Tip Displacement Estimation Using Fiber Optic Sensors for X2 Technology Rotor Blades

Rotor-state feedback will be important to realize the full capability of next generation high speed, highly efficient rotorcraft with attributes such as X2 Technology™. Being able to sense and regulate rotor tip clearance on an X2 Technology™ rotorcraft will maximize its capability while maintaining safety of flight without requiring an overly conservative deisgn. One concept for acquiring rotor tip clearance is to use a strain-displacement transformation to indirectly estimate blade tip displacement. This strain-displacement transformation relates on-blade strain measurements, acquired from fiber optic sensors, to blade deformation using a minimum number of sensors and the measured or estimated blade structural properties. Testing on a simple cantilever beam and on a model-scale rotor operated in the UTRC Pilot Wind Tunnel demonstrated feasibility of the concept. Even in the presence of airflow and centrifugal load, the tip displacement estimation did not exceed 7% deviation from reference sensor readings. The performance and endurance of the fiber optic sensors and sensing hardware were also studied during the tests.