Study On Active Control Of Vertical Tail Buffet With Piezoelectric Actuators

High performance combat aircrafts,especially those with twin vertical tails are likely to be subject to vertical tail buffet problem at high angles of attack.Vertical tail buffet can limit the performance of twin-tail fighter,lead to premature fatigue failure of the vertical tail,and increase the maintenance cost.Active vibration control can be used for response alleviation and damage reduction of buffet.Piezoelectric actuator is a kind of intelligent material actuators,it is suitable to be used in the aviation which is strict for weight because the light weight of piezoelectric actuator.In this paper,Macro Fiber Composite(MFC)piezoelectric actuators are used for tail buffet control,two Multi-input Multi-output(MIMO)buffet controllers are designed using acceleration feedback and dynamic strain feedback,respectively.Using Macro Fiber Composite piezoelectric actuators,a modified optimization criterion is development using output controllability theory by considering residual modes to limit the spillover effect,and the optimized layout of MFC actuators is studied.Based on the load equivalent principle of piezoelectric actuator and finite element method,the dynamic model of the vertical tail incorporating MFC actuators is obtained.Location and orientation of actuator are served as the design variables in the layout optimization of MFC with Genetic algorithms.In the optimization the first three modes are controlled modes,the fourth and fifth modes are residual modes.In order to develop the control system accurately,the experimental modeling method is adopted to build the tail buffet control system.The experimental identification method is designed to obtain the data which are effective for MIMO system identification.By using subspace identification method,the state space model of open-loop system with acceleration feedback and dynamic strain feedback is obtained.The accuracy of the model is confirmed by examing the best fit value and comparing output signals and frequency responses.A Linear Quadratic Gaussian(LQG)controller without considering the system uncertainty is designed.And a robust ? controller considering the parametric uncertainty caused by wind speed and additive perturbation caused by unmodeled dynamics is obtained.Using optimal Hankel norm approximation algorithm,the order of the plant model is reduced during the design of LQG controller,and the order of the controller is also reduced with this technique when it comes to design the robust controller,in this way the control system is easy to design and realize.Numerical simulation results shows that the designed controller can reduce the vertical tail buffet response.For the experimental study of active vertical tail buffet control,a vertical tail buffet control model is built;the effectiveness of active control system for buffet alleviation is investigated by ground tests and wind tunnel tests.The experimental results show that not only the acceleration feedback but also dynamic strain feedback can control vertical tail buffet response.The LQG controller can only control vertical tail buffet in the case of little uncertainty,but the robust controller can control tail buffet effectively for all the cases.