Simulation-Based Bandwidth Analysis of a Swashplateless Rotor Helicopter

The paper summarizes the operating principles of a swahsplateless rotor; discusses the issues of modeling a swashplateless rotor helicopter by means of a comprehensive simulation model suitable for flight dynamics calculations; and presents the results of a numerical systematic investigation into the effects of swashplateless rotor design parameters such as trailing-edge flap length and span-wise position, pitch index, and blade torsional stiffness on helicopter trim, poles and zeros, and bandwidth and phase delay for a medium weight articulated rotor helicopter model patterned after the UH-60A. Results indicate baseline swashplateless rotor helicopter bandwidth values are in the range 2.5-5.0 rad/s, and with phase delay values under 120 milliseconds, the helicopter model displays Level 1 handling qualities for Target Acquisition and Tracking Mission Task Elements as defined by the ADS-33 aeronautical design standard. In general, longer trailing-edge flaps improve the handling qualities, but flap placement does not have a significant impact. Pitch bandwidth, specifically, is found to increase substantially by increasing the pitch index and reducing torsional stiffness. However, analysis provides evidence of strong blade aeroelastic flap-torsion instabilities occurring as a consequence of the reduced torsional blade stiffness. In particular, pitch index is found to be a critical parameter which can easily excite severe blade instabilities if torsional stiffness is low enough. Potential adverse effects on the stability should be studied in more detail.