Static Test 99

Quick Links

Home

Propellants

Rocket Motors

Rockets

Rocket Electronics

Ground Support

Launch & Static Tests

Software

Links

Motor Class Table

E-Mail Scott

Don't Click Here!

This is another test of the erythritol propellant, for this test I added sulfur to try to increase the burn rate, and make the propellant easier to ignite. I used 65% granular KNO3, 32% granular erythritol and 3% sulfur powder. The dry ingredients were mixed by shaking for several minutes, then added the the melting pot at a preheated temperature of 275 degrees (F). The dry mix quickly melted and became a nice, pourable thick fluid. The propellant was cast into prepared castings stands lined with thin cardboard. Once cooled, the grains were cut to length and an extra inhibitor layer of aluminum foil tape applied.

After casting the grains I cast several strips of propellant for open air burn tests. After burning a couple of the strands, It seemed the propellant burned better than just plain KN/ER, but not much different from the last batch that used Fe2O3. Never the less, I was nervous about testing the propellant in a motor without doing any strand burn tests under pressure, so when I trimmed the grains to size, I reduced the total propellant weight.

When I went to assemble the motor, I was going to use a nozzle with a throat diameter of .32", then I chickened out, and used a nozzle with a throat diameter of .42".

Propellant Weight: .9226 pounds, 418.5 grams

Number of Grains: 4

Propellant Length: 9.875" (2.46875" each)

Diameter: 1.51"

Core Diameter: .63"

Kn:226, 248, 227

Nozzle Throat Diameter: .42"

Total Impulse: 47.18 pound seconds

Isp: 51.14

Burn Time: 2.753 seconds of recorded thrust

Peak Thrust: 31.14 pounds

Peak Chamber Pressure: ~200 psi

From looking at the thrust curve, it would appear the motor came to pressure quickly, it didn't. After pressing the ignition button down for some five seconds, I assumed the igniter had failed to light the motor, as I could see no smoke coming from the motor. I checked the power led on the launch controller, it was lit. I watched the motor for another 4 or 5 seconds, then finally a small stream of smoke appeared. Ever so slowly the stream of smoke increased, until after smoking some 20 seconds, the motor came to pressure and I could see thrust from my data acquisition screen on my PC. Once the motor came to pressure it seemed like a nice stable burn. After the thrust ceased, the motor continued to smoke for another 12 seconds or so. So I should have stayed with the .32" diameter nozzle, the Kn was way too low for this propellant.

I guess better safe than sorry, but this really was a waste of propellant. The only thing I really learned is that the sulfur didn't increase the burn rate dramatically. I'll have to repeat the test again using a smaller nozzle to increase the Kn.