload, providing a reliable and mistake-proof mechanism for securing and releasing the cable, enhancing safety and ease of maintenance.
Implementation Method 1
The neck is configured to transmit tensile forces from a cable secured to the attachment portion and to fracture with the tensile forces equal to or exceeding a predetermined fracture set point
Data Source
AI summary
A cable break-away device for a rescue hoist connects a cable to a cable drum of the rescue hoist. The cable break-away device provides overload protection to the rescue hoist by disconnecting the cable from the cable drum when the loads transmitted through cable become excessive. The cable break-away device is configured to fracture, releasing the cable from the cable drum, when the loads experienced by the cable break-away device exceed a predetermined failure set point. As such, the cable break-away device forms a mechanical fuse connecting the cable to the cable drum.