Newspaper

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Joe
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Newspaper

Post by Joe » Sun Oct 19, 2003 3:47 am

I lost the link to the "Rogue Movies" site with the exploding KNO3-newspaper rocket, but have a few thoughts to add on my own. First of all, Rogue Guy's rocket almost certainly burst because he sucessfully got too much surface area to burn. Newsprint propellant burns slowly, but that doesn't matter if it's burning on all its surface at once.
I've had some success by soaking strips of newsprint in hot saturated KNO3 solution and oven drying them (reduced drying time seems to mean smaller cyrstals) and rolling these into tubular grains for really small test motors. My casings for these were made from belted magnum rifle casings (usually .300 Winchester) by expanding the necks so the grains would fit in. Exhaust left through the primer hole, while the large open end was plugged with paper and crimped.
As for the propellant, I really have no idea if the oxygen balance is anywhere close; with no balance and me not regulating the amount of solution going onto the paper, there's no way to tell except the way it burns. On another propellant (more later) I think I may have put too much oxidizer in because of the salt "slag" it seems to leave after burning. The newsprint material burns in air with small globules of molten KNO3 visible but leaves a lot of soot behind. I think this is partially due to the way the oxidizer and fuel are mixed (smaller crystals are better). The actual burning behavior in a 3/4x3/8 inch tubular grain with a core just less than 1/8 inch wide is that the flame generally seems to hold to the surface (probably depends on how tight it's wrapped, but I want grain surface burning for obvious reasons).
The last few test motors used two of the grains I just described each as a bates configuration (the outer surface was inhibited with scotch tape), and seemed to burn regularly, which means that even though their ends were held together in the final assembly, they still burned.
The other stuff was a bit like Tundra Man's idea, with scrap pulp paper being food processed with stump remover. I eventually added some water and made it into a paste, which stuck to the sides of the processor thing, so I had to dry it out in the microwave. It took a lot of drying, but when it was done the KNO3 was very finely powdered, especially after the dried mass was ground up again, but it didn't burn that well.
I can't tell you how I know this, but that stuff won't blow up. What seems to happen is that the mixed fibers and crystals get compressed into a solid mass by the pressure from the first little bit of it burning fast, so the rest burns slow. The bad stoichiometry might also have something to do with it.
Some time in the not too distant future I plan to make bigger test motors, possibly model rocket engine reloads or pipe based motors, but making the propellant for them will actually be a lot of work, so don't hold your breath.

I've also been thinking about hot pressed propellants. I know someone has been making dried KNO3-sryup propellants, but has anyone cut the usual semi-dry mass into chunks, hot dried them, and pressed them into a mold while the sugar is partially molten? This should solve some of the problems of mixing things with molten sugar, especially in high ratios, like if you're using AN. I can't find any bulk AN or even KNO3 here in Colorado Springs, but I would like to make an AN based propellant sometime because of the possibility of reducing smoke. Another possible combination would be 1 AL: 5 AN: 1 paraffin, where the paraffin would mostly be expansion mass and binder. There would of course be limitations (mostly mechanical) imposed by this, but since I'm not going to make it, I figure I'll just let you shoot it down now.

