As mentioned in another post, I am writing up stuff for a Swedish roleplaying game that have Zeppelins in it. But before looking at things that are directly tied to game, I thought that I should think aloud a bit here and hopefully get some input from other that frequent this place
I guess this could be used for a pre-warp world in Trek as well.
What I am looking for is something that feels plausible to me even if looking at details. So it will have to be at least somewhat grounded in real world facts. Now, as I see the setting, it is a world where innovation is stifled, but improvements do happen even if it is slowly. So technology that is available during the 30s can be considered, and improvement of that technology can be considered up to the 50s or even the very early part of the 60s.
Airplane technology I think I will have reached only about what flew around at the outbreak of the first World War.
As it isn't limited to the real world, the real world availability of Helium does not have to be taken into account.
A good site that I have found is http://www.airships.net/ which have quite a bit of information.
As an example, some numbers about the Hindenburg can be found there; comparing hydrogen and helium (it was apparently originally designed for Helium).
Code:
LZ-129 Hindenburg kg lbs
Dead weight 118,000 260,145
Crew 5,400 11,905
Provisions 3,000 6,614
Fuel 58,880 129,808
Oil 4,000 8,818
Ballast 7,950 17,527
Misc. 9,120 20,106
206,350 454,924
Gross lift/hydrogen (68lbs/1,000 cu. ft.) 215,910 476,000
Payload for passengers, mail, freight w/ hydrogen 9,560 21,076
Gross lift/helium (60lbs/1,000 cu. ft.) 190,509 420,000
Payload for passengers, mail, freight w/ helium -15,841 -34,924
This example above have hydrogen being 13% more efficient than helium, and other sources have stated it being closer to 8%. I have also heard that Hindenburg had about 200,000 cubic meters of gas volume, and each cubic meter gives one kilo of lift. That would match that 8% difference.
Now, I imagine Zeppelins being used for both civilian and military uses. Civilian uses would probably be quite close to how they where used in the mid-late 30s. Germany tried to use Zeppelin during WWI, but that appears to have been quite a failure.
The current opinion seems to be that it was the paint of the Hindenburg that caught fire, and that fire ignited the hydrogen. So if the ship had been painted in a non, or at least less, flammable paint it might not have ended the way it did.
The Zeppelin used to attack England during WWI apparently had a tendency to end up in flames. One tracer seems to have been enough to ignite the hydrogen. But one of the sites I have been looking at (not sure if it is on the above mentioned or another one) claimed a statistic that only 1 in 8000 rounds managed to hit a Zeppelin, and that a normal round is not enough to ignite hydrogen. Flying in over a well defended area like London means a lot of bullets.
If the gas isn't ignited, it would just make the gas below that hole to leak out. Just as if it was filled with water, the gas would not disappear out of the hole immediately.
In a Zeppelin, the gas is in several large balloons. So even if the top of one balloon is punctured, the ship will still not lose all if its lift.
So if ship could be built with a lighter frame and more efficient engines, it would give quite a bit of extra payload. Segmenting the gas into more balloons, and having collector valves to recycle the gas, would cost weight but making the Zeppelin far less vulnerable and thus more suitable as a combat vessel.
From a combat point of view, I sort of envision Zeppelins firing at each other with light or medium artillery guns and medium to heavy machineguns. By not having a particularly hard hull, a shell would probably not be able to detonate on impact and have to be set with a timer that start counting when fired. So most shells detonate to early or to late.
So a good starting point is to look at how to shave of weight on the hull and balloons (better material and more efficient design), engines (better power/weight ratio and less fuel consumption); and roughly what a good gas collector system would require and weight (valves, pipes, etc).