الفهرس 
Improving dynamic and aeroelastic performance of helicopter rotors using periodic design and piezo active control
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Abstract
In the present study, we improve the vibration characteristics of sandwich helicopter rotor blades with periodic changes in the core material. This technique preserves the external geometry of the rotor blades to keep their aerodynamic characteristics.Since the construction and air velocity change along the rotor blade, we use the finite element technique in its dynamical and aeroelastic analyses. Theodorsen’s 2-D thin airfoil theory with a lift deficiency function is used in the unsteady aerodynamic analysis, with a correction which takes into consideration that each blade falls in the wake of the preceding blade. Results of the analyses show significant improvement in the dynamic response and flutter speeds of helicopter rotors in both hovering and forward flight, as a result of using the periodic design technique of the blades. Introducing piezoelectric smart material in the core design of the blades together with active automatic control is shown to further improve the dynamic characteristics of the helicopter rotor