Mark
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Re: Newspaper

Post by Mark » Sun Oct 19, 2003 2:38 pm

Joe wrote:I lost the link to the "Rogue Movies" site with the exploding KNO3-newspaper rocket, but have a few thoughts to add on my own. First of all, Rogue Guy's rocket almost certainly burst because he sucessfully got too much surface area to burn. Newsprint propellant burns slowly, but that doesn't matter if it's burning on all its surface at once.
I've had some success by soaking strips of newsprint in hot saturated KNO3 solution and oven drying them (reduced drying time seems to mean smaller cyrstals) and rolling these into tubular grains for really small test motors. My casings for these were made from belted magnum rifle casings (usually .300 Winchester) by expanding the necks so the grains would fit in. Exhaust left through the primer hole, while the large open end was plugged with paper and crimped.
As for the propellant, I really have no idea if the oxygen balance is anywhere close; with no balance and me not regulating the amount of solution going onto the paper, there's no way to tell except the way it burns. On another propellant (more later) I think I may have put too much oxidizer in because of the salt "slag" it seems to leave after burning. The newsprint material burns in air with small globules of molten KNO3 visible but leaves a lot of soot behind. I think this is partially due to the way the oxidizer and fuel are mixed (smaller crystals are better). The actual burning behavior in a 3/4x3/8 inch tubular grain with a core just less than 1/8 inch wide is that the flame generally seems to hold to the surface (probably depends on how tight it's wrapped, but I want grain surface burning for obvious reasons).
The last few test motors used two of the grains I just described each as a bates configuration (the outer surface was inhibited with scotch tape), and seemed to burn regularly, which means that even though their ends were held together in the final assembly, they still burned.
The other stuff was a bit like Tundra Man's idea, with scrap pulp paper being food processed with stump remover. I eventually added some water and made it into a paste, which stuck to the sides of the processor thing, so I had to dry it out in the microwave. It took a lot of drying, but when it was done the KNO3 was very finely powdered, especially after the dried mass was ground up again, but it didn't burn that well.
I can't tell you how I know this, but that stuff won't blow up. What seems to happen is that the mixed fibers and crystals get compressed into a solid mass by the pressure from the first little bit of it burning fast, so the rest burns slow. The bad stoichiometry might also have something to do with it.
Some time in the not too distant future I plan to make bigger test motors, possibly model rocket engine reloads or pipe based motors, but making the propellant for them will actually be a lot of work, so don't hold your breath.

I've also been thinking about hot pressed propellants. I know someone has been making dried KNO3-sryup propellants, but has anyone cut the usual semi-dry mass into chunks, hot dried them, and pressed them into a mold while the sugar is partially molten? This should solve some of the problems of mixing things with molten sugar, especially in high ratios, like if you're using AN. I can't find any bulk AN or even KNO3 here in Colorado Springs, but I would like to make an AN based propellant sometime because of the possibility of reducing smoke. Another possible combination would be 1 AL: 5 AN: 1 paraffin, where the paraffin would mostly be expansion mass and binder. There would of course be limitations (mostly mechanical) imposed by this, but since I'm not going to make it, I figure I'll just let you shoot it down now.
I read about an explosive of aluminum and ammonium nitrate and the binder is guar gum which makes it into a consistencey of a pencil eraser this university book said. You can shoot it with a rifle bullet and it won't explode. I don't see why you couldn't make a rocket fuel out of it if you didn't shock it into exploding. Guar gum can be purchased at health food stores or on the net.
Mark

Stephen H
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Post by Stephen H » Mon Oct 20, 2003 12:56 am

iiiiinteresting, very interesting!

Carry on the good work!!

Stephen

Axt
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Post by Axt » Sat Nov 15, 2003 2:21 pm

http://geocities.com/roguemovies2/

Complete with more dodgy movies. The bandwidth limit will limit the amount of downloads per hour, so you may not get in first try.

Ive never tried the newspaper fuel again, but I have a grain sitting here ready for use. Its the flame propogation between the sheets of paper (as you said - increased surface area) that increases the burn rate, and this is needed as the core alone with such inefficient fuel isnt enough. One should be able to get it to work with a larger nozzle and heavier PVC.

You should be able to get a better O balanced mix by using more pure cellulose paper, such as toilet paper but it wont hold together when wet like newspager which contains things like clay.

Joe, since your post suggests that you are a reloader you may wish to try rockets from shotshells. This is done by casting a grain from blackpowder/smokeless powder and solvent cast with acetone into a coreless cylinder. This is loaded into an empty, deprimed shotshell using the primer hole as a nozzel. Works great!

Vary the ratio of BP to SP to vary the burn rate, more BP the faster.

Joe
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Post by Joe » Mon Nov 17, 2003 8:48 am

"Ive never tried the newspaper fuel again, but I have a grain sitting here ready for use. Its the flame propogation between the sheets of paper (as you said - increased surface area) that increases the burn rate, and this is needed as the core alone with such inefficient fuel isnt enough. One should be able to get it to work with a larger nozzle and heavier PVC." -[b]Axt[/b]

I guess I don't know what the properties of your propellant are, but whatever the case, it seems like your last rocket definitely burned too fast. I guess a really fast burn might be necessary for a kick motor -maybe an RPG that burns out before it leaves the tube? But otherwise a longer burn should be acceptable, at least to get to know the propellant.

I haven't tried the BP/smokeless composite you suggested, although my first attempt at a rocket, long ago, was solvent recast smokeless, and it had a really serious shrinkage problem. Filling it with BP would probably fix it, though. I guess when I finally get some BP I'll have to try it.

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