Structural health monitoring of composite-based UAVs using simultaneous fiber-optic interrogation by fiber bragg grating point sensors and rayleigh-based distributed sensing

This work presents the use of both discrete and distributed optical fibers based sensing techniques for Health and Usage Monitoring System (HUMS) as applied on the Israeli Air Force High Altitude Long Endurance (HALE) Unmanned Aerial Vehicles (UAVs). Sensing is based on in-flight Fiber Bragg Grating (FBG) technology, combined with on-ground Rayleigh-backscattering distributed strain sensing. The in-flight instrumentation monitors loads, looking for excessive values, while the Rayleigh-based technique is used on-ground to track and monitor the strain signature of the wing critical components, under prescribed loading, over time. The sensing system has already gained many flight hours without any failure, demonstrating the robustness of this sensing concept. It is the purpose of this system to early detect and identify dangerous changes in the normal structural behavior of an individual UAV, prompting the required corrective action, thereby paving the way to Condition-Based Maintenance (CBM) in line with the emerging airworthiness regulations for UAVs.