Static Test 65

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This test uses the propellant from batch XL-8 on the Xylitol page, 65% KNO3, 20% Xylitol, 15% sucrose. The previous batch I had used less sucrose and more xylitol, 25% to 10% respectively. I think I went with a little too much sucrose in this batch, as the propellant is getting the brittleness of standard KN/SU propellant. I broke one of the grains in two while removing it from its casting tube, that's why one grain is so much shorter and one longer than the others.


Here are the grain numbers:

1) 110.2 grams at 2.47"

2) 124.1 grams at 2.86"

3) 170.2 grams at 3.74"

4) 87.3 grams at 2.05"

Density: .0665 lb/ci

Kn: 244 initial, 280 max, 169 ending

Propellant Weight: 487.8 grams, 1.07541 pounds

Total Grain Length: 11.17"

I wanted to test the propellant at higher Kn's, and in a longer casing. The longer casing will leave room for a post combustion chamber area ahead of the nozzle. To that end, I made a new motor casing with a length of 20", leaving over 17" of actual internal chamber length.

I installed new batteries in my load cell amplifier, and recalibrated the load cell. I calibrate my load cell with a stack of lead weights that are first weighed on a digital shipping scale. The weights are stacked on top of an empty 2" motor casing, after calibrating I check the high end of the calibration by perching myself atop the stack of weights. I'm really glad no one is around to see it, it's quite the balancing act!

Here is the thrust/time curve of the test.

Here is the data from the test:

Burn Time: 1.067 seconds

Burn Rate: .4147"/second

Peak Thrust: 331.7 pounds

Total Impulse: 131.46 pound seconds

Isp: 122.4

Estimated Chamber Pressure: ~1,600 psi

It seems this propellant burned almost exactly the same as regular KN/SU sugar propellant, with a slightly lower Isp and a perhaps a slightly lower burn rate. Too much sucrose I think, I'll go back to a lower percentage of sucrose and try this again.