Fuel Contents Gauging Probe Test Rig for the Light Combat Helicopter, resolving fuel level to ≤1 mm.

Introduction

The Fuel Contents Gauging (FCG) Probe Test Rig is specialized ground-based equipment designed for the Light Combat Helicopter (LCH) program. Accurate fuel measurement is vital in combat aviation, where missions often involve high altitudes, demanding maneuvers, and extended flight durations. Pilots must trust their instruments completely, and that trust depends on the performance of the FCG probes and associated level switches inside the aircraft's fuel tanks.

These probes function on capacitive principles, converting immersion depth into electronic signals that are processed by the Fuel Quantity Indicating System (FQIS). A faulty probe or switch could lead to misleading fuel readings, endangering missions and lives. This test rig acts as the quality gatekeeper, performing pre-installation checks, calibrations, and functional verifications to ensure every probe meets HAL's stringent requirements before flight integration.

System overview

The rig provides a controlled environment where FCG probes and level switches are tested under simulated tank conditions. It employs a stainless-steel wet test tank with a transparent glass level tube and millimetre scale, enabling precise correlation between actual fuel level and probe output.

The probe's output is measured as a time-period signal, which is logged and analyzed against fluid height to check linearity, repeatability, and stability. In addition, the rig verifies input current consumption, insulation resistance, dielectric withstand strength, and switch actuation points. All results are captured through an automated data acquisition (DAQ) system and compiled into traceable test reports.

Working principle

At the heart of the system is the wet functional test. The probe under test is immersed in a surrogate aviation fuel (such as Isopar M or Isopar K). As the liquid level rises or falls, the probe generates a changing time-period output corresponding to fuel height. This output is measured with microsecond resolution by a period counter, while the level is simultaneously tracked by the graduated glass tube.

The test rig thus creates a time-period versus fuel level curve, which is compared against acceptance limits. The process is repeated in both directions to account for hysteresis. Parallel measurements of current consumption, switch actuation, and insulation integrity complete the qualification cycle.

Key features

• Wet testing capability: uses a calibrated tank and surrogate fuel to replicate real tank conditions.
• High-resolution output measurement: captures probe output as a time-period variable with microsecond precision.
• Level switch validation: verifies actuation and reset levels with millimetre accuracy.
• Electrical integrity checks: includes insulation resistance and dielectric withstand testing.
• Automated data handling: DAQ-based system generates real-time graphs, stores results, and produces PDF certificates.
• Safety & reliability: grounding, overcurrent protection, spill trays, and optional explosion-proofing.

Advantages

Unlike conventional manual setups, this rig is fully automated, modular, and traceable. It reduces operator error, shortens testing cycles, and provides auditable reports aligned with HAL's QA processes. Its modularity ensures compatibility with existing probe families and flexibility for future upgrades.

Deliverables

• Main rig console with measurement and instrumentation modules.
• Wet test tank with glass level tube and precision scale.
• Probe fixtures and adapters for specified part numbers.
• Level switch testing chamber with relay monitoring.
• Calibration kit (reference capacitors, oscillator standard).
• DAQ-enabled industrial PC with pre-installed software.
• Documentation package including user manual, procedures, and calibration certificates.

Conclusion

The FCG Probe Test Rig is more than a test machine — it is a quality gatekeeper. It ensures that when the LCH takes to the skies, its pilots can rely completely on their fuel gauges, focusing on the mission with full confidence that their instruments will never let them down.