Prerequisites For The Closed Loop Control Of An Active Twist Rotor Blade

Due to the tremendous centrifugal forces, the measurement of blade motion is a challenging task. Within the paper an overview on blade motion measurement techniques is given. The different techniques are assessed concerning their real time capability as it is intended to use the sensors to close the control loop for a tip twist control of an active twist rotor blade. The challenges related to the measurement of blade motion in a model scale active twist blade are pointed out. After a brief summary about strain gage based blade motion measurement the focus is laid on accelerometers for the measurement of the tip twist. Since commercial available sensors do not fulfill the requirements to operate under such adverse conditions, a new sensor principle is presented. This novel sensor concept allows the measurement of static twist using centrifugal twisting moments. A parametric finite element model is used to perform a first optimization. In order to extend the dimension of the design space for the final optimization without increasing the computation costs, an analytical model is developed. Therefore analytical expressions for stiffness, strains and loads are formulated.