[IW] Zeppelins mean Alternate Timelines. So, how are they made feasible?

[Joseph Paul]

One of the roles that the military is looking at for airships is to plug the hole in heavy lift capability. When deploying armor there are two speeds slow and wet (naval assets take the armor over) and fast but dribbly and expensive meaning that you use very large planes to delivery not very much and pay through the nose in fuel, maintenance, and crew fatigue. Lockheed was supposed to have been working on such a design but 9-11 put it on hold. The goal was 500-1000 tons of cargo delivered faster than sealift which is 4-6 weeks, so probably 1-28 days.

http://aupress.maxwell.af.mil/saas_T.../Ryan/ryan.pdf is a thesis on the constraints of current programs of deployment.

[Luke Bunyip]

Originally Posted by Anthony

The basic problem with dirigibles is that they simply don't have the performance to compete with either ships or aircraft. A dirigible with basically equivalent performance to a 747 (same takeoff weight, same fuel consumption) would be about 1500' long with a cruise speed of less than 150 mph. The 747 is 231' long with a cruise speed of close to 600 mph.

Something that results in smaller dirigibles is the most useful option. Denser atmosphere would do the trick.

Like your comparison.

On the later, we just used a setting with airships, where the atmospheric density was a number of times what we have IRL. One of the unthought of consequences was that falling in a dense atmosphere would be that slow that you could effectively glide to the ground.

Another reason for airships vs ships is large continental areas, small oceans, and/or oceanic conditions which preclude ships (Kraken, Cthulhu, acid seas, tidal bores...)

[Anaraxes]

moving at modest highway speeds is a significant drawback

Which is why introduction of the 747 completely eliminated long-distance trucking and container ships.

Oh, wait. It didn't. There must be some factor other than just speed involved...

Price, of course. The operating cost of the airship is going to be important. Some air freight needs speed, and will stay on the 747s. Shippers that are less speed-sensitive and more cost-sensitive might prefer an airship.

The airship is more likely to take freight away from the ships and trucks. So, it needs to do something better than those vehicles. So, how can you cripple ships and/or trucks? Can we make the seas treacherous and nearly unnavigable without bad weather that's even worse for the airship? (If we can have a denser atmosphere, maybe we can also have a more corrosive ocean.) Trucks, eh, Cars-Wars-esque roving motorcycle gangs that you could fly over?

[Anthony]

Originally Posted by Luke Bunyip

On the later, we just used a setting with airships, where the atmospheric density was a number of times what we have IRL. One of the unthought of consequences was that falling in a dense atmosphere would be that slow that you could effectively glide to the ground.

Not unless the air density is absurdly low. Let's ponder a world with, say, 10x normal air density. Some effects (and their effect on the pulp genre)

1) Terminal velocity for a falling human will generally be in the 40-50 mph range. Effect: beneficial for pulp, a terminal velocity fall is worrisome but survivable. Also, it only takes a couple of seconds to reach that speed.
2) Given the same overall shape, stall speed, ideal cruising speed (minimum energy per distance), ideal loiter speed (minimum power), and power requirement for flying at those speeds are all multiplied by 0.32. This applies to all winged craft, as well as animals. This will make aircraft quite slow, at least near ground level (go up high enough and eventually air density drops just as far as on earth). In practice, you wouldn't use the same designs as you have on earth; about 0.4 is probably closer. This brings air combat down to lower speeds and shorter ranges, which is good.
3) At constant power, ignoring the energy requirements for lift, flying object speed will be multiplied by about 0.46.
4) Despite these factors, the energy requirements for moving any given distance by air are unchanged -- lower power and lower speed cancel out.
5) A zeppelin has all of its dimensions multiplied by 0.22. Overall, at any given speed, a zeppelin has to cope with 47% greater drag; at constant power, speed is multiplied by 0.88. This is a big bonus for zeppelins.
6) The way bullet energy drops with range is purely a function of drag, and will be 10x faster. Due to oddities in how GURPS handles 1/2D ranges (realistically, a pistol's 1/2D range should be 500+), this can't be done as a simple modification of range; something like 10*B for rifles, 5*B for pistols probably does the job, and also makes most fights occur at much shorter ranges, which is certainly good for pulp.
7) Atmospheric haze is a function of particulate matter. If we give the atmosphere a similar increase in particulate density, visibility drops dramatically.
8) The maximum size of flying animals is largely a function of the power/weight ratios needed for flight, along with structural requirements for big enough wings. The exact scaling is somewhat speculative, but multiplying the weight of flying creatures by ten is not unreasonable, resulting in some reasonably competent birds with weights above a hundred pounds.
9) Above 40 mph, air resistance is the primary limit on ground vehicle speed. This becomes much more severe in our sample world. Multiply the maximum speed of ground cars by about 0.46. This will make it quite rare for car chases to get above around 50 mph.

