This page will detail the data from different experimental composite formulas. All of these are experimental and
should not be duplicated by others. This page is archival information for me and should only be used by others
to promote their own series of tests.
CXP13: 34% AP, 20% KP, 20% AN, 3% Mg, 3% Al, 15% R45M, 3.8% DOA, 1.2% Mondur.
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Length |
Start Pressure | End Pressure | Aver. Pressure | Time | Burn Rate | Density |
| CXP13a | 1" | 666.59 | 920.98 | 793.78 | 1.917 | .5216"/sec. | .05185 lb./cu.in. |
| CXP13b | 1" | 378.89 | 591.65 | 485.27 | 3.067 | .3260"/sec. | " |
| CXP13c | 1" | 477.98 | 763.60 | 620.79 | 1.166 | .8576"/sec. | |
| CXP13d* | 1" | 568.33 | 845.21 | 706.77 | 2.433 | .4110"/sec. | |
This next propellant is a basic AP/Al formula.
CXP 14: 72% AP, 5% Al, 18% R45M, 3% DOA, 2% I143.
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Length |
Start Pressure | End Pressure | Aver. Pressure | Time | Burn Rate | Density |
| CXP14a | 1" | 632.45 | 874.35 | 753.4 | 3.35 | .2985"/sec. | .055127 lb./cu.in. |
| CXP14b | 1" | 338.08 | 606.22 | 472.15 | 2.717 | .3680"/sec. | |
| CXP14c | 1" | 378.89 | 585.82 | 482.355 | 4.5 | .2222"/sec. | |
| CXP14-2d | 1" | 276.88 | 466.32 | 371.6 | 5.2 | .1923"/sec. | |
| CXP14-2e | 1" | 597.47 | 842.29 | 719.88 | 2.783 | .3593 | |
| CXP14-2f* | 1" | 813.15 | 1037.6 | 925.375 | 4.85 | .2062 | *tape applied |
| CXP14g* | 1" | 460.49 | 772.34 | 616.415 | 4.716 | .2120 | *tape applied |
The burn rates are about what I expected, with the exception of sample 14b. Once in a while you get a strange burn rate, perhaps the igniter threw a large spark that burned through the inhibitor and started the grain burning at mid point. That's another good reason to do a few extra tests, to get a good average. I decided to go ahead and cast some grains for a test motor. The second batch will be designated 14-2. I kept the same formula except that I used Mondur MR as a curative, and added the extra weight as DOA. For this batch I'm going to use a 1.5" EMT casing I have, and make a new nozzle for it. The grains were cast in 1.25" PVC pipe that was turned down on the lathe to fit inside the EMT case.
For a 400 gram batch here are the amounts used.
R45M 18%=72.0 grams
DOA 3.56%=14.24 grams
Aluminum 325 mesh 5%=20.0 grams
AP 90 micron 14.4%=57.6 grams
AP 200 micron 57.6%=230.4 grams
Mondur MR 1.44%=5.76 grams
After mixing the R45 and the DOA I vacuum degassed it for about 5 minutes. The aluminum was then added and stirred in by hand with a wooden dowel. The 90 micron AP was added next and stirred in, then the 200 micron AP was stirred in. Once all the AP was coated, I used a hand mixer on the lowest speed to mix all the ingredients. It was thin enough that the hand mixer just worked, much thicker and it wouldn't have had the power to mix it.
I then degassed the propellant for a little over an hour. I'd degas for 15 minutes, then open it up and give the propellant a stir, close it up and degas again for 20 minutes and stir again. I did that three times before the final degassing of about 20 minutes.
Finally I mixed in the Mondur MR curative by hand, trying to mix it well without adding any air to the propellant. The mix was not pour able, but close. I would push it out of the bowl and it would flow into the casting tubes in a thin ribbon. I had just enough propellant to fill the four casting tubes and make three test strands for the strand burner. I'll do a test strand or two before firing the motor just to be safe.
CXP15: AN 68%, R45M 15%, Mg 12%, DOA 5%, Mondur MR .6grams. 50 gram batch (50.6grams total)
| Test# | Length | Start Pressure | End Pressure | Aver. Pressure | Time | Burn Rate | Density |
| CXP15a* | 1" | 367.23 | 568.33 | 467.23 | 3.566 | .2804"/sec. | |
CXP17: R45M 15%, DOA 5%, Al 10%, AP 200 micron 25%, KP 25%, KN 20%. (Mondur MR 1.5% of total) Isp 205, 4,060 F., Gamma 1.2275, C* 4355.9, Density .0687 lbs./cu in.
