Implementation of an Hoo Controller for the Helicopter BK 117
The active vibration reduction of rotor hub loads by means of piezoelectrically driven trailing edge flaps is addressed in the present work. Hoo control synthesis is used to develop a robust controller to be operated in different flight conditions, for instance different flight speeds, altitudes, and manoeuvres. Pre-flight specifications have been worked out for proving the controller on the BK117 helicopter. That needs the analytical decomposition of the controller in an observer form with full state feedback, the decoupling of the individual internal loops, and the discretization of the observer-based controller. Open-loop flight measurements have been performed with 4/rev flap inputs in the multi-blade coordinates and reliable transfer functions have been identified at this particular frequency to assess the rotor model (used to design the controller) and investigate, whether the designed controller would be robust stable when it is operated on the real helicopter. Finally, the Hoo vibration controller was tested in closed-loop showing robust stability and performance in on- and off-design flight conditions.