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Using ejection charge to inflate a balloon

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dwtno

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I'm picturing a rocket with a mylar balloon that inflates via ejection charge gases. The balloon would act similar to a streamer and slow descent, though if the rocket ends up being too large, may have to be combined with a parachute. Has anyone attempted this?

Issues to be solved would include:
- ducting the gases into the balloon
- preventing the hot fuel particles from burning/melting the balloon and ducting mechanism
- sealing the balloon to keep the gases trapped

I'm sure there are others!

Anyone see a way forward here or is this just a fancy balloon dream?

Thanks!
 

Funkworks

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I like this a lot but I doubt it can be done with a conventional ejection charge.

Using a separate gas cartridge on the other hand. I see no obvious barriers.
 

dwtno

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You may well be correct about the practicality of this, but I’d like to pursue the idea of ejection charge inflation even if just as a thought experiment.

If you *were* going to try this, how would you do it?

Thanks!
 
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kuririn

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Your starting point would be finding an inflatable lightweight thin membrane material that is fire resistant.
Oh, and cheap.
Don't know if such a material exists.
Then go on from there.
 

NateB

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There is a novelty firework where a cardboard tube with pressed whistle mix blows up a balloon to look like a chicken egg. It is small, but the balloon doesn't melt.

Car airbags are deployed by an explosive charge and e-match, so your idea has merit. I'm not sure if it is practical as a deployment technique or would be legal until any rocketry association rule. I dont think a small amount of BP would work and a different fuel would need to be used.

If I were to tackle that problem, the first thing I would attempt is using a CO2 cartridge that was broken by a pin fired by an ejection charge and triggered from a flight computer. CO2 cartridges work to inflate bike tires, so a balloon wouldn't be a far step.
 

dwtno

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Your starting point would be finding an inflatable lightweight thin membrane material that is fire resistant.
Oh, and cheap.
Don't know if such a material exists.
Then go on from there.
Doesn’t Mylar fit that description? It wouldn’t have to be an elastic latex type material to serve as the type of balloon I‘m picturing.

Thanks!
 

NateB

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Not necessarily cheap, but Gampi paper is used in Japanese fireworks for parachutes and other effects. The Chinese make some ball shells that deploy lanterns, streamers, and other effects and I assume they are more economical than the Japanese factories. The paper effects usually are separated from the BP burst by Rice hulls, paper, and other means to prevent the parachutes from burning.

 

kuririn

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If I were to tackle that problem, the first thing I would attempt is using a CO2 cartridge that was broken by a pin fired by an ejection charge and triggered from a flight computer. CO2 cartridges work to inflate bike tires, so a balloon wouldn't be a far step.

Rocket would have to be big enough to handle the additional weight of the hardware. And at that weight a heavier than air balloon would be less effective in slowing the descent rate than more traditional methods.
 

kuririn

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Doesn’t Mylar fit that description? It wouldn’t have to be an elastic latex type material to serve as the type of balloon I‘m picturing.
Mylar is not fire resistant. Not even close. Take a look at a mylar parachute after ejection and you will typically see pinholes in the material. Pinholes and balloons don't mix well.
 

kuririn

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There is a product called Nomex paper.
I think it is fire resistant to a degree, but it does burn when subjected to sustained heat.
I got some a few years ago and tested it.
Not flexible and stretchable though.
 

NateB

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Rocket would have to be big enough to handle the additional weight of the hardware. And at that weight a heavier than air balloon would be less effective in slowing the descent rate than more traditional methods.
Very true, I didn't notice this was in the LPR forum right away either.
 

NateB

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Here is a video of a balloon inflating by a small pyrotechnic device. Now that I think about it more, it might actually work to get some laughs in a mosquito or something safe with tumble recovery.

 

Joshua F Thomas

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Keep in mind that explosives (ie, ejection charge) just create a pressure wave, the air still has to come from somewhere. You need to be able to let air in to fill that balloon, and then not let it back out again.
 

NateB

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Keep in mind that explosives (ie, ejection charge) just create a pressure wave, the air still has to come from somewhere. You need to be able to let air in to fill that balloon, and then not let it back out again.
About 40% of the byproducts generated by the combustion of black powder are various gasses. The increase in pressure is because the gasses and solids generated by combustion take up more space in the container than air and recovery equipment.
 

Joshua F Thomas

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Oh, I forget how inefficient black powder will be [as an explosive]. Good point.
 

dwtno

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Mylar is not fire resistant. Not even close. Take a look at a mylar parachute after ejection and you will typically see pinholes in the material. Pinholes and balloons don't mix well.
Damn! Didn’t know that!

Thanks!
 

kbRocket

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Easiest solution:
Take apart a the chicken blowing balloon and put the components in a rocket.

Seems fire resistant. Just leave out the vertebrae.
 

kbRocket

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It is obviously problematic to properly seal a chicken skin. So, on a slightly more serious note, I have wondered about using water as nose weight which would be dumped out at apogee to reduce the descent mass.

