Direct Evidence of Spatial Burning Rate Variation as Cause of Midweb Anomaly

With the use of the ultrasonic pulse-echo technique, local burning rates are measured at different radial locations across the web during static tests of center-perforated solid propellant rocket motor grains. The measurement shows a higher burning rate in the midweb region and a lower burning rate toward the port and motor case. The measured motor pressure history could be very well simulated by using the measured local burning rates. Thus, direct evidence is provided that the variation of the burning rate across the web is the cause of the midweb anomaly in chamber pressure widely reported in solid motors with center-perforated grains. (Author)