Propellant Question

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Alan Smith
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Propellant Question

Post by Alan Smith » Fri Feb 06, 2004 3:31 pm

Which is more efficient to use, sucrose-sulfur-KNO3 or carbon-sulfur-KNO3 ?

Tom
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Post by Tom » Fri Feb 06, 2004 4:23 pm

i wont answer this, but i will give my observations. I did some work with pyro mixes, potassium chlorate and sugar or charcoal. the charcoal mixes burn much faster with a brighter flame, where as the sugar mixes were much slower. the fact that sugar/sucrose rockets are so popular may say something different though.
Experience speaks more then hypothesizing ever can. More-so in chemistry.

TonyG
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Post by TonyG » Fri Feb 06, 2004 9:33 pm

From personal experience, of those two mixtures I would go with the carbon/sulfur/KNO3 mixture.
The reason sugar/sucrose rockets are getting popular is due to the cost. I am also under the assumption that most view the sugar/sucrose mixtures as being safer then the carbon/sulfur/KNO3 mixtures.
I have made several successful rocket engines using the carbon/sulfur/KNO3 mixture, though they have been of smaller sizes only. Something long the lines of the estes C engines, just a little longer engine, with a .25 inch nozzle. Seems to work pretty good, though I have only used them for pyrotechnical purposes, not actually in any of my models.
I hand roll the cases for these out of kraft paper and white glue, trim the ends, pound in some clay and then pound in the mixture using a brass rod and a rubber deadblow mallet. Lots of work, and lots of time to make such a small engine.
I have been thinking about making one of the larger sugar based engines with a pvc pipe as the casing, but haven't had the extra time or money to mess with it in a while.

Alan Smith
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Post by Alan Smith » Sat Feb 07, 2004 8:15 am

I, too, was making small rocket engines using carbon mixes...
But this time I`m planning to do larger rocket of a length of 0.5m (1.64 ft).
Maybe putting a carbon mix in such a rocket will make it blow up if it had the same nozzle and width propotions as the small ones. Maybe if I had some kind of program for the calculations of the nozzle. Anyone got one of those?

Axt
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Post by Axt » Sat Feb 07, 2004 12:21 pm

Sugar is used as it can be cast, carbon (more accurately, charcoal) cant!

Therefore a solid consistant grain is easy with sugar by casting, but pressing a large grain of blackpowder consistant enough is very hard, so it aint often used for larger rockets as they will explode from any irregularities.

Some would argue that the cost difference between charcoal (not carbon!) and sugar is negligable, but sugar is definately more convenient.

Is efficiency means power, its probably still KNO3 + Sugar, higher impulse I believe, but slower burn rate.

Alan Smith
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Post by Alan Smith » Fri Feb 13, 2004 5:17 pm

I`m thinking of mixing both mixes. I calculated the stoichiometry, it is as follows:
14.5% Sugar
6.1% Charcoal
10.9% Sulfur
68.5% KNO3

Any sugestions?

Alan Smith
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Post by Alan Smith » Sun Feb 15, 2004 5:38 pm

I put some sugar in a metal pot, added a bit of water, and put it over a fire. When all the water evporated while the sugar was liquid, it turned brownish. I prepared a mix of gunpowder and an equivilent amount of KNO3 with respect to the sugar. I waited the brownish goo to cool down a bit, and then I added the mix.(the goo was still warm and not solid). I homogenized the whole thing. When it cooled down completely, it became a very hard solid. I ignited it and it burned wonderfully.
Just one problem, if I leave it for a certain time, it catches humidity, and becomes unpleasent to work with. Try it to see what i mean.
Anyone knows a substance I could add to prevent such a thing?

Tom
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Post by Tom » Sun Feb 15, 2004 7:50 pm

that is one of the major downsides of rocket candy. Its a hydroscopic mix. unfortunately, i knwo of nothing to prevent it.

Tom
Experience speaks more then hypothesizing ever can. More-so in chemistry.

paul skinner
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Post by paul skinner » Sun Feb 15, 2004 8:55 pm

Alan.

I found that storing the completed motors in a vaccuum sealed bag in the freezer did the trick for me....
You can also try commercial dessicants scattered around rolled and dry newspaper packing (the little white bags found sold with clothes or coats) that are great at absorbing moisture, but the sealed bag trick works the best.
You can also store them in a container packed with dry ice, sealed in a styrofoam container, but again there's the cost..


Luck,

Skinner.

:)

Alan Smith
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Post by Alan Smith » Mon Feb 16, 2004 5:39 am

Till now, I`am doing this. It seems that the sugar tends to regain it`s water molecules. If there is some kind of a solid powder that would act like the water molecules and stick to the sugar, it`s much better.

Hank
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Eraserhead

Post by Hank » Mon Feb 16, 2004 2:33 pm

Hello- Your best bet for a safe, easy to load fuel would be a metal powder, ammounium nitrate oxidizer with a plastic or rubber binder.
Phase stabilized ammonium nitrate is the oxidizer you want. It will not change grain size with changes in temperature. The stuff has a light zinc coating. HTBP resin or rubber cement works as a binder. Magnesium or Aluminum powder (1000 screen) for a fuel.
Sugar fuels crack with such consistency, changing the flame front with such rapidity, that I would not consider using them.
PVC Pipe, lined with bicycle inner tube as an ablation layer, worked as an engine casing. Nozzles were machined from various metals or cast from Durham's Water Putty. Hank

Greg O'Bryant
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Post by Greg O'Bryant » Mon Mar 14, 2005 5:04 am

:) Go with the sugar and KNO3 I have had quite a bit experiance with working with the traditional blackpowder and the sugar, KNO3 engines. Yes the sucrose propellant is a bit slower but that is no problem if you just increase the core depth. If you use a ratio of about 70 parts KNO3 and 30 parts sucrose you will have an almost balanced chemical reaction although the propellant seems to burn a little better if you go a little heavy on the sugar. The reason why I like the sugar propellant is because of how consistently it performs and how easy it is to make, you can make several pounds of it in under 30 min. I would disolve the KNO3 and the sugar in water and cook it in an electric frying pan until all of the water evaporates and your done. Be careful about having a boil over and getting wet propellant on the plug. I have seen this ignite the propellant because of the electrical current. Anyways let me know how things go I used to make engines that would have been about the f size all of the time. The only problem with the sugar propellant is that unless you pack it when it is still hot it tends to be hard to press together, I think that a jack hooked up to an electric drill would be able to pack the cooled propellant into some aluminum tubes quite nicely. Just a thought.
Good luck

Timbo12989
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re: Propellant Question

Post by Timbo12989 » Thu Jun 30, 2005 12:01 am

Hey, I was just wondering where you guys get your saltpetre or KNO3 for either of these propellents? I've looked all over but I can't find it except for in chemistry supply stores or websites.

Tom
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re: Propellant Question

Post by Tom » Thu Jun 30, 2005 12:08 am

kno3.com are uk based, as are all the others I know of, like LabPak, etc. Try farm supply stores for NPK fertilizer? You could always get shipping from Kno3, they offer worldwide.

Tom
Experience speaks more then hypothesizing ever can. More-so in chemistry.

Greg O'Bryant
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re: Propellant Question

Post by Greg O'Bryant » Thu Jun 30, 2005 3:14 am

I agree, try to look for it at the farm supply stores, you may have to check quite a few of them before you find one that will stock it but when you do it will be well worth it. When I used to make engines I could only find one store in the whole state that had it, but when you consider that it was less than $20/50lb. compared to almost $4/lb. you do the math.
Good Luck.

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