Experiment and Numerical Analysis of a Rotating Hollow Cylinder in Free Flight

The present purpose is to reveal the mechanism of a flying pipe from an aerodynamic point of view. At first, we conduct field observations of a flying pipe using a pair of high-speed video cameras, together with three-dimensional motion analyses. In addition, we conduct numerical analyses by a finite difference method based on the MAC scheme. As a result, the observed orbit is approximated to be not an obvious parabolic curve but rather a straight line, after an initial instable and complicated curve. The stable flight with this approximately-straight orbit suggests the importance of aerodynamics in flying mechanism. More specifically, the model is in an unstable and complicated flight during an initial flight, afterwards becomes in a stable and approximately-straight flight. In the initial instable and complicated flight, the model flies fluctuating its posture upward, downward, left-ward and right-ward. As flight distance increases, the absolute value and the amplitude of moment becomes small to zero. During such a decaying and stabilising process, the gyroscopic effect plays a primary role balancing not angular acceleration of the model but aerodynamic fluid moment. In the stable and approximately-straight flight, the flow in the stable and approximately-straight flight is nearly the velocity-potential one, and accompanies very-small drag force. And, we could ignore the influence of model’s rotation upon the flow and the orbit. In this context, the model’s rotation is only to stabilise its posture, and gives negligible contribution upon its aerodynamics.