Hot air balloons
For some years I was a Primary Science specialist, and hot air balloons were among the activities I used in a number of schools. Making them is a useful craft exercise, and there is some interesting physics in the way they work. (No, hot air doesn’t rise, it’s pushed by surrounding cooler air. Meteorologists often talk of ‘parcels of air’: these come wrapped.) There’s also some meteorology involved: what are the best conditions for balloon flying? Why is the balloon drifting in a different direction up there from the breeze at ground level?
Some students will take to this with relish and start making and flying their own from home, and at least one UFO report from the Elizabeth area north of Adelaide a few years ago was caused by one of my students. He was delighted.
The person launching the balloon is the one facing the camera and holding the base ring. Three helpers are holding the upper part. The person with his back to us is about to put the match to the burner. Just visible behind the balloon is the pump of the knapsack spray, ready in case.
Just after launch
The balloon is beginning to rise. Note that it has been launched from the middle of the oval, well clear of trees and other obstructions. Note also that no-one is directly beneath it: newly launched balloons sometimes dribble burning meths.
Above the trees
This one has been launched from a clear area at a campsite in the Hills.
The balloon is illuminated by its own flame.
The view from below
One of the larger balloons, seen through a 400 mm lens. Details of the burner are clearly seen.
This one is carrying a glider, released by time fuse. Anything carried by balloon must be very light. (Grainy appearance is because the pic has been enlarged from a small part of the negative.)
Making your own
Instructions for making balloons are in an Acrobat document, which carries this warning: ‘in flying these balloons you are playing with fire.’ Light fires in paper bags and you can expect fires now and then. Don’t say you weren’t warned.
Why not fly plastic bags? Paper is biodegradable, plastics (in general) are not. There’s enough plastics rubbish lying about as it is.