A CFD Database for Airfoils and Wings at Post-Stall Angles of Attack

This paper presents selected results from an ongoing effort to develop an aerodynamic database from Reynolds-Averaged Navier-Stokes (RANS) computational analysis of airfoils and wings at stall and post-stall angles of attack. The data obtained from this effort will be used for validation and refinement of a low-order post-stall prediction method developed at NCSU, and to fill existing gaps in high angle of attack data in the literature. Such data could have potential applications in post-stall flight dynamics, helicopter aerodynamics and wind turbine aerodynamics. An overview of the NASA TetrUSS CFD package used for the RANS computational approach is presented. Detailed results for three airfoils are presented to compare their stall and post-stall behavior. The results for finite wings at stall and post-stall conditions focus on the effects of taper-ratio and sweep angle, with particular attention to whether the sectional flows can be approximated using two-dimensional flow over a stalled airfoil. While this approximation seems reasonable for unswept wings even at post-stall conditions, significant spanwise flow on stalled swept wings preclude the use of two-dimensional data to model sectional flows on swept wings. Thus, further effort is needed in low-order aerodynamic modeling of swept wings at stalled conditions

Coordinated Control of Multiple UAVs : Theory and Flight Experiment

This paper proposes a nonlinear control law to realize a coordinated flight of multiple UAVs and evaluates its performance through flight experiments of small fixed-wing UAV platforms. Assuming all-to-all communication, a decentralized coordination control system is designed based on a virtual leader approach. The proposed control design uses a potential function defined on a phase distribution of multi agents. Two advantages of this coordination controller are; i) it can be applied to make different coordination configurations, ii) it is applicable to any number of UAVs, and so it can easily treat an event of addition/deletion of UAV units in a coordination team. The proposed coordination control law is proven to be locally asymptotically stable by using Lyapunov indirect method, and its large domain of attraction is observed in simulation. Furthermore, the controller is implemented onboard ONERA fixed-wing UAV platforms and tested with a mission scenario which includes four different coordination configurations