Over the decades well over a hundred patents have been filed for gas-generator compositions based upon ammonium nitrate (NH4NO3, "AN"), a very few of which might be applicable to Jetex. I'm experimenting with this old ICI patent (
) based upon AN and nitrocellulose (NC) , with "non-explosive carbonaceous fuel" (paraffin, or 2,4-DNT). Working from 12.2% nitrogen-content Hercules USP/Food grade nitrocellulose, I've made NC gels with acetone, then mixed in AN with 2,4-DNT or accaroides red gum per the patent. Tomorrow I'll mix the same based upon paraffin wax, and beeswax, if I find that near Mojave.
Today's burn rate tests in a 0.4" bore motor sustained steady combustion for more than 60-sec per inch at atmospheric pressure. Combustion more resembles decomposition than burning, is very low-key, modestly smoky, and produces modest ash with both 2,4-DNT and red gum. This long, slow burn rate is rather surprising, yet it accords with the patent and other references.
I deduct already this is a strong candidate for Jetex pellets. The essential energetic reagents are widely available (both AN and NC), inexpensive, and not terribly difficult to work with. The exhaust byproducts can possibly be tweaked to harmless gases, though right now there's probably a good bit of both CO and NOx being produced incidentally, due to faulty thermochemistry.
Likewise, I've extruded a single long pellet of this formulation. It's hard, tough, strong, pale white, and while difficult to ignite, burns very, very cooly, little visible combustion, not very unlike old ICI pellets. This is simply an early experiment, and there's much yet to be done.
Digital load cells, thrust transducers, and computerized rigging are en route from Colorado soon, and with that setup I expect begin publishing thrust curves so you can examine performance with me, and hopefully I'll soon include photos.
If you're seriously interested in Jetex propellants, please look through this informative ICI patent. I've attached also a Hercules report on the qualities of their nitrocellulose.
Was it not for the fact that ICI could make the fuel in non-explosive regulated buildings, that GN was such a good constituent? I realise the net must be cast pretty wide to find what will give us the results we all want, reproducible results that is, but would it not also help that it could be mixed and made in a bicycle shop rather than a concrete bunker in the middle of nowhere. Some of the chemicals being looked at seem to be on the border of regulation. Is this the case, and does it have a baring on your choices?
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Quite right in every regard, though I was not aware that ICI made Jetex pellets in non-explosive regulated buildings. I continue to give the matter of GN deep consideration. While GN has many excellent qualities (being entirely comprised of gas molecules: CH6N4O3, if we regard the carbon as readily converted to CO and CO2), it's only become available to the public in USA very recently, and even now it's sold to the public by only one purveyor that I know of (Firefox-fx.com). It'll likely be even more restricted as time goes on, and is already on the no-no list in Japan, and much (if not all) of Europe.
I'm the first to agree that we want and need something that can be mixed and made in a bicycle shop. At the same time, GN is a quite safe oxidizer, in my experience and opinion, not being as easily reduced as KNO3, for instance, or any of the perchlorates. Though it's an ingredient in low-flash explosives and military propellants, it's not itself an explosive (comparing GN to nitroguanidine, for instance).
A parallel example that I'm working with is 2,4-dinitrotoluene (2,4-DNT). It's a close sibling of old fashion TNT, and just one step away from that tri-nitro state, it's now also sold in USA and shipped via surface mail (as is GN, wet NC, AP, Zn powder), regarded merely as "flammable solid." I studied the qualities again long and hard before cautiously melting samples, and grinding a few grams in the coffee mill. In this case, 2,4-DNR (dinitroresorcinol) was the ICI choice, and that is indeed regarded as explosive, and isn't to be found on any market. I'm experimenting with 2,4-DNT as a safer, available alternative--nothing more--since 2,4-DNR won't be found anytime soon.
