by Andy Cooke
When it comes to signalling that the reader is in an alternate history, airships are superb for the purpose.
Whether Harry Turtledove's The Two Georges, Michael Moorcock's Warlord of the Air, Tabac Iberez's A Century Turns, Jared's Decades of Darkness, or Ed Feery's Zephyr Brigade, if you see an airship, you know you're in an alternate history.
Disused in our history following the Hindenberg disaster in 1937, their presence in the sky telegraphs to the reader that this is something different. Something changed in history - maybe something innocuous, maybe something with farther-reaching effects.
They also have a beauty of their own, attracting authors and readers, even when they may be impractical. The author of an Alternate History Timeline must bear in mind the limitations and capabilities of airships if they are to be used plausibly. But remember: constraints are the mother of creativity - plots inevitably arise from problems.
This series will go into the possibilities, constraints, and limitations of airships, as well as key PoDs - but for the first article, I'll quickly summarise their evolution, types, and needed infrastructure, as well as give some initial thoughts towards capabilities and roles.
Airships are simply an evolution of the balloon - a lighter than air vessel that is made mobile and steerable. More intuitive than heavier-than-air vehicles, you simply start with a hot air balloon and give it an engine. You make it a directable balloon (in French, a ballon dirigeable)
Of course, the traditional balloon shape is then unbalanced and a very poor shape for making headway - you need to make it streamlined and balanced. Just a few moments thought and almost anyone arrives at something close to the traditional 'blimp' shape.
In time, steam engines (with very poor power-to-weight attributes) would give way to internal combustion engines and even electric motors (the latter as long ago as 1883).
More rigid structures, to ensure stability and solidity in poorer weather conditions, became more prevalent. By the end of the nineteenth century, the first of the famous Zeppelins appeared.
One universal aspect: all airships used hydrogen as their lifting gas. Far lighter than any alternative, and cheap into the bargain. The downside was its flammability - but at least the gas was above the crew and passenger compartment, and would burn upwards. After all, it's not as though current aircraft are famous for being non-explosive.
"Isn’t hydrogen rather dangerous?"
"So’s kerosene, but we fly aeroplanes filled with the stuff"
(words spoken by Pip Allen in the book "The End and Afterwards")
Helium was a non-explosive and non-flammable alternative, but it was expensive, rare (when the US decided to use it, the USS Shenandoah, on its first flight, contained most of the world's then-supply of helium), and the reduction in lift capacity (coupled with engineering and operational considerations) could halve the payload capacity of an airship.
They began to be used for exploration and very limited cargo and passenger transportation as the Twentieth Century dawned, before being used as long-range bombers in WWI. Surprisingly difficult to shoot down (igniting the envelope was far more difficult than you would instinctively assume), they caused psychological terror to many.
Following the War, airships began to hint at their potential, providing luxury air transport, as well as exploration services. Even used as airborne aircraft carriers (beating Nick Fury of SHIELD by decades - albeit with somewhat more limited capacity), it seemed as though the sky was the limit.
(No, I'm not apologising for that)
Unfortunately, accidents tended to happen, with designs sometimes rushed too quickly into service or flown in dangerous conditions. High-profile disasters damaged the image of airships, such as the R101 crash (not properly tested following major modifications), the USS Shenandoah (destroyed in a severe thunderstorm) and the USS Akron (lost in a severe storm). There was little experience with large aircraft at the time, and the limits were often pressed too far - lessons painfully learned and taken into account for heavier-than-air aircraft when they grew larger.
Finally, the famous Hindenberg disaster destroyed the image of airships for good.
While airship development and use did not totally cease, following 1937, airships became very much a fringe method of air transport. There have been repeated and sporadic attempts to revive airships since, but these have always run into economic or credibility issues.
An ATL author needs to either find a PoD before (or up to) 1937, or come up with a plausible reason for a change since the Hindenberg's fate, caught on film and broadcast around the world, terrified people.
To plausibly write about airships, an author needs to have at least a passing knowledge of their characteristics. Airships may be:
- Non-rigid (no solid internal structure in the balloon envelope, which holds its shape simply by the pressure of the lifting gas, which may be in one or more internal gasbags). The Goodyear Blimp is a famous example of these. Carrying less solid weight than any alternative, they have the best lift capacity, but their size is limited by their lack of structure (they can kink in the middle), and sudden manouevres (or bad weather) can also cause kinking.
- Semi-Rigid (with a solid keel running along the envelope, giving it shape and preventing kinks). The keel provides structure and a safe attachment point for the gondola and engines, but the overall shape of the envelope is, again, provided by the lifting gas. These are more durable and reliable than the "blimp" type above, but have to carry slightly more weight for any given lifting volume. In certain circumstances, a weak keel can fail and allow kinking.
- Rigid (with a solid keel and solid internal framework supporting the shape of the envelope). The Zeppelin class airships are examples of this type. Most durable of all, but carrying more weight per lifting volume than any other.
Remember that, especially for rigid airships, the internal volume for passengers and cargo often goes within the gas-bag.
For directional control, airships have an engine (forwards and backwards control) and a rudder (left and right yaw control). As they fly so much slower than heavier-than-air aircraft, are exactly as light as the surrounding air at any time (in order to be stable at whatever altitude they are at), and have physically larger cross-sections, they are very sensitive to the wind and weather. Serious turbulence, storms, severe wind-shear - all should be avoided. High headwinds could cause an airship to either be brought to a standstill, or even driven backwards.
Altitude control is the least immediately intuitive aspect of airship control: how do you reduce altitude without letting out gas? The answer is in the use of ballonets within the airship envelope.
Balloons within the envelope itself, they either pump in air from outside (inflating the ballonet), or pump it out (deflating the ballonet). When the ballonets are inflated, the lifting gas within the airship has the same mass but less volume to take up - compressing it slightly and increasing its density. The airship seeks the same density of outside air as its own overall density, and sinks. Deflating the ballonets, allowing the same quantity of lifting gas more room, causes its density to decrease, and the airship seeks a less dense layer of air, rising.
Should the pumps break, difficulties could ensue, of course.
Any world with airships in it needs the infrastructure to support them. Production and transport of hydrogen, of course (or helium, if you take the safer route).
Mooring towers, in order for them to be able to park safely (note that these can be attached to ships, in order to integrate two transport types).
Airship hangars in which to store them away from the weather - and note that these are truly huge structures.
You will need a network of such facilities around the globe - or, at least, wherever you want your airships to be able to routinely go.
Airships can travel without these facilities, but it does make life more difficult for them.
Capabilities and Roles
The key characteristics of airships are what will give them their main capabilities and roles in your story. I'll go over these in more depth in later articles, but as food for thought, these are key traits you should bear in mind:
- Speed: airships can travel faster than most ground transport. However, other aircraft can do so to a far greater extent. - Reach and ubiquity: not limited by roads, rail, or runways, nor limited by seas or coasts, airships can go wherever there is air. - Height: Airships can gain the benefits from being high up (such as the ability to see further) - Agility/flexibility: You can send them somewhere at short notice, tied with the reach/ubiquity aspect above
WEAKNESSES: - Impermanence: they can't hang around forever. Well, at least, not without significant design efforts. Unlike heavier-than-air aircraft, though, you can effectively park one next to a cloud and stay there for quite some time. - Limited Payload: one reason you might be attracted to hydrogen as your lifting gas. It can be easier to evolve to heavier payloads for airships than aeroplanes, though. - Fragility: they break. See also "weather", below - Weather: in serious winds or stormy conditions, you don't want to be airborne in an airship. In clouds or rain, though, they're probably safer than early aeroplanes.
More in the next article!