SUBSIM Radio Room Forums - View Single Post

Platapus · 03-23-16, 07:02 PM

The problem with these big gas bags (the airships, not politicians) is what to fill them with.

A natural air mixture has a molecular weight of about 1.2 g/l. Generally speaking the density of a gas is approximate to its weight, so in order to get any lift we would have to use a gas or gas mixture with a molecular weight of less than 1 g/mol.

The best gas to use is hydrogen. Hydrogen is about 0.09g/l but hydrogen has a terrible public reputation.

Methane is about .7 g/l so while technically lighter than air is not that much lighter which means that the lifting power may be taken up by the structure itself. I would imagine that methane is as safe to use as hydrogen and just as publicly shunned.

That leaves our old friend helium which is about 0.17 g/l. Much heaver than Hydrogen but a lot safer from a fire stand point. The problem is that we don't have a lot of helium. Helium is used as a coolant for many IR and spectral sensors and with the current unpleasantness in the middle east, we are flying a lot of spectral sensors. And a lot of industries use helium from welding to scientific accelerators.

The US produces about 75% of the world's helium supply and some sources say that we will be running out of our supply in about 25 or so years. The 1966 Helium Privatization Act mandated that the US government sell off its helium supply to private industry by 2015.

In 2000 Crude Helium was selling at about $50.00 per thousand cubic feet (MCF). In 2013 it was selling at about $85.00 per MCF and the price is only going up.

Just for a comparison

Hydrogen can lift 60 pounds per MCF
Helium can list 53 pounds per MCF

A hot air balloon can lift about 17 pounds per MCF

There just is not enough helium to support an increase in airships and the cost of helium is also prohibitive.

Can hydrogen be used safely? Hydrogen will burn in Air (at 1 atm) when it reaches a volume percentage as low as 4% and will continue to be capable of burning all the way up to 75%. That's a pretty big spread.

Hydrogen LTA Aircraft have operated for many years with few accidents. Few but spectacular accidents.

In order for LTA aircraft to be viable, we have to

1. Make hydrogen LTA designs safe
2. Confince the public that hydrogen LTA designs can be safe

The first may be possible, the second very improbable.

I would love to see LTA take a bigger part in industry and tourism. I think it would be cool to cross the Atlantic in 3 days in the style of the zeppelins.

But I doubt it will happen in my lifetime or if it will happen at all. Maybe when we find a new super light gas from the planet Zog.

03-23-16, 07:02 PM	#4
Platapus Fleet Admiral Join Date: Oct 2006 Posts: 19,388 Downloads: 63 Uploads: 0	The problem with these big gas bags (the airships, not politicians) is what to fill them with. A natural air mixture has a molecular weight of about 1.2 g/l. Generally speaking the density of a gas is approximate to its weight, so in order to get any lift we would have to use a gas or gas mixture with a molecular weight of less than 1 g/mol. The best gas to use is hydrogen. Hydrogen is about 0.09g/l but hydrogen has a terrible public reputation. Methane is about .7 g/l so while technically lighter than air is not that much lighter which means that the lifting power may be taken up by the structure itself. I would imagine that methane is as safe to use as hydrogen and just as publicly shunned. That leaves our old friend helium which is about 0.17 g/l. Much heaver than Hydrogen but a lot safer from a fire stand point. The problem is that we don't have a lot of helium. Helium is used as a coolant for many IR and spectral sensors and with the current unpleasantness in the middle east, we are flying a lot of spectral sensors. And a lot of industries use helium from welding to scientific accelerators. The US produces about 75% of the world's helium supply and some sources say that we will be running out of our supply in about 25 or so years. The 1966 Helium Privatization Act mandated that the US government sell off its helium supply to private industry by 2015. In 2000 Crude Helium was selling at about $50.00 per thousand cubic feet (MCF). In 2013 it was selling at about $85.00 per MCF and the price is only going up. Just for a comparison Hydrogen can lift 60 pounds per MCF Helium can list 53 pounds per MCF A hot air balloon can lift about 17 pounds per MCF There just is not enough helium to support an increase in airships and the cost of helium is also prohibitive. Can hydrogen be used safely? Hydrogen will burn in Air (at 1 atm) when it reaches a volume percentage as low as 4% and will continue to be capable of burning all the way up to 75%. That's a pretty big spread. Hydrogen LTA Aircraft have operated for many years with few accidents. Few but spectacular accidents. In order for LTA aircraft to be viable, we have to 1. Make hydrogen LTA designs safe 2. Confince the public that hydrogen LTA designs can be safe The first may be possible, the second very improbable. I would love to see LTA take a bigger part in industry and tourism. I think it would be cool to cross the Atlantic in 3 days in the style of the zeppelins. But I doubt it will happen in my lifetime or if it will happen at all. Maybe when we find a new super light gas from the planet Zog. __________________ abusus non tollit usum - A right should NOT be withheld from people on the basis that some tend to abuse that right.