Tests of Smokeless Powder in Simulated Rocket Recovery
July 28, 2001
This is the long, chatty version - with more pictures and detail.
Click Here for the somewhat shorter, more concise version with better tables.
Construction of the test device
Series 1: Constrained vs. unconstained powder charges
Series 2: Finding the upper limit powder charge
Series 3: Finding the lower limit powder charge
Series 4: Tests using black powder
Series 5: More constrained powder tests
Series 6: Long-barrel tests
Discussion and conclusions
A topic arose on the Arocket discussion list a month or so back regarding alternatives to black powder as the ejection charge for recovery systems in amateur rockets. Mr. Thomas Engelhardt indicated that a nitrocellulose paper was being used successfully in Germany. I am not familiar with this paper and wondered if it is even available here, so I began to think about other possible sources of nitrocellulose, namely ping-pong balls, New Skin, and smokeless gunpowder.
The last of these seemed to hold the most promise, and I happened to have some in the cabinet. So I ran a few quick-and-dirty tests using one of the larger Estes models, and found that a gram of Red Dot provided a satisfactory ejection of old underwear and a light plastic nose-cone.
Upon reporting this to the Arocket list, Mr. William Westfield directed me to a website by Mr. Scott Aleckson, who describes his experiments with smokeless powder ejection charges. Mr. Aleckson reported some favorable outcomes, and suggested that powder should be contained in a case to ensure complete burning and thus good performance. A number of Arocket list members echoed this opinion, and suggested a variety of containment vessels.
But my first tests had obtained a strong, smooth ejection without such containment. Realizing that I already had everything needed, that assembling test devices would be quick and easy, and that I would get to light many fuses with little fear of injury or arrest, this adventure met all of my criteria. I decided to do some testing. Secondary benefit: it might yield useful information.
Construction of the test device
Ever the pack-rat, I found a 2-inch PVC tube in my scrap-heap with a male threaded adapter and a female screw-cap. The total length including cap is 12 inches. This seems to me a reasonable approximation of the recovery section of a modest-sized amateur rocket, and will hereafter be called the "tube."
A simulated ejection load is assembled by wadding up three double-page sheets of newspaper and ramming them down into the tube with an old hardwood chair-leg, one sheet-wad at a time.
Just to make sure we have absolute clarity here, the item on the left is what I am calling a "double-page sheet" while the one on the right is a "single-page sheet." For consistency, I used only common newsprint, no slick paper, and all pages the same sizes.
The newspaper wads are pushed down a bit from the muzzle and a golf-ball is placed on top. One single-page sheet is wadded up and pressed over the golf-ball to hold it in place. The golf-ball is to simulate the weight of a nose-cone. The fact that it will be pushed down into the tube before firing creates one of many discrepancies between these tests and a real-rocket ejection.
I test the resistance to load movement by placing small cans filled with lead on the top wad until the weight moves the load column. Two of the cans are enclosed in denim "socks" to make them friendlier to handle but don't be fooled, each weighs a bit over 4 pounds. All together the three cans-o-lead weigh 13.5 lbs.
Finally, a clean, white paper towel is placed on the powder-side of the load column, to register the effects of the burning powder charge.
Here is a load that has been pressed, then disassembled:
And here is a load on the scale (previously-fired, test #3). All together it weighs 113 grams.
Series 1: Comparison of pressure-contained vs. unconstrained charges.
Test 1 - Unconstrained charge
I start with an uncompressed powder charge. In all but one of thest tests, I am using Red Dot, a fast-burning double-based powder used in light shotgun and pistol cartridges. My can of Red Dot is about 20 years old. It does not seem to have degraded significantly: Perhaps that assumption should be tested.
I cut a piece of double-ply paper towel (Bounty) about 2" square, pour on it 1 gram of Red Dot, lay a thin fuse on it, and tie it into a tidy bundle with thread. Isn't it cute! The fuse is inserted through a 1/16 inch diameter hole in the side of the PVC pipe, drilled about an inch from the end of the tube. Note that the botttom wad of the ejection load is about 1/2 inch from the hole. I will endeavor to keep this distance consistent in these tests to minimize differences in headspace, except for the the last two tests where there was a rationale for moving the load forward. The cap is screwed on, and the fuse is anxious to be lit!
