Static Test 75

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This is the first test using fully cured xylitol/KNO3 propellant. Both the KN and the xylitol were in the granular form and melted at a setting of 225F. After 8 days I decided it was time to see if the grains had fully cured. I tested a grain by attempting to core it with a .5" drill bit. After drilling in about an inch, I removed the bit to see what the propellant looked like inside. It seemed very hard, so I proceeded to core these grains on my lathe using a .625" spade bit. Again, the grains cored easily with no gumming of the bit.

Here are the grain numbers:

Number of Grains: 4

Grain Length: 2.86" each

Total Propellant Weight: 1.1563 pounds

Grain Diameter: 1.6"

Grain Core: .625"

Kn: 183 initial, 211 maximum, 200 ending

Nozzle Throat: .5"

This grain geometry wasn't exactly what I wanted, I could see the Kn would be too low. But I didn't feel like making another new nozzle, so I went with what I had which was a .5" throat nozzle. I really wanted the Kn at about 240 to 260, but this being the first test of the fully cured propellant, I decided it was probably prudent to keep the Kn a little lower anyway.

Here is the motor at full thrust.

Here's the time/thrust curve from the test.

Here are the test numbers:

Burn Time: 3.284 seconds

Peak Thrust: 48.05 pounds

Total Impulse: 121.6 pound seconds

Isp: 105

Chamber Pressure: ~200 psi (estimated)

With such low chamber pressure the Isp of 105 is really very good. I have more grains cast that will allow me to run a higher Kn, I'm sure the performance will improve dramatically with the higher Kn.