Lighter Than Air Craft Idea

Some of you probably haven't seen airships flying around recently. I can tell you one reason - He (Helium) is becoming extremely scarce on the planet. So the big question is this: How can we get airships flying wihout lifting gas?
Hydrogen is explosive, and ever since the Hindenburg disaster, using H (Hydrogen) was illegal.
But I think I know of a way to fly without H or He.
If you don't know, a vacuum is really space with nothing in it at all - not even air.
So that means a vacuum would probably be lighter than air.
So if we had an air-tight container with an airlock like door, and we pumped every last particle out, it would be a vacuum. There will be two doors, just like every airlock, an inner and outer door. The inner door closes first once everything is out. Then, the pump is taken out and the outer door closes.

Please give your opinion on my idea. Thanks.

~Sean

I think you are forgetting that the vehicle itself has a mass and just creating a vacuum inside the vehicle does nothing for its mass in the environment, only for the environment inside the vehicle. This does not make it lighter than air. You would have to have a "medium" inside the vehicle that is lighter than air, but substantial enough to cause the mass of the vehicle itself to have no weight. This is why Helium works and why the outer shell of anything filled with helium is light weight and can float, such as a balloon.

Just my thoughts, though I am no scientist or expert by anyones standards.

-B

Originally posted by seanpf

So that means a vacuum would probably be lighter than air.
~Sean

As already pointed out this is where your ideas goes off track. A vacuum is not lift

[edit on 22/08/06 by Canada_EH]

Originally posted by Canada_EH

As already pointed out this is where your ideas goes off track. A vacuum is not lift

[edit on 22/08/06 by Canada_EH]

a vacuum would give lift as the op suggests, the only problem would be to contain the vacuum. a vacuum would be weigh nothing and so is far lighter than air.

the only dificulty is that you would need an incredibly rigid container (to combat natural athmospheric pressure) that weighs less than the air displaced by it. so if we say that the displaced air weighs 10 kilo's, then the maximum weight for the container must be 9.99 kilos and that wouldn't create much lift. 10 kilos of air is a lot of air, it seems a difficult task to create lift this way.

reply to post by pieman


Difficult, but not impossible. There are some very interesting plastics and fabrics these days that may make a light enough shield for the vacuum. I would definitely suggest the strength of a sphere or cylindrical shape.

This reminds me my rock bottom point in life concerning physics. Given I had been under the influence all day, this is still inexcusable...
I found a very interesting hollow limestone rock one day. It was so hollow that it looked like a misshapen egg with two holes in it. For a moment in time I thought it would be really cool to see this rock float on water, tried it, and failed epically. I don't know which brain cell told me that would work, but I eliminated a whole colony of them just to try and get the faulty one. You know, shock and awe.... Mission Accomplished.

Canada is right, a vacuum does not produce any form of lift. Just because there is nothing, doesn't make it lighter-than-air. There is simply nothing...

Lighter-Than-aircraft work on the basis of a gas inside that is well, lighter in density than what makes up atmospheric gases around it. Having a vacuum would do nothing for your cause.

Shattered OUT...

Originally posted by ShatteredSkies
Lighter-Than-aircraft work on the basis of a gas inside that is well, lighter in density than what makes up atmospheric gases around it. Having a vacuum would do nothing for your cause.

Shattered OUT...

Close, but no Blimp.


Lighter-than Air Vehicles "work" because the weight of the volume of the the air they displace exceeds the weight of the vehicle and its payload

A contained vacuum, also known as a "Vacuum Cell" could be an efficient means of providing an LAV (Lighter than Air Vehicle) with lift....

IF a sufficient volume of vacuum (odd concept: A sufficient amount of nothing!) could be contained to displace air, at altitude, to exceed the weight of the craft.

Since a vacuum weighs nothing, it would naturally weigh less than an equal volume of air. The amount of "lift" generated would be determined by whether, and by how much, lighter the vehicle structure and its payload were, compared to the weight of the air displaced by the LAV.

The advantage of H, He gas is they're lighter than air at atmospheric pressure so a flimsy contaner like a plastic bag is all that's needed to contain them. A vacuum needs some serious hardware to keep it in place and it would be probably more dangerous than hydrogen if you consider the risk of implosion on that scale.

No, the Vacuum does not allow for lift plain and simple, I have never ever seen a vacuum cell used as a form of lift and don't plan on seeing it simply because it's not possible. At least not by the physics I was taught.

A vacuum weighs nothing, at all, you still have the weight of the structure and a vacuum displaces NOTHING.

A vacuum adds nothing and negates nothing, so how is it possible for an airship with a vacuum instead of a gas, to make it lighter than air? The gas pushes the airship up because it was to rise since in the atmosphere anything that is lighter than air naturally rises, but a vacuum is not lighter than air, it has no weight/no substance.

