In-flight structural sensing of helicopter landing gear using fiber bragg grating

A field-deployable structural monitoring system for helicopter landing gear based on fiber Bragg grating (FBG) sensors was implemented on the rear gear of a Sikorsky S-64 and exercised across taxi, take-off, hover, approach, landing, and roll-out. Four FBGs were interrogated at 1 kHz, and time–frequency features were extracted via segmented fast Fourier transforms to track the evolution of spectral content (≈0–500 Hz) associated with rotor-induced excitation, ground contact, and braking. The resulting families and their phase-dependent amplitudes indicate sensitivity to load-path variations and asymmetric load distribution, supporting inference on usage, fatigue accumulation, and hard-landing severity. The flight activity represents a direct translation to operational conditions of methodologies previously validated in laboratory drop tests, weight-on-wheels studies, and bonding durability assessments, thereby demonstrating end-to-end feasibility of FBG-based sensing for in-service monitoring. The findings support integration of strain-based features within Health and Usage Monitoring Systems (HUMS) for objective event detection and structural integrity assessment on rotary-wing landing gear.