| Test# | Length | Start Pressure | End Pressure | Aver. Pressure | Time | Burn Rate | Density |
| CXP17a | 1" | 463.41 | 617.88 | 540.645 | 6.783 | .1474 | .05733 lbs./cu in |
| CXP17b | 1" | 612.05 | 763.6 | 687.825 | 6.044 | .1654 | |
| CXP17c | 1" | 556.67 | 679.08 | 617.875 | 5.55 | .1802 | |
| CXP17d | 1" | 195.27 | 294.37 | 244.82 | 10.75 | .0930 | |
| CXP17e | 1" | 317.68 | 443.01 | 380.345 | 8.534 | .1172 |
For these burn rate tests I made a new batch of igniters. I had been making them about like motor igniters and I think they were a little too hot for the strands, and on some tests they were lighting the grain away from the end and giving to fast burn rates. So these igniters used a single thin dip of pyrogen. The only test I'm going to throw out is 17c, above in yellow. Test 17c sample strand failed to ignite on its first attempt, so I used a second igniter on the same strand, it resulted in a faster burn rate. I suppose some of the propellant burned off, or vaporized slightly in the first ignition attempt.
Using the four tests above, the c=0.0041, n=0.567. Using "Burn Rate" software the burn rates all fell right on the log rate burn line. This should make for a nice propellant, using only 25% AP and 10% aluminum it would be fairly inexpensive as well. The physical properties are very nice as well, a nice firm yet very flexible propellant that is easy to mix and cast. The only draw back I can see is that it's fairly hard to start, and may require a vigorous igniter.
Static Test 53: I cast some grains for a small test motor. Using FPRED software to predict the chamber pressure and thrust and the c and n numbers from Burn Rate. According to the software I should have had a max chamber pressure of 376 psi and a burn time of about 4 seconds. The Kn was 338 initial to 409 maximum.
The motor didn't ignite on the first two attempts, and I was using some hot composite igniters too. Finally on the third attempt the motor lit, chuffed twice, then thrusted hard for a fraction of a second and blew out the nozzle. I recovered the upper two grains, very little propellant had burned off. The surface of the grains was odd, it was deeply pitted. It appeared some of the propellant had burned quickly and deeply into the grain.
The recovered grains were hard to dispose of too, I couldn't get them to burn by themselves. I had to use some other propellant scraps just to get them started. Once started, they burn well but slowly.
This doesn't seem to be a viable combination for some reason. It really has too many different chemicals in it anyway. I don't think I'll pursue this combination further.
CXP19: AN 68%, AP 10%, Polyester Resin 20%, Charcoal 2%.
1" PVC (1.01") x 2.5" =32.2 grams each
Density 0.0707, Temp. 4510F, Gamma 1.2115, C* 4094.16, Isp 189.
This propellant is based on KP (potassium perchlorate) and epoxy. The epoxy used was garden variety (Hobby Lobby) 30 minute epoxy. There are some drawbacks to using KP. As a rule propellants made from KP have high burn rates with a high pressure exponent. So you may question why use a KP based propellant?
With that in mind I'm sure a KP based propellant will need a very neutral grain geometry to keep chamber pressure steady.
| Test# | Length | Start Pressure | End Pressure | Aver. Pressure | Time | Burn Rate | Density |
| CXP20a | 1" | 308.94 | 568.33 | 438.635 | 1.767 | .5659 | .0 lbs./cu in |
| CXP20b | 1" | 262.31 | 542.1 | 402.2 | 2.033 | .4919 | |
| CXP20c | 1" | 212.76 | 512.95 | 362.855 | 1.15 | .8695 | |
| CXP20d | 1" | . | . | . | . | . | |
| CXP20e | 1" | . | . | . | . | . |
The first two tests were fine, the third test shot the first two down. This happens once in a while, I'm not sure why but I can only guess that the test strand for whatever reason starts burning in the middle of the strand. Regardless, the burn rate is higher than I want. I'm sure I can leave the iron oxide out for the next test.
CXP21: KP 69%, KN 10%, Epoxy 21%.
| Test# | Length | Start Pressure | End Pressure | Aver. Pressure | Time | Burn Rate | Density |
| CXP21a | 1" | 160.3 | 413.9 | 287.1 | 1.584 | .6313 | .0 lbs./cu in |
| CXP21b | 1" | 174.87 | 405.12 | 289.995 | 1.267 | .7892 | |
| CXP21c | 1" | . | . | . | . | . | |
| CXP21d | 1" | . | . | . | . | . | |
| CXP21e | 1" | . | . | . | . | . |
Interesting, CXP21 has faster burn rates than CXP20. I wouldn't have thought that. It is also harder to burn in the open air, where CXP20 burns pretty well, CXP21 starts then goes out. Moving in the wrong direction with this formula.
CXP22: KP 72%, Epoxy 21%, Iron Oxide 7%.
