Thistle in the Sky | #NONC2022 | ✔

Airship Disaster FAQ

Hello, friends! With this book now concluded, I have a couple chapters of bonus content that I wrote to share here. For the first of these, I wanted to take a moment to answer one of the most common questions I heard throughout the later chapters of this novella:

How the heck is this airship still floating?

This is an excellent question. Not because it doesn't have an answer (it does!) but because I too asked it with my mouth hanging open as I read true stories that taught me about airship durability. Those stories formed the basis of the Ariomma's extended survival and eventual demise—which is to say, no liberties were taken in writing just how long this fictional airship lasted.  

While airships might look like giant balloons with gondolas on them, the first key to their resilience comes from one simple fact: they're not pressurized. A punctured airship will not pop. Its envelope is filled with lifting gas that's lighter than air, but it's just sitting in the gasbags because any pressure will decrease its lifting capacity—compressing it is actually how airships descend to land. You can rip and tear the gasbags all you want, but so long as the tears are small compared to the total surface area, the gas will only leak as fast as it happens to find its way out and float away.

The gasbags are also separated into independent cells. One airship might have a dozen or more, and damage to one leaves all the rest intact. Those intact ones are often enough to float the ship on their own! There are real-life examples of airships that had their envelopes halfway caved in during combat and still managed to limp home weeks later without any significant repairs. As I wrote the later chapters of this book, I kept a rough mental tally of what percentage of the Ariomma's envelope had been destroyed, so I knew when I needed to start thinking about a loss of altitude.

Airships remain resilient against a range of weather conditions. They can be heavily iced, and will keep right on floating. Their natural buoyancy, fuel efficiency, and ability to maneuver at low speeds make them well-suited to riding out storms. High winds can be a danger, but I didn't have to deal with that in this book! Paradoxically, this resilience can lead to disasters of a different kind. British Zeppelin R-101 and Soviet semi-rigid V-6 Osoaviakhim both crashed into mountains in poor weather, not because they were blown off-course, but because their pilots drove confidently into storms with poor maps or faulty navigation equipment, and didn't see the mountains (because of bad visibility thanks to the poor weather) until too late. Oops.

Back to airship structure, though. The other thing to understand about airships is the size ratio between their different component parts. Something like 95% of an airship's volume is taken up by its envelope, and that's just an estimate on my part: the real number is probably higher. In a zeppelin, the envelope's structure is so fragile that it works like a car's crumple zone: hit one part of it, and only that part collapses. This means you can do a ton of damage to the envelope and still miss the decks, the gondola, and the three catwalks (keel, port, and starboard) sneaking around near the bottom. The axial catwalk in the middle is much more vulnerable. Together with the crumple-zone effect and the length of the decks, this all means it's quite plausible for crew members to still have ways around a ship that's been heavily damaged... so long as it doesn't catch fire. 

Hydrogen was the lifting gas of choice during the era of zeppelin airships. It's cheaper and more buoyant than helium, but it's also extremely flammable. Yet here, too, airships have some unexpected advantages. You need both oxygen and a certain concentration of hydrogen to light a hydrogen fire. There's no oxygen inside the gasbags. Firing incendiary ammunition into them will just extinguish the ammunition. A fire needs to be lit at the interface between the outside air and leaking hydrogen, and that leak needs to be big enough to provide fuel for the flames. Because of the aforementioned lack of pressurization, you need a pretty big hole for this. Then you need a source of ignition in just the right place at just the right time. 

If all these conditions are met, though, you have the potential for a high-profile and singularly dramatic disaster on your hands. Once a hydrogen airship catches fire, it's game over. It'll sink within minutes.