The tube is fastened to my picnic-table with a band-clamp. Here, the odd flare at the muzzle-end comes in handy. The tube is a remnant from another project, and the flare is a connector which I cut off with my chop-saw. It now serves the purpose of keeping the tube level with the table, as well as preventing the it from flying backward if there is significant recoil.
So here is the first shot. The golf-ball and wads first hit the ground about 15 feet from the muzzle of the launcher. The wads scattered themselves near that spot, while the ball bounced and rolled to 31 feet. Note that the ground is neither level nor even. There are some hazards on this curse, er... course.
And please do not call PETA on me - the cat was nowhere near when I fired this thing. She spent the remainder of the day in the house, being entirely too curious about my stuff. Most of the cats are either smart enough to get scared when they see a lighter, or lazy enough to pay no attention. Here is an example of the latter:
The paper-towel wad was examined for damage. It fell about 8 feet from the muzzle, smoldering at one point. Remnants of the powder-container were still in the tube. Newspaper-wads were intact, not obviously scorched or frayed.
So now a test with a pressure-container for the powder. I threaded
a thin fuse through the flash-hole of a .44 magnum brass cartridge and
tied it in a knot. Keeps it in. 1 gram of Red Dot fills it
slam full. The wooden plug compresses the powder about 1/4 inch (more
on this later.) The tube is assembled with wads and golf-ball just
like in the first test, but now the .44 cartridge will contain the pressure
for a fraction before the plug lets go - or so the theory goes. I
noticed that the tube is a bit sticky, probably with residue from the first
shot, but the load moves with little more than 13.5 lbs pressure.
The screw in the wood plug is for weight-lifting, as described later.
Upon firing, the golf-ball hit at 11 feet, bounced and rolled to stop at 38 feet. The paper towel bottom-wad is scorched more than in the first test, although not as badly as it looks in the photo, as I did not get around to putting out the smolder as quickly as I should. The wads were scattered from 11 to 18 feet. The .44 cartridge case and wood plug were still in the tube.
Test 3 - repeat of test 1, One gram Red Dot contained only in paper
Ball hit at 16 feet, bounced and rolled to 39 feet. Wads clustered from 21 to 26 feet, bottom-wad is hardly scorched, not smoldering at all. The red marks are where I tried to determine the position of the powder charge, suspecting that the residual fuse causes the smoldering. Could not determine that in this test.
Test 4- repeat of test 2, one gram Red Dot contained in .44 casing with
Tube is very sticky at this point, the three lead-cans not nearly enough weight to get the load to move. I fired it anyway.
Golf-ball hit at 8 feet, stopped at 25 feet. Wads scattered from 13 to 17 feet. Bottom wad smoldering at one spot, not otherwise scorched. .44 casing still in tube, wood plug on ground just under tube.
Test 5 - repeat of A3 with new wads but uncleaned tube. 1 gram
Red Dot in paper-towel container.
Golf ball hit at 12 feet, stopped at 39 feet. Wads scattered from 12 feet to 23 feet. Bottom-wad slightly scorched, not smoldering.
Test 6 - a new pressure container.
One of the maxims of modern reloading is that smokeless powder should
not be compressed much, if at all, in the cartridge case. A bit of
compression is often OK, as is a little headspace. But the ideal
is for the powder to exactly fill the case. Thinking that compression
might have diminished the performance of tests 2 and 4, I found an old
30-06 case, cut it off below the shoulder, and trued-up the end.
This case is about 1/2 inch longer than the .44 case and slightly smaller
diameter. It holds 1 gram of Red Dot with just enough headspace for
the wooden plug. Fortunately, the same plug used in the .44 case
But I wanted to get a notion of how much pressure it would take to blow off this plug, so I tied a cord to the screw and used it to lift weights. Yes, we are out of sequence here, I did that before putting powder in the cartridge. At this point, the plug held with 12 pounds, came out with 13.5. Thinking that repeated firing might loosen the plug, I tried it again after test 20 and got essentialy the same result.
