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The mixture was then heated and melted in the usual manner. The PG was added at the end of the heating time to the melted propellant and stirred in rapidly until no visible steam appeared. The propellant was then poured into prepared, 2" x 6.5" PVC casting stands lined with light cardboard. Two 3/4" diameter wax covered steel rods were inserted to core the propellant grains.
Number of Grains: 3
Propellant Weight: 1.596 pounds
Grain Length: 3.5"
Core: .76"
Diameter: 1.9"
Throat Diameter: .5"
Kn: 205 initial, 236 maximum, 224 ending
Density: 0.06385 pounds per cubic inch
Total Impulse: 197.861 pound seconds
Isp: 123.97 seconds
Burn Time: 2.15 seconds
Peak Chamber Pressure: ~650 psi
Again, with this test the MS seems to slow the burn rate somewhat, it certainly takes the "edge off" the high peaks I often see in standard KNSU propellant. I didn't like the slow build up of thrust on this test though. I have a gut feeling the MS slows the burn because more water is retained, and I think the propellant is even more hygroscopic with the MS. As we move into summer, the humidity goes up. Even though I had these grains in a desiccant box for 3 days before testing, they did seem a bit tacky to the touch.
The Isp seems fine for a chamber pressure of about 650 psi. Notice the little hump at the 1.4 second mark. I believe that's the lower inhibitor going through the nozzle. That's really the same thing I've seen with most all sugar based propellants, they seem to have significant erosive burning, even at a core to throat ratio of 2.31 as in this case.
I'm not sure where I'm going with this, I may try the propellant again this summer and see how it performs in real humidity.