Static Test 78

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This test uses KNO3 and xylitol again, with a slightly higher Kn and more neutral burn profile. 4 of the six grains did use powdered KNO3, and 2 were standard grains using granular KNO3.

Number of Grains: 6

Total Grain Length: 15.15", 2.525" each

Total Propellant Weight: 1.65038 pounds, 748.6 grams

Grain Diameter: 1.6"

Core Diameter: .5"

Nozzle Throat Diameter: .435"

Kn: 306 initial, 355 maximum, 311 ending

Density: .0605 pounds per cubic inch

Burn Time: 2.534 seconds

Total Impulse: 215.47 pound seconds

Isp: 130.5

Peak Thrust: 212.35 pounds

Maximum Chamber Pressure: ~1,000 psi (estimated)

Well, here we go, the inverted "V" thrust curve. I'm becoming more convinced it's a result of running the propellant at higher chamber pressure. The problem is, the Isp of 130 is very nice, but to get the high Isp the propellant must run at higher chamber pressure which seems to lead to the odd thrust curve.