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Zeppelins


mattingly

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Re: Zeppelins

 

I'd guess that the efficiency of the propulsion and the strength to weight ratio of the structure itself would be a major deciding factor.

 

Another might be just how big it could get before becoming inherently uncontrollable in even the lightest breeze. Ground-handling was always a tricky business, with more than a few airships being damaged or even wrecked not in flight, but while being moved between moorings and hangars.

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Re: Zeppelins

 

I think I've asked this before' date=' but is there a practical upper limit on how large one could make a rigid airship?[/quote']

 

Yes: the old WW1 "Height-climber" zeppelins were pushing the lower limit, in terms of weight to lifting capacity, though we can do a bit better today, given lightweight materials. I don't think anyone has pushed the upper limit, though some of the earlier metal-skinned rigid airships were coming close. The problem is the amount of reinforcing you need to make ever-larger flight reservoirs (or ever longer series of reservoirs) structurally sound. You reach a point where the extra weight is more than the gain in lifting power.

 

cheers, Mark

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Re: Zeppelins

 

http://community.seattletimes.nwsource.com/archive/?date=19951027&slug=2149105

 

 

I think something with 1000 tons of cargo lift capacity, maybe shaped like a hybrid(ala the Aeroscraft) and capable of a decent airspeed, would probably be the upper limit.

 

Note that that article is 17 years old: as far as I know, those plans were shelved a while ago. The company that was going to make the Skycat went bust without making anything larger than a scale model, and the HULA project was cancelled as impractical. You can put it in perspective - the Hindenburg had a lift capacity of over 230 tons. That sounds pretty cool - it's nearly a quarter way to the 1000 ton goal, right? Except that the unladen weight of the Hindenburg was about 140 tons, leaving a lifting capacity of about 110 - and that's using Hydrogen. Using Helium, you're down to about 100 tons. Then you have to add crew, food, fuel ... IIRC the Hindenburg had cargo capacity of 10 tons, plus 90 passengers. Just to get a thousand tons of lift, you're going to need something with roughly 10 times the volume of the Hindenburg ... and the Hindenburg's length was 2/3rds the height of the Empire State building - and that's without any safety margin at all. To meet even reasonable safety margins you are going to need another 10%. To get 1000 tons of cargo into the air, you'd need an airship that dwarfs anything ever considered. The rigid lift wing approach suggested by Skycat and Aeroscraft loses efficiency rapidly as you scale up. Although both companies made claims about 1000 ton lifting capacity, they've never (as far as I know) convinced any aeronautical engineers that they could actually build it.

 

Here's the deal: we've all seen pictures of the HULA heavy lifter, right?

[ATTACH=CONFIG]44146[/ATTACH]

The aircraft in that image is roughly 4-5% of the size we're talking about. We're talking about airships so huge, it's actually hard to imagine them.

Here's a picture comparing the Hindenburg to a 747.

Now try to imagine an airship 10 time larger than that!

 

I'm not saying it can't be done - and hell, I'd pee my pants with delight to see something like that actually fly. But so far nobody's come close to a workable plan for such a beast.

 

And since we mentioned the Hindenburg, I can only end with:

 

[ATTACH=CONFIG]44150[/ATTACH]

 

cheers, Mark

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Re: Zeppelins

 

Yeah, helium has been a limited commodity for decades now: the Hindenburg was only filled with Hydrogen (against the wishes of its designer) because the US government would not sell helium to the Nazi-controlled syndicate that owned it. So supply has been a problem for a long, long time: the US helium reserve was set up specifically to address this problem, and now that the "market efficiency" fiends have done away with the helium reserve, we're going to be back to scarcity.

 

This issue has been foreseen since the legislation shutting down the helium reserve made it into law: it's why there's a resurgence in interest in using hydrogen, despite the fire risks. DARPA's ISIS project for example, gets lifting power from hydrogen, and it's the last of the US military's airship projects still standing as far as I know. And other groups are looking at how to make hydrogen-based airships safer. Hydrogen's cheap and easy to make, and gives about 10% extra lift (important for high altitude projects) so it has some clear advantages, despite one big limitation.

 

cheers, Mark

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