Steam hydrogen airship hybrid.

[Jackaccount]

Hydrogen airships fell out of favor because they explode, steam airships have been proposed but never caught on because their marginal improvements over hot air aren't worth the slew of problems they present. I was wondering whether it would be possible to make an airship that uses a steam/hydrogen mix as a lifting gas, preferably one that wouldn't explode.

[enderlord99]

That's not how any of this works.

...

Helium is best: it's roughly as light as molecular hydrogen, but doesn't explode.

[factotum]

Helium is about twice as dense as molecular hydrogen, actually, although that probably doesn't make a huge difference in terms of its lifting capacity, that much is true.

I'm really not sure where steam comes in, though? It's far denser than either hydrogen *or* helium and requires constant heat to maintain. I don't think steam has *ever* been used to lift a balloon--hot air obviously has, because it's a lot easier to handle than steam is.

[Jackaccount]

I'm really not sure where steam comes in, though? It's far denser than either hydrogen *or* helium and requires constant heat to maintain. I don't think steam has *ever* been used to lift a balloon--hot air obviously has, because it's a lot easier to handle than steam is.

Sorry if I was unclear with my question, I remember reading that steam is theoretically a better lifting gas than hot air and I was wondering whether hydrogen could be combined in the same area as steam to help offset the problems inherent in both as a lifting gas. I'm trying to think of an alternative to helium as it's beginning to become rather expensive.

[Mechalich]

Mixing hydrogen with water vapor doesn't make it less explosive. In fact, insofar as oxygen can be liberated from water vapor to serve as fuel for the combustion reaction, it makes it worse.

[Jackaccount]

Mixing hydrogen with water vapor doesn't make it less explosive. In fact, insofar as oxygen can be liberated from water vapor to serve as fuel for the combustion reaction, it makes it worse.

Darn, I'd forgotten to account for what water's made of, I can almost feel my old chemistry teacher judging me. Oh well, back to the drawing board, thanks for the responses everyone.

[Mando Knight]

Helium is about twice as dense as molecular hydrogen, actually, although that probably doesn't make a huge difference in terms of its lifting capacity, that much is true.

It's nominally 93% the lifting capacity of hydrogen, and impurities brought that down to 88% using Hindenburg-era sources of lifting gas. At least, according to a video made by Bill Hammack, an engineering professor who wrote a book about the demise of a specific airship. Losing 7-12% of your potential not-lifting-gas mass is pretty significant.

[Knaight]

Sorry if I was unclear with my question, I remember reading that steam is theoretically a better lifting gas than hot air and I was wondering whether hydrogen could be combined in the same area as steam to help offset the problems inherent in both as a lifting gas. I'm trying to think of an alternative to helium as it's beginning to become rather expensive.

It's definitely a better lifting gas - the molecular weight of steam is about 18, whereas the molecular weight of nitrogen is about 28 and oxygen about 32, resulting in 29ish for a typical mixture of air. This means steam would work as a lifting gas to some extent without even being heated.

That said, helium is just so much better than it in that role.

[jayem]

It's definitely a better lifting gas - the molecular weight of steam is about 18, whereas the molecular weight of nitrogen is about 28 and oxygen about 32, resulting in 29ish for a typical mixture of air. This means steam would work as a lifting gas to some extent without even being heated.

Of course if it weren't heated it either needs to be kept at low pressure (in which case we're back at vacuum ships) or it tends to be a non-lifting liquid.

Mixing hydrogen with water vapor doesn't make it less explosive. In fact, insofar as oxygen can be liberated from water vapor to serve as fuel for the combustion reaction, it makes it worse.

Cold pure water (magically) gas. I suspect it ought to make it (slightly) less explosive. You effectively get half the concentration of hydrogen (and about 3/4 of the total amount) and I think while water can burn any reaction with hydrogen is going to be fairly boring.

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If the oxygen is liberated then it also has to release it's hydrogens which leaves you more or less where you start.
The 'hydrogen bond' that water does between molecules is less than the bond inside molecules. So that's probably not explosive, but bad for lifting.

I think it's the heat that swings it to the more dangerous, or any air that you allow in with the water.

[halfeye]

There is a reason steam is used for powering things, it's very high energy stuff. You get steam by boiling water, there is very little steam that occurs below that temperature, the pressure tends to be high, and the thermal capacity of steam is also high, meaning there's enough heat in it to easily kill people, you can get a bad scald by putting your hand in front of the spout of a boiling kettle (british kettle).

Basically, steam is not a useful idea in this context, it's dangerous stuff, and you don't usually want that in combination with other explosives (there might be a case for it as a rocket fuel, I don't think so, but maybe).

[Jackaccount]

(there might be a case for it as a rocket fuel, I don't think so, but maybe).