I'm sure there's others.

[Langy]

You wouldn't need a more corrosive ocean - just less ocean/rivers. If the planet was mostly covered in hills/mountains/etc it would make planes less useful due to there being fewer places they can land and make ships less useful due to there being fewer places they can go. Boom - airships, which have VTOL capability, are much more useful.

[Kelly Pedersen]

Originally Posted by Anaraxes

Oh, wait. It didn't. There must be some factor other than just speed involved...

Price, of course. The operating cost of the airship is going to be important. Some air freight needs speed, and will stay on the 747s. Shippers that are less speed-sensitive and more cost-sensitive might prefer an airship.

Unfortunately, they have others options available - automobiles and trains (and ships, for oceanic transport). That's what you need to compare the economics of airships to - the economics of auto transport. And airships tend to lose out pretty heavily on that. They need more support infrastructure than trucks, and they need far more crew to manage start and stop locations.
There are reasons airships are not popular these days, and it really doens't have much to do with early PR failures. Airplanes have had some pretty spectacular disasters over the years, and people still use them.

[Peter Knutsen]

Originally Posted by Anthony

Something that results in smaller dirigibles is the most useful option. Denser atmosphere would do the trick.

How much denser would it have to be? Keeping in mind what an earlier poster wrote about denser air also making winged airplanes less feasible...

Would the air have to be so dense that it becomes unrealistic to posit that humans still live on the planet, with biologies pretty much similar to us? Are we talking about 25% higher nitrogen partial pressure, or 200% or even 800% more nitrogen? What's the ballpark figure?


(I imagine that with much denser air, there'd be some helium in there too, and maybe a little more of other noble gasses, but that wouldn't make any difference, would it? I'm thinking it won't make a difference if the nitrogen partial pressure is so high as to cause physiological problems to the point where we have to go back in time and make evolution take a radically different path in order to produce intelligent bipeds.)

[Anaraxes]

That's what you need to compare the economics of airships to

That's just what my following paragraph said. You might not have to make airships look better if you can come up with a plausible reason to make trucks look worse. It's all relative.

They need more support infrastructure than trucks,

I'm not convinced. There's this mighty big Interstate Highway system in the US, with gas stations and truck stops at every exit. Plus all the mechanics and service stations scattered throughout the town. That's a lot of support infrastructure. The airship might need more crew at the beginning and end of the flight, but it doesn't need nearly so much infrastructure maintained along the way.
Besides, all that crew just to tie the thing down probably wouldn't exist in a mature design with a modern TL. The ropes could drop and find their own way to the anchors, perhaps with little robot cars attached. Or not so robot; they could always be wirelessly controlled from the zep, maybe RPVs, but even current robots can seek a fixed charging station. In the 1930s, maybe humans were the most cost-effective rope-handlers around, but a modern zep might not need them any more than a modern cargo ship needs a dozen men to hoist sails and raise anchor.

[Joseph Paul]

Originally Posted by Anthony

The basic problem with dirigibles is that they simply don't have the performance to compete with either ships or aircraft. A dirigible with basically equivalent performance to a 747 (same takeoff weight, same fuel consumption) would be about 1500' long with a cruise speed of less than 150 mph. The 747 is 231' long with a cruise speed of close to 600 mph.

Something that results in smaller dirigibles is the most useful option. Denser atmosphere would do the trick.

Wait a minute.

1) Do you know what the fuel tankage is for an airship? For the 747-8 it is 60,925 gallons of fuel. I doubt the airship needs that much since low cost per ton is one of the things being touted.

2) The take off weight for the 747-8 is 970,000 lbs. To equal that with the same distribution of the Hindenburg the airship would be closer to 1900 feet long. However we wouldn't use that shape for heavy lifting so the length can be much less.

3) There are more modern designs of airships that could carry a couple of times the payload of a 747-8. In fact the CL160 exceeds that by 22 tons.

Speed is not the primary attribute of an airship. However modern designs and materials technology may make it possible to cruise at 150-200 mph. Lockheeds P-791 testbed is designed for 100 kts and it's 800 foot long Aerocraft design was to have done 125kts while carrying 500-600 tons. It could carry the 747-8.

One of the other groups looking into airships are scientists. They want high endurance and more rapid travel than ground based vehicles provide for exploring planets. As a very mobile base for adventurers it makes sense. It can go into the wilds and barring a catastrophic loss of lift gas it can come back. Places that have been recently settled may opt for airships run by private couriers rather than pay for roads to connect communities.

[Anthony]

Originally Posted by Joseph Paul

1) Do you know what the fuel tankage is for an airship?

Depends on how fast you want it to go. If you want it to go at the speeds I cited, similar to the 747 (at least, for the same range. You may not be going as far, of course). You can get large reductions in fuel requirement for going slower, but once you go that slowly you're competing with trucks and trains, which have vastly lower requirements.