Structural Health Monitoring of a UAV Fleet Using Fiber Optic Distributed Strain Sensing

This paper presents the application of distributed fiber optic strain sensing as a standard procedure for airworthiness assessment of an entire fleet of operational High Altitude Long Endurance (HALE) Unmanned Aerial Vehicles (UAVs) during service. The Rayleigh-backscattering-based sensing concept is applied to a standard optical fiber, which is embedded within the full length of the wing main spar. Individual under-load strain signatures (with a spatial resolution of 1cm) are periodically collected during service for each UAV and compared to a baseline. Excellent repeatability of the strain signatures under a prescribed loading protocol has been obtained so far, demonstrating the concept robustness, as well as the excellent structural performance of the wing. Simultaneous strain readings, using both distributed Rayleigh backscattering and the more conventional fiber-optic Bragg grating point sensors, imprinted on the same fiber, were compared for validation, showing excellent agreement. In addition, the same sensing concept was applied to a full-scale test article to monitor its structural performance during a fatigue test, simulating several life times of this UAV. Principal Component Analysis (PCA) was applied to the collected data in order to isolate the information which is more likely associated with changes in the structural health of the wing. The UAV fleet accomplished many flight hours under this airworthy monitoring policy with no false alarms or any damage to the sensing optical fibers. doi: 10.12783/SHM2015/371