A State-space Rigid-elastic Coupling Aeroelastic Model with Geometrical Accurate Boundary Condition

Flying-wing aircraft has become an ideal choice for advanced aircraft design due to its excellent aerodynamic characteristic and strong loading capacity. However, this kind of aircraft usually has poor flight stability and controllability because of the small pitch inertia. In addition, with the widespread use of composite materials on aircraft, the stiffness and deformation of the aircraft should be carefully considered due to the composites' design diversity. The minimum structural elastic natural frequency of the aircraft is becoming lower and closer to the maximum frequency of rigid-body flight modes. These factors lead to the occurrence of rigid-elastic coupling aeroelastic instability phenomenon on the aircraft and the flutter speed may become much lower compared to the one without considering rigid body flight modes, which can be a crucial safety disadvantage of applying flying-wing layout and needs appropriate analysis model urgently. Based on the flight dynamic model, flight kinematic model, the unsteady vortex lattice method (UVLM), and the modal-superposition structural dynamic model, a rigid-elastic coupling aeroelastic model can be built, which is fully coupled at each time step to provide a relatively accurate description. In order to present the coupling model in state-space form which is convenient for solving, the UVLM has been transferred into a state-space format and achieves joint modelling with flight dynamic equations. To obtain a more accurate aerodynamic response, the UVLM has been improved with geometrical accurate boundary condition, which can consider the impact such as geometric nonlinear structural deformation, rudder deflection, and the change of unsteady wake through integral boundary changing and normal vectors deflection. According to the coupling model, the analytical solution of the model can be derived. This can be a credible reference when computing the time-domain response. A flying-wing model was built for the rigid-elastic coupling aeroelastic analysis. The results of rigid-elastic flutter analysis were proved to be consistent with commercial software MSC. Nastran and ZAERO. A significant decrease in critical speed after considering the rigid-body flight mode was obtained, which revealed the unignorable coupling effect between flight mode and structural elasticity. Those results show that the state-space rigid-elastic coupling aeroelastic model with geometrical accurate boundary condition can provide a kind of powerful and reliable analysis method for flying-wing aircraft aeroelastic design to improve the flight safety. In addition, the rigid-elastic coupling effect and the geometrical accurate boundary condition influence cannot be ignored.