Instructables
This instructable will show you how to make a hot air balloon. This balloon will not use any sort of flame to make this, though. Instead, it uses the sun to heat the balloon. I saw this at American Science & Surplus, but it was $17.50 USD, so I wanted something cheaper; I went out and made my own!
 
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Step 1: How it Works

Picture of How it Works
The black color of the trash bags makes the air inside heat up. Everyone knows that hot air rises, thus making the balloon rise.

Step 2: Materials

These are the things you need:
  • 30-Gallon Black Trash Bags
  • A large roll of duct tape (preferably black color), or a large roll of clear packaging tape
  • Scissors
  • A LARGE, dirt free environment without wind
  • Something to pump air with adequate volume (like the exhaust port of a shop vac)
  • Two or more hands
  • Free Time

Step 3: Prepare the garbage bags

First, take out about seven garbage bags. These will be the body of the balloon. After the bags are taken out, cut off the sealed ends of all but two of the bags. These are to extend the body of the tube, and also act as a coupler for each other garbage bag. Then, lay out four garbage bags, including one uncut garbage bag, on the large, clean surface. The surface needs to be clean, otherwise dust and dirt will prevent the tape from sticking to the bags. Finally, place the garbage bags inside one another, about 1 inch. Make sure that you place the bags inside one another so the air can travel though, without getting stuck in any crevices.
pkmn4 years ago
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Eye Poker pkmn2 years ago
I refer you to Charles Gas Law.

http://physics.info/gas-laws/
ongissim (author)  pkmn4 years ago
Of course, it isn't going to stay inflated.
Thanks for this. Might try this with Ados glue instead of duc tape? Filled with home made Methane might be fun. http://www.youtube.com/watch?v=SrVC4XKR2s4
homemade methane: you mean fart in a bag?
(didn't watch youtube link)
brokengun3 years ago
My friend and I used to do this for fun. Our most successful flying design was more of a pyramid shape. I would also suggest filling them initially using a hair dryer, be careful not to melt the plastic but it really improves the lift.

The hardest part is just getting them off the ground a ways, once they're airborne and above the trees they will be blown around and will usually take off.

Check out our flight: http://www.youtube.com/watch?v=Yuj8LnTBFLY

I think this is an AWESOME idea. But I have one question, How many bags would I have to use to lift a small point and shoot camera?
my guess is that on a sunny winer/fall day at least double for this design.. but their are other designs that use less tape such as a very long tube.but to be honest i wouldn't trust this with my camera i would use a couple helium filled weather or a bunch of party sized balloons.
sorry i didnt know i was on the long tube instructable.. but if you search for solar balloons youll find a ton
nate1215 years ago
yea heh heh dont let this go near air ports ther think its a ufo or sumthing and cancelle a lot of flights and comircil airports will have it shot down...by the airforce thinking its a threat to national security or somting like that. i know my local small air port the owner comes out with a rifle and shoots em till they come down.
1- In most places in the U.S., it's illegal to discharge a weapon into the air. 2- Everywhere in the universe it's stupid to discharge a weapon into the air. Don't know why? I shot a arrow into the air it came to earth, I know not where. That's right, boyz 'n girlz, gravity. Don't be stupid like Mr. Airportowner, 'cause once you kill someone, you can't unkill them.
Just firing a .22 caliber round can travel up to a mile, not accurately but still you could do a lot of damage if you shot your weapon into the air.
lol!!
...
I can see why he would shoot them down; aircraft approaching or taking off could easily get the balloon sucked into an engine, much like a bird strike. The farther up in the sky they go, the smaller the chance of an aircraft colliding with one. I wonder if there have been any weather balloon strikes on aircraft...
Paymeister3 years ago
Might also try it with a surrounding bag of clear plastic. It would add weight, but it would keep the heat of the black bag from radiating.
Paymeister3 years ago
Hm... (regarding added weight of duct tape)...

How 'bout adding no weight at all? Just need a heat sealer (I've purchased 'em used for $30 or so):

1) Placing the cut bag (=tube element) inside the end bag;
2) With edges even with each other;
3) Use impulse sealer (=industrial heat sealer) to seal exposed ends;
4) Roll bag assembly towards or away from you until you've sealed the whole circumference;
5) Pull the cut bag (=tube element) out of end bag, leaving the sealed edges sticking outwards (trim them with scissors if desired);
6) Add the next cut bag (=tube element) and repeat;
7) Continue 'til last bag: use the end bag rather than a cut bag (tube element) stuffed into the assembled long tube, with edges aligned.

Might be a bit rough, as the 'bite' of the impulse sealer will be more like a series of scallops as you twiddle the bag (you can't seal continuous lines longer than the unit's size, so you have to lay just that length into the sealer, then move along). But it would probably be doable. Will try and post results... in my spare time...

