Stability study of spiral motion based on calculated flight data

To investigate the stability of spiral motion of spinning munitions in flight, a novel analytic method based on flight data is proposed. A mathematical model of spiral motion was established in body coordinate system. The partial dynamic stability condition of spiral angular movement was derived. It could be found by simulation and analysis of flight data that the spiral angles and their changing rates change periodically over time. The spiral motion of the body presents as the form of limit cycles when the body state is in partial dynamic stability, while, in partial dynamic instability, it presents the pattern of extending cycles. The spiral angles and their changing rates could be utilized to design a control loop. One possible control manner is that the opposite changing rate data of first half cycle could be used to improve spiral angle of late half cycle. As a result, the average spiral angle could be reduced by 17.3%.