Effect of competing V-tail models on a UAS 6-DOF nonlinear simulation

A Six DOF nonlinear model of a large unmanned aerial system is developed using two competing approaches in modeling aircraft with V-tail configuration. In one approach the V-tail is projected into horizontal and vertical planes and the aircraft airflow angles, angle of attack and sideslip angle, are used for analysis. This approach has been successfully used to model aircraft with low horizontal tail dihedral however the nonlinear aerodynamics generated by the angularity of airflow is not captured. At large dihedral angles these nonlinearities can increase the uncertainty in physics based models. The second method employs lifting line method to calculate the local angle of attack on the V-tail and the pressure gradient effects from one lifting surface on another in close proximity. This method should reduce that uncertainty in the V-tail dynamics. For comparison of the two competing methods, fuzzy logic modeling techniques with nonlinear aerodynamic modeling capabilities are used for parameter identification of a large unmanned aerial system with a V-tail. Both methods fail to accurately capture nonlinear and unsteady aerodynamics such as yawing moments however, simulation results show moderate improvement in the quality of 6 DOF nonlinear models for longitudinal dynamics if the nonlinear projection method is used.