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RPG (not dungeons and dragons you nerd)

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: magnum9987 » Mon May 12, 2008 1:58 pm

Combustion more often than not is contained in a chamber that propels a spud. But, rather than the spud being propeled, The chamber itself could be propelled. A chamber made of 3in diameter pvc pipe and two caps would be built. Then a hole is 1in di is placed in it. Their the igniter and handle go in, as well as where fuel is placed. Ignition is a simple trigger. A cork keeps the whole shut, until ignition. This wuld be in relation to other guns a big launcher. Rather than a gun, this is more like a rocket.
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Unread postAuthor: Sticky_Tape » Mon May 12, 2008 2:27 pm

I think that there wouldn't be any thrust more like a puff of air. Rockets keep supplying thrust while what you described would olny give a puff of air. try water rockets.
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You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: magnum9987 » Mon May 12, 2008 2:47 pm

ive also thought of using dry ice and water. As the dry ice expands into gas it would provide superior thrust do to the presence of water.
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Unread postAuthor: iknowmy3tables » Mon May 12, 2008 2:55 pm

magnum9987 wrote:ive also thought of using dry ice and water. As the dry ice expands into gas it would provide superior thrust do to the presence of water.

no water has more mass than CO2 gas, so by using air presure to blast water in the opposite direction you get more thrust, you know Newton's law, whatever just think about it like this which as more recoil; cannon loaded with cannonball or paperball

the result you get sucks you can do this with a lighter and a bottle and the bottle will skid across the table, your thinking of pulse jet stuff, but with no fuel input
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Unread postAuthor: magnum9987 » Mon May 12, 2008 3:09 pm

by the presence of water i meant that the water cannot compress. Thus as the gas expands, the water will limit the gas into a certain volume of space for the gas to expand, pushing the water into the cork, pushing the cork out and the rocket forward. Exactly how bottle rockets work. compare the results of a bottle rocket with water and a bottle rocket with no water. But i really want the combustion system to work. How could the rocket system work.
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Unread postAuthor: LynyrdSkynyrd » Mon May 12, 2008 3:21 pm

I don't think the dry ice would provide continuos thrust tho. You'll have the initial from the cork popping out and whatever water squirts out, but that'll just be a pulse. unless you make the hole like 1/4 in. Then it may give you enough thrust to go 10 ft. b/c of the weight of the rocket.

Also, you'd be only able to fire it above like 45 degrees.
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Unread postAuthor: magnum9987 » Mon May 12, 2008 3:26 pm

Do any of you watch mythbusters?
They made bottle rockets by filling bottle with water and pump air into it. THey then made bombs with dry ice and water in two liter bottles. The power the bomb had could be harnessed by simply popping a cork in the neck. If the bottle could be replicated with pvc, and made even larger, couldnt it achieve huge distance?
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Unread postAuthor: LynyrdSkynyrd » Mon May 12, 2008 3:33 pm

theoretically maybe. but you would have to control the force in one direction. Also the reason dry ice bombs have so much power is the fact that the dry ice fills the bottle with CO2 to its bursting point. A cork wouldn't be able to hold the pressures needed for the same effect. The other issue is that PVC is heavy. If you find a way to control the release of gas to provide propulsion, the weight of the PVC will inhibit the distance of the rocket.
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Unread postAuthor: psycix » Mon May 12, 2008 3:47 pm

It might work if you add a bottom of water to your chamber.
This way the pressure generated by the combustion will make it work as a water rocket.
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Unread postAuthor: brogdenlaxmiddie » Mon May 12, 2008 3:49 pm

magnum9987 wrote:ive also thought of using dry ice and water. As the dry ice expands into gas it would provide superior thrust do to the presence of water.


Your a dumbass.... You have prolly never used dry ice and water and by the way you describe your "idea" it sounds as if you should be in elementary school... Ther isn't a fesable way to use dry ice! It does produce high pressure, but rather slowly, also you would need to add water... which would just simply fall out of your contraption through the hole... :evil:
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Unread postAuthor: Sticky_Tape » Mon May 12, 2008 3:49 pm

I make water rockets and I know that if a rocket is too heavy it really limits the distance. Reamember do not use dwv... just kidding I meant don't get primer everywhere... no but really for this to fly strait you need the center of gravity ahead of the center off area look up information on water rockets and you will probably know whatb I mean. Oh yes don't use dry ice bad idea.
RPG? What is the grenade part if you didn't know it means rocket propelled grenade.
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Last edited by Sticky_Tape on Mon May 12, 2008 3:55 pm, edited 1 time in total.
You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: brogdenlaxmiddie » Mon May 12, 2008 3:54 pm

yeah, don't use dry ice, because of the previous statement i made and also, dry ice is cold.... PVC + DRY ICE = BRITTLE PVC = BOOOM IN YOUR FACE
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Unread postAuthor: LynyrdSkynyrd » Mon May 12, 2008 4:01 pm

maybe if you figure out how to make solid rocket fuel you can use that.... but then there's a possibility of a real big explosion. if it was built i'd hide behind a bunker b4 i fired it.
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Unread postAuthor: magnum9987 » Mon May 12, 2008 7:51 pm

@ Sticky_Tape: I call it rpg because itll semi-sort-of look like one. If their where an actual grenade it would be illegal
@Brogdenlaxmiddie: I should build this thing just to prove you wrong and then watch the moronic look that will appear on your face while you hide in your basement. And I'm the dumbass? I did mention using water
magnum9987 wrote:ive also thought of using dry ice and water. As the dry ice expands into gas it would provide superior thrust do to the presence of water.


While on the subject of fuel, could'nt say a simple vinegar/baking soda reaction work or is that TOO weak? Probably is and i havent tested it.
And Maybe rather than pvc ill just use plastic bottle.
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Unread postAuthor: judgment_arms » Mon May 12, 2008 8:12 pm

Sticky_Tape wrote:RPG? What is the grenade part if you didn't know it means rocket propelled grenade.


Actually its “Ručnoj [Hand-held] Protivotankovyj [Anti-Tank] Granatomjët [Grenade Launcher]


Brogdenlaxmiddie is right, dry ice is far from ideal for a propellant, particularly in PVC.

You’re going to wind up with performance akin to a unglued end-cap, no matter what you use for a propellant; unless you make a bona-fide water rocket, as I plan on doing this summer when it’s hot enough to fry eggs in the sidewalk.

For the record, yes, that means I still pan on making a water rocket Panzerschreck, for those who remember.
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