RE: zep
Bruce-
Thanx for the numbers
So for a envelope of 2 cube meter, we can get somewhere between 0lb to 4lb boyancy (lift, "lightness") max. This is of course skewed to the 0-2lb range for stp gasses, or a wee bit more for low pressure envelope.
I'm looking at it as a matter of compromise: give a little on everything.
A vacuum would implode the craft, but what about just 1 or 2 psi of LowPressure to drop the ammount of mass in the gas. Or as I said, heat it some to drop the gasmass without Implosion. Play PVNrT to strike a ballance of Presure & Temp to get a lower Number of molecules
Hydrogen would work better than air (stupid 60%N), but while helium is not as good as hydrogen, its far better than air.
Lighter than air is really hard, but Almost as Light As Air is easier. Using Vectored thrust you can cheat the weight of the ship to get "Float" & "Rise" with less than a pound of thrust if a 3lb craft has 2lb of gas Positive Boyancy (lift,Lightness), thrust vectoring will eliminate the need for excessive winglets
I hope you can get the particulars worked out, would love to see a build thread on it