General Question

jumpfrog's avatar

Given a specific mylar bladder filled with helium,if I continue to add more gas [pressure] would the vessel lift more weight than its previous lifting strength?

Asked by jumpfrog (13points) January 18th, 2013

I’m fabricating a large replica of an ocean sting ray

Observing members: 0 Composing members: 0

12 Answers

Buttonstc's avatar

You do realize that Mylar balloons are not a unibody construction? They have seams which are heat sealed only and not impervious to bursting from too much pressure.

You’d be better off with latex balloons. They have some really large super thick ones which are used for weather balloons.

Remember the “balloon boy” hoax that nutjob cooked up a few years ago? That’s what he used :)

gasman's avatar

Once the balloon envelope is filled, adding more helium by increasing the internal pressure of gas without increasing its volume will actually make it heavier and less buoyant. Even helium has mass.

To increase lifting ability, it needs to be larger in volume so it displaces more of the surrounding air.

dabbler's avatar

@gasman is correct once the balloon is full, adding more gas will make it heavier and less bouyant.

Buttonstc's avatar

With a SN like that, I would listen to @gasman if I were you.

Plus if you stick around here long enough, (Welcome to Fluther, btw) you’ll realize that he generally knows what he’s talking about on a variety of subjects.

He’s not just full of hot air :)

gasman's avatar

@Buttonstc: Why, thank you kindly!
@jumpfrog I didn’t notice you’re new here. We welcome you with open tentacles.

Buttonstc's avatar

You’re welcome. I usually do try to drop a clue to newbies to the site as to who’s advice might be worth listening to in the midst of all the Internet opinions accumulating.

On threads with medical Qs I also try to point out that Rarebear is a real life Doc, so they may want to give more weight to his take on things medical.

And in matters of grammar, spelling etc. we all bow before Jeruba and Gailcalled.

So you’re in the pantheon as well (in my pantheon at least :)

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jumpfrog's avatar

In response to Gas Man on my HE filled sting ray. Given that the HE molecules are lighter than air, so then if I add more HE,hence more lighter than air molecules why wouldn’t it rise more? I realize that HE has mass,but less than air, so I’m confused. Also if I fill a mylar balloon to what appears to be its full capacity, then squirt even more [prior to exploding] HE in, It feels like it wants to rise faster, but I haven’t added more weight yet. I’ll do that next. Rob

dabbler's avatar

No, The lifting power of your balloon is the difference between its weight and the weight of an identical volume of air at the same temperature and at the same ambient pressure (sea level?) as air where the balloon is doing the lifting.
Because the volume of your balloon is fixed (mylar doesn’t stretch). The best lift you can get is when it is just full of the lifting gas, i.e. at the same pressure as outside air. Any more gas put into that balloon will increase its weight, and without changing its volume that means it gives up lifting power.

jumpfrog's avatar

Ok, I give up, you all have convinced me. But I still have to build this project.I have calculated that I will have 80 cubic feet of HE. Given the volume of HE it should lift 2.5 to 3 #s incl. the mylar sting ray balloon itself. Assume ,1 cu. ft. will lift 15 grams.

dabbler's avatar

You will need an 80 cubic foot balloon, “large replica of an ocean sting ray” is right!
Sounds like fun. I hope it gets off the ground well.

jumpfrog's avatar

I thank all who responded. Your answers where helpful ! When I get it off the ground and flying I’ll post a pic. Thanks Rob

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