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Hot-Air Zeppelins?

by MattRob
Tags: hotair, zeppelins
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MattRob
#1
Apr11-12, 07:27 PM
P: 100
For something I'm writing I'm constructing a world with an early twentieth century level of technology, and Zeppelins are there, and I couldn't help but notice;

Why did they use room-temperature hydrogen? Did they?

Wouldn't it decrease the density, and thus increase the lifting capacity, if they heated the hydrogen?

Seeing as it was never done, though, there must be some very good reason for it, I just can't think of why. The explosive nature of hydrogen aside, of course, but heating it to ~200*F or 300*F shouldn't make it any more dangerous than it normally is, right?

What about helium? Why not heat that?

Thanks in advance.

EDIT: I do realize that "Zeppelin" actually means a German airship, I guess I mean to apply this to rigid-hulled airships in general, though. With non-rigid hull, it's fairly obvious that the increase in volume would rupture the container. But with a rigid hull, excess hot hydrogen can be let off in one-way check valves that require a certain pressure difference to open, so that the density can be allowed to decrease.
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Borek
#2
Apr12-12, 01:43 AM
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Whole idea about using hydrogen or helium is to get rid of the heating system - you don't need to carry fuel with you, letting you take more cargo instead.
MrSid
#3
Apr12-12, 04:42 AM
P: 81
This scenario was central for several SF stories on Jovian planets for upper atmospheric laboratories. Central to the use of Hydrogen is that the atmosphere is reducing so no chance of accidental combustion. The engineering for doing it in an oxidizing atmosphere is nightmarish, as holding hot H2 or He is an exercise in managing a slow leak.

The heat source was fusion reactors, and fueled by scoop-as I recall the interaction of the equivalent of plankton plugging the scoops posed the problem that had to be solved ;-)

don't recall the author, but a little research to find and read the "literature" with an appropriate citation (call the vehicle by the author's name, maybe?) is one of the aspects of the SF community that make it much like the scientific community. to paraphase it...stand on the shoulders of giants!

Jobrag
#4
Apr12-12, 05:09 AM
P: 475
Hot-Air Zeppelins?

Arthur C Clark used hot hydrogen balloons on (in) Jupiter in one of his short stories.
Apart from Borek's comment about carrying fuel it would be very difficult to heat gas in an envelope without quite a lot of kit probably weighing more then you would gain in expansion of the gas. How about going for a vacuum filled balloon, but support the idea with a bit of credible design detail.
Borek
#5
Apr12-12, 05:10 AM
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Quote Quote by MrSid View Post
This scenario was central for several SF stories on Jovian planets for upper atmospheric laboratories. Central to the use of Hydrogen is that the atmosphere is reducing so no chance of accidental combustion. The engineering for doing it in an oxidizing atmosphere is nightmarish, as holding hot H2 or He is an exercise in managing a slow leak.

The heat source was fusion reactors, and fueled by scoop-as I recall the interaction of the equivalent of plankton plugging the scoops posed the problem that had to be solved ;-)

don't recall the author, but a little research to find and read the "literature" with an appropriate citation (call the vehicle by the author's name, maybe?) is one of the aspects of the SF community that make it much like the scientific community. to paraphase it...stand on the shoulders of giants!
http://en.wikipedia.org/wiki/A_Meeting_with_Medusa
Mech_Engineer
#6
Apr12-12, 08:53 AM
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A large airship has a relatively thin skin holding the lightweight gas in. Because of this it's a poor thermal insulator, so when you look at the total surface area of a large airship which is flying at 10,000 ft (ambient of ~60*F in summer, maybe 0*F in winter depending on location) my guess is it would take a prohibitive amount of energy to keep the gas heated inside the chamber. Especially if you consider the energy is probably better used in things like propulsion.

Still, if the airship is black you could achieve some natural heating from the sun, which could help increase buoyancy some. I'm not sure you'd want to actively heat the gas unless you have some huge amount of surplus of energy generation and nothing to do with it...
etudiant
#7
Apr12-12, 12:45 PM
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Balloons always had problems adjusting to the solar heat input.
Daytime, the envelope heats up, the balloon rises too much, so you need to vent gas.
Nightime, the gas cools and contracts, lift declines, need to inject more gas to provide more lift. That is why long range balloons introduced the guide rope, a length of heavy rope dragged along the ground, to keep the balloon down during the day and up at night.
A Zeppelin would avoid some of this, because the exterior skin would insulate the gas cells from the daytime temperature swings. Indeed, in WW1, a Zeppelin flew from Germany to Africa, crossing much of the Sahara to carry supplies to German forces in the colonies.
A nuclear gas heater providing unlimited hot air would certainly open the door for global ballooning. No envelope would be needed, unless more speed and agility was essential.


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