Individual Blade Root Control Demonstration Evaluation of Recent Flight Tests

A collaborative programme is underway to explore the potential of the individual blade control (IBC) technology with regard to two aspects: Control laws will be developed and evaluated in flight using an improved blade root control system, and in a parallel activity, a smart actuation concept with trailing edge flaps will be developed and investigated in a wind tunnel test. This paper focuses on the first flight test activities with the full equipment integrated in a BO105 testbed. It consists of the IBC-system itself and a powerful experimental setup including a comprehensive sensor equipment and fast ruggedized data acquisition and processing computers. The objectives of the flight tests are the test of the IBC-system with full authority, the test and evaluation of several realtime algorithms for the blade vortex interaction analysis, and a comparison with results from several wind tunnel tests, which have shown a remarkable potential of IBC for the reduction of the external noise, induced during the approach phase of the helicopter. The blade root control system has been installed on a BO105 helicopter and was already used by EUROCOPTER DEUTSCHLAND GmbH (ECD) and ZF Luftfahrttechnik GmbH (ZFL) in 1990 and 1991 at limited control authority. Compared to these tests, now a three times higher control authority of the actuators and a newly developed experimental system provides an optimum testbed for the evaluation of the potential of this IBC-system. The paper reports about the bench and ground tests of the actuators, the system tests on the helicopter and the dynamical behaviour of the blade root actuators embedded in the conventional control system. Beside these test activities during the preparation, results from the evaluation phase are included, which comprise flight tests with full IBC-authority using open loop control laws. In parallel to the test and integration of the IBC-system for the open loop tests, the algorithms for the identification of the blade vortex interaction noise were developed and the realtime software was integrated in a fast preprocessing computer. This activity was mainly performed by the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) with support from the Daimler-Benz research establishment and ECD. The paper describes the development of the algorithm together with a correlation between the blade surface pressure measured in wind tunnel and flight test. In addition results from the blade vortex analysis will be shown including several approaches for the software code and realtime realization aspects. The outcome comprises the comparison of the application of this code on wind tunnel and flight test data and the realtime application in flight, which is an important step towards an effective noise controller. The presented flight tests are the first of several further test campaigns, including open and closed loop tests for the reduction of the external noise induced by blade vortex interaction, the reduction of the cabin vibration and the investigation of the potential of further control laws aiming at rotor stabilisation, stall delay, load and power reduction.