Landing Gear Shock Absorber Servicing Without H-Dimension Measurement
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Solution Overview
Problem
Current methods for servicing aircraft landing gear shock absorbers, particularly during weight-on-wheels operations, face inaccuracies and inefficiencies due to friction and human error, leading to potential underestimation of gas levels and increased maintenance time and cost.
Innovation Solution
A method and apparatus for servicing shock absorbers that involves exhausting all gas from the chamber, degassing dissolved gas from hydraulic fluid, and delivering a pre-set mass of gas while ensuring hydraulic fluid levels meet specific criteria, allowing for accurate servicing without the need for measuring the H-dimension, using a portable servicing cart equipped with a vacuum pump and control unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If H-dimension measurement method is used to assess gas and hydraulic fluid levels, then servicing can be performed, but measurement accuracy is reduced due to friction between moving parts
Solution Approach 1:
The patent extracts the gas from the shock absorber chamber completely, separating it from the hydraulic fluid. This eliminates the friction-based measurement method and replaces it with direct mass measurement of the gas, achieving both speed and accuracy without relying on H-dimension measurements that are affected by friction between moving parts.
Solution Approach 2:
The patent replaces the mechanical H-dimension measurement system with a mass-based measurement system. Instead of measuring physical extension that is affected by friction, the system measures the mass of gas directly, eliminating the measurement accuracy problem while maintaining rapid servicing capability.
2Loss of time
If weight on wheels service is performed assuming H-dimension reduction is due to N2 leakage alone, then servicing is faster, but accuracy is reduced because other reasons for H-dimension reduction are ignored
Solution Approach 1:
The patent extracts all gas from the chamber and separately measures and replaces both gas and hydraulic fluid based on their actual losses. This eliminates the incorrect assumption that H-dimension reduction is solely due to gas leakage, allowing accurate identification and replacement of both gas and hydraulic fluid regardless of the underlying cause.
Solution Approach 2:
The patent uses feedback from direct mass measurements of gas and volume measurements of hydraulic fluid to determine actual losses. This feedback mechanism replaces the erroneous feedback from H-dimension measurements, enabling accurate refilling decisions for both gas and hydraulic fluid based on actual consumption rather than assumptions.
3Reliability
If weight off wheels service is performed to accurately refill shock absorber, then refilling accuracy is improved, but maintenance time increases to one or two days and aircraft is taken out of revenue service
Solution Approach 1:
The patent replaces the complex weight-off-wheels mechanical servicing procedure with a simplified mass-based measurement and replacement system that can be performed quickly in weight-on-wheels condition. This substitution maintains high accuracy in refilling while dramatically reducing maintenance time and avoiding aircraft downtime.
4Adaptability or versatility
If manual actions are followed during servicing procedure, then flexibility is maintained, but human error risk increases resulting in incorrectly serviced gear
Solution Approach 1:
The patent implements a self-service system where the equipment automatically measures the mass of gas and volume of hydraulic fluid, calculates the required replacement amounts, and guides the servicing procedure. This automation eliminates human error while maintaining the flexibility to handle different servicing scenarios, as the system adapts its measurements and calculations to the specific conditions of each shock absorber.
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
This approach enables accurate and efficient servicing of shock absorbers, reducing human error and maintenance time, while ensuring the correct gas and hydraulic fluid levels are maintained, even during weight-on-wheels operations, thus improving the reliability and efficiency of aircraft landing gear maintenance.
Implementation Method 1
a first part for exhausting gas from the chamber
Implementation Method 2
exhausting all gas from the chamber
Implementation Method 3
degassing at least some dissolved gas from the hydraulic fluid
Data Source
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AI summary
A method and portable apparatus for servicing a shock absorber (102) on a landing gear assembly (108; 110) of an aircraft (101) in a weight-on-wheels state is described. The shock absorber comprises at least one chamber (111) containing both hydraulic fluid (135) and a gas (121) in fluid communication with each other. Gas is exhausted from the chamber. Dissolved gas is degassed from the hydraulic fluid. The portable apparatus (117) comprises a source (gas cylinder 120) of gas and a source (128) of hydraulic fluid. The amount of hydraulic fluid in the chamber is corrected, preferably such that the chamber is then filled with a known amount of degassed hydraulic fluid. A pre-set mass of gas is then delivered into the chamber under the control of a gas delivery system (inflation kit 119) of the portable apparatus. More accurate servicing of a shock absorber may thus be provided since account is additionally taken of gas dissolved in hydraulic fluid. Also, by delivering a pre-set mass of gas into the chamber, there is no need to rely on a measure of gas pressure or H-dimension (h) when servicing the shock absorber (102).