Hot Air Balloon Competition
We use 5 large sheets of tissue paper for each balloon. That's four sides and one for the top. The paper only costs 10 cents a sheet from Gordon Harris Art Supplies, 4 Gillies Ave in Newmarket, Auckland (yes, they're open on Sundays and have teacher discounts).
I really can't recommend putting too many of these things into the air as they go so high. The flame isn't a danger though as the balloon will only come down when the fire goes out. Balloon combustion upon launch, however, is incredibly common. We had a success rate of about 2 in every 10 - the rest burn. The paper only needs the slightest provocation to launch into impressive fiery death :)
Some websites suggest all kinds of crazy things for the heat engine, one even suggests flaming coals! May I point out that using flaming coals would be the most stupid idea of all time. As we do not recommend incendiary bombing our neighbours, use meths on cotton wool. This results in a very limited "hot" time.
The main thing with these balloons is to launch in absolutely calm weather conditions! Inside a class room is fine. The balloons stick to the ceiling for about 2 minutes. Have a fire extinguisher handy but tissue paper balloons don't take a long time to disappear in a puff of ash and are quite amusing if they do.
Around the bottom of the balloon is a cardboard frame about 25cm wide. Across the frame is a wire cross holding a small ball of cotton wool dipped in methylated spirits. Use as little sticky tape as possible during construction because tape is heavy. Any type of glue works fine (eg. gluesticks or PVA).
Before handing over the tissue paper I make each group construct a balloon out of newspaper. This proves if they can work together in a group or not, something essential when working with lightweight tissue paper.
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