Vacuum Balloon

Meaningful discussion outside of the potato gun realm. Projects, theories, current events. Non-productive discussion will be locked.
User avatar
Lentamentalisk
Sergeant 3
Sergeant 3
Posts: 1202
Joined: Tue Aug 07, 2007 5:27 pm
Location: Berkeley C.A.

Thu Sep 02, 2010 11:09 pm

Ok, here is a question in the exact opposite direction of what we deal with normally.

I want to make a negative pressure chamber.

I am trying to figure out a way to build a vacuum lighter than air ship.


STOP. Don't tell me it is stupid.
I know, helium and hydrogen, and just about everything is more practical, but this is purely for the experiment, to show it is possible.

Many people have come up with ideas of a metal frame with a cloth stretched between that holds the vacuum, like this:
Image

I want to try going about it in another direction. Rather than relying on tensile strength, I want to try one that is based off compressive strength.

My idea is to create a hollow sphere out of Styrofoam, (blown with hydrogen to make it extra light maybe?) so that the shell can be very thick, and the smallest imperfection won't cause it to implode. Also, with thickness, if I am not mistaken, comes exponential strength.

Do you guys have any suggestions, or relevant equations, or anything of the like to point me in the right direction?




Yet again, please don't tell me it can't be done. That is exactly the point. I want to try something new.
Do not look back, and grieve over the past, for it is gone;
Do not be troubled about the future, for it has not yet come;
Live life in the present, and make it so beautiful that it will be worth remembering.
User avatar
linuxexorcist
Private 4
Private 4
Posts: 61
Joined: Sun Mar 30, 2008 7:52 pm

Thu Sep 02, 2010 11:27 pm

how will you get the air out?
A homemade vacuum pump like This would work, but you may not reach a near complete vacuum

Also, what sort of valve would you use? a regular schraeder might get pulled open by the vacuum, right?
User avatar
hi
Staff Sergeant 2
Staff Sergeant 2
Posts: 1619
Joined: Thu Feb 01, 2007 9:28 pm

Thu Sep 02, 2010 11:40 pm

Just take a rubber balloon and take the air out of it.

Edit- ... never mind.

haha just kidding, but keep us posted if you make it, i've never heard of that concept before. i think the problem would be having a truly air tight balloon/frame. Maybe having a vacuum constantly suck air out would be a solution?
"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 26179
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 543 times
Been thanked: 319 times

Donating Members

Fri Sep 03, 2010 1:20 am

Don't look to airships for inspiration, rather deep sea submersibles ;)

In this regard a thick tube or a series of spherical chambers would be ideal.
a regular schrader might get pulled open by the vacuum, right?
A schrader needs a pressure difference of 50-70 psi to open, while in this case the difference is 15 psi.
i think the problem would be having a truly air tight balloon/frame
That's nothing compared to avoiding this problem:

[youtube][/youtube]
hectmarr wrote:You have to make many weapons, because this field is long and short life
User avatar
Gaderelguitarist
Corporal
Corporal
Posts: 580
Joined: Sat Aug 16, 2008 9:56 pm
Location: Columbia, MD
Contact:

Fri Sep 03, 2010 1:26 am

Won't the atmosphere around the chamber compress it across it's entire surface consistently? I realize that vacuum means no air, and thus is lighter than air, but taking a balloon and removing the air from it does not make it more likely to float.

This just confuses me on several levels.
so many muchness
User avatar
Insomniac
Sergeant 3
Sergeant 3
Posts: 1297
Joined: Mon Dec 18, 2006 3:47 pm
Location: Australia

Fri Sep 03, 2010 1:39 am

Yes, but the point is to make a rigid, lightweight chamber which can hold a fairly high vacuum... thus lowering the overall density and causing it to float.

Ie a helium balloon floats because helium is lighter than air, and if you've got enough helium its buoyancy overcomes the weight of the balloon itself. A vacuum is lighter than helium, so if you could 'fill' a balloon with a vacuum, it too would rise. The issue is stopping the balloon from collapsing.
I wonder how much deeper the ocean would be without sponges.
Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before.

Add me on msn!!! insomniac-55@hotmail.com
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 26179
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 543 times
Been thanked: 319 times

Donating Members

Fri Sep 03, 2010 1:42 am

Gaderelguitarist wrote:Won't the atmosphere around the chamber compress it across it's entire surface consistently? I realize that vacuum means no air, and thus is lighter than air, but taking a balloon and removing the air from it does not make it more likely to float.
Simple buoyancy, same volume and less weight - if it works for helium, it will work even better with vacuum. Not much better, really, but Lentamentalisk doesn't want us to talk about that ;)

So let's see, 4 foot diameter sphere, 0.9" wall thickness, made from 2lb/cubic foot styrofoam, weighing almost 14lbs - but only displacing around 3.5lbs of air...
hectmarr wrote:You have to make many weapons, because this field is long and short life
User avatar
Gaderelguitarist
Corporal
Corporal
Posts: 580
Joined: Sat Aug 16, 2008 9:56 pm
Location: Columbia, MD
Contact:

Fri Sep 03, 2010 1:49 am

Simple buoyancy, same volume and less weight - if it works for helium, it will work even better with vacuum. Not much better, really, but Lentamentalisk doesn't want us to talk about that Wink
Granted. I must be weakened in my more tired state.