Thanks for the fun idea!
25_0.jpg
overlap your plastic at the seams and put wax paper on top and bottom and use an iron to heat/melt them together (practice beforehand to know best temp and speed for moving the iron to seal completely). Much lighter/smoother...give it a go!
Paymeister3 years ago
If you pressurize your balloon you'll lose bouyancy and risk leaks or tearing, so you want the less dense hot air pressure to be the same 'pressure as the outside air. To do that you do the weather balloon trick of starting with a partially filled balloon.
.
Doing the math: Let's assume the air inside the bag is going to get 25 degrees hotter than outside. I'll measure it if I try this project, but let's just throw some numbers around. (I chose 25 for a reason: stick with me.) A change of 25 degrees F = a change of about 14 degrees C (C=F*5/9, ignoring the 32 degree fudge since it's a difference we're talking about); this is also the change in degrees Kelvin, since the C and K degrees are the same size.

PV=nRT is the universal gas formula where P=pressure, V=volume, n=number of molecules, R=gas constant, and T=temperature in degrees Kelvin 

P you want the same (see above); n and R don't change, so what you get is: V=fT (f being a fudge factor), so

V1=fT1 and V2=fT2

Solve for f:     f=V1/T1 and f=V2/T2

Combine the two: V1/T1 = V2/T2

Collect Volumes on one side an Temps on the other: V2/V1 = T2/T1

Thus the percent change in volume (V2/V1) is proportional to the change in temperature (T2/T1) ...which you knew: hotter = bigger

But what is the percent change in temp? Thus, if T goes up by 25 degrees F = 14 degrees Kelvin (from the wild guess, above), it's going from about 300K to 314K, or a change of about 5%. (This assumes that it is 80 degrees outside.)

So, if one UNDERFILLS the bag by five percent, it will inflate completely and to neutral pressure when it warms to 105 degrees F.

To do this one would measure the bag length in inches and multiply that by 0.05, and roll up that length of plastic at the end and put some books or a board on it, fill to desired plumpness, seal, then remove the weight and let the bag slump a bit. For a ten-foot-long balloon that would come to six inches rolled up before inflating.

I think. It's 3:41 AM...
pkmn4 years ago
(removed by author or community request)
ongissim (author)  pkmn4 years ago
I've only used mine during the summer, usually about an hour before dusk.  I suppose it would work better in the winter, though only if you can keep the bags' internal air heated adequately.  My hypothesis on this is that colder temperature means lower pressure, and the heated air in the balloon is hotter, which has a higher pressure.  Therefore, the balloon would go higher when the external air is colder.
Not quite. As air expands it becomes less dense. If the air in the trashbag becomes less dense relative to the air outside the bag it will rise. So, the best time to do this is on a very sunny, cold, low wind day. Even if it's really cold outside the black of the bag will absorb the heat and transfer this heat to the air inside the bag.
Mine works great in the winter, but I've never used it in the summer

ANDY!4 years ago
i made one and left it outside under a book. it's gone now...
lolifer4 years ago
When I was in Ukraine a few years ago, I saw a man flying a whole mess of these balloons shaped like dolphins in a local park. It was really wonderful and surreal.

I'm glad I now know what these are, and I'll def try making one.
My balloon made its best flight ever a few days ago, It went soooooo high! but when I tried pulling it down (mines attached to a string) it landed in a tree.

