Rugged Fiber Optics Monitoring System for Helicopter Rotor Blades

Health and Usage Monitoring (HUM) and Structural Health Monitoring (SHM) technologies play an increasingly important role in aerospace applications, for example in support to fleet maintenance and for test and development purposes. We describe the design, manufacture and integration of an advanced blade strain monitoring system for the tail rotor of the AWƒ‰ helicopter. The goal was two-fold: to demonstrate the feasibility of a rugged rotor-based interrogation system and the practical embedding of Fiber Bragg Gratings (FBG) sensors within composite rotor blades. This task required careful study of the optimal fiber path within the constraints of the blade composite structure and the ply stacking sequence. A temperature compensation method was developed to decouple thermal strain. An integrated interrogation-communication system housed in a dedicated beanie was developed with the capability to withstand the harsh high-g environment of a rotor hub. In order to avoid the need for slip rings for power and data transfer between fixed and rotating frames, the interrogator was designed as a self-contained unit equipped with batteries and wireless data transmission capability. This rugged monitoring system offers cleaner aerodynamics and longer sensor life compared to traditional strain gauges and represents a stepping stone towards the development of future fiber-based HUM with photonics chip interrogators.