<https://educationforum.ipbhost.com/topic/19-aviation/page/2/#comment-2688>
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"One of two activities I have used with students \nThis is designing and flying hot air balloons. \nhttp://www.btinternet.com/~n.j.f/OIL2/EXPT...tairballoon.htm "
<https://educationforum.ipbhost.com/topic/19-aviation/page/2/?tab=comments#comment-695>