Fired it. the golf-ball hit at 9 feet and rolled to 21 feet, where it may have hit a tree. Wadding scattered from 11 to 20 feet, bottom-wad smoldering at one spot.
Test 7 - slower-burning powder.
This one is a repeat of tests 1 but using a slower-burning shotgun powder, intended for heavy loads. 1 gram Alcan AL-8 is contained only in paper-toweling. The test tube was cleaned with alcohol, so the load slides with little more pressure than the 13.5 pounds of lead-cans. Upon firing there is a "shoooo" sound that continued after the load left the tube, suggesting that the powder was still burning at that point. The golf-ball stopped at 4 feet 7 inches. The wads were scattered from 5 to 7 feet. Bottom-wad a bit more scorched than with the uncompressed Red Dot tests. Due to this lethargic performance, I gave up AL-8 testing for the moment. Perhaps its day will come. Possibly it would benefit from a pressure-container.
Series 2: Finding the upper limit.
Since I had seen little damage to the wadding in the first tests, I wondered how much powder would be too much.
Test 8 - 2 grams Red Dot in paper-towel container. Tube not clean, load very tight. Went "pop" when fired - not real loud but louder than other tests. Ball hit at 17 feet, stopped at 62 feet. Wads scattered from 31-37 feet. Bottom-wad slightly discolored but not badly burned or smoldering. Tube had shifted backward a bit from recoil.
Test 9 - 3 grams Red Dot in paper towel container. Tube cleaned with new wads. I placed a cement block behind the tube to absorb recoil, and cowered behind a sturdy tree. The ball hit ground at 20 feet, hit tree at 37 feet and bounced back to 31 feet. Wads were scattered from 20 to 27 feet. Bottom wad was discolored a bit but not torn or badly scorched.
Test 10 - repeat of test 9 with uncleaned tube. I suspected that the sticky tube would allow pressure to build before the load moved, providing a more complete combustion of the powder charge and thus higher velocity. But the results were not much different from #9. Ball hit at 18 feet, bounced off the sheet of tin in the distance at 58 feet and came to rest at 53 feet. Wads scattered from 26 to 35 feet. Bottom wad very slightly discolored. Remnants of the powder container smoldering on ground 5 feet from the tube.
Test 11 - 5 grams Red Dot in paper towel container. Tube not cleaned,
but rubbed with candle-wax. This lubricated the tube enough that
the load would slide under the pressure of 3 lead-cans.
Ball hit at 19 feet,stopped at 51 feet - I suspect that it hit something. Wads scattered from 27 - 39 feet. Bottom wad slightly scorched, very slight discoloration. Powder container in flames at 5 feet from muzzle.
Test 12 - Ten grams Red Dot in paper towel container. Tube not cleaned, but residual wax still providing some lubrication. Note the long fuse. I hid behind a larger tree at greater distance for this one. The firing was energetic but not otherwise eventful. Ball hit ground at 28 feet, hit tin backstop at 58 feet, stopped just past tin. Wads scattered from 31-48 feet, some frayed and torn a bit. Bottom wad slightly discolored, and has a small hole! This is the first damage that seems to have come about from pressure, not from fire. Remnants of the paper towel containing powder was smoldering at 2.5 feet.
Series 3: Finding the low limits
Test 13 - one-half gram Red Dot in paper towel container. Ball hit ground at 13 feet, rolled to 38 feet. Wads scattered from 17 to 23 feet, bottom wad in pretty good shape.
Test 14 - 0.3 gram Red Dot in paper towel container. Golf ball hit at 10 feet, bounced off tree at 21 feet. Wads scattered from15 to 20 feet, bottom wad still in mouth of tube, discolored but not damaged.
Test 15 - 0.2 gram Red Dot in paper towel container. Failed to eject. Load moved top wad to mouth of tube and stopped there. "Whish!" sound through fuse-hole.
Test 15b - repeat of 15, just pushed the load back and added another powder charge, 0.3 grams as in test 14. This time it did eject, ball hit at 10 feet and stopped at 16 feet, may have hit tree. Three wads at 20-21 feet but one back at 3 feet. Bottom wad still in tube, discolored but not damaged, even after two shots.