I guess I saved the best for last
pkmn4 years ago
(removed by author or community request)
ongissim (author)  pkmn4 years ago
It usually heats up within three or four minutes on a non-cloudy day.  I wouldn't recommend a hair dryer, just because the initial temperature of the air doesn't matter (unless it's really, really cold).
I made one of these, it worked! It was really cool. It only works on very sunny days, no clouds. I used some thin fishing line (8 lb I think) and and old fishing rod and reel to keep the balloon from floating away and ending up in a sea turtles stomach.
AdamYea5 years ago
to fill just run with the bag open above ur head then u dont need an air compressor
hahahahahahhhhhh
beezee24 years ago
It would be nice to see a short video clip that shows that this will actually float... It seems that with all the duct tape it would be too heavy...? In my high school there were a bunch of guys that did this same type of balloon, but filled it with natural gas which is lighter than air, but not nearly so as helium... But their balloons floated pretty well!
twocvbloke5 years ago
hehehe, phallic... :P If you get it all set up right, you can use them to get aerial shots by attaching a wireless camera to it, if you can get it high enough that is... :D
eugarps5 years ago
Gathering from the sum of most of the comments above, it seems that "Lightweight construction" is a crucial element in success. Having said this, I was wondering how much "pull" this balloon has in ideal conditions? I was thinking of scaling this idea up in order to do some aerial photography, very akin to "kite" photography. It seems that this would be a better solution in my geographic area, as there is rarely enough wind to fly a kite reliably. I have a nice digital camera and Handycam, each in the realm of 1-2 pounds. Something tells me that the proposed "airship" would have to be bigger than I think, but what are your opinions based upon the balloons you've already created? Thanks for your input!
ongissim (author)  eugarps5 years ago
Well, the largest balloon I made was a 32 bag (bags were double layered- 16 bags long) and it was able to get airborne with a couple of nets draped over it, totaling about 3 lbs. of lift. I know, without a doubt, it could lift a small camcorder up.
Me and my kids built one of these last year. It was doing pretty well till it snagged on the barbs of a fence. Otherwise I think it might have gone airborn. They are a lot of fun. The cheaper (thinner) the garbage bag, the better.
Kaiven5 years ago
How do you keep air from coming out?
ongissim (author)  Kaiven5 years ago
The air stays inside of it fairly well. If I find that it is deflating a bit, I will just refill it with air.
SerJ7 years ago
looks like a huge body bag. cool idea though. might just try it this summer. i live on a small island though, so always windy. maybe as it will heat up properly, you could let it go, and then it would just keep climbing, if its a completely clear day? until a helicopter hits it or something. how large do you think you can make it? thanks for the instructable.
SerJ SerJ7 years ago
oh oh just thought of another thing. if launching next to your house, get an extension cord and inflate with a hairdryer! or if you have 2 people and 2 holes in the bodybag, inflate with 2 hairdryers! you get the idea... this way you will have it full of hot air straight away.
ongissim (author)  SerJ7 years ago
It would keep lifting, as long as the air in the bags remain hot. Also, if the air is humid, the air will weigh more. In addition: the bigger the better! You would only have to think about any leaks that may arise in the seams. Finally, if you keep the bags in the sun too long, small holes will form in the bags!
I have been flying solar balloons for a few years and have never had the sun form holes in the bags. I get holes in my balloons from things like trees and mailboxes. Right now I am building a 15-foot solar balloon shaped like a regular hot air balloon, made from clear painter's plastic (super-thin) that will have black solar collectors inside the envelope.
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ongissim (author)  DELETED_afw116 years ago
When I started testing sizes, only two trash bags sufficed. However, I am impatient, and using more trash bags gives quicker results. 2-3 trash bags will suffice, though.
You could get smaller by using masking or scotch tape, and thinner bags. I'm surprised you got this to fly considering how heavy it would be; good job on making something fly that I would be too doubtful to try. I use 0.4 MIL trash bags and masking tape. If you want more info on solar balloons I run the site http://www.solar-balloons.com/ - check it out and enjoy
static7 years ago
The first time I saw this http://www.intothewind.com/shop/Toys/Flying_Toys/UFO_Solar_Balloon for 3.99 I wondered if one could duplicate it with a black trash bag, but, never got around to trying it.. I always figured someone had already. Good job on creating the instructable.
zyon7 years ago
before taping (sealing) the last section, turn the whole thing inside out so that only 1 taped seam shows. another way to seal is make a donut shape and seal the last one.
ongissim (author)  zyon7 years ago
Good idea! I'll try that and see how that works.
zyon7 years ago
turn the whole thing inside out and then tape (seal) the last seam (only 1 seam will be visible. another shape is a donut shape, should be interesting.
It would be fun to try the plastic welding technique here from this other instructable
http://www.instructables.com/id/EZEZIAVMIMEP286W1W/
mje7 years ago
Here's another, slightly more sophisticated, approach:

http://www.nkfreedom.org/oldsite/resources/BYOsolar_balloon.pdf
dchall87 years ago
This is a fun idea and would be great for picnics. If I understand this right, instead of yarn you could use rope. You made a pretty big deal out of the yarn and getting it just right. And you left out the part about flying the thing. I assume you need some direct sunlight or else all you have is a black balloon. The pix show you outside on a cloudy day. Does it float on a cloudy day? Do you want a long tether on it or just a few feet? The air compressor is a huge consumption of time. You'll find that a leaf blower will fill your balloon up in a few seconds.
ongissim (author)  dchall87 years ago
Yes, you need a good source of direct sunlight to heat the air inside the balloon. And by the way, I like your idea on a leaf blower. However, I do not see how you can full up the balloon with a small hole, other than making a custom fitting for the leaf blower.
Make a bigger hole ;)
theRIAA7 years ago
pretty cool, some suggestions: the leaf blower is a good idea use a lighter tape, like packaging tape, and just do one side with no overlap (seam in middle of tape) would make it about 1/2 the weight. (would be less durable though) use the cheapest (thinnest mil) trash bads you can find obviously your way should work, but a lighter one will work on less sunny days
papa-g7 years ago
I always wanted to get one of those solar baloons, but was wary that it would be just cheap plastic. Hey, now I can make my own out of cheap plastic. 5 stars on the cool factor.
knexer17 years ago
That's cool.