Future Airships

ppragman said:
I'd straight up go old-school - hydrogen as my lifting gas, etc. Much cheaper...
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Hydrogen isn't that much better of a lifting gas than Helium. Its primary advantage lies in its cost, which is much cheaper than Helium. Also, Hydrogen is much more common and easier to produce than Helium.

As far as lifting ability, Hydrogen isn't significantly better either. First, Hydrogen only exists in its gaseous form as a diatomic molecule. Basically this means as a gas, Hydrogen only occurs as two Hydrogen atoms bonded together; H2. Helium, however, does occur as a singluar atom in its gaseous form. Even though Hydrogen has an atomic weight of just over 1.00 (whereas Helium's atomic weight is about 4.00), because Hydrogen as a gas is always diatomic, its atomic weight is actually 2.00.

Now, static lift is primarily determined by the differential density between the lifting gas, and the surrounding fluid medium (in our case, the atmosphere). Under standard atmospheric temperature and pressure, diatomic Hydrogen has a density of 0.0052 lbs/ft3. Helium under these same conditions has a density of 0.0102 lbs/ft3. Air has a density of 0.07647 lbs/ft3 under standard atmospheric conditions at sea level.

For one cubic foot of Hydrogen, static lift under standard sea level conditions is 0.07647-0.0052 = 0.07127 lbs/ft3 of lift

For one cubic foot of Helium, static lift under standard sea level conditions is 0.07647-0.0102 = 0.06627 lbs/ft3 of lift

So, a 1,000 cubic foot envelope filled with Hydrogen would have just over 71 pounds of lift at sea level standard conditions, and the same 1,000 cubic foot envelope filled with Helium would have just over 66 pounds of static lift under these same conditions.

You can see the difference isn't very significant, certainly even less so when we consider the dangers of using Hydrogen as a lifting gas due to its flammability.

Apologies for the overly verbose explanation, but hopefully this sheds a bit of light on the topic.
 
Minuteman said:
I wonder if an unmanned airship at 50k-60k ft would make for a good observation platform, comm relay (cheaper and more capacity than a satellite), or, I dunno, a receiver for passive radar detection of low-observable vehicles?
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Quite simply, no, it wouldn't work. The volume that the gas expands from sea level to 60K feet is huge. So, you've got 2 choices. Build an airship with gigantic ballonets (air chambers, as helium volume expands, air is pushed out, to keep the total volume the same) or vent gas. Venting gas isn't practical on a cost standpoint and building a ship with gigantic ballonets isn't practical because as the size of the ballonet increases, so does its weight, so basically you end up in a positive feedback loop, in terms of size and weight.
 
Venting gas also causes you to lose static lift, which reduces the useful load of an airship. All of these ridiculous airship designs are nice and pretty in theory, but not so much in practice.
 
Tethered balloons, vice airships, are all the rage for surveillance. DHS uses them on the US/Mexico border, and DoD uses them at posts in combat zones. Outstanding capability. I always wished they were mobile, though.
 
KSCessnaDriver said:
Quite simply, no, it wouldn't work. The volume that the gas expands from sea level to 60K feet is huge. So, you've got 2 choices. Build an airship with gigantic ballonets (air chambers, as helium volume expands, air is pushed out, to keep the total volume the same) or vent gas. Venting gas isn't practical on a cost standpoint and building a ship with gigantic ballonets isn't practical because as the size of the ballonet increases, so does its weight, so basically you end up in a positive feedback loop, in terms of size and weight.
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Is venting really that expensive? Like compared to the U2 and other aircraft that have assumed this high altitude observation position? I have thought about that for airships too. I remember reading somewhere that the government was working on an airship that could stay up for something like three weeks at high altitudes.
 
smack300 said:
Is venting really that expensive? Like compared to the U2 and other aircraft that have assumed this high altitude observation position? I have thought about that for airships too. I remember reading somewhere that the government was working on an airship that could stay up for something like three weeks at high altitudes.
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Yes. A U2 would be way cheaper than any airship. Helium isn't cheap, even at wholesale bulk rates. The government is working on a 3 week endurance airship, its called the LEMV. They've spent hundreds of millions on it, for a grand total of 1 hour of flight time. It will never fly 3 weeks at a time, may not even get 3 weeks of total flight time on it.
 
