Making a balloon go up

There seem to be 2 obvious choices for making the balloon go up in the air, helium and hydrogen. Initially, helium seems like the obvious choice, it's cheap, plentiful and safe. Except, it might not be terribly plentiful or cheap in the quantities needed to lift a multi-pound payload into the air. The type of balloon needed to lift a 2-3 lb payload requires 100-125 cubic feet of gas to fill it up.

Helium

By looking at a number of balloon and party places, it looks like renting a helium tank with enough volume is 50-100 bucks. (Here's a Seattle place that will sell you a tank and then fill it up for a hundred bucks). This looks like around 50 dollars a launch. Not a show stopper, but it would be nice to do better.

Hydrogen

Sure, hydrogen burns really, really well. But other than that it seems like a great choice. It's actually lighter than helium and every grown male in the US made it in their backyard as a kid. Hydrogen can be made by electrolysis, but it is easier to make using a chemical reaction as this "fun with Lye" article from Popular Science in 1940 outlines. The big question is how quickly can hydrogen be safely made using this technique.

A little experiment

So we saw lots of recipes for making hydrogen, some from acids, some from bases, some wet and some dry. In the end the cheapest and easiest seemed to be controlled reaction between aluminum and lye in a water solution. The reaction is exothermic, so once you get it started it 'makes it's own gravy'. So the obvious questions are:

At what rate can we make hydrogen, how much will it cost and can we do it without winding up with Tyler Durdenesque chemical burns.

Ok, so after 30 minutes, the reaction was still going, but without the fervor it did initially, and the trash bag seemed to have at least a cubic foot of hydrogen in it, maybe more. So I disconnected the bag and weighed it with the gas in it. This time it was 29 grams. So 20 grams of lye created 33 grams of lifting force in about 30 minutes. At this ratio, it will take .6 pounds of lye to lift a pound of payload. This website for sounding balloons, says that an 1150 gram payload probably requires a gross lift capability of 3350 grams. Since 2 pounds is 900 grams, this is pretty close to our scenario, so we'd need around 6.5 lbs of lifting power. That's 4 lbs of lye and at $3.79 for the 1 pound bottle of lye, this would put the cost of a launch at around $15. Are you thinking that doing anything with 4 lbs of lye is not worth saving 35 dollars? Yeah, that's kind of what I'm thinking too...


So pure lye was harder to find than I expected. The first 5 stores I tried had all kinds of gels, liquids and other safe, eco-friendly, hate-free drain cleaners. I finally went to the old-timey hardware store and found old-school drain cleaner that didn't even try to disguise the fact that it was 100% lye. I appreciated the irony of the warning on the label about aluminum.
After that I found a large, stout glass bottle. A quick look at the recipe on the back of the bottle didn't actually suggest any ratios for lye
The first experiment was a conservative one: 8 ounces of cold water, 10 grams of aluminum foil and 3 grams of lye. All were added to the bottle and a small latex balloon was snapped over the neck of the bottle to catch the hydrogen that was made. (Oh, and all of this was done with copious amounts of safety equipment, long sleeves, gloves, safety glasses, a face shield and beacoup ventilation.) Turns out this wasn't really enough to get anything going. After 5 minutes the balloon was no longer flaccid, but that was it. So off came the balloon and 6 more grams of lye were added. That started a good reaction that merrily inflated the balloon. The kids played with the balloon until I we talked them into igniting it. It gave off a satisfying 'foomp'.
The next little experiment was to measure the amount of hydrogen that could be produced in a relatively small amount of time (say, 30 minutes). For this experiment we ran a few feet of plastic irrigation tubing between the bottle and a deflated black plastic garbage bag. To not lose any of the hydrogen, we taped the bag closed and sealed it around a one foot piece of tubing with a coupler to connect to the tube running from the bottle. Pre-inflation, the bag, foot of tube and duct tape weighed 62 grams. 10 ounces of hot tap water, 30 grams of aluminum and 20 grams of lye were added to the bottle and the tube was interted. The combination of more lye and starting with hot water got the reaction going very fast and it was boiling almost to the neck of the bottle. It was a little alarming, but the tube was still cool a foot or so past the end of the neck of the bottle, and by running the tube vertically, the lye-steam seemed to be condensing and running back into the bottle. Clearly any real hydrogen-producing rig should have some kind of metal coil to cool and condense out any nasty steam. (Like those moonshine stills Uncle Jessie was always getting in trouble for on the Dukes of Hazzard. Who knew that show had educational value.)