Theoretical: C* 3757, Temp. 4086F, Density .0741 lbs./ci, Gamma 1.205, Isp 174.
I suspected the iron oxide was stabilizing the burn, so with this batch I went to 7% iron oxide. It definitely helps the combustion stability, in open air it burns very well, much better than in the previous tests.
| Test# | Length | Start Pressure | End Pressure | Aver. Pressure | Time | Burn Rate | Density |
| CXP22a | 1" | 171.96 | 378.89 | 275.425 | 2.95 | .3389 | .0636 lbs./cu in |
| CXP22b | 1" | 148.6 | 323.51 | 236.05 | 3.233 | .3093 | |
| CXP22c | 1" | 469.24 | 746.11 | 607.74 | 1.833 | .5455 | |
| CXP22d | 1" | 367.23 | 644.11 | 505.67 | 1.95 | .5128 | |
| CXP22e | 1" | . | . | . | . | . |
Grains:
1) 3"x1.88" diameter .76" core 198.1 grams
2) 3.02"x1.88" .86" core 190.8 grams
3) 2.28"x1.88" .86" core 143.9 grams
Kn: 114 initial, 120 max.
Nozzle: .625" throat, .85" exit cone
Predicted Max Pressure: 362 psi
To speed up the process, I measured out the KP and Fe2O3 in advance in separate paper cups. The epoxy was then weighed into the Pyrex mixing vessel and stirred for one minute. The Fe2O3 was then added and mixed for one minute, the mixing was done by hand using a wood dowel. The KP was added all at once and mixed by hand with a pastry blender. The first impression is that there is no way this is all going to get mixed into the epoxy, but after a few minutes of hard mixing it starts to smooth out and become a homogeneous mixture. I continued to mix with the pastry blender, occasionally scraping the sides down with the dowel. After six minutes of mixing I began loading the casting tubes.
I used 2" vacuum tubing to cast in. The vacuum tubing fits nicely into my 2" PVC support stands. I applied wax paper to the bottoms of the stands, and wrapped my coring tools with wax paper as well. The coring tools were inserted into the stands and the propellant was rolled into strands and dropped into the casting tubes, the propellant was then packed into the casting tube using a wooden dowel. This was repeated until all the casting tubes were full. I finished packing in the propellant 17 minutes after the epoxy was first mixed. I then cleaned up the mixing vessel and tools with alcohol and went back to check on the propellant, it was 26 minutes after the epoxy had been mixed and the propellant was now warm to the touch and firm.
I had mixed up a total batch weight of 550 grams, and I fell a little short as the last grain was only filled to 2.25". Density of the grains was measured at .06343 lbs./ci.
Total Propellant Weight: 532.8 grams, 1.1735 pounds
I let the grains cure for another hour or so, then removed them from the casting stands. The grains looked very good, came out easily and the wax paper removed from the core and bottoms with little trouble. I started prepping the motor casing. I had purchased some EPDM rubber sheet. I found a local green house that sold it as pond liner. It was advertised as 45 mil, or .045" thick. Once the rubber sheet was cut to size, I used high temp RTV silicone to seal the joint in the liner.
CXP23: KP 70%, Epoxy 21%, Iron Oxide 5%, -325 mesh Al 3%.
Density .0739, C* 3883, Gamma 1.2, temp 4392F, Isp 181 @ Pc500 psi.
| Test# | Length | Start Pressure | End Pressure | Aver. Pressure | Time | Burn Rate | Density |
| CXP23a | 1" | . | . | . | . | . | .0604 lbs./cu in |
| CXP23b | 1" | . | . | . | . | . | |
| CXP23c | 1" | . | . | . | . | . | |
| CXP23d | 1" | . | . | . | . | . | |
| CXP23e | 1" | . | . | . | . | . |
Density .0675, C* 3693, Gamma 1.1721, temp 3894F, Isp 194 (Theoretical at 1,000 psi).
| Test# | Length | Start Pressure | End Pressure | Aver. Pressure | Time | Burn Rate | Density |
| CXP24a | 1" | 346.2 | 418.3 | 382.25 | 8.05 | .1242"/sec | .0593 lbs./cu in |
| CXP24b | 1" | 620.0 | 745.2 | 682.6 | 5.40 | .1852 | |
| CXP24c | 1" | 730.8 | 865.4 | 798.1 | 5.133 | .1948 | |
| CXP24d | " | . | . | . | . | . | |
| CXP24e | " | . | . | . | . | . |
c=0.0029, n=.632
This is very interesting. A very slow burn rate with a good pressure exponent. In fact, this propellant burns in almost the same way AN/Mg/R45 burns, with a little better density and somewhat lower Isp. I'm a little reluctant to believe I'll get anywhere near an Isp of 194, but, this looks promising. I'll have to cast some grains and see how it does in a motor.
