The modern high performance air vehicles are required to have extreme maneuverability,which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenome...The modern high performance air vehicles are required to have extreme maneuverability,which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the selfinduced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at a = 60°. The free-to-roll results show that the model with whole strake wings(baseline), the model assembled with three strake wings(Case A)and the model assembled with two opposite strake wings(Case C) experience the spinning, while the model assembled with two adjacent strake wings(Case B), the model assembled with one strake wing(Case D) and the model with no strake wing(Case E) trim or slightly vibrate at a certain "×"rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at a = 60°.展开更多
The previous studies of time delay compensation in flight control systems are all based on the conventional aerodynamic derivative model and conducted in longitudinal motions at low angles of attack.In this investigat...The previous studies of time delay compensation in flight control systems are all based on the conventional aerodynamic derivative model and conducted in longitudinal motions at low angles of attack.In this investigation,the effects of time delay on the lateral-directional stability augmentation system in high-a regime are discussed based on theβmodel,which is proposed in our previous work and proved as a more accurate aerodynamic model to reveal the lateraldirectional unsteady aerodynamic characteristics at high angles of attack.Both theβmodel and the quasi-steady model are used for simulating the effects of time delay on the flying qualities in high-a maneuvers.The comparison between the simulation results shows that the flying qualities are much more sensitive to the mismatch of feedback gains than the state errors caused by time delay.Then a typical adaptive controller based on the conventional dynamic derivative model and a gain-prediction compensator based onβmodel are designed to address the time delay in different maneuvers.The simulation results show that the gain-prediction compensator is much simpler and more efficient at high angles of attack.Finally,the gain-prediction compensator is combined with a linearizedβmodel reference adaptive controller to compensate the adverse effects of very large time delay,which exhibits excellent performance when addressing the extreme conditions at high angles of attack.展开更多
文摘The modern high performance air vehicles are required to have extreme maneuverability,which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the selfinduced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at a = 60°. The free-to-roll results show that the model with whole strake wings(baseline), the model assembled with three strake wings(Case A)and the model assembled with two opposite strake wings(Case C) experience the spinning, while the model assembled with two adjacent strake wings(Case B), the model assembled with one strake wing(Case D) and the model with no strake wing(Case E) trim or slightly vibrate at a certain "×"rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at a = 60°.
基金the National Natural Science Foundation of China(No.11872209)。
文摘The previous studies of time delay compensation in flight control systems are all based on the conventional aerodynamic derivative model and conducted in longitudinal motions at low angles of attack.In this investigation,the effects of time delay on the lateral-directional stability augmentation system in high-a regime are discussed based on theβmodel,which is proposed in our previous work and proved as a more accurate aerodynamic model to reveal the lateraldirectional unsteady aerodynamic characteristics at high angles of attack.Both theβmodel and the quasi-steady model are used for simulating the effects of time delay on the flying qualities in high-a maneuvers.The comparison between the simulation results shows that the flying qualities are much more sensitive to the mismatch of feedback gains than the state errors caused by time delay.Then a typical adaptive controller based on the conventional dynamic derivative model and a gain-prediction compensator based onβmodel are designed to address the time delay in different maneuvers.The simulation results show that the gain-prediction compensator is much simpler and more efficient at high angles of attack.Finally,the gain-prediction compensator is combined with a linearizedβmodel reference adaptive controller to compensate the adverse effects of very large time delay,which exhibits excellent performance when addressing the extreme conditions at high angles of attack.
