Solar Hot Air Balloon Message-in-a-Bottle





Introduction: Solar Hot Air Balloon Message-in-a-Bottle

This is a hot air balloon made from trash bags and heated by the sun. Once airborne, it should stay up 'til the sun goes down or behind the clouds. Needless to say, it can travel a long, long way. Attached to it is a "message-in-a-bottle" asking anyone who might find it to email their location, just to see how far it flew. There's just something romantic about a message seeking out who-knows-whom in far away who-knows-where.

As a note, as boys, my brother and I lived on a tidal river in Florida. Walking the mangroves, we found a couple of messages-in-bottles that people sent. One came from another state. It said something like, "Send a postcard with your address and we'll send a present." My brother sent a note and sure enough they sent back a King James Bible (it was a "Fishing for Men" outreach project by a Georgia church). He still has that Bible. It was inspiring to think of how far that message had come and the path that it took. The magic of a message-in-a-bottle is to imagine, "Where will it go?" and, "Who will find this?"

Step 1: Materials and Tools


1. Trash bags -- They must be THIN, I used 0.6 mil but the thinner the better. Most quality bags are heavy, at least 1.0 mil. We want the cheap-O bags.
2. Tape -- I used regular masking tape. Likely scotch tape is okay too. Don't use the wide package tape though--too heavy.
3. Thread
4. Pen and paper
5. Plastic bottle -- I actually had to get rid of the bottle because it added too much weight.

1. Scissors
2. Blow drier

Step 2: Layout and Taping

This may look harder than it actually is. To go with the pictures, I tried to sketch some diagrams. Just realize that it's pretty simple.

Get 4 bags and cut them open by cutting the bottom and ONE side. It'll unfold then to a big rectangle. Lay out all 4 opened bags like in the picture/diagram. Tape them together to make a huge rectangle.

STEPS 2 and 3
Fold the huge rectangle over then tape the two sides closed. You now have only the bottom untaped and open.

STEPS 4 and 5
Hold the center of the open seam and lift it open so that the points marked A & B in the diagram come together. Tape and seal off the last open seam.

Step 3: Write Your Message and Inflate It

Get your message ready. Once it's inflated, it's go-time! I scratched the plastic bottle after it became clear that it was weighing down the balloon. I just rolled up the message, then tied it off with a piece of thread about a foot long. Essentially, the message asked for an email back to me simply saying where the balloon was found.

Just as a note, since this is a SOLAR balloon, so you'll want to do this on a bright sunny day.

Cut about 3 inches off of one corner. Just cut enough to shoot hot air in it from your blow drier. Simply start blowing hot air into the balloon. Be careful not to burn or melt the bags. The balloon will quickly take shape.

As soon as it's inflated, twist the opening so it closes, then tie your message onto it. Once inflated, I moved into the sunlight so the sun would start heating it up.

Step 4: Watch It Go!

Nothing much to say here, launch it and watch it go!

After floundering around a bit, it started to gain some altitude, bounced off some power lines and shrubbery, then finally got above the treeline. Then it was gone!

I intended to chase after it on my bicycle. I quickly saw that was pointless. Within 10 minutes, it was out of sight last seen heading north--still gaining altitude. It's hard to guess the distance, but I'd say 5 miles in 10 minutes (that'd make it 30 mph once it got up high).

Now, it's just wondering where it went, how far, and hoping that someone finds it and shoots back an email.

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    114 Discussions

    THis is TOO FUNNY a big argument over the moisture content of the air in tha bag BUT WAIT ! There's MORE .That bag can get caught in the JET ENGIONE of a plane. when that happens the plane will come down or land and They will read your message and know where you live. We used to set off huge bags with helium in them . and Like fools the bags had the company Logo on the side.
    They were 10 feet long and we would watch them at the "Lunch Launch. But one day The cops showed up because they were getting in to the flight path of the Air port 15 miles away. We got 1 warning to stop. Next they would have put us in jail YEP that's fact.

    3 replies

    plus, if it gets in a jet ENGINE, in would likely be destroyed. might not even hurt the ENGINE.

    Plastic bag versus super heated pressurized air plus jet fuel inside a jet engine with titanium blades?????? Lets say shredded and burnt only to become fuel for the engine and adding to the its thrust.

