We have moved away from the idea of making polyethylene film lift bags and now prefer the purchase and use of chloroprene meteorlogical balloons of 8' diameter. These are available online and it shoud require about 25 of them to lift the total lift off weight of an ultralight dirigible, i.e., 500 pounds.

The discussion below is for information archival only and is not our current plan.

Lift Bags are the numerous, [around 20], plastic cylinders, which contain hydrogen and are arranged within the Skyboat's aerodynamic plastic skin [[#|envelope]]. The polymeric composition of plastic gas-proof food wrappers is fairly technical but let's tackle it now, on this page. [[#|Food packaging]] is a big industry that has made progress with [[#|cheap]] plastic gas barriers. We cannot [[#|buy]] fancy space suit material to keep the lift-gas inside the Skyboat.

Lift Bags may measure 4 X 10 feet, flat, which are commercially available as tubes that may be cut to best length. They are available in polyurethane or polyethylene.

One type of effective gas-proof plastic film is EVAL, ethylene vinyl acohol. It is stretched during manufacture to close its pores and then mated with the polyurethane base film.

Think food packages. They are tough and strong and gas-proof for oxygen and water vapor, at least. Research is needed on how they will perform with H2. The good news is that H2 comes in pairs of atoms and therefor H2 is a larger molecule than the tiny He atom and that gives us one design advantage, we don't need such a gas-tight fabric as helium ballooners would need.

Bags maybe can contain oxygen absorber pellets for safety, keeping the O2/H2 ratio below the ignition ratio for [[#|long periods]]. Also, silica gel pellets might be wothwhile to [[#|absorb moisture]] inside the bags? I don't know

It looks like standard food-pack aluminized plastic bags may be the best for cheapness and gas-tight. I haven't price d them yet
- allenmeece allenmeece