Capacitive Load Sensor for Aircraft Landing Gear Torque Link
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Solution Overview
Problem
Existing load monitoring systems for aircraft landing gear torque links are not robust enough to withstand environmental exposure and flying debris, and they lack sensitivity and accuracy, especially when adhesive bonding is used instead of positive fixation.
Innovation Solution
A capacitive sensor system comprising a main pin with an axial bore and a core pin, where a capacitor is mounted to detect relative displacement due to external loading, producing signals indicative of loads, and optionally includes additional outer capacitor plates and an angle sensor for increased sensitivity and accuracy, with a hermetic bulkhead for protection and wireless transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a linear capacitive sensor capsule is mounted to a torque link using adhesive bonding, then the sensor can be positioned in a location optimal for sensitivity, but the sensor becomes vulnerable to environmental exposure and flying debris
Solution Approach 1:
The sensor capsule is nested within the hollow interior of the torque link, with the capsule positioned in a recess or cavity that is part of the link's structure. This nesting protects the sensor from environmental exposure while maintaining its measurement capabilities through the link's web.
Solution Approach 2:
The torque link's web structure serves as an intermediary between the sensor and the external environment. The sensor measures strain in the web indirectly through its effect on the capsule's capacitance, while the web itself provides protection from debris and elements.
2Ease of manufacture
If conventional capacitive sensors are mounted using adhesive bonding, then positive fixation by fasteners is avoided (no holes in loaded elements), but the mounting becomes less robust
Solution Approach 1:
The sensor capsule is nested within the hollow torque link structure, eliminating the need for external mounting hardware. The capsule fits into a precisely formed recess that provides both mechanical support and environmental protection, achieving robust fixation without holes or fasteners.
3Measurement precision
If foil strain gages are bonded to the strut piston, then measurement of pure shear due to torsion is achieved, but the gages are not reliable over the long term
Solution Approach 1:
The mechanical foil strain gage system is replaced with a capacitive sensing system. Instead of using bonded electrical resistive gages that degrade over time, the invention uses a capacitive capsule that measures strain through changes in capacitance caused by relative displacement of its plates, providing long-term reliability without bonding materials.
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 system provides sensitive and accurate load monitoring while being robust against environmental factors and debris, with the ability to measure high torque loads and maintain reliability and accuracy, even in harsh conditions.
Implementation Method 1
The resultant linear strain on the link can be measured in a linear capacitive sensor capsule by monitoring the change in capacitance as the capacitor plates are moved away from or toward each other under the strain motion in the torque link
Data Source
AI summary
A sensor for monitoring loads in a landing gear torque linkage includes a main pin having an axial interior bore defined therein. The main pin is configured and adapted to engage a torque link to a strut lug of a landing gear strut. A core pin is mounted axially within an interior bore of the main pin and is spaced radially inwardly from the interior bore for relative displacement with respect to the main pin. A capacitor is included having an inner capacitor plate mounted to the core pin. An outer capacitor plate is mounted to the main pin. Relative displacement of the core pin and the main pin due to loads acting on the torque link and strut lug results in relative displacement of the inner and outer capacitor plates. Signals can thereby be produced indicative of the loads acting on the torque link.