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Old May 15, 2009, 10:05 PM
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Hydrogen Blimp

I am interested in making a RC hydrogen gas(from now on just called hydrogen) filled blimp. I choose hydrogen because it has greater lift, and it's a lot easier to get. (Electrolysis with bi-carb anyone?). However, i am currently storing the hydrogen in 2L PET bottles. I want to know whether 2L of hydrogen gas is enough to even slightly, create lift over the PET bottle's weight. A PET bottle ways about 50 grams, but i could lesson that by not including the bottle cap and just making sure it does not go upside down. If it's not possible to use PET bottles as the container, what other extremely cheap/around the home material is there. I have the awesome ability to make paper balloons by origami.

I plan on combining lots of little lift bags if possible, so i can lift up a fair amount. Though, i don't want the dimension of the final thing to be greater than 1m x 1m x 50cm

(BTW, i'm new. hello everyone )
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Old May 15, 2009, 10:22 PM
Blimpman
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Whow!
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Old May 15, 2009, 10:51 PM
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Listen up my friend and listen up good!!!!!!!
Hydrogen + plastic in the presence of oxygen= hybrid rocket fuel, take it from someone who is from defense research!!!!
You are going to get yourself killed. One static spark and instead of a loud bang you are going to get an explosion with shrapnel flying around the place.
My advice cease all your amateur experiments and buy a canister of helium from a florist or a balloon /novelty store.

And by the way soda bicarbonate and acid produce carbon dioxide not hydrogen. And I hope that this is what you are playing with and not making hydrogen!

As to origami keep it up, just a bit of information in lighter vein, did you know that specialist in origami are employed in R&D into folding of parachutes, inflatables, antennas, solar arrays and other structures?
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Old May 15, 2009, 11:31 PM
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The bi-carb bit is about what i use to ionise the water, so that electrolysis can work. Table salt is bad, because that produces chlorine gas.

Anyway, I don't plan on letting a spark get anywhere near the hydrogen. I screw the bottle caps on under waters, so that i don't contaminate the hydrogen with air, which increases combustibility. This also reduces the chance of a spark hugely. I realize that if a spark was introduced when the cap was on, or narrowed, I would get shrapnel. I don't know if the neck of the bottle (which is about 2cm i guess) is enough to keep it safe. I don't think so though.

Quote:
Hydrogen + plastic in the presence of oxygen= hybrid rocket fuel
How exactly does that work? static electricity?, if so, do PET bottles get static electricity? I haven't experienced it. Are you saying the PET (Polyethylene terephthalate) is the solid fuel? The hydrogen the other?
Biaxially-Oriented PolyEthylene Terephthalate is a variant of normal PET bottles. It's other name is mylar. Mylar generates static electricity, only because it's so thin, and i'ts in a roll, or something like that. Normal PET soft drink bottles don't generate static electricity i believe.

What i really wanted to know by coming here, was how much lift (in the metric system), do you get per litre of hydrogen.
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Last edited by Jak_o_Shadows; May 15, 2009 at 11:53 PM.
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Old May 16, 2009, 10:26 AM
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The theoretical buoyancy of helium is -1.11 grams, To lift 35 ounces (1kg) you need 974.364 liters helium.

Essentially you are having an oxidizer propellant combination. Hybrid rocket engines use Liquid oxygen and Hydroxyl terminated Polybutadiene.
Hydrogen+ PET + Oxygen produces a similar albeit weaker sustained impulse reaction.
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Old May 17, 2009, 03:08 AM
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Quote:
Originally Posted by raejus
The theoretical buoyancy of helium is -1.11 grams, To lift 35 ounces (1kg) you need 974.364 liters helium.

Essentially you are having an oxidizer propellant combination. Hybrid rocket engines use Liquid oxygen and Hydroxyl terminated Polybutadiene.
Hydrogen+ PET + Oxygen produces a similar albeit weaker sustained impulse reaction.
Thx. For the rocket fuel, you still need to ignite it right? It won't spontaneously combust will it?

For the theoretical lift, by my maths there are 20 50s in 1000. (the PET bottle is about 50grams). So i divided 974.364 by 20 and got 43. Is that saying that i would need 48 Litres to lift 50g?


Thx for your help.
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Last edited by Jak_o_Shadows; May 17, 2009 at 03:56 AM. Reason: got the maths a little wrong.
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Old May 17, 2009, 08:30 AM
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48.715 Liters to be precise, rule of thumb assume 50 liters. This does not mean that if you compress 50 liters of helium into a PET bottle it will float.
It is the displaced volume of 50 liters in air caused by the relatively lighter helium that creates the negative buoyancy. So if you keep compressing it into the bottle instead of getting more lift you are in fact increasing the gas density making it heavier.
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Old May 18, 2009, 01:21 AM
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Quote:
Originally Posted by raejus
48.715 Liters to be precise, rule of thumb assume 50 liters. This does not mean that if you compress 50 liters of helium into a PET bottle it will float.
It is the displaced volume of 50 liters in air caused by the relatively lighter helium that creates the negative buoyancy. So if you keep compressing it into the bottle instead of getting more lift you are in fact increasing the gas density making it heavier.