Shattered OUT...

A vacuum "balloon" will create lift, loads of it.


The problem is keeping the balloon shape whenever there is nothing inside it.



Hot air balloons or Helium/Hydrogen work on the basis of equalising pressure with ambient. Go from the perfect gas law:

Pressure = Density * R * Temperature.


R is a constant dependant on the gas - its 287 J/kg/K for air, 2,077 J/kg/K for Helium (He) and 4,124 J/kg/K for Hydrogen (H2).

In a hot air balloon, the increase in temperature results in a reduction of density for a constant pressure (ambient) - thus the volume of the balloon is displacing so many cubic metres of air, but is less dense so is acting in an identical fashion to a boat.

In a He or H2 airship, the density is lower, but R is higher so the pressure stays constant.



Having the pressure constant inside and outside of the balloon does not produce lift, it reduces the forces on the balloon itself.




Now, if you had a vacuum there instead, you would generate much more lift for the same displaced volume (as you've nothing filling it and weighing you down). However, to stop your balloon collapsing, you need alot of structures, and the weight is prohibitive - hence it doesn't happen.

I'm having extreme difficulty trying to grasp this concept, do you have diagrams/video of anything that would demonstrate this?

Or like most other science is it hypothetical?

EDIT:Ok well after doing a search, I seemed to have found several people who all agree on one thing, Vacuum Cells are a possible alternative; not at the current time of technological state however.

Seems kilco is right on the weight thing, it would require far more exotic materials to make any form of Vacuum lift airship viable.

So the answer to the question is Vacuum cells an alternative form of lift? No.

Now for the question, do vacuum cells provide some form of lift? Apparently yes.

I'm still a little on the fence with this one. Still not sure how exactly a vacuum provides that lift, but some people on the internet seem to agree that it's possible, just not at this current time and not before the helium runs out.

Shattered OUT...

[edit on 21-11-2007 by ShatteredSkies]

Let's see if I can explain this, Shattered.


It is Not the gas in the bag (the technical name for the gas-bags in a blimp or dirigible is a Cell, or alternately, a Lift-Cell) that does the "lifting".

As stated previously, the helium or hydrogen or even hot air, merely gives the cell volume, which displaces an equal volume of air.

Air has weight.

If the weight of the volume of air displaced by the volume of airship's lifting-cell(s) is greater than the weight of the airship, the airship will loft.

If you can increase the volume of the atmosphere you displace, without increasing the weight of the container that does the displacing, you will increase the amount of lift available.

If you could build a container that could contain an absolute vacuum, and that container weighed less than the air it displaced, it would loft.

Airships loose lifting power as their altiude increases.

Why?

Because the as you gain altitude the atmosphere thins out.

It is not that the the air availble loses weight; it is that the there is simply less air in any given volume of atmosphere at the given altitude.

To maintain positive lift, your airship either has to lose weight (drop ballast, perhaps) or increase the volume of air it displaces (by stretching the lift-cell material) without gaining weight.

Either option is tricky, difficult and of only limited practicality.


An experiment I've wanted to try for years now would involve sending an inflatable structure into orbit.

The structure (probably carbon fiber) would be coated with a resin that would harden in the high UV environment of space. Once inflated and hardened, the interior would be depressurized to equal the vacuum of space. It would then be sealed again.

This vacumm contained in a hard shell would then be slowed to a relative orbital velocity of 0 MPH by way of a simple retro-rocket pack.

Without orbital velocity, the "Egg" would begin to de-orbit, but at a very slow, "free-fall" velocity, escaping the rigors of a typical high-speed, high-tempurature return.

I'd be curious to learn just how far into the atmosphere the "ball" would drop.

Would it drop to hover at an equalibrium point somewhere in the upper atmosphere? Or would it be crushed in the dense lower atmosphere?


Anyone got a few hundred million dollars to spare?

Originally posted by ShatteredSkies
I'm still a little on the fence with this one. Still not sure how exactly a vacuum provides that lift, but some people on the internet seem to agree that it's possible, just not at this current time and not before the helium runs out.

Let's have some fun with chemistry and math! No, it's not an oxymoron, regardless of all evidence and experience to the contrary.

I'll grab an example of a blimp, and compare the original blimp to a blimp filled with vacuum (that would be an oxymoron). Believe it or not, the vacuum blimp will be have a better weight:displacement ratio, which means it lifts more.

