Above is pictured the first of my 1.5" EMT conduit casing motors designated the T-1. EMT casing length was 12.5", with a top closure of 3/4" and a nozzledepth of 3/4", yeilding a grain length of 11". The nozzle was turned from cold rolled steel bar, with a convergent half angle of 30 degrees and a divergent half angle of 15 degrees and a throat diameter of .4". The T-1 was designed for an outside inhibited, core and end burning grain.
The first design of the T-1 used (8) 1/8" diameter steel pop rivets to retain the nozzle, and (6) #10-32x 3/8" machine screws to retain the top closure. I wasn't sure about the pop rivets, and my concern was justified as the first firing of the motor resulted in the nozzle blowing out. See launch test 15.
Prior to the next firing of the motor, the nozzle was reworked to included (8) 1/4" set screws, the top closure remained the same. In this test, the forward closure suffered a blow out in flight, resulting in a rather dramatic destruction of the rocket. See launch test 16. Despite several hours of searching, the motor was not found.
With the loss of the T-1 motor. It was aparent some changes were needed in the design of the T motor. While other dimentions all remain the same the throat area was increased to .42". I machined the nozzel with a groove in which the retaining screws would set, rather than threading directly into the nozzle as before. The theory was to keep the stress on the screws as shear stress only, not allowing any pulling stress from case expansion. The forward closure was drilled and tapped for a total of (8) 10-32 machine screws.
The T-2 motor was then static tested successfuly in two tests, see static test 19 & 20. And has since been launch tested in launch test 21. While the rocket lost its fins during the motor burn and made a premature hard landing, the motor performed flawlessly.
Future plans for the T-2 motor include using it in the booster stage of a 2 stage rocket.