Oh the benefits to huge manatees!

April 6, 2006 6:12 AM

I often have dreams where i'm floating above the ground...

...and I was considering the possibility of helium backpacks for this purpose. Make them so you are almost weightless, and make them very slightly leaky for emergencies. And then you can leap long distances, no?

Has this been attempted and what are the technical and cost considerations?

posted by thirteenkiller to science & nature (26 comments total)

Wiki
posted by poppo at 6:20 AM on April 6, 2006

i think the volume of helium needed would rule oout any wearable solutions
posted by BSummers at 6:24 AM on April 6, 2006

From the IMDB entry for "From The Earth To The Moon":

To simulate the low gravity on the moon the actors had large helium balloons attached to their space suits by long wires. The wires were removed digitally in post production.

I imagine this is also how NASA created the illusion of the astronauts walking on "The Moon." :-)

This would be a very cool party game.
posted by bondcliff at 6:26 AM on April 6, 2006

The hard part would be reducing your effective weight to zero. It would be easy to slip up and end up too buoyant or too heavy. The Wiki article that poppo links to mentions a guy who made himself way, way more buoyant than he meant to — and if I remember the story right, he got himself in a fair bit of trouble and needed to be rescued.
posted by nebulawindphone at 6:53 AM on April 6, 2006

See here. Search for "Lawn Chair Larry."
posted by DelusionsofGrandeur at 6:57 AM on April 6, 2006

Have you actually seen how much helium it would take to make you float? It's a heck of a lot larger than a backpack.
posted by Rhomboid at 7:12 AM on April 6, 2006

The Mythbusters did a couple of segments on using helium as means of transport, one used several hundred helium ballons to lift a small child, the other used gigantic lightweight plastic columns. Both required an insane amount of helium that rendered either mode incredibly inefficient and impractical. Both segments go into great detail about the math involved in how much helium is needed to counter 1 lb, etc.

What you need is a personal jetpack.
posted by SoulOnIce at 7:46 AM on April 6, 2006

Leap long distances
posted by fidelity at 8:56 AM on April 6, 2006

Don't want to hijack this thread, but I'm not sure this deserves its own question: presuming you could make a light weight rigid frame, how much better would a vacuum be than helium?
posted by tkolar at 9:43 AM on April 6, 2006

I don't think such a thing would be possible. With helium you have equal pressure on both sides of the balloon, but with a vacuum you have full atmospheric on one and nothing on the other.... and that pressure (14.7psi) adds up FAST. Essentially you would be building the structural equivalent of a submarine. I can tell you with some certainty that if you drew a vacuum in a submarine (which would be equivalent pressure-wise of diving to a depth of 2 atm) it would not float at all...
posted by Rhomboid at 9:56 AM on April 6, 2006

Yes, but that just has to do with the materials that a submarine is constructed from.

The fact that a full atmosphere adds up so quickly is what makes me believe that (with the right materials) a vacuum chamber would be a far superior form of upwards lift.

"Believe" is the key word here. I lack the physics grounding to fully understand the situation. I think the question I'm trying to get at, is:

What is the upward lift produced by a square inch of helium at sea level, and what is the upward lift produced by a square inch of vacuum.

I want to say that a square inch of vacuum would lift 14.7 pounds at sea level, but I'm pretty sure that's too simplistic.
posted by tkolar at 10:07 AM on April 6, 2006

Vacuum has no lifting ability whatsoever in the sense you're describing. Take a balloon. Suck all the air out of it. Does it float? No. Do light bulbs float? No.

That is because vacuum is not something. It is nothing. When you expose something that contains a vacuum to air, the vacuum doesn't escape; the air rushes in to fill where the vacuum was. How much lifting ability do you think nothing has?
posted by kindall at 10:21 AM on April 6, 2006

Assuming we're talking about cubic inches, a cubic inch of vacuum must be less massive than a cubic inch of helium.

A cubic inch of vacuum has no lifting ability, but a cubic inch of helium weights more and has even less.

The trick is to make a light enough frame to hold a significantly large volume of vacuum. A kind of reverse balloon.

I have long wondered if a foam of some sort where the holes in the foam are filled with vacuum (evacuated) would work. Or could it be done on a molecular level with giant vacuum filled buckyballs? They might be quite strong.

