Shape memory alloys compact actuators for aerodynamic surfaces twisting

The present paper focuses on the characterization of compact actuators, based on shape memory alloys (SMA) technology and aimed at producing the twist of aerodynamic surfaces. The idea at the basis is to integrate a conventional blade of a rotorcraft with compact actuators, able to cooperate in absorbing loads and to alter the original twist law to enhance the aerodynamic performance at specific flight conditions (hover and vertical speed), without penalizing the other flight phases. The SMA rods are mounted in pre-twist condition along the span to enforce the austenite into martensite transformation during the switch off state. On the basis of the heating level and of the stress generated by the elastic reaction of the twisted structure, a certain phase transformation towards austenite is enforced, with the macroscopic effect of recovering angle. At first, the blade architecture is presented, with specific reference to the layout dedicated to the integration of the SMA; then the setup used for training and pre-twisting the SMA specimen is described together to the test procedure. Finally, the twist-torque results obtained for rods of different diameters are discussed and applied to the model of blade twist considered for preliminary investigations.