Moving past GN for a moment, what's left is ammonium nitrate (AN, again all gas components: NH4NO3), and again becoming very hard to find and buy. The only readily avail AN in USA these days is prilled (small round pellets, for easy-flowing into mine bore holes, etc) and even that is limited to (IIRC) one-pound per year. Most pyro dealers here don't even offer it any more.
GN isn't easy to formulate into a self-sustaining mixture. It is a fine oxidizer at pressure, but getting it going takes considerable energy input (unlike the perchlorates, or some other nitrates). 2,4-DNT itself isn't going to substitute for the 2,4-DNR, so now I'm sliding again back to AN-oxidized Jetex.
The one way I've found, after many experiments and considerable research, to get GN formulations going at atmospheric pressure and temperature is by adding a serious "helper," either a dichromate, for instance, or NC. I prefer the latter, and I'm continuing experiments with both.
My perspective Andy is to look only at reagents that will likely work, and only those "fairly readily available" to experienced, unlicensed pyrotechnics experimenters. If it's too pricey, or too toxic, or too sensitive, or regulated out of use, I skip that avenue.
FWIW, the Rapier compositions are excellent propellant, in that context. I'm working today to see if it's possible to make a variation on that AP/Zn/DICY/epoxy-bakelite mixture that can be used in regular Jetex motors. Sure-fire ignition thru the tiny nozzle is one hurdle (many mixtures are simply too hard to get lit so they will keep going on their own). Adjusting the size of the AP granules is another, to achieve best burn time *and* good specific impulse (Isp: ounce-seconds of thrust per ounce of propellant).
Nifty reply, I seem to remember the Herr Doktor Simmonds telling me of guncotton being used in a copy of jetex fuel. Yep, it's just come to me, V-max it was called and if memory serves it was NC and wood pulp as the main drivers. I've fired some of this myself and personally I thought it was rather good. The pellets looked like solidified brown gravy granules with a shiny coat! It burned down to a curious white to grey ash. If burned in open air it curled over like a dog turd -strange but true.
On a slightly different tack, I've been given some smoke pellets that are made for plumbers to test out the flow characteristics of flues. These seem to be fibreous and although they burn well and give off a harmless white smoke for up to a minute, I'm not sure if they can be ignited in an air tight motor and sustain themselves without air.
I wonder what's in them?
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I think what Andy is referring to is the story of RAF mechanics using the cartridges from ejector seats in Jetex motors.
The stuff was called (if I remember correctly ) 'Mechanite'. It was a hard green wax-like substance based on cordite. Being used for ejector seats, it gave a 'whoosh' rather than a bang, and was quite effective when cut to shape and used in Jetex motors. I don't think the motors lasted very long with this propellant, though, which, according to my source, gave more thrust and sent their RTP models in a whirl.
It should also be remembered that the LSARA motors, similar in design to the early Jetex motors, like the 200 and 300, used a cordite propellant.
The great thing about GN formulations is of course their stability and non toxic nature. Thus ICI using them for all manner of applications - hammer drills, engine starters, etc. But it was Jetex that grabbed the journalists' attention when the ICI 'Power Cartridges' were launched in 1948.
If Dr Jones can come up with a one shot GN Rapier type motor I think it would solve a lot of problems of commercial distribution associated with AP/plastic propellants.
But it isn't easy - it is far easier to make a 'bang' than a 'whoosh' and then of course there is the tooling up for production.
All power, though, to JPL!
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Simply selecting and testing motor tubes for flight testing isn't a trivial task. Dr Zigmund has spent years developing that "simple" part of the equation, and Rapier motor cases are quite a far cry from conventional Estes-type (and fireworks) rockets. I've a few samples of carbon-fiber composite tubing, thicker-wall for ballistics tests, thinner for flight test prototypes, that I'm preparing for experiments. Carbon-fiber composite tubing is much stronger and these tubes are quite lighter than their equivalent (dissected and disassembled) Rapier counterparts--but they're not cheap, going for more than US$1 per inch in small lots, made in Utah. Otherwise, methinks they're a dream for use as light-weight, strong free-flight motor cases. And they're not likely to replace strong, thin-wall, impregnated (phenolic or epoxy) convolute paper motor cases in my lifetime.
