Why Airships Make Sense for France/Spain/England And why they make NO sense for the USE
The Airship FAQ v1.2
By Charles Prael
Quite a few people (myself included) have brought up the question of “why doesn’t Grantville/the USE/etc. build airships?” This essay is an attempt to answer that question – as well as the related question of why they DO make sense for France, Spain, England, and others. For the moment, I’m going to refer to the Grantville/Swedish/German/USE mix, collectively, as the USE. Similarly, I’m going to refer to the Franco- English- Spanish-etc. alliance as the FES.
The key questions that really come up when discussing airships, and their utility is “bang for the buck.” How much “bang” can you get for a given amount of resource and technology “buck”? To begin with, I want to examine the key technical areas involved in building an airship. And to do that, we need to discuss the different kinds of airships.
Types of Airships
Realistically, there are two kinds of airships: rigid (zepplins/dirigibles) and non-rigid (blimps). Technically, there’s also semi-rigids, but I’m going to lump them in with non-rigids, since they operate pretty much the same way.
Rigid airships have a solid external frame. Inside that frame, you have sets of gasbags, to provide lift. Wrapped around that frame, you have a “skin” (doped linen/canvas, in this case), to provide an aerodynamic shell. Suspended from that frame (and possibly comprising part of the bottom-interior of the frame), you have crew spaces, engine spaces, storage, and so forth. Finally, on the rear you have large movable fins, for navigation and height-keeping.
Non-rigid airships dispense with the external frame. They have a keel-frame, much the way a rigid airship does, that contains all of the storage, engine spaces, crew spaces, etc. But the gasbags, rather than being suspended inside the frame, are suspended from it (or rather, the frame is suspended from them). The aerodynamic shell is wrapped directly around the gasbags – which is why, when they’re deflated, it’s “limp”. Oftentimes, non-rigid airships are somewhat smaller than rigid airships, due to the material issues involved.
Technical Issues Involved in Building Airships
There are a number of technical areas that you have to deal with to build airships:
Gasbags: A common misconception is that building a usefully gas-tight bag is very difficult to achieve at the kind of technical level available to the USE and FES. This isn’t true. Throughout WW1, the heyday of rigid airships, the primary material used to make gas-tight cells was goldbeaters skin. What’s goldbeaters skin? Well, it comes from the intestinal liner of an ox. And it works just fine. The problem is that you need a lot of them. To given an example, a “standard” late-WW1 rigid airship would use over 200,000 of them. That means slaughtering 200,000 oxen.
Aerodynamic Shell: This one’s actually pretty easy to deal with. For most purposes, a tightly-woven linen, or sail canvas, will work just fine for either design application. Doping compounds are, similarly, not all that hard to work out.
The Frame: Now here’s where you get into interesting problems. What you want is a frame that combines light weight with high strength. Some aspects you can resolve through design – using cross-braced box trusses instead of solid members, for example. But others are inherent to the materials you use. And, unlike WW1, you effectively don’t have aluminum as a structural element. You’re down to wood, iron, and if you’re willing to pay a LOT of money, some steel. Realistically, your best option is laminated wood. So that limits what you can do, and it’s going to add weight to any given size of dirigible.
Propulsion: Here’s a real killer. There’s only a few engines available in the USE for this kind of thing. And, until they can solve the engine availability issue, there are NO engines available in the FES that would work in this environment. The one good thing is that you don’t face as stringent power-weight limitations for airship engines as you do for airplane engines. And you don’t have to worry about little problems like inverted flight. Which means there’s a wider variety of engines available. But you still need a certain amount of power to get things going properly.
Hydrogen and Helium Generation: Again, this has been a “but it’s really hard” thing. For helium you’re dern tootin’ it’s hard. You’ve got 3 realistic options. The first is to go to the US and mine the stuff. The second is to distill it from natural gas. And the third is to generate it from a working nuclear fission reactor. Somehow, I just don’t see any of those happening. What about hydrogen? Well, that’s easier. It turns out you can generate hydrogen using nothing more than steam (under pressure) and red hot iron filings. The iron strips the oxygen from the water (steam), turning to iron oxide (you know, rust), and liberating the hydrogen. Very easy to do, very easy to implement in a low-tech society. Alternately, you can use the sulfuric acid method, or any of several others.
Useful Lift: Now we get get into the juxtaposition of all these factors. The problem, especially with rigid airships, is that you have to build an awful lot of airship to get a relatively small amount of useful lift. The R.34 only had about 42 tons of useful lift – and that included the crew, and fuel, and food. Not a lot left over for armaments, cargo, and so forth. Think of it like building a small ocean liner to move the contents of a single railroad car. It’s a big resource investment, for a relatively small return. Now, having said that, at this time you will get more absolute payload from an airship than from any realistic airplane design. That’s just the reality of the beast.
But, for the resources expended in building an airship, how many planes can you build? Well, let’s use equivalent dollars to get an idea of the resource commitments involved. That’s an imperfect tool, and doesn’t measure all of the issues that the USE/FES would face, but it does give some idea of the scales involved. In 1929, Alliance Aircraft sold the A-1 Argo for $4500 per. It was was 20’l x 28’8” wide, had a 125 HP engine, and carried a 650lb load. In contrast, R.34, built in 1919, cost £350,000. Assuming a 2:1 exchange ratio, that means that R.34 cost roughly 155 times as much as the kinds of airplanes we’re looking at for the USE. Realistically, we’re probably talking a cost multiple anywhere from 20:1 up to 50:1. So the question isn’t, “is an airship more effective than a plane?” but rather “is an airship more effective than 20-50 airplanes?” To which the answer has to be an unqualified “no”.
But What About the FES?
Looking at this from the perspective of the FES, things look a little different. Why? Well, for several reasons.
First, they are, to a much greater extent than the USE, command economies. Not totally, and certainly not to the extent you might find in, say, a Marxist, Stalinist, or fascist environment. But to a reasonable extent, they are. Which means they can mobilize greater resources for specific projects. In practice, this means that for truly strategic projects, they’re a bit less concerned with cost-effectiveness issues, and much more concerned with effectiveness issues.
Second, their critical resource gap is much smaller, and concentrated entirely around uptime-based technologies. The intestines from 200,000 oxen? No problem. Four 100HP motors? That’s a different story – that may well represent almost all of the high-power motors available in the entire country. So they’re much more concerned with getting maximum effect from those uptime resources – not in making the uptime resources perform more cost-effectively. To frame this a little differently, the question for the FES isn’t which is more cost-effective, 20 planes or 1 airship. It’s which is more effective, four planes (the total number they can build with the engines at hand) or one airship.
Finally, labor resources. The FES is much more able to mobilize marginally-skilled workers than the USE. As a result, they’ll be able to marshall the appropriate resources to build an airship much more easily.
So, saying all that, what kind of airship would they build? Most likely a non-rigid airship. Blimps are easier to build, easier to get into test, and have fewer structural load issues than a fully rigid airship. They’ll also deliver useful performance with small structural loads and smaller sets of engines (so you might build 4 smaller airships, instead of 1 bigger one, using the above example).