Decentralized Vibration Control and Coupled Aeroservoelastic Simulation of Helicopter Rotor Blades with Adaptive Airfoils

In helicopters, a high vibration level of the airframe occurs due to higher harmonic aerodynamic loads acting on the rotor blades. However, when the airfoil shape is adaptive, the aerodynamic loads can be affected to reduce vibration and moreover, the airfoil shape can be adjusted to the periodically changing flow conditions to increase aerodynamic efficiency. Adaptation of the airfoil shape may be achieved by discrete trailing edge flaps or continuously by a variation of the airfoil camber and bending of smart tabs. For vibration reduction applying feedback [4], stability augmentation of the lagging modes becomes indispensible. This is discussed first for rotors with discrete trailing edge flaps. The disadvantages of a discrete flap, such as kinks of the airfoil contour and concentrated masses, may be overcome by continuous shape adaptation, investigated in the second part.