Vehicle: Aircraft: Airship
Log Flume-style Airship   (+8)  [vote for, against]
Low friction airship system for long distance bulk freight and leisurely passenger transport.

This system is a combination of Roman aquaducts, log-flumes and cylindrical, unpowered zeppelins. Picture a series of columns supporting an elevated network of U-profiled chutes (preferably of transparent plexiglass) which are partially filled with sulphur hexaflouride. As this medium is approximately 6 times the density of air, you wouldn't be required to tap into diminishing supplies of helium or use dangerous hydrogen gasses to inflate your freight airship but could use simple air.

A network of such flumes would crisscross the country and be constructed in such a way that the SF6 would flow down the channels in a manner analogous to water in an aquaduct or log- flume. Build as many cylindrical zeppelins as you like for transporting non time sensitive bulk goods such as timber, ores and grains throughout the network. When the terrain no longer permits a downstream flow, the zeppelins are towed up the sloped chute to gain elevation and potential energy in the same manner as the "logs" are returned to the top in the log-flume rides found at amusement parks. The sulphur hexaflouride is also pumped uphill in either gaseous form or, if chilled below -65C, liquid form.

The zeppelin network would be slow but could run autonomously with the switching junctions working similar to shipping locks. I could imagine there would be a boutique market for passengers seeking to see the countryside at a leisurely pace who would book staterooms in the upper half of the freight zeppelins (ABOVE the SF6 and the sides of the chutes so they can do that breathing thing which high-paying passengers demand these days).

A major difficulty is that sulphur hexaflouride is a major and long- lasting greenhouse gas. One way to mitigate the damage done is to source your gas from sulphur hexaflouride which is in, or at least going into, the atmosphere already such as from volcanic outgassings. Another way is to encapsulate the entire system by using tubes instead of chutes but it would negate the safe tranport of passengers.

The advantages of this network compared to alternatives such as rail is that it would be quiet, have extremely low rolling resistance and the power stations would only need to be built at those points where elevation needs to be gained. One could presumably do the same thing with water but that medium is heavy, attracts algae and mosquitoes, freezes in cold weather and doesn't inspire that 'half-baked' feeling.
-- AusCan531, Apr 22 2012

Put the lotion in the basket... http://www.ebaumswo...deo/watch/82065888/
[2 fries shy of a happy meal, Apr 22 2012]

Log flume ride at Knotts Berry Farm
SF6 would behave similar to the water. [AusCan531, Apr 22 2012]

re: fate of birds & frogs
Bears, also. [mouseposture, Apr 22 2012]

Interesting article on the relative merits of helium vs hydrogen for airships. http://www.airships...m-hydrogen-airships
[AusCan531, Apr 24 2012]

This is just nuts enough. [+]
-- Alterother, Apr 22 2012

Canals is a fundamentally good idea, but water is heavy. In suitable geography, you just dig a trench, and the weight of the water dosn't matter. But in hilly terrain, you have to build elevated -- thingies (are they viaducts or aquaducts?), and that's where this idea really shines. [+]

re: //A major difficulty...// A third way is to do this on some other planet. What would be climate change on Earth would be terraforming on Mars. Plus, it's just not right that Mars doesn't have canals, and this would be a way to get those built.
-- mouseposture, Apr 22 2012

The kids would have fun with this one. [link]
-- 2 fries shy of a happy meal, Apr 22 2012

Thanks for the link [2 Fries]. I'm trying to imagine what any chirping birds or croaking frogs would sound like if they managed their way into one of my SF6 filled chutes.
-- AusCan531, Apr 22 2012

//what any chirping birds or croaking frogs would sound like if they managed their way into one of my SF6 filled chutes// They'd sound like silence <link>.
-- mouseposture, Apr 22 2012

Yes, I meant what they would sound like for a minute or two. Their imminent silence was left unspoken - as silence usually is.
-- AusCan531, Apr 22 2012

Tempered glass, if the zeppelin is carrying heavy items the plexiglass might not not hack it strength-wise. Being such a wildly dangerous idea, it gets my vote, despite the absence of either cheese, or stripes.
-- not_morrison_rm, Apr 23 2012

When you need to go uphill, don't tow them. Just in stall a lock like you would in a normal canal. +
-- scad mientist, Apr 23 2012

Depends on the gradient I suppose [scad]. Long gentle slopes would be towed whilst steep cliffs would entail a lock.
-- AusCan531, Apr 23 2012

//six times the density of air//
So the airships can be 1/6 the size... maybe larger if you absolutely insist on the passengers breathing.

