Any thoughts on this article out in this week’s New Yorker:
Helium Dreams: A new generation of airships is born.
By Jeanne Marie Laskas
http://www.newyorker.com/magazine/2016/02/29/a-new-generation-of-airships-is-born?
I wonder how often these airships would be economically preferable to alternatives.
There are three issues: temperature, pressure, and total oxygen supply.
A mask can compensate for reduced air pressure by increasing the amount of oxygen taken into the lungs. But only up to a point.
Above about 25,000 feet, even breathing 100% oxygen isn’t going to keep you properly oxygenated. There needs to be more pressure. Hence most WWII airplanes cruised not much higher than 25,000 feet and were unpressurized while the crew has oxygen masks. It worked, but barely; good enough for a war.
To fly much higher you need a fully enclosed pressurized cabin (or suit, but that solution has its own issues). One of the other benefits is that even below 25,000 and with an oxygen mask, the low pressure is fatiguing on the whole body and leads to ear, sinus, and other physiological problems. A cabin pressurized down to, say, 10,000 feet or less avoids all those issues.
Last of all, it’s damn cold at altitude. The standard temp at 25,000 is around 45F below zero. The waist gunners on WWII bombers were standing in a drafty tube near big openings facing into a 200mph hurricane blowing by at -45F. And they stood there for hours. Which is also pretty tiring. Once you’re pressurizing a cabin, it becomes practical to heat it to shirtsleeve temps.
Which of course would be necessary for any customer acceptance of modern zeppelin travel
I think your argument is focussed on the technological feasibility or practicality of that project, which is, of course, demonstrated by the existence of passenger service dirigibles in the past. But my interpretation of the OP’s question is targeted towards the commercial feasibility. The experience of the passenger services on dirigibles in the 1920s and 1930s doesn’t help us much in this regard, since the airships back then weren’t exposed to the competition from jet airliners as they would be today.
In my view, there could be commercial feasibility for a project like this as a niche market, comparable to cruise ships, as noted by several posters before. How big that niche is, is difficult to estimate without giving it a try. There are plenty of examples in today’s world where technologically obsolete products continue to exist in niches because they are bought by nostalgic aficionados even though technologically far superior alternatives are available, and for less money (records are an example that comes to mind). The commercial viability of airship cruises would depend on how well the idea would be received by people who have some money to spend, and I’d find it really difficult to predict that.
I already pointed out my typo in my reply, where I typed “WWII” instead of “WWI”.
The switch from piston engines to turbines is what allowed helicopters to go from vehicles that could barely lift their own weight to troop carriers and skycranes.
The Hindenburg had 4 engines, each of which produced 1200 horsepower and each of which weighed over 2 tons. (1976kg)
A quick search finds a version of the Allison Model 250 turboshaft engine that produces about 600 horsepower with a weight of 124 kg.
So 8 of those Allison turbines would have the same horsepower as the 4 engines on the Hindenburg, but combines they would weigh less than half what one of Hindenburg’s engines weighed.
Turbines can be used to run props, and turbine engines are MUCH lighter than piston engines.
Early Atlantic routes were along the northern rim which provided stops along the way. They call this the blue spruce route. It’s the closest they could come to a great circle route in the early days of flight. So while it looks like a curved flight path it’s really much straighter when looked at on a globe. But it’s based on the limited distances planes could fly so it was based on the need to refuel along the way. It would still be used today for planes with a limited range.
Well, the problem there is air pressure, or the lack thereof.
Remember that these things “fly” (“float”, more accurately) because their density is less than the density of the air they displace. Or rather, they float at an altitude where their density matches the density of the surrounding air.
So the higher you want it to fly, the lighter it is going to need to be.
Giving some VERY rough approximations, at about 10,000 feet the air is around 70% the density at sea level. At 30,000 feet, it is about 30%. That means that if you want to fly at 30,000 feet, the total weight of your dirigible (including the gas in the bags) has to be about 30% of the weight of the volume of air it displaces at sea level (which is about 1.2 kg/cubic meter).
Once you have built your superlight high-flying zeppelin, you’ll find the next problem: as you climb, the air pressure outside drops. But the pressure of helium inside your gas bags is still the same. So the gas bags are going to try to expand. You are going to need to vent some helium to reduce the pressure, or you risk rupturing the gas bags.
BUT, when you are coming back down, the increase in pressure outside will cause your gas bags to deflate. This is effectively taking space that was filled with helium (very not-dense), and filling it with air (comparatively very dense).
I’m not saying science couldn’t build a dirigible or blimp that could survive dramatic changes in altitude, but I am saying that it wouldn’t be easy.
One of the great advantages of hot-air balloons is that they can make more hot air any time they need it. Airships underway generally can’t get more of the gasses they use for lift or the ballast they use to counteract it either.