(Today marks my 74th solar orbit, and I can think of no more happy way to spend the day than mixing and mashing GN, AN, NC, and their gently reactive non-toxic cousins, fully intent upon progress and advances. With a copy of Dr James Taylor's "Solid Propellent [sic] and Exothermic Compositions," London 1959 at hand, and more esoteric gas-generating formulation patents that I can keep up with, this little California desert lab brings to mind Jack Parsons' experiments in the Arroyo Seco canyon of Pasadena in the late 1930s, while he was part-timing it at Bermite Powder Company, and getting acquainted with Dr Theodore von Kármán at Cal Tech. Those formulations became the first composite propellants, and led to America's first JATO patents [in Parsons' name, and assigned later to Aerojet Engineering], the creation of Aerojet, and the birth of JPL [following GALCIT rocketry advances].)
(Jack Parsons, Frank Malina, and Dr von Kármán together made early rocket tests on Muroc Lake, which is about 30-miles from here--now within Edwards AFB and NASA Armstrong Flight Test Center. Those fellows were one and all, along with Robert Goddard, "amateur" rocket experimenters.)
Along with gentle GN, I'm working with ammonium nitrate (NH4NO3), another gentle oxidizer that exudes only gases, and with the correct thermochemical balance, can be made to yield only non-toxics. AN has it's own share of luggage (phase changes in the compound at near room temperatures, which tend to cause propellant cracking, to name just one) and is difficult to keep decomposing at atmospheric pressure. To overcome that, patents suggest adding small amounts of nitrocellulose, and that I'm doing.
Cordite, by the way, is both a British invention and a double-base propellant. It employs both NC and nitroglycerin--unlike the single-base smokeless varieties. Single-base (almost straight NC) are much easier to devise, much safer to handle, and simpler to fomulate. A simple single-base Jetex-type propellant would burn to rapidly, but with burn rate modifiers and added fuels, it's doable.
I don't know the situation in Europe, but in USA thus far NC is sold and shipped via mail as a "flammable solid" when in the usual wet form (12.2% nitrogen content, about 25% water soaked by weight). Just dry in open air (or a gentle warm breeze) and it's ready to go: smokeless, ash-less, and bright orange flame, not much different from the more nitrogenated guncotton. Mix with a bit of acetone, and NC forms a volatile gel easily mixed with NG, AN, or other reagents. If compressed at 10,000-psi while still moist with solvent, it forms a hard, brittle pellet that's like a white Jetex pellet. Add a wee bit of accaroides "red gum" from Australia, and it's nearly a twin in appearance to Jetex pellets. With a bit of V2O5, you might think it's Red Spot, or even original ICI formulation.
So far, I'm using this in thick-wall test motor tubes of cardboard, and will know next week if it's too hot for Jetex motor cases. In any event, I'm striving for Rapier-type one-shot motors, and already have a formulation (AP, Zn, DICY, epoxy, zinc stearate) that runs just like the Czech product of Dr Zigmund. I'm using kaolin/gilsonite/clay/Durham's mixed nozzles and end caps, but have not yet located suitable tubes for flight-weight motors.
A full static test rig with load cells, digital-analog converters, preamps, etc etc that will yield calibrated results on a computer screen is en route from Colorado, generously donated by Edwin Brown, who's both part of our JPL development team and a seasoned Estes veteran who's still a consultant to that venerable company in Colorado. Ten different gentlemen have thus far contributed reagents, motor cases, dozens of sample Rapier motors of all sizes, Jetex motors of all sizes, Jetex pellets of assorted flavors and vintages, state-of-the-art electric igniters, carbon-fiber composite tubes, Visco fuse, sieves, solvents, arbor press, and more.
And about those "self-heating soup cans," more in another post.
Thanks for the encouragement, Roger!
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