# Vacuum Air Balloon

1. Dec 11, 2008

"Vacuum" Air Balloon

I have bounced around various sites and forums but I wanted to get a feel from some of those that may actually know. I have a theory on how this could work but basically wanted to get some opinions.

My theory is not new but has a few added components. A geodesic sphere could be made that is say 1000ft in diameter. At that size it could be lifted or severely weight reduced with warmer air for displacement. Rigid Zepphlins have been build to incredible sizes. That is with aluminum I feel that weight could be more adventageous with composite materials (Carbon, M5...).

At this point if a rigid ship such as this pulled a tiny pressure differential towards a vacuum within the ship it would become bouyant. Due to the combination of temperature and pressure differential. This would seem to have a few applications one of which would be the interior of the sphere would be habitable.

It would also allow a "vacuum" balloon to be built without the use of the notorious unobtainum.

If someone could explain to me where I am mistaken, I would love to hear from them.

2. Dec 11, 2008

### Integral

Staff Emeritus
Re: "vacuum" Air Balloon

Back in the '70s a lot of people thought that geodesic domes would make cool houses. Unfortunately they failed here in the PNW because of the inability to seal all of those edges against our winter rains. I would bet that you would run into similar difficulties in preventing leaks while attempting to hold a vacuum. What looks good on paper often proves impossible in the real world.

3. Dec 11, 2008

### mgb_phys

Re: "Vacuum" Air Balloon

With a vacuum inside the air pressure outside is about 10 tons/m^2.
All you have to do is build a balloon that can survive this sort of force without having to make the walls out of inch thick metal.

4. Dec 11, 2008

Re: "Vacuum" Air Balloon

Perhaps you did not read my whole post. I am not referring to a full vacuum which is always the first number I see against this idea. I am stating a small pressure differential. Perhaps between 0.5-1.0 psi.

Oh before you run the numbers I am already aware that is between 72-144 lbs/sqft

5. Dec 11, 2008

Re: "Vacuum" Air Balloon

Integral,
I do apreciate your reply, it is valid. That would be a real concern but perhaps not one that is completely impossible to overcome.

6. Dec 11, 2008

### mgb_phys

Re: "Vacuum" Air Balloon

Even if the pressure inside was 99% of atmosphere a 1m^3 would only have 120g (4ounces) of lift but would have to support 100kg (eg a quaterback) on each face.

As you get larger it becomes easier - the volume of gas and so the lift increases with the size cubed but the area and so the weight of the envelope increases as the square. But then you have the problem of makign a large surface rigid enough.

7. Dec 11, 2008

### Mech_Engineer

Re: "Vacuum" Air Balloon

I suspect you'll find that it's pretty much impossible to make a structure that can hold up to a small negative differetial pressure while still being light enough to float itself and some extra weight for payload.

A 1psi difference doesn't seem like much, but when you start trying to run the numbers, designing a structure that can enclose a volume large enough to float its own weight and a payload without buckling is impossible with the current materials available... You also kill yourself by using a small pressure difference, because that means a much larger volume has to be enclosed (and hence a much larger surface area), making it much more difficult to design a rigid structure that can contain it.