Your physics is dead right. To be able to float at 30K feet and also at the surface you need to be able to alter your total lifting volume over a range of about 3x. As big as a traditional zepp is on the ground versus the size of the payload car, imagine one with a 3x larger envelope. That’s what a zepp at 30K feet would have to look like. Can you say “A pimple on an elephant’s belly”?
It get progressively worse. At 40K feet you’d need an envelope about 5x the size of the sea level one.
In the jet biz we often remark that in the old days of 727s & DC9s rattling around at 31,000 & 33,000 feet we’d be trapped in the middle of the thunderstormy weather. Whereas in modern jets at 39,000 & above we truly are above the vast majority & can easily avoid the few boomers taller than we are.
For something as flimsy as a zepp, if you can’t make the top of the 30s you’re better off staying close to the ground. At least in the US in the spring & summer.
The solution to managing pressure changes is to either use ballonets or for larger changes to not vent gas overboard, but rather pump it back and forth between compressed gas cylinders (or LH2 dewars) and the gas bags. To be sure those are very heavy storage vessels, and it takes power to compress or liquefy the gas. Real quickly this goes exponential and you can’t grow the vehicle faster than the support infrastructure does.
There are a number of issues that prevent this from happening.
First, putting aside engineering issues it’s suicide to try to fly over bad weather in a dirigible. It moves too slowly in relation to the speed that storms build. a “normal” thunderstorm will be in the neigbhorhood of 30 to 40, 0000 feet high. They can spike up to 65,000 feet. It’s not just the height but the speed in which they can build relative to the speed of the airship. It would be reckless to attempt to fly anywhere near bad weather because at 40,000 feet they would not be able to divert away from cells that pop up around it.
Getting caught in an actual storm cell is fatal. Even for an airliner. The difference is that an airliner can move away from it at 500 mph and climb/descend at a rate of 1,500 feet a minute. That’s a big deal in an emergency.
Second, a dirigible is much more prone to wind sheer damage by virtue of it’s size. What a normal airplane would fly through becomes a twisting bending nightmare for engineers. As was posted earlier they don’t do well in bad weather.
Third, there is no point flying slowly at 40,000 feet. There’s nothing to see and a lot of time to see it.
Fourth, The jet stream would make an East/West trip virtually impossible as the wind speed would exceed the speed of the craft or come so close as to make it too slow to go anywhere.
Could you pump the unneeded-at-altitude helium into a storage tank, then pump it back into the ballonets when you descend?
Of course, the pump, motor, and storage tank would add additional weigh, but aviation is all about trade offs anyway.
Psst. See last paragraph of #128. 
Also, in LTA design, the ballonet is the bag full of air, not the one full of lifting gas. By inflating and deflating the ballonet with air, you compress or decompress the adjacent sealed bag of lifting gas within their common outer envelope.
In Building Blocks of the Universe (1957), Isaac Asimov wrote about the Hindenburg disaster, adding “no large dirigibles have been built since or are likely to be built. Airplanes have taken over completely.”
(The German carpenter I was working with in the '70s, who was 15 years old when the Hindenburg caught fire, answered when we saw a local Goodyear blimp, that as far as size is concerned, the Goodyear blimp would be the “embryo” of the Graf Zeppelin or the Hindenburg.)
Asimov also wrote that even with helium (which Americans were using in dirigibles in the '30s), they were a failure “because, even [so], when caught in storms, they buckled or broke.” (as noted upthread)
And–something not widely known in this country–to give the Germans their due, they had worked out tried-and-true safety precautions to make it safe to use hydrogen in dirigibles long before politics made helium unavailable by purchase from the United States.
And even a west-to-east trip would be dodgy - any entry into or exit from a jet stream would be extremely risky due to stresses imposed by turbulence and wind shear.
Those aren’t blimps son. They’re Joint Land Attack Cruise Missile Defense Elevated Netted Sensor Systems. JLENS - Wikipedia
Israel has the Skystar, as a big one. http://www.aeronautics-sys.com/home-page/page-systems/page-systems-skystar-aerostats/
I’m pretty sure Israel uses smaller ones at tactical level; but it seems to me tethered rotary quadcopters are what’s being done now.
Snap 'em with your finger and see what sound they make. 
Huh. Not like a weasel?
Fine. I’ll go visit mom.
Never say in one syllable what you can say in eighteen. :rolleyes:
Bumped.
Some interior pics of the Hindenburg I hadn’t seen before: http://www.dailymail.co.uk/travel/travel_news/article-4530520/Rare-photos-Hindenburg-s-lounge-dining-quarters.html
Sergey Brin (of Google fame) is working on a dirigible:
https://www.bloomberg.com/news/articles/2017-04-25/with-secret-airship-sergey-brin-also-wants-to-fly
If only there was kind of way to look for photos of dirigibles, you know, some kind of Internet “search engine” type of thing.
