In-flight Tracking and Vibration Control using the DLR's Multiple Swashplate System

Abstract

This paper discusses the design, Integration and test of a Higher Harmonic Control algorithm capable of both vibration control and in-flight blade tracking in conjunction with DLR's multiple swashplate control system (META) while honoring predefined limits in usable control autority. The design of the control algorithm is described in detail and the results of coupled numerical investigations with both a general purpose multibody cody by Politecnico Milano and DLR's com prehensive rotor code to determine the algo-rithm's performance, are presented. The integration of the control algorithm into the realtime control software is shown for the META system, where for safety reasons a semiopen loop approach was implemented. First tests of the controllers in-flight tracking mode to reduce 1/rev loads during hover yielded an almost complete reduction in 1/rev vibratory loads while maintaining constant rotor thrust. Following the experiments at DLR's own facility, extensive wind tunnel tests were performed in 2016 with META and a 5-bladed rotor system at the Large Low-Speed Facility of the German Dutch Wind Tunnels. The control algorithm was adapted to the 5-bladed rotor and successfully applied for in-flight blade tracking as well as the reduction of 5/rev hub loads using multi-harmonic pitch inputs with frequencies from 4/rev to 6/rev in cruise and high-speed flight condition. In both cases, the controller showed excellent performance and yielded satisfactory reductions of 1/rev rotor imbalances as well as a reduction of 5/rev hub vibrations by more than 80% while at the same time adhering to user-set limits for the higher harmonic control amplitudes.