Not that I’m likely to actually do this, but if I were, how much would I need? I’d like to get a harness and attach helium balloons (weather ballons, actually) to it so that I float. Not to go zipping up into the sky, just enough so that I can kick off the ground and stay off. Like so that someone could walk around with me on a string like a balloon…
How much cubic footage of helium balloon would I need? How many weather balloons would it take? Assuming I never went more than 10’ off the ground are there any legal concerns?
Back of the envelope time:
Well, a mole (22.4 liters) of nitrogen gas (which is about 78% of the atmosphere, I think) would weigh about 28 grams, and a mole of helium would weigh about 4 grams. So, each mole of helium is about 24 grams worth of bouyancy. If you weigh, say, 60 kg, you’d need 2500 moles of helium, or 56,000 liters of helium. I’m not sure how many balloons that would be, and that’s a rough estimate that doesn’t take into account temperature effects on density and so on, but it should be kind of difficult to do. Unfortunately
Or another way: air at STP has a density of 1.29KG per cubic meter. That means that a cubic meter of vacuum would pull upwards with a “weight” of 1.29KG, and if it was instead filled with helium, it would lift 1.29*(1-4/28) = 1.1KG.
So, a portly 110KG human would need a hundred cubic meters of helium balloons. I think a small (inexpensive) weather balloon might contain about one cubic meter.
Hey, why go for zero gee? Why not instead just reduce your weight by half? You could go bounding across the landscape, maybe even cross water by running fast. Or maybe all those balloons would act like a sail, and the viscous drag would halt you quick unless the wind was blowing in the right direction. Don’t try this anywhere near power lines or highways!
My local dirigible expert (the husband, who likes to invent things) tells me a good rule of thumb is 1 cubic foot of helium lifts 1 ounce in “standard conditions” - that’s sea level, 59 degrees (roughly).
Remember to take into account not just yourself but your clothes, loose change in pockets, and any sort of rigging/harness used to secure you to the balloon(s).
According to our calculations, about 8000 cubic feet of helium will lift around 500lbs. By extension 4000 cubic feet for 250 lbs and 2000 cubic feet for 125 lbs.
Another note: last time we priced helium it was $0.26 per cubic foot. Not a whole lot - until you need a whole lot of it.
Not 10 feet off the ground, no. I do feel compelled to warn you, however, that the odds of surviving a fall go down as the altitude goes up. 10 feet isn’t too bad - that’s broken leg territory (sometimes no injury at all, if you land properly on a suitable surface) but up around 20 things can become fatal a large percentage of the time. And all bets are off if you land on your head. A crash helmet is advisable.
If you can keep the combined weight of the rigging and balloons to under 154 lbs (that’s before filling with helium) you will qualify as an unpowered ultralight under US Federal Avaiation Regulation Part 103 (I’m assuming we’re talking United States, here). There are no mechanical, licensing, medical, or training requirements for such “vehicles”.
(Larry Walters would have qualifed, too, except that category didn’t exist at the time of his flight. And even if it had, they would have busted him for violating Class B airspace over LAX)
Without getting into a lengthy, technical, and boring discussion of airspace rules, stay away away from airports, especially big ones. Pretty much everywhere you’re OK up to 700 feet, most places to 1200
For safety reasons, it is also a good idea to avoid powerlines, getting caught in trees, billboards, and such like. Pick a calm day with no wind if possible.
Another thought - have some way to vent helium in a controlled from your little science project or you may unexpectedly find yourself ascending when you don’t want to (which is partly how Mr. Walters got into so much trouble).
Wouldn’t this be the coolest thing to do for Halloween or something? Dress up like a balloon, get a bunch of other ballons to hold you up (say, 6 feet up) and have a friend or two be holding onto you as if you were their balloon…probably not convenient for long stretches of time, but it would go over SO well! hehe