15 By 12 Ft Solar Hot Air Balloon Float Test I took this photo while testing my solar hot air balloon. It's much bigger than it looks from this angle. It's filled with air by hand then the sun heats it up and it rises. It's made by cutting off a 30ft * 12ft piece of 0.3 mil painter's plastic drop cloth ($30/300ft), folding it in half and sealing the remaining edges with clear packaging tape. The pillow shaped balloon then has one corner cut off and a cardboard mouth/ring put in for filling and the tether. The dark coloration is from air-float charcoal ($15 1lb) put inside and shook around till it coated the surfaces. These types of "free balloons" can lift a good fraction of a pound to over 60,000ft. But until I can understand and fulfill the FAR 101 regulatory requirements fully these are just brief handheld tests below local structure heights. I learned how to make this type of balloon from the excellent documentation at Danny Bowman's Bovine Aerospace website and youtube videos. http://erewhon.superkuh.com/big-solar-hot-air-balloon-down-low-for-scale_sm.jpg The cardboard ring holding the balloon mouth open for inflation can be folded down onto itself a couple times to close the mouth and prevent wind from deflating the balloon. This folded cardboard block also provides a good place to wrap and knot the tether to the balloon. It's also fairly air-tight so a long flat tube casually rolled up as a pressure release valve might be necessary for non-tethered flight. http://erewhon.superkuh.com/solar-hot-air-balloon-mouth-ring-construction.jpg http://erewhon.superkuh.com/big-solar-hot-air-balloon_sm.jpg http://erewhon.superkuh.com/solar-hot-air-balloon-unfolding-plastic-film.jpg First lay out 30ft of the unfolded sheet. Then unfold it sideways and fold it vertically to make it two joined overlapping 15ft long sheets. Weight it down with random soft objects. Then go around the remaining 3 edges taping them together. http://erewhon.superkuh.com/solar-hot-air-balloon-tape-technique_sm.jpg http://erewhon.superkuh.com/finished-test-15x15-balloon_sm.jpg Now that I've figured out construction and everything works I'll move on to making a proper large envelope with normal diamond-like gores joined with strapping tape to distribute the load.