Acquiring and Modeling Unsteady Aerodynamic Characteristics

In order to develop and demonstrate a systematic approach to assessing and modeling dynamic characteristics for advanced configurations, a comprehensive dynamic wind tunnel test program was conducted for the F-16 and the F-22 at the 12-ft Vertical Wind Tunnel at WPAFB. Using the recently-developed Multi-Axis Test rig, body-axis forced oscillation, velocityvector steady rotation, and the new combined motion tests were performed from 0° to 90°α and 0° to 30°β. Both configurations exhibited linear and nonlinear dynamic characteristics along with variations due to sideslip, particularly in the stall and immediate post-stall region. These dynamic effects were organized into an aerodynamic math model for simulation applications while preserving all the nonlinear characteristics. Combined motion results were contour-plotted to reveal the multidimensional dependencies for the vehicle's dynamic characteristics and were used as the reference to evaluate the effectiveness of the existing dynamic mechanization techniques. Simulation overdrive comparisons clearly demonstrated the importance of the rotary terms as well as nonlinear expression of the body-axis forced oscillation-damping data in the aerodynamic model build-up. Additionally a new "Excess Roll Rate" mechanization algorithm was formulated and tested to demonstrate its effectiveness.