Thx. That means i've gotta work out another method of getting a balloon. This makes it incredibly harder. I gotta have a think on it now.
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Old Jun 05, 2009, 03:45 AM
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I have been getting the hydrogen, but not very fast. I first tried a mixture of aluminium, copper (which is just the wires) and iron. The iron and aluminium disintegrated into their respective carbonates, massively weakening the reaction. I then changed the contacts to the carbon/graphite (the lead) out of lead pencils. That's kinda corroded, but i don't think i'ts carbon carbonate (cause i don't think that exists). I think it's just dissolved because the water was acidic/caustic. I took the oxygen bottle out, so that the non-hydrogen contact (can't remember it right now) was not in the water entirely. Just the carbon/graphite.Not the copper. The other contact (the hydrogen one) obviously has to be in the water. I think that might have corroded now. It's not working.


For the balloon, i'm thinking making origami balloons out of plastic bags. Not lightweight checkout-style bags, the thicker ones that lay flat. I'll have to use a bit of tape to join several together so more volume, less surface area, less weight. I'll use wire to join to the corners a bit up. Then maybe close the end up. I haven't really thought of how to get the hydrogen in, but i'll figure it out when i have enough.
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Old Jun 06, 2009, 06:03 PM
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Well, it aint working at all. The water is apparently not conducting electricity. When i put my hand in the water (not when battery is connected), when i take my hand out it feels all slimy and slipperly. I remember being told bases sometimes feel like this (if that's relevant). Anyway, i have yet to test for other conductivity through different wires, mostly because i don't have any torches i could dissemble to use the light bulb. That's probably what i'm gonna do next.
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Old Jun 06, 2009, 10:19 PM
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Yeesh! Ok listen up, I'm taking no responsibility for the following advice. If its hydrogen you want via eletrolysis you are going to need a set of platinum electrodes, those are the only things aside from graphite that are not going to react with the nacent hydrogen or oxygen. I'm not sure what precautions you are taking to contain the 2 gasses produced but all I can say and emphasize is that you are seriously treading dangerous ground with your experements. The water you felt is probably sodium hydroxide, and I would not be surprised if your hand is itching. And if you do get sludge on the top in the form of green/ brown scum its cupric or ferric chloride/ sulphate. My honest suggestion would be to please go out and buy yourself a canister of helium from a florist/ balloon store. And as to using polythene material for bags, it is not too good an idea, first of all hydrogen is such a small molecule that it will simply leech out of the bag really fast without giving you much practical time or lift as the material is heavy and at a microscopic level would look something like trying to hold water in a cotton bag, further more, there are additives called fillers and colouring agents like carbon/ titanium dioxide that make the material more porus. I would suggest you try looking for Poly vinyl chloride sheets (PVC). Good luck.
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Old Jun 07, 2009, 06:48 PM
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well, you're right with the fact that it'll leech out. It leeched out massively and didn't work at all. At the moment i'm water-testing the capturing system, because i think it kept leaking. So it'll be a while before i actually get to do anything. Plastic bags don't work, i'm guessing paper won't, so i'll have to try something else.

Thanks for helping me, even thorough you've made it clear you think i'm an idiot. :P
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Old Jun 07, 2009, 10:03 PM
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You have me wrong. It is not my prerogative to judge your actions. I was merely stressing upon you the dangers of handling hydrogen.
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Old Jun 07, 2009, 11:21 PM
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Quote:
Originally Posted by Jak_o_Shadows
When i put my hand in the water (not when battery is connected), when i take my hand out it feels all slimy and slipperly. I remember being told bases sometimes feel like this (if that's relevant).
Um your hand feels slippery because the base is literally dissolving your skin into a soap-like substance. DONT put your hand to see if something is basic (or acidic for that matter)!!! lol
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Old Jun 09, 2009, 01:32 AM
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well, thanks, i know that now. My skini started peeling a tiny bit. Next time when i need to put my hand inn i'll wash it after, not just dry it :P

I'm working on figuring out a stable system. So far, the copper has dissolved too much. That stops it working. I want it to work 24/7. I think using carbon/graphite from lead pencils is the way to go for me, but i gotta stop water from getting access to the copper. Either that or get platinum wire :P
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