Minimal modelling approach to describe turbulent rocket roll dynamics in a vertical wind tunnel

Abstract

The roll dynamics of a 5-kg, 1.3 -m high sounding rocket are analysed 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-dependant damping were considered. The mean absolute roll rate of the rocket frame observed in experiments was 16.4°/s and both models predicted the roll rate with a mean absolute error less than 0.10°/s with a standard deviation less than 0.08°/s. The roll angle (measured by an encoder), was tracked by the model with a mean absolute error less than 0.20° and a standard deviation less than 0.15°. These results prove the concept of this minimal modelling approach which will be extended to varying wind speed, and pitch, and yaw dynamics in the future.

Minimal modeling methodology to characterize non-linear damping in an electromechanical system

“…(4) and (5), an integral based approach is used. The concept was first developed on first order differential equations [10], and in this section is extended to second order differential equations. Eq.…”

“…Furthermore, this approach allows an integral based method for parameter identification to be developed that linearizes the optimization problem. This identification method has been validated in biomedical applications which tend to involve coupled first order systems [11,8,27,9], and rocket roll dynamics which are overdamped and first order [10]. The extension to second order systems is not straightforward as dynamics can be significantly oscillatory and initial conditions involve derivatives.…”

Vertical Wind Tunnel for Prediction of Rocket Flight Dynamics

“…In a standard horizontal wind tunnel there is extra friction since an additional moving surface, like a bearing is required, so roll response is less realistic. For pitch and yaw dynamics, a gimbal frame [13] is used to allow three˝of freedom control. This gimbal frame set up is important for debugging the avionics control hardware and software before flight.…”

The Development of Rocketry Capability in New Zealand—World Record Rocket and First of Its Kind Rocketry Course

“…The approach of UC Rocketry is to use off-the-shelf high-power solid propellant rocket motors and to manufacture simpler robust rocket vehicle designs that have the capability of testing instrumentation, sensors and control algorithms. This philosophy includes minimal modeling of the major rocket dynamics where complexity is only added if it results in a significant improvement to the rocket response and an increased understanding of the major mechanisms involved [31].…”