Little experiment: how much material can a mylar balloon filled with helium lift? Can you then use said weight of material to hold a mylar balloon open to the same volume with a vacuum inside? If so, shouldn't it float?
posted by blue_wardrobe at 10:33 AM on April 6, 2006

See also: article about potentially floating evacuated containers
posted by blue_wardrobe at 10:37 AM on April 6, 2006

kindall wrote....
Vacuum has no lifting ability whatsoever in the sense you're describing.

I believe you are mistaken. The reason that helium and hydrogen float is not because they have a particular lifting ability, but because higher density air seeks to displace them. The net effect of an atmosphere in a gravity well is that lower density regions move upwards.

The force that they move upwards with is what I'm trying to determine.
posted by tkolar at 10:40 AM on April 6, 2006

blue_wardrobe wrote...
See also: article about potentially floating evacuated containers

Yes, this is the sort of thing I'm talking about. I just haven't been able to find a rigorous scientific analysis for it yet.

Perhaps I should make this a question of its own.
posted by tkolar at 10:48 AM on April 6, 2006

tkolar: I agree. It is an issue of displacement, rather than "lifting ability".

Another thoughtful article deduces that if a vacuum ballon gives "100%" lift, then a helium balloon gives 86% of the same lift. And thus may not be economically sensible, even if possible.
posted by blue_wardrobe at 10:48 AM on April 6, 2006

^ballon^balloon
posted by blue_wardrobe at 10:50 AM on April 6, 2006

All of this discussion is based on the concept of buoyancy. These effects are easier to visualize when the "working fluid" is, say, water, and not air. The reason a basketball floats in water is that the weight of the volume the basketball occupies (with the air inside it) is less than the weight of an equal volume of the water it displaces.

Similarly, the reason helium filled balloons float in air is because the volume of the balloon and the helium is lighter than the air they displace (because of the difference in densities between the two gasses. This only works because the densities are different enough that the weight of the balloon is negligible. Steel balloons filled with helium do not float in air (but might in water)

So, tkolar, the "lifting force" of a given balloon (helium, hot air, or otherwise), would be the net difference between the weights (ie, densities) of the two gases, less the weight of the container.

In equation:

F_lift = (rho_he*vol_he*g + W_container) - rho_air*vol_air*g
posted by toomanyplugs at 10:55 AM on April 6, 2006

strike that, reverse it. For F(positive lift):

F_lift = rho_air*vol_air*g - (rho_he*vol_he*g + W_container)
posted by toomanyplugs at 10:58 AM on April 6, 2006

blue wadrobe wrote...

http://www.newton.dep.anl.gov/askasci/phy00/phy00844.htm

Sweet link. Thanks!
posted by tkolar at 10:59 AM on April 6, 2006

toomanyplugs wrote...
F_lift = rho_air*vol_air*g - (rho_he*vol_he*g + W_container)

So, assuming that...

rho_vacuum*vol_vacuum*g = 0

...and that W_container remains constant, the difference in F_lift for helium and F_lift fo a vacuum is going to be

rho_he*vol_he*g

i.e., the weight of the helium. This appears to be confirmed by the commentary in blue wardrobe's link.

Sigh, another childhood dream shot to shreds by cold physics. I really wanted to be a pioneer in the vacuum ballon industry.
posted by tkolar at 11:15 AM on April 6, 2006

There's really no reason at all to use a Vaccum. The density difference between air and Helium is pretty high, much higher then the density difference between Helium and a Vaccum. I believe you would only save about 10% on volume, but you'd have to make a structure rigid enough to hold the air out, which would end up weighing much more then helium.
posted by delmoi at 11:51 AM on April 6, 2006

thirteenkiller, I have the same dreams, and have had the same idea. Looks like others have beat us to it. It's nice to know that such a thing is possible, though not as compactly as we may have wished.
posted by MrMoonPie at 1:11 PM on April 6, 2006

Some of my friends once lifted people using helium baloons at Burning Man:



See their website for more details and pictures
posted by mbrubeck at 2:49 PM on April 6, 2006

By the way, I've also had flying/floating dreams, and I figured out how to do it. First, you take all your weight off your left fot and lift it off the ground. Then, without returning any of the weight to your left foot, simply take all your weight off your right foot too and lift it off the ground. Now tuck your legs under you and voilà, you are floating.

I haven't had the nerve to try this awake, however.
posted by kindall at 5:38 PM on April 6, 2006