CFD Analysis of Directional Stability for the American Challenger Rocket Car

This paper describes how computational fluid dynamics (CFD) has recently been used to design the directional stability components of the American Challenger racecar. Under development by Bill Fredrick, the missile-shaped, rocket-powered car is intended to break the World Land Speed Record, achieving a top speed greater than 800 mph. Designing a transonic car presents many unique challenges that are almost never encountered by land vehicles or aircraft. Previous papers [1, 2] on this project have described the use of the CFD++ flow solver in the selection of a rear strut profile and the positioning of the canard to achieve the desired pitching characteristics and aerodynamic loading. Following completion of these phases, the directional stability was examined at several sideslip angles and through a large range of speeds.

As with previous phases of the design, maintaining desirable aerodynamic performance through both subsonic and transonic flow regimes is difficult. While directional stability is easily achieved at low to mid-subsonic speeds, the changes in flow characteristics as the vehicle transitions to transonic speeds can yield drastic changes in surface force distribution. Conversely, design modifications that improve performance in the transonic regime can compromise stability at lower speeds. The current paper focuses on the process of designing and positioning the vertical tail to achieve adequate vehicle stability throughout the drive envelope.