Static Test 73 (CXP24)
I went on with casting a set of grains. I wanted to keep the batch size small so if I run into problems I don't waste a lot of chemicals. So I decided to use 1.25" PVC pipe turned down on the lathe as casting tubes. The batch size was 410 grams and was prepared exactly the same as the test batch used for the strand burns. Density was a little better, measured at .0601 lb/cubic inch.
Here are the grain numbers, all have a .5" core.
1) 2.11" @ 67.8 grams
2) 2.11" @ 68.5 grams
3) 2.12" @ 70.3 grams
4) 2.12" @ 70.1 grams
5) 2.07" @ 68.5 grams
Total Grain Length: 10.53"
Total Grain Weight: .76103 pounds, 345.2 grams
Nozzle Throat: .2968" diameter
Kn: 416 initial, 462 max, 408 ending
This motor burned for about 10 seconds, chuffing the entire time with no recorded thrust.
Static Test 74 (CXP24)
I cast another set of larger grains for the motor increasing the Kn to a maximum of 650. I had the same result as the first test, the motor had a long burn and chuffed the entire time with no recorded thrust. I had suspected I may need to add some IO to stabilize the burn, and now I'm pretty sure I'll have to. Of course, a new set of strand burn tests will need to be performed as well.
Just a few notes on density. I use 1/2" cpvc pipe 1" long, it weighs 3.6 grams empty. It has a volume of .178610 cubic inches. So a factor of 5.59879x is added to the actual propellant weight of the strand to obtain the density in pounds per cubic inch.
For example, in CXP 23 above. My strand sample weighed 8.5 grams.
8.5 - 3.6 (empty weight)=4.9 grams propellant weight.
To convert grams to pounds: 4.9(grams)/454=.01079295 lbs.
.01079295x5.59879=.0604 lbs./cubic inch
While it is a rather small cylinder to get accurate measurements from, it does give me a good idea of how the propellant is doing in terms of density. Chem-II calculated an ideal density of .0739 lbs./ci. My measured density was .0604, or about 81.7% of theoretical. That's not a very good percentage, I'd like it around 90% or better. I really thought the density would have been higher, after cutting into a few of the propellant samples there were no visible voids or bubbles. I'm sure there is microscopic voids, well, there has to be I guess. Vacuum degassing I'm sure would help but using a 30 minute epoxy doesn't leave much time for degassing.
I inspected a few cut strands under my microscope. It really looked pretty good, while there are some small voids, they are very small. About the same size as the KP particles, and they really aren't as frequent as I would have imagined. It's possible the epoxy is lighter than the software is predicting as well, and my density may be better than I think.
CXP25: 65% KP, 20% Mr. Fiberglass Epoxy, 15% Al
Theoretical Properties: Density 0.0734, C* 4351.994, Temp. 5671, Gamma 1.1832, Isp 204.6
I started by mixing the epoxy into a plastic container, then added the aluminum and mixed thoroughly, the KP was then added and mixed again. The mixed propellant had a very putty like texture, and pressed into the small cpvc tubes easily. This was a small test batch of 50 grams cast into (6) 1" cpvc test strands, and a couple of unrestrained strands for open air burn tests.
I formed a small amount of the uncured propellant into a small strand, then lit it to see what would happen. It lit fairly easily, and burned slowly and steadily with a bright orangish-white flame and some white smoke, throwing an occasional white spark now and then.
| Test# | Length | Start Pressure | End Pressure | Aver. Pressure | Time | Burn Rate | Density |
| CXP25a | 1" | 451.92 | ~1,900 | 1175.96 | .583 | 1.715"/sec. | . lbs./cu in |
| CXP25b | 1" | . | . | . | . | . | |
| CXP25c | 1" | . | . | . | . | . | |
| CXP25d | 1" | . | . | . | . | . | |
| CXP25e | 1" | . | . | . | . | . |
CXP26: 68% AP(200 mic), 17.5% R45, 13% Al, 1.5% Mondur MR
I made a 100 gram batch of this composite formula to make some igniters for KN/ER motors. I am hoping the AP based igniters will be more effective in bringing the erythritol based propellant motors to pressure in a timely manner. I'll have to do a few tests to see how much pressure they induce in a motor, I don't want to fracture the propellant either. I made 12 igniters from this batch, 4 each of 1", 1.5" and 2" soda straw tubes.
I also cast another 8, 1" soda straw sections for burn rate tests, and one grain cast in thin walled 3/4" PVC pipe, which has an actual inside diameter of .9". I've been thinking of making a small rocket, and this would make a nice little two grain "G" class motor.