Flight strain measurement of helicopter rotor blade flaps using fiber grating

Traditional electrical strain gauges face limitations in rotor blade applications due to complex wiring, susceptibility to electromagnetic interference susceptibility, and reliability issues. This study presents a Fiber Bragg Grating (FBG) based in-flight strain measurement system that overcomes these challenges by leveraging the FBG sensors' compactness, electromagnetic immunity, and suitability for distributed measurements of FBG sensors. A key innovation is the direct integration of the system into the rotor hub without slip rings or optical connectors, which significantly simplifying simplifies deployment and enhancing enhances robustness. Comparative validation against electrical strain gauges and theoretical models on an equal-strength beam confirmed the accuracy of FBG measurements. Ground and flight tests on a helicopter demonstrated real-time, interference-free strain measuring during blade elastic deformation, with FBG data closely aligning closely with conventional gauge results. Critically, the system’s installation did not affect helicopter performance, as confirmed by pilot evaluations. Furthermore, analysis of blade flap strain trends under diverse flight conditions provides valuable insights for blade design optimization. This work advances rotor blade monitoring by establishing a reliable, lightweight solution for complex electromagnetic environments, addressing critical gaps in existing strain measurement methodologies.