Design and aerodynamic characterization of a small UAV: stability and control derivatives

In the present thesis, an unmanned aerial vehicle (UAV) is designed in terms of wing geometry and control surfaces available on it to represent a wide range of civil aircraft. However, unlike civil jet aircraft, the UAV will have a V-Tail. The wing airfoil is chosen considering the UAV’s flight regime. The airfoil’s choice is done through two-dimensional CFD analysis at low to moderate Reynolds numbers. Due to the low computational power available, the analyses are done only for reduced angles of attack, which are representative of the flight condition of the cruise, and where the problem can be considered in the first approximation as steady-state. The CFD tool employed is ANSYS Fluent, and the Reynolds Averaged Navier Stokes equations are solved using the transitional model k −kl −w for the incompressible flow over the airfoil. A more detailed analysis is performed on a test case to do the mesh independence study and compare the obtained numerical results with the experimental values available in literature. With the found mesh and model settings, two different class of airfoil are investigated, and the best airfoil in terms of effectiveness is individuated for each airfoils family. The aerodynamic characterization of the UAV is done using XFLR5, open-source software that implements the panel method. Its numerical results are compared with the experimental results obtained for another UAV. The mesh independence study is conducted to individuate the optimal distributions of the panels and the best type of VLM. Therefore, the found XFLR5 settings are used for the UAV characterization. In the longitudinal static stability study, two wings are investigated. Thanks to the approximation of linear lift and moment at low angles of attack, the flight angle of attack and the elevator deflection are calculated. Thus, the wing that allows the plane to fly at a minimum angle of attack and minimum elevator deflection is chosen. Therefore, the sideslip angle’s influence on the UAV is examined. Finally, the control surfaces are studied, and it is showed how they affect the UAV’s dynamic. A finite-difference finite scheme is used to calculate the UAV’s aerodynamic and control derivatives, starting from the results obtained in XFLR5, where all the simulations are performed assuming small perturbations angles. The obtained results indicate that the UAV is statically stable, directionally stable, and the control surfaces can maneuver it. The UAV configuration seems to avoid the aileron-adverse yaw. However, the results obtained by XFLR5 need to be refined and validated using more accurate CFD analysis solving the RANS equations considering the effects of the parasite drag, and the fuselage. For doing that, the CAD file of the UAV would be used.