Minimal modeling of rocket roll response and aerodynamic disturbance in wind tunnel

Abstract

The roll dynamics of a 5 kg, 1.3 m high sounding rocket are analyzed in a vertical wind tunnel. Significant turbulence in the tunnel makes the system identification of the effective inertia, damping and asymmetry with respect to roll challenging. A novel method is developed which decouples the disturbance from the rocket frame's intrinsic roll dynamics and allows accurate prediction of roll rate and angle. The parameter identification method is integral-based, and treats wind disturbances as equivalent to a movement in the actuator fins. The method is robust, requires minimal computation, and gave realistic disturbance distributions reflecting the randomness of the turbulent wind flow. Two models, one with constant damping and one with fin angle dependent damping were considered. The mean absolute roll rate of the rocket frame observed in experiments was 16.4 degree/s and both models predicted the roll rate with a mean absolute error less than 0.10 degrees/s with a standard deviation less than 0.08 degrees/s. The roll angle (measured by an encoder), was tracked by the model with a mean absolute error less than 0.20 degrees and a standard deviation less than 0.15 degrees. These results prove the concept of this minimal modeling approach which will be extended to varying wind speed, and pitch and yaw dynamics in the future.