Series 4: Black Powder
Test 16 - 1/2 gram commercial black powder. Ball hit at 20 feet, wads 22 - 34 feet, bottom wad smoldering heavily. Quick photo then I stomped it out
Test 17 - 2 grams of homemade black powder, ground fine. Ball hit at 19 feet, wads scattered from 31-37 feet, bottom-wad smoldering even more heavily. here is
Here is a collection of some of the wads used in tests 1 - 17. Note that most are still wads, not torn, scorched, nor badly disseveled, despite having been protected from the powder charge by a little paper toweling.
Test 1 on left, test 2 on right. For this one test I used a full paper-towel, Bounty two-ply, measuring 11 by 12-1/4 inches and weighing 3.6 grams. Much of the excessive burn seen in test 2 is my fault, I let the wad smolder while taking measurements. After this lesson, I put out any smolders fairly quickly.
This seemed wasteful, and I was running low on paper towels, so used
1/2 sheet (one "select-a-size" sheet) in the remaining tests.
One quickly notes that the even-numbered tests show more burn-damage
to the bottom wad. These are the tests in which the powder was contained
in a pressure-case. I suspect that this is due to the positioning
of the case within the tube, as I will test later.
Test 7 - left, 1g Alcan AL-8
Test 8 - right, 2g Red Dot
Apparently black powder accelerates the combustion of paper toweling. I put these out within a few seconds of their emergence from the tube, both were burning at several points.
Series 5: More pressure-tests
I suspected that the cause of greater wadding damage in the pressurized tests above (2, 4, and 6) was due to the primer flash-hole being pointed straight at a corner of the base wad. This was thought to shoot a jet before the wood plug popped, setting fire to the paper towel wad.
So I plugged the previous fuse hole with a screw, and drilled another one in the cap. Now the containerized powder charge will sit with its flash-hole facing the rear. Having made a run to the store, the paper towel crisis is over. So I folded one to fit the cap, poked a hole in it and ran the fuse through the paper towel before the fuse-hole. This will be called the "base wad" as in a shotgun shell, and should demonstrate the effects of the flash-hole jet.
Test 18 - 1g Red Dot in 30-06 container with wood plug. The ejection tube is quite clean, having soaked overnight in the drizzling rain and being towel-dried by me a few minutes ago. It is raining a lot here these days - note plastic bag covering the fuse.
There was a lethargic "ploop" and the ball rolled to 9 feet. Wads scattered from 5 to 9 feet. Base wad slightly discolored, but no holes or serious scorches. The cap-wad was cleanly burned where the fuse had been.
Test 19 - repeat of 18 except ejection tube not cleaned, waxed to lubricate providing same load resistance as with clean tube. Load moved forward 3 inches to create clearance ensuring that cartridge can open freely.
When fired, a sharp "snap" sound was followed by a "whoosh" and a low "pop." Golf ball fell right at muzzle, the wads 12 to 24 feet away. Very odd. I suspect that the powder container held the pressure for awhile, leakage through the flash-hole moved the load forward enough that the ball fell, then the powder container opened, propelling the wads their normal distance. Anyone have a better explanation for this? Again, the base wad
Test 20 Repeat of test 19 but the gram of Red Dot is not pressurized. I wanted to see if the poor performance of tests 18 and 19 were due to the wet weather. They were not. The ball hit at 16 feet and rolled out of sight. I have not yet found it, probably in the tall grass to the right. Notice that the base-wad (right) is in good shape, with only a tiny scorched hole where the fuse went through. Comparing this to the larger holes burned in tests 18 and 19 tends to verify my notion that in the pressure-cartridge tests, a hot jet from the primer flash-hole tends to burn what it is aimed at. Also, the undamaged bottom-wads in tests 18 and 19 suggest that the burst of burning powder released by the popping of the plug is not particularly hard on the wading.
