Unsteady Aerodynamics Modeling for a Flexible Unmanned Air Vehicle

An unsteady aerodynamics model of a flexible unmanned air vehicle is presented in this paper. The unsteady aerodynamics results from structural vibrations of the flexible airframe which affect the airflow around it. The doublet lattice method, which is a potential flow based panel method, is used for obtaining the basic unsteady aerodynamics model. It gives the pressure distribution on a lifting surface harmonically oscillating in steady flow. The basic concepts, underlying assumptions and approximations of the method are discussed. The extensive post processing which is done for the model obtained from the doublet lattice method is also described. The aerodynamic model is first transformed into suitable coordinates to account for structural vibrations effects. A rational function fitting is then carried out to obtain the final model which is suitable for time domain analysis. We use these methods to obtain an unsteady aerodynamics model of the Body Freedom Flutter vehicle, a flexible test bed aircraft. The results of this application are discussed. The final model is used for developing a nonlinear simulation for the flexible aircraft which is capable of simulating phenomena such as flutter and is important for integrated control law synthesis for the aircraft. The software for DLM as well as the post processing tools are made available as an open source research tool for aeroelastic systems research.