An extension of this would be to use a weak acid like vinegar. At apogee something like an igniter pops a hole in the vinegar bladder and allows it to mix with baking soda and inflates the balloon. It's probably difficult to both inflate and subsequently dump acid rain...
 

Kelly

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If it had to be pyro, I would use something slower burning than an ejection charge - maybe a compressed pellet of propellant; and pass the gasses through some sort of heat-absorbing filter - like a pot scrubber, e.g. - before going into the balloon. Some sort of one-way valve would be needed to keep the balloon inflated. Seems like a lot of trouble.
 

Funkworks

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You may well be correct about the practicality of this, but I’d like to pursue the idea of projection charge inflation even if just as a thought experiment.

If you *were* going to try this, how would you do it?

Thanks!
The ejection charge could blow out the cardboard body tube, so i think I’d first glue a metal tube around the motor and along the inside tube, but this is borderline "legal", thus my initial post.

Assuming the rocketry associations accept that, epoxy is the most obvious way I see to seal in the gases and force them into a chosen direction (forward inside the metal tube).

So now at least the gases are forced away from the cardboard, but they might be able to blow out the motor itself and release from the back end instead of the front (depends on the valve used to control flow in balloon). So now further progress depends on how tough is the motor barrier that separates the propulsion charge and the ejection charge.

Basically, blowing the balloon needs to be controlled, but the ejection charge releases too much energy in too short a time. Model rocket materials can't contain this and therefore don't allow controlled gas flow.

Gas cartridges, which are already made of metal and don't release energy as quickly as an ejection charge, seem like the way to go.
 
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Funkworks

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This post is a double post so maybe a moderator can delete it.
 
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Steve Shannon

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Keep in mind that explosives (ie, ejection charge) just create a pressure wave, the air still has to come from somewhere. You need to be able to let air in to fill that balloon, and then not let it back out again.
Black powder and other gun powders function as gas generators, not as high explosives.
 

GlenP

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Maybe not helpful in this situation, but have you seen those new water balloon kits that hook up to a garden hose with about 50 balloons on their own individual straws with a rubber band around theinecks? The water pressure fills the ballon and when their weight is sufficient they have enough force to pull themselves off the straw and the rubber band seals them as they pop off.

None of that would work in a high temperature environment of course, but the principle might inspire an idea here.

Can you use a through tube partially inserted into the Mylar heat resistant balloon? Can you have some kind of venting or baffle to prevent overheating? Can a small spring mechanism be used to seal the ballon after it pulls off the tube? Or does the Mylar balloon have a self sealing neck? I will leave it up to you. Good luck!
 
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Kelly

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Some sort of one-way valve would be needed to keep the balloon inflated.
EH, I don't know why I thought a valve was needed, the whole thing needs sealed, anyway. So here is what I would do: Take long, thin cardboard tube. Seal one end, and pack a bit of black powder or other gas-generating mixture into it. Place an ignitor on top of that. On top of that goes some metal pot-scrubber material, and, finally, the balloon goes over the other end of the tube. You need a gas-tight exit point for the igniter wires in the middle somewhere.
 

lakeroadster

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Oh man... I so want to see a "Bench Test" of this.

I wonder how NASA did the inflatable balloons on the Apollo capsule?
 
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les

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What if you used a baffle, one of the types with a metal mesh, to absorb the heat and the output of the baffle feeds the balloon?
 

Kelly

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What if you used a baffle, one of the types with a metal mesh, to absorb the heat and the output of the baffle feeds the balloon?
That's what I mean by a 'pot scrubber' - one of those stainless steel, or copper, meshes you use to clean pots & pans.
 

Kelly

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Aw, heck, I was bored, and haven't played with pyro for a while, so I whipped something up. Here it is, the Rocket Balloon Inflating Device, version 0.3:
IMG_20200924_205313233.jpg

















That tube is about 1/4" ID and 7'16" OD. To the left of the igniter wire is a clay plug, and about 1/4" of pyro comp. To the right is packed with stainless steel scrubber, and the balloon.
QED
 

jqavins

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I confess I haven't read all the posts.
I'm picturing a rocket with a mylar balloon that inflates via ejection charge gases. The balloon would act similar to a streamer and slow descent, though if the rocket ends up being too large, may have to be combined with a parachute. Has anyone attempted this?

Issues to be solved would include:
- ducting the gases into the balloon
- preventing the hot fuel particles from burning/melting the balloon and ducting mechanism
- sealing the balloon to keep the gases trapped
- Having just the right amount of gas to fully inflate the balloon but not burst it (assuming a non-stretchy balloon like a mylar one).
- Pushing the balloon out so its inflation doesn't just burst the body tube.
- The balloon effectively deflating as the ejection gas cools.

As for sealing the balloon, there are small, cheap plastic check valves meant for balloon inflation. Here's an example.

I'd start with a dead simple test.
  1. Put a balloon's opening over the ejection end of the motor size of your choice (I assume either 13 mm or 18 mm).
  2. Clamp the motor to something.
  3. Light the motor and see what happens.
  4. Post a report, preferably including video.
If that goes well, we can talk about the next development and testing stage.
 
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