Considerations for Impact Identification on a Helicopter Main Rotor

Previous research has focused on developing a methodology to locate impact loads to composite structures utilizing a data-driven model of the structure. Impact loads can create damages that cannot be seen from the surface; therefore time consuming techniques must be used to inspect the structure. A system that can monitor a structure for impacts can guide a detailed inspection so the compromised areas of the structure are located in a timely manner and labor and other resources are not wasted inspecting parts of the structure that are undamaged. This impact identification technique has been successfully implemented on a variety of complex structures including composite fiber-wound missile canisters, the fuselage of a retired helicopter, and protective helmets. For these structures, the aforementioned data-driven model has accurately described the behavior of the structure in its operational environment. This thesis works towards implementing the impact identification technique on an operational helicopter main rotor, a structure for which the operating environment involves boundary conditions and forces that are different from those in the model training environment. The helicopter blades must be tested using modal impacts when the rotor is stationary, but when the rotor is operational, the behavior of the blades is altered by the presence of centrifugal and aerodynamic forces and a change in the boundary conditions at the droop stop. This thesis presents two strategies to correct the blade model for the effects of the droop stop and implements these strategies on a UH-60 Black Hawk blade. The first strategy trains the blade model while the blade is lifted off of the droop stop with a sufficiently compliant elastic support. When this technique is used, 100% of impacts to 120 points on the blade are correctly located. The second strategy conditions data collected while the blade is in contact with the droop stop with relationships derived using frequency domain impedance modeling. When this strategy is used, 90.2% of impacts to 120 points on the blade are correctly located