With help from my Dad, RJ Steinert, Samantha Mitchell, Robby Kraft, and Molly Danielsson, I’ve been flying balloons most weekends since the workshop in June, gathering lift and flight data on helium and solar hot air balloons.**
Regular charcoal sucks, no matter how finely ground. In my tests over this month I couldn’t get it to coat the balloon well. My previous successes were with Char-Kole brand compressed charcoal, ground up. Jeffery Warren copied my building instructions and tried charcoal in Georgia (EU) without success.
I still want to test lamp black, but Cabot pigments STILL hasn’t sent me samples (ordered them the 2nd week in June). Go with iron oxide black (sold as tempura pigment, or from industrial suppliers). Iron oxide black consistently generates roughly 500g of excess lift from a 12-foot tetrahedron. the easiest way to test the lift of a balloon is to tie a water bottle to it and empty out the water until the balloon is airborne.
Use a mattress blower to disperse the pigment when the balloon is mostly full. It pulverizes and disperses, and possibly, through proximity to the motor, charge them a bit.
I stand by my dislike of black HDPE, because it is weak and tears easily when hot.
My balloons have, until now been all solar, so these were my first helium flights. Helium is great. it rides proudly in the wind, owing to a favorable ratio of static lift to surface area/drag. But helium is expensive. I spent four times as much on helium as I did on all other supplies. After flying my very thin HDPE .3mil balloons and watching the helium leak out over a 3 hour period, I think a more substantial balloon aught to surround such an expensive gas.
I might try some PET film, which retains helium better, but it’s cost ($15 vs $0.50) makes me averse to it.
Or I might switch to hydrogen. I’m excited about this method of urine electrolysis. Apparently it’s far more efficient than water, and I’m already carrying it around!