One of the very first large solid rocket motor static tests that I witnessed was out at the RRS nearly ten years ago. That motor was huge, 12 inch diameter if I remember correctly. A couple of seconds into an 8 or so second planned burn the casing failed... spectacularly! The first thing I heard was Dave Crisalli on the PA system calmly declare "test complete!" I was hooked, this amateur rocket thing was for me.
Ok, so yesterdays failure was not nearly as spectacular, but a fraction of a second after ignition I heard Dave's voice in my head declare "Test Complete". I have a couple of theories on what went wrong and a ton of video that I will post. The likely cause of the failure was probably a combination of things, but I think the leading cause was not the motor design, but how we retained it to the "test stand" and the pressure port....more on that later.
In the first image you can see the motor is up to pressure. In the second image (separated from the first by 1/30th of a second) the bulkhead has been blown out of the casing. The third image shows one of the two camera's close to the motor and the pressure gauge in the lower right hand corner on their way out. The fourth image shows the casing and nozzle "landing" after a full ten seconds in the air.
I'll need to make a new casing and bulkhead, and with a few small adjustments to the design I should be ready to test again soon. There were a couple of interesting observations concerning the alloyed sugar propellant that I'll post once I get the videos in order. Overall, I think the KN/ER/SB has advantages over KNER or KNSB and I'm going to continue down this path for a while.