Static Test 102

70% KNO3, 30% Xylitol

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When using granular KNO3, xylitol makes for a very easy to cast propellant, so I decided to try to push the Isp up a little by increasing the percentage of KNO3 versus xylitol. Not only should it increase the Isp to about 141, but also reduces the cost of the propellant as the xylitol is about 5 times as expensive as the KNO3.

For this batch I dry mixed 550 grams total batch weight, once melted I stirred for several minutes, then poured/spooned the propellant into 2 prepared casting stands. I also poured (4) 1" CPVC pipe strands for burn rate tests.

The propellant was noticeably thicker, pouring the propellant into the 1/2" CPVC pipe proved difficult. It took a little prodding to get the propellant into the pipe.

Test#	Length	Start Pressure	End Pressure	Aver. Pressure	Time	Burn Rate	Density
st102-x1	1"	447.12	1033.7	740.41	3.117	.3208	.
st102-x2	1"	721.15	1365.4	1043.275	3.0	.3333	.
st102-x3	1"	331.73	817.31	574.52	4.15	.2409	.
st102-x4	1"	278.85	759.62	519.235	4.267	.2343	.
.	.	.	.	.	.	.	.

Here are the results of four strand burn tests I did on the 70/30 KNO3/xylitol. I should note these burn rates did not fall very well on the log burn rate line, so it looks like this propellant's a and n values are going to vary in the different pressures ranges. I wouldn't bet my life on four strand tests either, but here's the a and n values I came up with.

520 to 575 psi range: a= 0.0421, n= 0.275

740 to 1043 psi range: a= 0.1535, n= 0.112

What this would seem to indicate is that the propellant is more sensitive to lower pressures relative to burn rate, and less sensitive at higher pressures. Which would be a good thing to have, but again, with only four samples it's really hard to draw any hard conclusions. But this does give me a good starting point.