To achieve efficient attenuation of noise and vibration characteristics within the helicopter environment, solid-state actuators are seen as one of the most promising smart technologies. The Smart Hybrid Active Rotor Control System project is expected to demonstrate the ability of smart structure systems, employing multiple active material actuators, sensors, and closed-loop controllers, to reduce simultaneously rotorcraft vibration and noise. Within this project, piezoceramic elements were used as actuators to vary the dry friction and the stiffness of the whole helicopter blade system. This active control concept, named Smart Spring, originated a prototype used to demonstrate the ability to attenuate vibrations. Before testing the Smart Hybrid Active Rotor Control System in operative conditions, the dynamic properties of the Smart Spring installed on a nonrotating helicopter blade are investigated. The effects of the Smart Spring actuator on the modal properties are studied through experimental activities carried out at Carleton University. Furthermore, the capability of the Smart Spring to change the dynamic behavior of the helicopter blade is demonstrated by analyzing the shifts in the modal parameters. Finally, a beam finite element model of the blade, with stiffness and mass properties tuned to the experimental structure, is presented.

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Journal Journal of Aircraft
Coppotelli, G. (G.), Marzocca, P. (P.), Ulker, F.D. (F. D.), Campbell, J. (J.), & Nitzsche, F. (2008). Experimental investigation on modal signature of smart spring/helicopter blade system. In Journal of Aircraft (Vol. 45, pp. 1373–1380). doi:10.2514/1.35139