"Zeppelin Question" Topic

I'm working on a novel and a technical question came up. The chapter I'm currently working on has one of the characters aboard a Zeppelin scouting over Arabia. I am making an assumption about the way the things work, but I'm not sure I am correct and Google searches aren't turning up any real information. My assumption is that in the heat of the day, the gas cells are going to get warm, expand, and produce more lift. To prevent gaining too much altitude (or even worse, have the increased pressure rupture the cells, some of the hydrogen would need to be vented. But at night, the cells will cool and shrink and lift would be lost. This could be countered by either dropping ballast, and/or releasing more gas into the cells from reserve cylinders carried on board. This process would be repeated each day, but eventually they would start to run out of ballast and/or reserve gas. This would limit their range as much as fuel for the engines would.

Is this reasonable, or am I out of my reckoning?

The temperature at high altitude over the desert will be quite cool, I imagine.

Didn't a zeppelin make it from Germany to East Africa (well almost) during the Great War?

I was assuming that the intense sunlight on all that surface area would heat things up considerably. And the altitudes would probably be no more than 10,000 feet.

And yes, there was an attempt to fly to East Africa that almost got there.

I suspect the key may be that the gas cells are not directly exposed to the sun as the external skin of the Zeppelin is – I think, I'm no expert – NOT the external wall of the gas cells.

Don't forget the effect the change of pressure at altitude had on the volume of gas too and the bouyancy effect of fuel being burned. This article may be helpful: link

The surface is silvered, right?

I vaguely recall that one explanation for the crash of the U.S. zepplin the U.S.S. Shenandoah was that the captain removed certain safety valves. The purpose of the valves was to vent helium from the zepplin's bags to keep the expanding gas from ripping the bags.

I have done some reading on zeppelins and airships in the past. And most of the reactions above contain parts of the answer.

First the differrence between airships and Blimps. Blimps are a bag full of gas with some controls put on it. Because the shape is maintained by the presure, the gas will have a slighly higher presure then the atmosphere. Therefore providing a little less lift as it would have equal presure. The airship does have a rigid frame, with internal gas bags. Often these are filled up to 95% to allow some expansion. As long as it was not expanded to 100% lift was optimal. Weather forecast could be used to calculate optimal filling.

During flight if presure was to high, gas would be vented. This was done automatically with vents on the top of the airship. The gas will rise and flow away. During flight there are no refilling options. So lost gas reduces flight time. Therfore this was carefully monitored. Changing flying height could be used to help with this, as air presure will differ with height. Balast is a second measure, to regulate height. But weather will also have impact as airship for example will get heavier due to rain. Reducing the flying height. Further the fuel burned will make the airship leighter.

The last item quickly overlooked is aerodynamic lift. Due to the forward speed, the airship will get some lift. The Germans used this to lift from the ground when they departed. The zeppelins were around 4-5% overloaded. With zero speed they would descent to the ground. Due to the forward speed this would be compensated, and the airship could stay in the air. This made sure that the airship did not directly have to drop balast to compensate for the burned fuel.

Combining and eatimating all these descisions was the most diffcult part. That was what the Germans had mastered the best. They have run regular passenger service for over 10 years with Zeppelins. Also they have done a world round trip with the LZ-127 Graf Zeppelin.

I hope this provided a little more background information.

Aerodynamic lift and exhaust condensers. As GJG says, the ship was gassed to be slightly heavy and stayed up due to lift generated. Exhaust condensers were fitted to later airships to recover as much water as possible from burnt fuel – those boxy things on the sides of the engine cars. A great deal of effort was expended to keep the right balance of gas to ballast and 'expendables'.

If you want an interesting read that has lots of incidental 'colour' on airship operations have a look at 'The Flying Cloud' link which has a couple of years worth of weekly text story set in a fictional/alternate Post WW1 Pacific.

You're mostly right, Scott.

But the air at ~10kft is fairly cool, even over the Sahara.

It's also why the outer skin (fabric, technically) is painted silver, to reflect as much heat as possible. The gas cells are inside the skin, and do not touch the outer envelope.

Will the Zeppelin be able to carry a "parasite" fighter as in Indiana Jones and the Last Crusade.
If your hero and the Zeppelin are going to fly multiple missions, your story will have to account for whence comes the hydrogen supply for refueling.

I would think that they would run out of fuel quicker than ballast or gas.

@Ferozopore, it is possible to cary multiple fighter aircraft with an airship. The Americans have done some extensive testing. And had two airships with aircraft carrier capabilities. In coorperation with the Germans they also did some test with the Hindenburg. Altough this was without the internal storage. If intrested check the USS Macron.

Image from wikipedia:

Will the Zeppelin be able to carry a "parasite" fighter as in Indiana Jones and the Last Crusade.

Absolutely, as long as you're talking about a big Zeppelin.

The Zep-carriers, USS Akron (ZRS-4) and USS Macon (ZRS-5) carried 5 of those little Curtis F9C Sparrowhawk fighters. They were 785ft long and 133ft in diameter (basically the same size as the Graf Zeppelin and Hindenburg)

I would think that they would run out of fuel quicker than ballast or gas.

Probably. Ballast is water, that's easy to find. If you're good about engineering, you can minimize the liftgas loss. The Akron-class displaced 7.4million cubic feet, so would need 37,000 cubic feet of compressed gas (assuming 3000psi cylinders) to fill initially. But I wouldn't expect a zepp to carry a complete refill of liftgas.

Then you're down to fuel. You should have fuel at your destination, but the engines are rather thirsty. You're probably looking at 50 gallons per hour at full power, per engine pair, so 200gal/hr total.

Deserts do seem to have posed a problem for Zeppelins, due to the extreme changes in temperature. Cycling between heat and cold, could cause the zeppelin to exhaust both spare lifting gas and ballast.

You may want to research the journey of the L.59 (the Africa Zeppelin) to see some of the potential problems --

At 0515 on the 22nd she crossed the Libyan coast and headed across the desert, experiencing violent updrafts from the hot sands . . .

At nightfall she reached the Nile and began following the river southward, but at about 0300, after hours of cooling had diminished her lift, she suddenly stalled and nearly crashed.

On the return trip:

Another near-disaster over western Turkey — again the result of rapid cooling at night coupled with insufficient ballast to compensate — almost wrecked the ship before she landed again at Jamboli at 0740 on the 25th.

source:
avalanchepress.com/L59.php

Also the deserts had an effect on the crews:

The crew also suffered from headaches, hallucinations and general fatigue in the mid-day heat and freezing cold at night.

link

Although those WW1 Zeppelins were not actually designed to be in the air that long, (the flight of the L.59 being exceptional) so crew comfort was not that high, compared to the long range post war civilian and navy zeppelins.

During the interwar period I seem to recall either Akron or Macon had trouble over Arizona, but I can't find a source at the moment. The Graf Zeppelin flew all around the world, and I don't recall any particular trouble over deserts -- but it was carefully flown to avoid poor weather conditions.

Macon had trouble over Arizona and Texas. link

Probably at least partly because she was not designed to fly high enough to clear the mountains around there! 3000ft pressure height is just not high enough to fly across the US!

I would suggest reading the following books
link

and

link

+1 re "Zeppelins in Combat".

B