Multiple Input Describing Function Analysis of Non-Classical Aileron Buzz

This paper focuses on the computational study of nonlinear effects of unsteady aerodynamics for non-classical aileron buzz. It aims at a comprehensive investigation of aileron buzz phenomenon under varying flow parameters utilizing the classical approach of describing function technique with multiple input variables. Limit cycle oscillatory behavior of an asymmetrical airfoil section has been studied initially using an expensive high-fidelity model basd on a coupled CFD/CSD time marching approach. Using this high fidelity model, a multiple input aerodynamic describing function was developed that can effectively represent lumped nonlin-earities of aerodynamic subsystem. Limit cycles can be closely identified through multiple input aerodynamic describing function representation, taking into account also the bias effect due to the use of non-symmetric airfoils. Traditional LCO analysis of sensitivity with respect to hinge moment of inertia is performed. Further, outburst points of limit cycle amplitude for varying Mach number and angle of attacks are investigated. By using developed aerodynamic describing function, it has been demonstrated that limit cycle analysis methods may still be used while including the effects of aerodynamic nonlinearities. Results from both methods, direct time marching and multiple input describing function, have been broadly compared for validation.