Airship Hydrogen resupply

[Anomalocaris]

JuliaL, brilliant.

I don't know where I got the 12 m^3 per kWh from. brainfart.com? Possibly a case of "don't drink and derive".
Seriously, I don't know how that number slipped in, probably a confusion of /kg and /kWh - thanks for catching it. The result looked too good to be true, eh?

So, your idea of using parts of the Aluminum structure sounds very interesting. I wasn't aware of that reaction. Yes, they land in a nice forest - they might have the good sense to land near a forest on purpose.
Of course, if they rip 6 metric tons of aluminum out, that will save them almost the 7000 m^3 lifting gas, doesn't it? This would make replenishing the gas pointless. But dropping ballast (from the hull or the engines), is too boring, I want them to have to do some mad science, either electrolysis or chemistry, to make it.

Could the electrolysis be driven simply by burning wood? They'd need a lot of wood, but that shouldn't be a problem for our friends.

The will-they-make-it-back is definitely a subplot.

The density of hydrogen is about 0.1Kg/m^3.  The density of air is about 1.21kg/m^3.  So bouyancy of hydrogen is about 1.2Kg/m^3, or about 12kg of bouyancy per kg of hydrogen.  So the original 70000 m^3 of hydrogen would have had lifting power of about 84000 kg, or 84 tons.  

If this airship carried 22 tons of fuel and 50 tons of payload, that leaves 12 tons.   Take out engine, envelop, hydro bladders, crew, and Swedish nuns, what remains would be aluminum structure.   With 1920 technology 240 hp motor durable enough to run for days, including radiator, oil pump, nacelle, etc would probably weigh 500kg each.  Let's say crew of 10, they would weigh about 1000 kg.  Swedish nuns might be lighter than air, but being thin they probably don't displace much air and so can't provide much bouyancy.  That leaves 9 tons for structure, envelop, and hydrogen bladders.

So I don't see how there is enough structure such that removing 6 tons of it would still leave the airship able to hold itself together.