boogabooga
Bug Crusher
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Update:
Making some progress.
At the moment the ballonet is automatically adjusted to keep the pressure difference inside the envelope at 500 Pa above the outside pressure. A warning is displayed at 600 Pa and the airship starts venting gas at 750 Pa. These 600 and 750 Pa values are guesses so I'll have to dig out some references and maybe adjust these.
The 500 Pa in my spreadsheet comes from Zepplin-NT (5 millibar overpressure). Airlander uses about twice as much overpressure. This is just from Wikipedia
I was rather surprised when warnings were given when the airship climbs faster than a few metres per second. This is because the simple algorithm I have used doesn't change the ballonet size quickly enough to maintain the correct pressure. I am wondering if real airships climb or descent rates are have to be limited in a similar way due to a limit on the rate of air pumped into or out of the ballonet. Something to look into.
I'm sure "pumping out" is fast and easy because you are just releasing pressure through a valve. The old Goodyear blimp used its propwash to inflate its ballonets. I'm not sure what is done these days.