Modeling Full-Envelope Aerodynamics of Small UAVs in Realtime

This paper focuses on full six degree-of-freedom (6-DOF) aerodynamic modeling of small UAVs at high angles of attack and high sideslip in maneuvers performed using large control surfaces at large deflections for aircraft with high thrust-to-weight ratios. Configurations such as this include many of the currently available propellerdriven RC-model airplanes that have control surfaces as large as 50% chord, deflections as high as 50 deg, and thrust-to-weight ratios near 2:1. Airplanes with these capabilities are extremely maneuverable and aerobatic, and modeling their aerodynamic behavior requires new thinking because using traditional stability derivative methods is not practical with highly nonlinear aerodynamic behavior and coupling in the presence of high propwash effects. The method described in this paper outlines a component-based approach capable of modeling these extremely maneuverable small UAVs in a full 6-DOF realtime environment over the full envelope that is defined in this paper to be the full ±180 deg range in angle of attack and sideslip. This method is the foundation of the aerodynamics model used in the RC flight simulator FS One. Piloted flight simulation results for four small RC/UAV configurations having wingspans in the range 826 mm (32.5 in) to 2540 mm (100 in) are presented to highlight results of the high-angle aerodynamics modeling approach. Maneuvers simulated include tailslides, knife edge flight, high-angle upright and inverted flight (“harriers”), rolling maneuvers at high angle (“rolling harriers”) and an inverted spin of a biplane (“blender”). For each case, the flight trajectory is presented together with time histories of aircraft state data during the maneuvers, which are discussed.