I'd like to see a video of this working though.
so many muchness
User avatar
Technician1002
Captain
Captain
Posts: 5189
Joined: Sat Apr 04, 2009 11:10 am

Fri Sep 03, 2010 2:27 am

The best I can suggest is to work on it as an engineering problem.

How much air must you displace to get the desired lift. I assume you want as much lift as the airship weight.

With a known volume, the tough part begins. Find the force on the shell from atmospheric pressure and find the shell and support structure that is within your weight allowance. This is where most designs fail as you are trying to build a structure to support several tons of force but weighs only a few pounds.

Note the amount the rail car collapsed. The volume shrank to nearly 10% of the original volume. How much did the tank car weigh? How much weight of air does it displace?

Somehow even without wheels and other non essentials attached, I highly doubt the rail car was anywhere near equilibrium.

Designing a container with the strength of a rail car, but light as a hot air balloon is where the trouble arises.

A typical hot air balloon weighs about 600 lbs with the gondola and fuel. The balloon contains about 2.5 tons of air inside. If you can make a tank that size able to hold a vacuum, and the size of a hot air balloon and weigh under 2.5 tons, you are close to flight with a vacuum.
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 26179
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 543 times
Been thanked: 319 times

Donating Members

Fri Sep 03, 2010 2:28 am

Gaderelguitarist wrote:I'd like to see a video of this working though.
After a quick play with the numbers, it's not looking very feasible...
hectmarr wrote:You have to make many weapons, because this field is long and short life
User avatar
al-xg
Corporal 2
Corporal 2
Great Britain
Posts: 643
Joined: Fri Jan 19, 2007 12:29 pm

Fri Sep 03, 2010 3:58 am

If I had to give it a go without trying any calculations before hand, I'd try a carbon fibre structure fitted inside a an airtight envelope. And then try and make it very big.
User avatar
Crna Legija
First Sergeant 2
First Sergeant 2
Posts: 2333
Joined: Sun Jul 20, 2008 5:14 am
Location: australia

Fri Sep 03, 2010 5:49 am

linuxexorcist wrote:how will you get the air out?
A homemade vacuum pump like This would work, but you may not reach a near complete vacuum

Also, what sort of valve would you use? a regular schraeder might get pulled open by the vacuum, right?
you could use a fridge compressor it suck the air out idk how if it could make a complete vacuum tho.

and the vacuum would suck the schraeder closed even tighter
'' To alcohol... The cause of, and solution to, all of life's problems.”
--Homer Simpson

Add me on ps3: wannafuk, 8/11/11 cant wait
User avatar
POLAND_SPUD
Captain
Captain
Posts: 5402
Joined: Sat Oct 13, 2007 4:43 pm
Been thanked: 1 time

Fri Sep 03, 2010 6:42 am

and the vacuum would suck the schraeder closed even tighter
only if it is installed the other way round
Don't tell me it is stupid.
uhmm... ok, I can do that for you...

The only problem is that air at sea level weighs about 1.2 kg per cubic meter... your balloon + frame has to weight less than that
Children are the future

unless we stop them now
User avatar
jhalek90
Specialist 4
Specialist 4
Posts: 498
Joined: Fri Aug 14, 2009 5:37 pm

Fri Sep 03, 2010 7:13 am

jackssmirkingrevenge wrote: So let's see, 4 foot diameter sphere, 0.9" wall thickness, made from 2lb/cubic foot styrofoam, weighing almost 14lbs - but only displacing around 3.5lbs of air...
this will be your biggest problem.

as jack stated, your first issue will be finding out how much weight i air you will be able to remove for a give volume....

I suggest starting there.

once you have that done, you can determine what your chamber can weigh.
jackssmirkingrevenge wrote:I wonder... if you put flammable vapours inside a lady... could you get her to diesel?
POLAND_SPUD wrote:Anything is possible with the proper 3-way valve.
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 26179
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 543 times
Been thanked: 319 times

Donating Members

Fri Sep 03, 2010 7:38 am

Let's go with a 1 metre radius sphere.

If the total weight is more than 5kg, it won't float.

Let's say the foam has a density 150 kg/m<sup>3</sup>

Going with the 5kg limit, ie for enough buoyancy for the sphere to lift only itself, even with a wall thickness of less than 1/8", it will still be far too heavy to float - and at that thickness, a 1 metre foam sphere is guaranteed to implode in a spectacular fashion.

I'm not saying it can't be done, but the grade of high strength and low weight material required for such a project suggests it's beyond the reach of the average individual.

edit: fine, yeesh :p :D
Last edited by jackssmirkingrevenge on Fri Sep 03, 2010 11:28 am, edited 1 time in total.
hectmarr wrote:You have to make many weapons, because this field is long and short life
Post Reply