Rocketman, you are right. I don't know what I was thinking; chamber pressure is not the same as hoop stress. Looking at the other article I mentioned, Bell calculated the chamber pressure by measuring the hoop stress via a strain gauge mounted on the barrel. The strain gauge measures the hoop stress, which can then be used to calculate the chamber pressure. The photos of his pressure traces show the 'EST' pressure, so I imagine he caliberates the output of the strain gauges to trace the hoop stress curve in terms of chamber pressure, easy to do since hoop stress is directly proportional to chamber pressure.

Last edited by KirkD; 03/06/12 09:53 AM.