Handling the Air Resonance Mode for Flight Control and Handling Qualities Evaluations on the DLR Research Helicopter FHS

Abstract

The paper presents the research carried out to handle the air resonance mode which occurs on the DLR EC135 FHS (Flying Helicopter Simulator) research helicopter. The air resonance mode on the FHS is excited in particular when roll rate feedback loops in the flight control system are closed. A flight test campaign was conducted to gather data of the air resonance mode for different roll rate feedback gains. A model, determined by system identification, is tuned to optimally match the model response with the flight test data for different roll rate feedback gains. Based on this model, subsequently, an air resonance controller was developed and tested that effectively suppresses the excitation of the air resonance mode resulting from roll rate feedback. The final air resonance controller concept was extensively flight tested to study the influence on the flight control performance and handling qualities.