    The volume of 1 mole of any gas at slandered temperature and pressure is 22.4 liters.

    1 mole of oxygen gas (O2) = 32 grams. 1 mole of nitrogen gas (N2) = 28 grams. 1 mole of water (H2O) = 18 grams.

    In terms of density (O2) = 32G/22.4L; (N2) = 28G/L; and (H2)=18G/22.4L

    Water vapor, at 18 grams a liter has a lower density than the two main components of our atmosphere. liquid water is is not governed by gas laws and has a density of 18 grams per milliliter over a wide range of temperature. You don't need to separate the compounds in water to determine its density, but you do need the atomic masses of the atoms that make up water to determine molar weight.


    Damp air is lighter than dry air. Maybe you can inflate the balloon with your lungs (many persons, because it is a great volume) instead of the hair drier. That should give it longer scope/range.

    14 replies

    Maybe you can get a spray bottle and 'spritz' the air going into your hair dryer. That possibly could make the air damp, especially if you put the heat on high.

    DON"T DO THIS!!!!
    The water will make the thing too heavy to fly, and you'll be too dead to observe the effect.

    The volume of 1 mole of any gas at slandered temperature and pressure is 22.4 liters.

    1 mole of oxygen gas (O2) = 32 grams. 1 mole of nitrogen gas (N2) = 28 grams. 1 mole of water (H2O) = 18 grams.

    In terms of density (O2) = 32G/22.4L; (N2) = 28G/L; and (H2)=18G/22.4L

    The bigger issue is with air a few degrees above ambient temperature, how do you keep water in vapor form rather than in condensed form. The answer is that it can hold only as much water as 100% humidity for a given temperature and pressure. at 100% humidity, a drop in temperature will cause water to condense to smaller than 1/1,600 its vapor form.

    Incredibly DANGEROUS and stupid idea...
    Your post should be removed
    Spraying water into a hair dryer? surely you jest!

    as long as you don't spray salt water you should be fine. Saltwater conducts electricity more than tap water. Everybody knows that.

    Distilled water would be the safest. Tap water has all kind of minerals and iron in it. Ever see rusty water? That's iron and it is conductive.

    Too Funny!!!....... true salt water does conduct better than tap water..... Tap water will still kill you ... maybe you will not be as dead with tap water as with salt water but dead is still dead :-)

    Air is about 78% Nitrogen (N2) , about 21% Oxygen (O2) and about 1% other gases. Nitrogen has a molecular weight of 14 so a N2 molecule has a molecular weight of 28. Oxygen has a molecular weight of 16 so an O2 molecule has a molecular weight of 32. given the ratios of air and the molecular weights of the components, air has a molecular weight of 28.6 (0.78 * 28 + 0.21 * 32 = 28.6).

    Water is made up of two hydrogen and one oxygen atoms (H2O). Hydrogen is the lightest element and has a molecular weight of one. So a water molecule has a molecular weight of 18 (2 * 1 + 1 * 16 = 18). Water is a very light molecule and much lighter than the average weight of the molecules found in air.

    as you can see above water vapor is lighter than air, and when the air is moist, water vapor displaces an amount of air (replacing heavier air with lighter water vapor), thereby making the moist air lighter. Of course the temperature and pressures must be the same for this to be true.

    Included is a link to calculate weight of dry air, moist air and amount of water vapor in moist air.

    Yes, water vapor is a little lighter than air, but when it condenses on the bag, which is cooler than the air inside, it turns to liquid water, which is hundreds of times heavier.

    Yes, liquid water is indeed heavier than water vapor by volume, but you don't just add mass. You keep the same mass you had, but it's in a smaller package.

    Here, you have X grams of water in the form of vapor inside the bag (if you do the trick he suggested). Once the surface of the bag cools below the dewpoint for that humidity, those same X grams will drop out of vapor form into liquid water on the inside of the bag. But you won't ADD mass - it will just be in a different form.

    By turning the vapor into liquid the bag's volume will decrease (since X grams of liquid water is a lot smaller than X grams of water vapor - remember the capped steaming tin can demo in high school). Thus the total mass of the airship will still be there but the volume will have dropped, making it more dense (density being mass/volume), so it will lose bouyancy.

    Well, yes, Paymeister, I should have said 'hundreds of times heavier than the same volume of air', which is what I meant.