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water balloon combustion

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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water balloon combustion

Unread postAuthor: Dgealy » Sat Dec 20, 2008 11:28 pm

Does anyone think that a combustion launcher can launch a water balloon without breaking it?

My thought is that the pressure spike would pop it. Also it would need to be full enough to rupture on target (Generally the ground or a tree or something of that sort).
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Unread postAuthor: twizi » Sat Dec 20, 2008 11:35 pm

i launch water ballns with airsoft bbs in them in airsoft wars some time they pop but this is in a pneumatic
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Unread postAuthor: IA_Armourer » Sat Dec 20, 2008 11:40 pm

a combustion would make the balloon pop because it will burn a hole in the rubber. you could put a wooden plate between the combustion chamber and the balloon or sabot the balloon
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Unread postAuthor: Dgealy » Sat Dec 20, 2008 11:43 pm

I'm not sure if it would burn a hole in the balloon, because the balloon will be filled with water, which would absorb the heat.

Watch one of those videos where they take a lighter to a water balloon for 30 seconds or so.
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Unread postAuthor: inonickname » Sun Dec 21, 2008 12:23 am

http://scifun.chem.wisc.edu/HOMEEXPTS/FIREBALLOON.html

But water balloons are a lot thinner. I've also tried burning water balloons with a propane torch, they burst instantly. I'd just try it.
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Unread postAuthor: Eddbot » Sun Dec 21, 2008 1:22 am

If it pops in the barrel *ahem* When it pops in the barrel, it will be from the pressure spike, the amount of time the flame from deflagration is in contact with the balloon isn't long enough to actually burn it.

This has been discussed before, here, and built, here, just don't use DWV fittings like that guy...
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Unread postAuthor: Pyro Ninja » Sun Dec 21, 2008 3:40 am

I've heard of people using a paper cups as a sabots for water balloons, with success.
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Last edited by Pyro Ninja on Mon Dec 22, 2008 1:20 am, edited 1 time in total.
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Unread postAuthor: FishBoy » Sun Dec 21, 2008 8:35 am

Pyro Ninja wrote:I heard of people using a paper cups as a sabots for water balloons, with success.


You stole my reply. Eddbot is correct, a plain water balloon will burst from the pressure spike. However, If you can make a good sabot for it, like a paper cup, or some kind of foam, it will work fine.
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Unread postAuthor: jimmy101 » Sun Dec 21, 2008 12:03 pm

FishBoy wrote:
Pyro Ninja wrote:I heard of people using a paper cups as a sabots for water balloons, with success.


You stole my reply. Eddbot is correct, a plain water balloon will burst from the pressure spike. However, If you can make a good sabot for it, like a paper cup, or some kind of foam, it will work fine.

No it won't. The pressure spike, even if the pressure spike was a zillion PSI won't burst the balloon. Water is essentially incompressable so even if the pressure in the balloon changes significantly the force on the rubber changes very little.

A water balloon will tend to break in a barrel because of the friction between the ballon and the barrel, not because of the acceleration directly affecting the ballon.

Using a paper or plastic cup as a sabot I've launched small water ballons at ~300 FPS. I would think they would survive even higher accelerations and velocities. During launch the balloon will just deform to match the shape of the cup. The total volume of the ballon changes very little and the forces on the rubber don't really change at all.
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Unread postAuthor: Giorgio » Sun Dec 21, 2008 6:36 pm

actually your half right... but the friction, and also the acceleration is what bursts the balloon... and the area of spike you have... if its the size of a pin head with 20zil psi... the balloon will explode and water will be shot out... but its less likly for a balloon to burst if the pressure spike is the size of the balloon or larger..
You use a cup.. i use a cup to protect the round things (balloons, not nuts) and it works.... ive tryed to heavily oil the inside of my barrel and the pressure plus friction still bursts.. even one time i use oil based lube... nup nothing..
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Unread postAuthor: Dgealy » Sun Dec 21, 2008 6:53 pm

Alright. Yeah, i've been testing that today. I was making hour glass shaped sabots out of dixie cups. It worked beautifully.

