Helicopter Rotor Blade Impact Detection and Characterization: Formulation and Application of a Data-Driven Model for the Operational Environment

The incorporation of real-time structural health monitoring has the potential to substantially reduce the inspection burden of advanced composite rotor blades, particularly if impacts can be detected and characterized using operational data. Data-driven impact identification algorithms require that a model be developed in the operating environment, typically in the form of frequency response functions (FRFs). However, if the FRF model is developed for a stationary aircraft (as is common practice), the model does not accurately describe the operational characteristics of the rotor system. The discrepancies are predominately due to two sources: the change in the blade root boundary condition and the presence of the centrifugal force. An analytical methodology is employed in this research to compensate for these effects. Derivations of the method are included, as well as analytical and experimental results. Additionally, the impact identification method is discussed, with a novel methodology presented to provide estimates of the in-plane area of the impacting object.