Design, manufacturing, and testing of an active twist rotor

Abstract

An Active Twist Rotor (ATR) is developed for future implementation of the individual blade control for vibration and noise reduction in helicopters. The rotor blade is integrally twisted by direct strain actuation using active fiber composites (AFC). In order to design and analyze an active blade, a general framework is proposed. A multi-cell thin-walled active composite beam model is developed. The model is validated against a combination of other theoretical models and experimental data. Actuation trend studies are conducted by examining the formulation, and the results are verified by numerical examples. Design requirements are proposed by combining general ones applicable to passive model-scaled rotor blade and specific ones to the current ATR blade. A design flowchart is established for the current design task of the ATR blade since it enables systematic handling of a number of the parameters. Several different concepts of ATR candidates are suggested, and compared with each other with regard to the requirements. Other design aspects such as manufacturing simplicity and cost-effectiveness are also considered in the process. The final design is selected, and final adjustments are added to it in order to simplify its manufacturing. A prototype blade is manufactured in accordance with the final design. A couple of testing articles are fabricated in advance to the full-span prototype in order to debug the manufacturing process. Various tests are conducted with the testing articles and the final prototype to verify the design and correlate with model predictions. A maximum static tip twist of 1.5' (peak-to-peak) was achieved at half of the designed operating electric field before five of the 24 AFC packs failed. Electrical breakdown of the embedded active material caused degradation of twist actuation in the prototype blade, and the causes are presently under investigation. The ATR prototype blade is leading to a complete fully-articulated four-blade active twist rotor system for future wind tunnel tests.