Active Controls For Airplanes To Suppress Body Freedom Flutter And To Alleviate Maneuver Load

The flexible structure has gained an increasing popularity in the design of modern aircraft in order to meet the requirements of high speed,high mobility and long flight endurance for an aircraft.The flexible structure,however,gives rise to a stronger interaction between the aerodynamic force and the elastic force of flexible structure.Such an interaction,named aeroelasticity,may degrade the flying qualities of an aircraft and greatly shorten the structure life.The past decades have witnessed the developments of active control of aeroelasticity,but some open problems as well.For example,the active suppression of the body freedom flutter and the adaptive control of maneuver load alleviation are far from matured.This dissertation studies the aeroelasticity of aircrafts and focus on two major problems.The first is the body freedom flutter suppression of a flying-wing Unmanned Aerial Vehicle(UAV).The second is the adaptive maneuver load alleviation of a high-performance fighter.The main contributions of the dissertation are summarized as follows:1.For the aeroelastic modeling of aircraft,first the model of unsteady aerodynamic force has to be constructed.In this dissertation,a high order panel method has been adopted to model the unsteady aerodynamic force.Then couple it with plane's structure to construct the aeroelastic equations in state space.The transformation of axes has been taken to deal with rigid-body freedom of the plane with the introduction of airframe states.Finally,the equations consider both aeroelasticity and flight dynamics have been set up.2.To study the body freedom flutter of a flying-wing UAV in subsonic airflow,the model has been constructed base on the techniques in step 1.The body freedom flutter has been found out during the numerical simulation at low flying speed.To suppress the flutter,controllers based on robust control theory have been proposed.The synthesis consists two cases,in case 1,only one pair of control surfaces has been used while two have been used in case 2.The results show remarkable suppression in both cases while the latter one provides higher closed-loop flutter speed.3.An adaptive controller based on Recurrent Neural Networks(RNNs)has been proposed to realize maneuver load alleviation of military fighter.The controller is constructed by two RNNs to realize on-line system identification and load alleviation.Meanwhile,a new factor has been introduced to the initialized weight of RNNs.The numerical simulations show good adaptability of the controller over a wide range of Mach numbers.4.To realize fighter's maneuver load alleviation at varying flying conditions,a robust loadalleviation controller has been proposed.First,a Linear Parameter Varying(LPV)model has been constructed and the uncertainty modeling has been realized to deal with the effect of parameter variation.Then,a robust load alleviation controller has been synthesized based on the LPV model with the uncertainty.To compensate the loss of performance in the load alleviation,a controller based on RNNs has been designed to deal with the flight control.The cooperation of the two controllers has been demonstrated by a series of numerical simulation.The results show good performance and robustness of the maneuver load alleviation system.