Let's go with the Hindenburg. We'll say it had helium rather than hydrogen, it gives us a better viewpoint as to how modern blimps would stack up. And, yes, I'm aware the Hindenburg is not exactly a modern blimp, but it works. It carried 200,000 m3 worth of gas. At helium's weight, this is about

200,000m^3 * 1000^3 (cm/m)^3 / 1000 cm^3/L / 22.4 L/mol * 4.04 g/mol / 1000 g/kg= 36,071,428 kg

Yes, that's an absolutely massive mass of gas. For those that don't know what's going on, I took the volume (in metres cubed), converted it to centimetres cubed (which is also called milliletres), converted it to litres (which is litres), multiplied it by molar volume at STP (giving us the amount of molecules of gas), multiplied it by the molecular mass of Helium (giving us its weight), and converting it to kilograms. Yay! Let's compare that to the mass of the air it displaces. It's the above equation, except with 28.58 g/mol (average molecular mass of air). This gives us 255,178,571 kilos of air. It's a lot more, as you can probably see. About 7 times as much, actually.

Now, what if we had a vacuum instead of helium? It would multiply out to 0 kg displacing that 255,178,571 kg of air. Let's all get out our calculators. Those of us particularly skilled in their use will be able to tell the masses: 0 kg is significantly less than 36,071,428 kg (as it happens, it is an infinite amount of times smaller). While a perfect vacuum won't happen, we can still get the pressure down pretty far. Going strictly by the rules, we can say that the vacuum, displacing the same volume with less weight, actually does make that buoyant force exist.

However, we have to consider supporting structure. Helium can be kept in reinforced plastic bags. Vacuum can be kept in reinforced metal containers. The reinforcements necessary to contain that vacuum will take the weight up, so we won't have an infinite acceleration upwards if we use a vacuum (which would be really, really entertaining). However, if the weight of the support can be kept down to a point where vacuum becomes more efficient, it could be workable.

Hope this has helped. I also hope that my math work was right, which it's probably not.

I asked an old physics teacher of mine and he made it clear.

It would be possible, but the weight of the supporting structure required to keep the mass in question from imploding (since the pressures are different and everything outside the airship wants to crush the airship) is simply too heavy for the effects of the vacuum cell's lifts to even come into play.

Technology simply hasn't evolved to that point.

Shattered OUT...

Another bright side to this idea, should it become viable one day... is that membrane leakage would be minimal, because there is a negligible number of tiny hydrogen and helium molecules to worm their way through.

Structural integrity seems pretty far off, large scale. I bet it is doable on a smaller scale.

Definitely doable on a radically small scale, however the slightest dent in a vacuum cell will cause enough structural deficiency for it to implode.

Shattered OUT...

True.

But leakage would still occur due to the fact that free hydrogen and helium atoms are available in the atmosphere.

And, given the pressure differential between the closed vacuum cell and the surrounding atmosphere, ANY leakage into the cell could percipitate a catastrophric failure (implosion) of the cell's shell.


Think of how just a small leak can cause the total failure of a dam or levy.


Interestingly, the greatest risk of implosion with a vacuum cell exists at the Lowest altitudes of operation, rather than the highest altitudes, as with other airship paradigms, due to the increased pressure of the denser lower atmosphere.

Kind of like a submarine being at a greater risk of being crushed the lower it sinks.

Originally posted by kilcoo316
A vacuum "balloon" will create lift, loads of it.

Hot air balloons or Helium/Hydrogen work on the basis of equalising pressure with ambient. Go from the perfect gas law:

Pressure = Density * R * Temperature.


R is a constant dependant on the gas - its 287 J/kg/K for air, 2,077 J/kg/K for Helium (He) and 4,124 J/kg/K for Hydrogen (H2).

Do your math. The Density, R & Temperature of nothing is......0
0 * 0 * 0 = 0 Pressure

0 Pressure

The only way a vacuum would create lift is if your were able to displace enough air by your vaccum ballon that the weight of the material is lighter than the amount of air you displace.

That would have to be a big ass vacuum baloon.

"Give me a lever long enough and a fulcrum on which to place it, and I shall move the world."
- Archimedes

The New York Times 4/26/1887

While possible, it is not plausible with current structural technology.

Originally posted by MrKnight

Originally posted by kilcoo316
Hot air balloons or Helium/Hydrogen work on the basis of equalising pressure with ambient.

Do your math. The Density, R & Temperature of nothing is......0
0 * 0 * 0 = 0 Pressure

0 Pressure

The only way a vacuum would create lift is if your were able to displace enough air by your vaccum ballon that the weight of the material is lighter than the amount of air you displace.

Read that line I left in the quote...

Then read it 5 more times. Then stop and think about what it might mean before posting.



The pressure differential of a vacuum 'balloon'* is what causes the structural loading.

*i.e. it DOES NOT work on the basis of equalising pressure.



For an alleged aeronautical engineer.....