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# Not Jetpak, BalloonPack!

Get there faster with a small balloon. Save the helium when you get there!
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This idea expands on the concept from parabounce.com The Problem: While having the ability to jump really high is cool, you would not want to continue wearing this when it gets windy or when you get to point B, nor would you want to simply deflate it because helium is expensive and rare!

The Solution: By integrating a helium storage cylinder and a recompressor into a backpack unit, We have a practical and economical personal transportation! The recompressor uses fuel to compress the helium. Performance specs: Inflate time: less than 10 seconds Bouyancy effect: at least 90% payload Deflate time: less than 1 minute Backpack weight: less than 80lbs Backpack volume: less than 6ft^3

Alternatively, if too much power is needed to recompress the balloon, hydrogen can be used for its expendability.

Is machine feasible with modern off-the-shelf parts? To liftoff 170lbs payload with helium, at least 2730ft^3 are needed. What size storage cylinder is needed? How much power is required to recompress the helium to spec?

 — thisispeterstanley, May 26 2007

Halfbakery: Balloon Backpack Balloon_20Backpack
[jutta, May 26 2007]

//Deflate time: less than 1 minute Backpack weight: less than 80lbs Backpack volume: less than 6ft^3// Were those the numbers you would like, or the number you think are feasible?
 — MaxwellBuchanan, May 26 2007

I'm not sure of the exact power, but it depends how much you compress the helium. If most of the final volume is helium, the volume ratio is about 3000 ft^3 / 6 ft^3, or about 500. That will need to either be at 500 atmospheres of pressure, or be cooler in storage than in use. Unfortunately the cooling won't be easily effective since helium doesn't liquify until a very low temperature. Hmmm, I'm not sure if that's still true under high pressure.
 — caspian, May 27 2007

I think you need to tether your balloon whenever you don't want to use it, or when it's too windy to use it. I don't think it's feasible to carry a compressor and 6ft³ 500 bar tank around with you - it's is going to be a lot too heavy.
 — Cosh i Pi, May 27 2007

 From google search: Compress Helium -

 I think you'll find that when you compress the gas you'll need a chamber or gas bottle to contain it. This alone will be heavy. At work I have large bottles of Hydrogen, which is a lighter gas, these bottles are 40 litres in capacity (5 feet high) and have up to 200 bar pressure. The bottle full weighs well over 60 Kg's

 At AirProducts dot com, you can calculate various aspects of gases. [Link tbd]. 40 liters of (besides the bottle) weigh about 2.5 kilograms in liquid form and expands to about 33.9 cubic meters. Nitrogen, the most common gas in air, at that volume weighs 39.3 kg, so you have a lift of 36.8 kg for each canister (that weighs 60 kg's).

 Helium gives you even less: 40 kg of liquid helium expand to 29.3 cubic meters, displacing only 34 kg of nitrogen, and the helium weighs 4.9 kg, so you get only a 24.5 kg lift.

 Calor light are 49.7% lighter than steel gas-cylinders, lets say it would be 50%, you still don't have enough to lift each canister alone!! But you are getting close. Perhaps a single 80 lightweight canister could do the job.

As a side remark, interestingly, although nitrogen is atomic number 7 and oxygen only 6, still, according to the conversion details on the website, 33.9 cubic meters of oxygen weigh a bit MORE than that of nitrogen. Perhaps because of some packing effect due to electron repulsion in oxygen. So you get maybe an extra 1 kg of lift.
 — pashute, Oct 19 2014

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