700 gram batch:
17.55% R45: 122.85 grams
12.00% Al: 84 grams
68% AP: 476 grams
2.45% I143: 17.15 grams
This batch was hand mixed and not de-gassed. I cast into 3) 3" long PVC vacuum tubes with an internal diameter of 1.9"
Grain 1) 175.6 grams, 3.1"
Grain 2) 175.1 grams, 3.1"
Grain 3) 164.3 grams, 3.0"
Propellant Weight: 1.1354 pounds, 515 grams
Propellant Length: 9.2"
Outside Diameter: 1.9"
Core: .75"
Throat: .54"
Kn: 157, 174, 157
Density: 0.05159 pounds/cubic inch
I was waiting to test this motor until after NASA's launch of the Atlas V mission to Pluto, but the launch was on hold. So it gave me a chance to set up the test stand and equipment. Still no Atlas V launch, so...
All clear; 5,4,3,2,1 and ignition. Pop! Then nothing, I used a sugar igniter, it didn't do the trick. So I waited several minutes and installed a composite soda straw igniter.
All clear; 5,4,3,2,1 and ignition. A little smoke, then a little more smoke, then a small flame, then
The motor took off all at once. Click Here for a short video of the test.
It was a very nice burn, very clean with little smoke, as would be expected with the high aluminum content. A longer burn than expected too. As soon as the motor quit burning I went out to see how hot the casing was. This was the casing I had anodized a nice blue. The casing was cool enough I could handle it by hand. So I brought the casing in and started analyzing the data.
Here is the thrust/time curve.
The data:
Burn Time: 3.966 seconds
Total Impulse: 214.79 pound seconds
Isp: 189.17
Peak Thrust: 64.73 pounds
Peak Chamber Pressure: ~210 psi
You've got to love the nice flat thrust curve of AP based propellants. I've said it before, and I'll say it again. I think APCP is easier to work with than sugar propellants. I really disagree with the common conception held by many, that EX'ers should start with sugar because it's easier. I'm going to guess that concept has been propagated by APCP builders that haven't worked with sugar. I was a little surprised at the long burn of this motor, of course I like to start with fairly low Kn's to be on the safe side, and increasing the Kn would shorten the burn time considerably I'm sure, as well as increase the Isp.
Speaking of Isp, the calculated 189 Isp was very good considering the low chamber pressure. I calculated Isp's in Chem 2 on this burn at 210 psi, and a burn at 750 psi, the difference is 33 seconds. So, should this hold true, at 750 psi I should be able to get an Isp of about 220 out of this propellant. Now that would be a treat!