This time we thought we'd give the tetroon design, we'd seen at http://www.solar-balloons.com/ a go. With this design, you end up with a cross between a hot air balloon, and an upside down pyramid. It's a little more complicated to build than the tube, but it still only requires four black garbage bags (30 gallon size, with a .5 MIL thickness). Besides the garbage bags, all that is needed is a roll of Scotch tape, scissors, some thread, and an optional paper clip.
Following the directions from solar-balloons, we laid four bags out flat.
Then we cut off the bottom, and slit open one side on each bag. After opening them up the rest of the way, we taped them together into a rectangle.
We folded the long side in half (bringing the short sides together).Next, we taped the the sides together (what used to be the long sides, but after folding are now the short sides), leaving the bottom (opposite our folded edge) open.
We lifted up the middle seam, bringing the two side seams together, and then taped the open side closed. Solar-balloons has a very good set of diagrams that make this much easier to do than it sounds.
Then, we cut off a few inches from one of the corners, to form the mouth of the balloon.
Finally, we attached four pieces of thread to the mouth, and tied them together on a the end of a paper clip, which we attached to a the free end of our thread still on the spool. The Sunday forecast said partly cloudy, but we went to bed hopeful.
Partly cloudy turned into completely cloudy very quickly today. The sun made a brief appearance this afternoon, and we rushed the balloon outside, but by the time it was starting to rise, the clouds had moved back into place. Still, even though it was brief, we had the that moment of thrill as the sun heated balloon lifted off.
I rolled the balloon back up and stashed it out of the way of little hands until our next sunny day (the plastic is very thin and tears easily). All is not lost though, it's Mother's Day, and sunshine or no, the conditions are perfect for a Sunday afternoon nap!
It's great to be a homeschooler.