KSCessnaDriver said:
Yes. A U2 would be way cheaper than any airship. Helium isn't cheap, even at wholesale bulk rates. The government is working on a 3 week endurance airship, its called the LEMV. They've spent hundreds of millions on it, for a grand total of 1 hour of flight time. It will never fly 3 weeks at a time, may not even get 3 weeks of total flight time on it.
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Really? Wow, I had no idea. Thanks for the info. And yea that was the airship I was thinking of. And 20,000ft doesn't sound to high for a surveillance platform.
 
smack300 said:
Really? Wow, I had no idea. Thanks for the info. And yea that was the airship I was thinking of. And 20,000ft doesn't sound to high for a surveillance platform.
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Even 20,000 ft is sufficient, as long as you've got air superiority. But, even 20,000 feet is a lot of gas to get rid of. There is a reason 95% of the time, you see airships down low to the ground, its because we are at or near our service ceiling that particular day. Bunches of things factor into that, not limited to amount of gas in the airship, outside air temperature, temperature of the helium and barometric pressure
 
KSCessnaDriver said:
Even 20,000 ft is sufficient, as long as you've got air superiority. But, even 20,000 feet is a lot of gas to get rid of. There is a reason 95% of the time, you see airships down low to the ground, its because we are at or near our service ceiling that particular day. Bunches of things factor into that, not limited to amount of gas in the airship, outside air temperature, temperature of the helium and barometric pressure
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Sorry for the dumb questions but Airships are interesting and I know nothing about them. Ha. I just figured they were low cause it took to much effort to get them much higher and most purposes of airships is advertising or filming so its pointless to go high, didn't realize that you couldn't go higher because of your service ceiling. To vent the gas is it a pretty labor intensive job for the pilot or is it just done by computers and the pilot just monitors what is going on?
 
smack300 said:
Sorry for the dumb questions but Airships are interesting and I know nothing about them. Ha. I just figured they were low cause it took to much effort to get them much higher and most purposes of airships is advertising or filming so its pointless to go high, didn't realize that you couldn't go higher because of your service ceiling. To vent the gas is it a pretty labor intensive job for the pilot or is it just done by computers and the pilot just monitors what is going on?
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Haha, computers. No, its all manual. Its very easy, pull a handle, open the valve. Very easy, very quick, very expensive. Yes, advertising is easier done down low too. And generally the wind is more favorable for us down load, especially in a headwind.
 
smack300 said:
Sorry for the dumb questions but Airships are interesting and I know nothing about them. Ha. I just figured they were low cause it took to much effort to get them much higher and most purposes of airships is advertising or filming so its pointless to go high, didn't realize that you couldn't go higher because of your service ceiling. To vent the gas is it a pretty labor intensive job for the pilot or is it just done by computers and the pilot just monitors what is going on?
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Both of our Helium valves (well, technically there are three, but the third valve is a rip panel that will quickly deflate the entire ship), are manually operated through spring loaded toggles located above the pilot's head on the left side of the gondola. You basically hold open the valve, and time how long the valve stays open. Each valve vents helium at a nominal rate, so you can easily calculate how much static lift you've lost by simply calculating how long you've held open a respective Helium valve.
 
MV22Pilot said:
Tethered balloons, vice airships, are all the rage for surveillance. DHS uses them on the US/Mexico border, and DoD uses them at posts in combat zones. Outstanding capability. I always wished they were mobile, though.
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Aerostats (unmanned tethered balloons) are really the only application I can see where Hydrogen could be used as a lifting gas vice Helium. It would shed some significant cost from operating the Aerostats, and assuming the necessary precautions were taken, the flammability risk could be somewhat mitigated.
 
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