Thanks
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Unread postAuthor: jonnyboy » Sun Dec 21, 2008 7:52 pm

IA_Armourer wrote:a combustion would make the balloon pop because it will burn a hole in the rubber. you could put a wooden plate between the combustion chamber and the balloon or sabot the balloon

It won't pop.Fill up a balloon with water and put a match to it. The plastic gets burnt but won't pop for a while.
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Unread postAuthor: Hotwired » Sun Dec 21, 2008 8:13 pm

jonnyboy wrote:
IA_Armourer wrote:a combustion would make the balloon pop because it will burn a hole in the rubber. you could put a wooden plate between the combustion chamber and the balloon or sabot the balloon

It won't pop.Fill up a balloon with water and put a match to it. The plastic gets burnt but won't pop for a while.

To go mildly off topic for a post I read a patent not too long ago which was about resisting attacks on bank safes.


Bear with me :P



The idea was to resist attacks by thermal lances which can cut through pretty much anything a safe is likely to be built of, concrete, steel, hardened steel plate which resists drilling etc...

The patent covers the use of copper plate and water behind the conventional stuff to act as a massive heat sink for the safe door. The tests run showed that although not even that could resist a thermal lance indefinitely, it would take so long and consume such a vast quantity of oxygen that it would make such an attack impractical.

Random recollection of the day.
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Unread postAuthor: btrettel » Sun Dec 21, 2008 11:34 pm

One of my hobbies is water guns and I run a forum about it. We discuss water balloon launchers too, but to a more limited extent.

I remember some discussion about how water balloons are limited to a certain amount of acceleration. Someone basically took their most powerful spud gun, which had a 2 inch piston valve actuated by a QEV if I remember correctly, and used it to launch balloons. The balloons were in a sabot so friction was not a problem. I'm not sure if he used actual water balloons or regular balloons, but I think the diameter was 3 inches so I'd lean towards regular balloons. He found that no matter what pressure he used, he couldn't shoot water balloons without popping them with that gun.

He could shoot water balloons with weaker guns, but his best was too much for the balloon. The initial acceleration must have been too high he concluded.

I'll have to look for the discussion and post a link because my memory's a little shady. It was interesting.
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Unread postAuthor: jimmy101 » Mon Dec 22, 2008 3:13 pm

Giorgio wrote:actually your half right... but the friction, and also the acceleration is what bursts the balloon... and the area of spike you have... if its the size of a pin head with 20zil psi... the balloon will explode and water will be shot out... but its less likly for a balloon to burst if the pressure spike is the size of the balloon or larger..
You use a cup.. i use a cup to protect the round things (balloons, not nuts) and it works.... ive tryed to heavily oil the inside of my barrel and the pressure plus friction still bursts.. even one time i use oil based lube... nup nothing..

Nope, you still don't have it right. Only in the rather bizzare case of trying to push a balloon out's a barrel with a sabot that looks something like an oversized thumb tack.

The force on the balloon's butt is the same everywhere, there is no focused load. The water and the ballon will nearly instantly reorganize into a cylindrical shape. That puts very little load on the balloon. Only friction between the barrel and the ballon distorts that shape. Since the load is evenly distibuted across the balloon's butt it won't pop from the pressure or the acceleration. Only friction between the balloon and the barrel will burst the balloon. With a cup shaped sabot or a frictionless barrel you should be able to accelerate the balloon to as many Gs as you want. The balloon won't be bothered by the G forces. (Of course, it might not survive long once it exits the barrel.)

As I said before, water is incompressable, so the pressure in the balloon doesn't change as it is accelerated. (well, it changes by a very slight amount at very high accelerations, not enough to affect the balloon.)

If you take a water balloon and put it in a pressure chamber you can pressurize the chamber to any pressure you want and it won't bother the balloon. Pressurize the chamber to giga-atmospheres of pressure, won't bother the balloon one bit.
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