Table: Tests 1 through 20
|Test #||Powder Charge||Contained in:||Tube Condition||Golf-Ball hit at||Ball stopped at:||Wads scattered from __ to __ feet||Paper Towel condition:|
|1||1g Red Dot||paper towel||clean||15 feet||31 feet||12-17 ft.||slightly scorched, smoldering at one point|
|2||1g Red dot||.44 case with plug||cleaned with alcohol||11 feet||38 feet||11-18 ft.||smoldering at one point, more scorch than (1)|
|3||1g Red Dot||paper towel||not clean, sticky||16 feet||38 feet||21-26 ft.||hardly scorched, not smoldering|
|4||1g Red dot||.44 case with plug||not clean, very sticky||8 feet||24 feet||12-17 feet||smoldering at one spot, not otherwise scorched|
|5||1g Red dot||paper towel||not clean, very sticky||12 feet||38 feet||12-23 feet||slightly scorched|
|6||1g Red Dot||trimmed 30-06 case with plug||not clean, very sticky||9 feet||21 feet||11-20 ft.||smoldering at one spot|
|7||Alcan AL-8||paper towel||cleaned||not sure||4 feet 7 inches||5-7 ft.|
|8||2g Red Dot||paper towel||not cleaned, load very tight||17 feet||62 feet||31-37 feet||smoldering|
|9||3g Red Dot||paper towel||clean tube, new wads||20 feet||hit tree at 37 feet and bounced back to 31 ft.||20-27 ft.||discolored|
|10||3g Red Dot||paper towel||unclean tube||18 feet||bounced off tin at 58 ft||26-35 ft.||very slight discoloration|
|11||5g Red Dot||paper Towel||unclean, light coat of candle wax||19 feet||51 feet (I think it hit something)||27-39 feet||slight scorch, slight discoloration|
|12||10g Red Dot||paper towel||uncleaned, light wax||28 feet||hit tin at 59 feet||31-48 feet||slight discoloration, but a small hole!|
|13||1/2g Red Dot||Paper towel||uncleaned, waxed||13 feet||38 feet||17-23 feet|
|14||.3g Red dot||paper towel||uncleaned, waxed||10 feet||21 feet||15-20 ft.||still in mouth of tube|
|15||.2g Red Dot||paper towel||uncleaned, waxed||did not eject||did not eject||did not eject|
|15b||.3g Red dot||paper towel||uncleaned, waxed||10 feet||16 feet (may have hit tree)||20-21 feet (one at 3 feet)||still in tube|
|16||.5g commercial black powder||paper towel||uncleaned, waxed||20 feet||53 feet||22-34 feet||smoldering heavily|
|17||2g homemade black powder||paper towel||uncleaned, waxed||19 feet||not found||31-37 feet||smoldering heavily|
|18||1g Red Dot||30-06 casing||well cleaned||rolled to 9 feet||9 feet||5-9 feet||load-wad slightly discolored, base wad scorched hole|
|19||1g Red dot||30-06 casing||uncleaned, waxed||dropped at muzzle||7 inches||top wad an -1 inch, lower wads at 18-24 feet||load-wad smoldering at one point,|
|20||1g Red dot||paper towel||unclean, waxed||16 feet||not found||19-25 feet||load-wad barely discolored, base wad discolored, tiny scorching at fuse-hole.|
Series 6: Some superfluous tests with a longer PVC ejection tube
I recalled seeing another tube 2 inch diameter tube in my PVC pile with a male threaded end. It was 4 feet long, leading me to wonder how the smokeless powder ejection process would work with a longer "barrel." So I loaded as in test 1 with 1 gram Red Dot contained in paper toweling.
When the charge fired, I barely heard a whoosh, and the load did not eject. It had moved to within an inch of the end of the PVC tube and stopped there. I examined the bottom-wad and base wads, which appeared similar to those in tests 18 and 19, no substantial damage was observed except for a burned hole where the fuse went through. Perhaps the powder gasses rushing through the fuse-hole caused this.
So I tried it again, using 2 grams of Red Dot. The same load was pushed back, new bottom-wad and base-wad installed, and a charge of 2 grams Red Dot inserted.
This one ejected well. The ball hit at 15 feet and continued on to hit the sheet of tin at 58 feet. Wads were scattered from 19 to 30 feet, and slightly splayed. Base-wad scorched here and there but not badly damaged, bottom-wad discolored but not scorched or torn.
|Test #||Powder Charge||Contained in:||Tube condition||Ball hit at:||ball stopped at:||Wads scattered from:||Bottom wad condition:|
|21||1g Red Dot||paper towel||clean||did not eject||n/a||n/a||discolored, 1 small scorch|
|22||2g Red Dot||paper towel||uncleaned||15 feet||58 feet||19-30 feet||discolored, 1 small scorch|
This test suggests that a single gram of Red Dot might not be adequate
for reliable ejection in larger systems.
