This was the first test of my new 1.125" diameter (29 mm) motor. Using KNER propellant in a motor this small provides some challenges. To get enough thrust, the motor must be fairly long, and to keep the propellant loading down the core must be fairly large. I ended up using 6 grains, about 2.5" long and .86" in diameter, with a .52" core.
I made a graphite nozzle for this motor, but my graphite is medium density, and looked a little too fragile when done. So I thought this would be a good chance to see how an aluminum nozzle held up. The burn should be just under one second, so perhaps the aluminum will hold up...
Total propellant load was about .35 pounds.
Being Mother's day, I did noon lunch with mom, then loaded up my van to do two static tests, the small 1.125" motor and another test of the ER1.75I motor. Being a rather windy, raw day for this time of the year. I went out to our farm pond to try to get out of the wind. Since I had two motors to test, I actually set up my table and chair, with the launch controller and computer on the table...
The 1.125" motor was set up, the computer was recording, all clear. 5,4,3,2,1 and ignition. The little more sort of poofed at ignition, burned a second or two then came to full thrust. It was quickly clear the motor was burning way too long, with a long tail off to thrust. So I went to the test stand and took a look at the nozzle, a rather large, gaping hole was visible where the once small throat had been. Oh well, it was worth a try.
Here's the time/thrust graph. You can see the motor came up to pressure, then the throat opened up and there was a long tail off of thrust.
Here is the nozzle propped up against the forward closure, a quarter is next to them for scale. It's hard to see in the picture, but the convergent cone is almost gone. The black ring you see on the upper inside is the o-ring, yes it burned all the way through.
Here's the divergent end. As you can see the throat is almost the same size as the exit.
No meaningful data on burn time, thrust or Isp can be derived from such a burn. The only data I gather from this test is that an aluminum nozzle isn't going to work on even a small motor.
The second test of the day, Static Test 124 went better. The ER1.75I had a nominal burn, but for some reason I can't find the data file from the test. I may try a file recovery program to see if it's still there somewhere. I'm not sure why it didn't save...