For the past month or so, our Pathfinder Club has been working on the Model Hot Air Balloon honor. We’re simultaneously in the middle of shooting some video for a production we’re working on for Pathfinder Sabbath next month. I chose Hot Air Balloons because we can take a couple of kids out at a time to shoot their portion of our video, while I work with the rest of the kids on the balloons.

The balloons are made from tissue paper – we bought the kind you’re supposed to wad up and stuff into a bag when you don’t feel up to wrapping a gift. I guess.

Anyhow, the balloons are not that hard to make, and each kid has been working diligently on their own without needing too much help from the adults.

Yesterday we were ready to launch a few of them. We used a hot air gun to fill them:

Filling it up

Filling it up

I did some calculations and estimated that these balloons are a little more than 260 liters in volume (about 70 gallons). I did some more calculations and determined that if it was about freezing outside (0°C) and we were able to pump the balloons up with air on the order of 40°C (about 100°F), they should have about 40 grams of lift. So as long as the balloons were 40 grams or less, they should rise.

I didn’t measure the temperature or weigh the balloons, and both of those are likely to be wildly off. But none the less:

We have lift off!

We have lift off!

They achieved buoyancy. Not much though. We tethered them with fishing line, and in the photo above, I’m trying to get away from the heat gun and not get tangled in the fishing line.

Recovery!

Recovery!


This particular balloon did pretty well. None of them stayed aloft for very long, and I think that was because they lost their heat pretty quickly.

So now I’m thinking I might like to build another using a Mylar emergency “space” blanket. They weigh 85 grams (or so I have read), but they should reflect all the heat back inside, and therefore, stay aloft longer.

That will require about an 80° temperature rise, but honestly, we might have had that already with the tissue balloons. As I said, I didn’t weigh the ones we have.

Anyways, this was a very fun project. I might be hooked!