Discussion and conclusions: All tests
1. Criticism: My test-system is leaky. The expediency of a fuse compromises the containment vessel. An audible whistling was often heard upon firing. This loss of gas may have changed the burning characteristics of the powder, and certainly reduced the force of the ejection by at least a small amount.
Perhaps leakage is more a factor in the tests where a plugged cartridge constrained the charge, attempting to build some pressure. Leakage through the flash-hole might have prevented pressures from rising to a useful level.
Defense: In most tests, forceful ejection was obtained in spite of this leakage. I plan to repeat some of these tests using electric ignitors, but do not expect the difference to be significant.
2. Criticism: I am burning a large amount of smokeless powder in a manner markedly different from that for which it is intended. Smokeless powders are designed to be ignited at once from the flash of a primer, and to burn at a carefully determined rate under pressure to accelerate the load at high velocity. My charges are ignited at one spot and burn at low pressure, the flame spreading from particle to particle. I suspect that this is inefficient, extracting less energy than the powder is capable of producing. If memory serves, a gram (15.43 grains) would be a moderate charge for a 12-gauge shotgun shell. Two grams (of slower powder!) is about the amount used in a 30-06 rifle cartridge (reloaders, please correct me!)
Defense: High velocity might be desirable for the the rocket as a whole, but a typical ejection system only needs to push a nose cone off and a parachute out. Excessive velocity can be detrimental to the integrity of these components, as in broken shock cords and ripped parachutes. High internal pressures could also damage recovery system components before they exit the tube. Considering the energy of a shotgun or rifle shot, inefficient burning might be a good thing. I believe that the ideal is to generate the minimum pressure that provides reliable ejection, and to build that pressure rather slowly to minimize shock to the ejection components.
The problem of unburned powder which Mr. Aleckson reports in his tests was not observed in mine. Very little, if any, unburned powder remained in the ejection tube after any of these tests. I suspect this is because the head-space allowed for the powder-charge is smaller in my tests, a cylinder about 2 to 2-1/2 inches long by 2 inches diameter in most tests. Thus the grains of powder cannot fly far, and all get ignited. Perhaps the best containment vessel is the parachute/wadding itself. I hope to verify this notion by repeating some tests but using a larger headspace for the powder, and a better way of finding unburned powder grains.
3. Criticism: The golf-ball is not a nose-cone, especially when it's set back 4 inches into the tube. This may give the ball more momentum as it is exposed to the forces of acceleration for a longer period. And newspaper wads aren't much like a parachute. There is no shock cord, and I am not using fire-resistant wadding!
Defense: none. I need to do more testing, using real recovery-system components.
4. Criticism: These are static tests: the ejection system
is neither in motion nor at altitude upon firing.
I wonder how smokeless powder performance might change at high altitudes, expecting that it would generate higher relative pressure because of the lower ambient pressure. This might be countered somewhat by air resistance if the rocket is not at apogee, and is either rising or falling. Since the consequences of a failed ejection can be dire, I might use a little more powder than the minimum to ensure reliable ejection. Fortunately, the range seems wide - I had successful ejection using charges as light as 0.3 gram and as heavy as 5 grams.
Defense: None. I hope to find a way to test this system as it falls through the air, with a real nose-cone and deploying a parachute But I can't fire much of a rocket around here and need to be able to do it over and over. Thought about using a big slingshot to get the short tube up a little ways. :) If only I had a hot-air balloon, or a microlight aircraft!
Conclusion: I believe that the present results support the notion that smokeless powder can be an effective ejection charge, that limited headspace provides adequate constraint to ensure full ignition, and that smokeless powder offers some advantages over back powder. But at least one more round of testing is needed before trusting it in a launch of any consequence.
Please feel free to share your comments, questions, and suggestions regarding this project. I am sure many will have criticisms and ideas that have not occurred to me, and I look forward to hearing them all.