A man actually attempted that rather recently, Mike Hughes launched himself 1,875 feet over the Mojave desert in an attempt to prove the earth is flat.

[Mando Knight]

(there might be a case for it as a rocket fuel, I don't think so, but maybe).

Not stored as steam, but water is the primary exhaust product of a LH2/LOX rocket engine like the Rocketdyne RS-25 (the space shuttle main engine) or J-2 (Saturn IB and the Saturn V's upper stages--the first stage uses RP-1/LOX-fueled Rocketdyne F-1 engines instead).

Steam's energy is used somewhat more directly in naval aviation, though--aircraft carriers in the CATOBAR configuration (mostly) use steam-powered catapults to assist the launch of carried craft that can't take off vertically.

[gomipile]

Sometimes alcohol fueled rockets used watered-down fuel. The steam produced in the combustion chamber did contribute to thrust.

[factotum]

Sometimes alcohol fueled rockets used watered-down fuel. The steam produced in the combustion chamber did contribute to thrust.

I suspect they did that primarily to make the combustion cooler and thus require less cooling of the rocket motor itself, though, because I'm pretty sure the contribution of the steam to the thrust would be much less than just burning additional alcohol!

[Lvl 2 Expert]

Mixing hydrogen with water vapor doesn't make it less explosive. In fact, insofar as oxygen can be liberated from water vapor to serve as fuel for the combustion reaction, it makes it worse.

Water is fully burned hydrogen, there is no net energy gain in splitting the water only to burn it again.

I think the main problem with steam is the conditions needed for it to be steam. It needs to either be quite hot or under less than atmospheric pressure, you either need to keep it completely enclosed or have a way to replenish it and any weight you add in order to use steam rather than hot air negates the density advantage it has.

[Jackaccount]

I think the main problem with steam is the conditions needed for it to be steam. It needs to either be quite hot or under less than atmospheric pressure, you either need to keep it completely enclosed or have a way to replenish it and any weight you add in order to use steam rather than hot air negates the density advantage it has.

I think the idea I read about was to use a steam engine to both replenish the steam and provide power to the airship.

[halfeye]

I think the idea I read about was to use a steam engine to both replenish the steam and provide power to the airship.

It is still very silly. Boiling steam is very dangerous stuff, even when barely boiling and only at atmospheric pressure. If you had a rigid container air pressure would crush it flat when the steam condensed, if it's flexible it needs to be boiling water proof, and that eliminates almost all fabrics, particularly plastics, but wool and cotton aren't great at being boiled either.

[Jackaccount]

It is still very silly. Boiling steam is very dangerous stuff, even when barely boiling and only at atmospheric pressure. If you had a rigid container air pressure would crush it flat when the steam condensed, if it's flexible it needs to be boiling water proof, and that eliminates almost all fabrics, particularly plastics, but wool and cotton aren't great at being boiled either.

Would a semi-rigid or metal-clad airship work? I'm especially interested in the latter.

[factotum]

Metal cladding is heavy. is the big problem. Even with the best lifting gasses available (hydrogen and helium) the actual lifting capacity of your airship is a small fraction of its total mass. and anything that adds to the mass of the airship reduces your usable lifting capacity. Steam engines and metal cladding all add mass that would be more usefully used for cargo or passengers.

[Alent]

Steam Powered Balloons have been experimented with, but it has been so long since I looked at the Flying Kettle site I couldn't tell you much past that it was a mess of a bad idea.

As to Rigid Airships, I suggest you check out the ZMC-2 Metalclad. I would love to see that idea revisited.

[enderlord99]

Water is fully burned hydrogen

As opposed to hydrogen peroxide, which is more-than-fully burned hydrogen?

[Lvl 2 Expert]

As opposed to hydrogen peroxide, which is more-than-fully burned hydrogen?

Hydrogen peroxide is unstable and converts to water and oxygen, a process which releases energy. H2O sits at a lower energy point, there's no way to create energy by letting water react with more oxygen. That's one of the reasons we have oceans full of the stuff.


At least, as far as I know.

[Knaight]

As opposed to hydrogen peroxide, which is more-than-fully burned hydrogen?

It's fully burned hydrogen that also adds an oxygen-oxygen single bond, which is why it's so unstable.
2 H₂O₂ -> 2 H₂O + O₂. With bound counting that's breaking two O-O single bonds to form one O=O double bond, which involves a fairly significant energy release.

[Jackaccount]

Steam Powered Balloons have been experimented with, but it has been so long since I looked at the Flying Kettle site I couldn't tell you much past that it was a mess of a bad idea.

As to Rigid Airships, I suggest you check out the ZMC-2 Metalclad. I would love to see that idea revisited.

The flying kettle website and ZMC-2 were actually inspirations for this question.