The landing gear nitrogen charging task has two engineering challenges: correctly interpolating the AMM pressure-vs-extension table, and detecting slow leaks reliably.
AMM Pressure-Extension Table Lookup
A cubic-spline fit through the AMM extension/pressure data points lets the rig compute a target charging pressure for any measured strut extension, with a defined acceptable tolerance band around it. The chart below shows the interpolated curve, the AMM table data points, and a sample lookup at 175 mm of extension.
Leak Rate Monitoring
Detecting a slow nitrogen leak requires holding pressure for a fixed interval (10 minutes per AMM) and applying temperature compensation via the ideal gas law (P1/T1 = P2/T2) before fitting a linear regression to the corrected pressure trend. The slope of that fit is the leak rate. The chart below shows a sample 10-minute hold test, the raw vs temperature-corrected readings, and the resulting pass/fail verdict against the AMM limit of 0.1 bar/min.
The Neometrix Landing Gear Testing and Charging Test Rig implements this logic in its control system — AMM table interpolation, temperature-compensated leak monitoring, and automated maintenance record generation.
→ https://neometrixgroup.com/products/testing-and-charging-test-rig-for-main-and-nose-landing-gears
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