//terraforming on Mars// the WP article on that is interesting, and it does mention SF6. It'd certainly be an easy way (comparitively) to get Earth-normal pressure. Wonder if you could use octo-oxygen.
-- FlyingToaster, Apr 23 2012

I assumed that this was going to be a network of upside-down canals on stilts. These canals could be filled with a lighter-than-air gas such as Helium. Airships would 'float' on these canals and be guided from one place to another.
-- hippo, Apr 23 2012

sorry, all the possible uses are satisfied fine by rail and zeppelin already. Rail isn't THAT loud (for you city-dwellers used to overhead metro lines, the directly-in-ground lines aren't nearly as loud as the ground absorbs the vibrations, frankly the horn is the loud part), and it's infrastructure is cheaper than this cockamamie thing you describe. And zeppelins already provide a leisurely air ride.
-- EdwinBakery, Apr 23 2012

Yes, but this is nuts. It has that going for it.

PS: the 'horn' of a North American locomotive (it's actually still called a whistle) blasts at 96-110 db @ 100' from the source, making it the loudest commercial land transportation vehicle in the US & Canada (and probably in the world, but I can't back that statement). The diesel power plant of a freight locomotive at full revolutions can exceed 85 db @ 100', which is also pretty damn loud. Braking and air pressure release can approach 95 db.
-- Alterother, Apr 23 2012

^quizzically^ You say "cockamamie" like it's a Bad Thing? This confuses me.

Seriously [Edwin], you shouldn't make sweeping statements on the HB like "all possible uses are already satisfied by rail and zeppelin". What about the difficulties caused by rail lines which divide a farmer's field in twain, separating his milk cows from his rhinoceroses thus spoiling his plans for breeding milkers unafraid of wolves? What about relieving the drain on helium supplies or obviating the dangers of hydrogen filled airships? Or are you one of those people who get off on footage of the Hindenburg disaster? Oh the humanity!

My plan would partially sequestrate the SF6 currently being emitted by volcanoes thus contributing to the battle against Global Warming. What have the polar bears ever done to you? (disclaimer - if you or a close family member have ever been mauled by said polar bears then I withdraw that last statement).
-- AusCan531, Apr 23 2012

//The diesel power plant of a freight locomotive ... is also pretty damn loud.// Darn tootin'. In fact, damn' straight.
-- mouseposture, Apr 24 2012

//So the airships can be 1/6 the size...//.

Not because of the relative densities of the gasses. A helium airship floats in air which is 4 times heavier than helium. My air-filled airship would be floating on a gas 6 times heavier than air so there could be a marginal reduction in size to achieve the same lifting capacity. Reality gets more complicated, however, than just the relative weights of the gasses otherwise hydrogen would lift twice as much as helium instead of just 13% more. [link]

The big savings in payload come from not having to carry the motive power and fuel. The same link shows that the Hindenburg carried up to 58 tonnes of fuel compared to only 9.5 tonnes of passengers and payload. No weight is given for the motors. This would allow for a massive reduction in airship size relative to payload with my sulphur hexaflouride flume system.

[NotationToby] you need to amend your link to point to your post rather than just the category. Perhaps we could combine our systems where my chutes morph into tubes when traversing below water bodies.
-- AusCan531, Apr 24 2012

//Reality gets more complicated// umm... gets simpler ackshully. If you need to displace <x> volume of gas1 to get to neutral buoyancy then, if gas2 weighs 6x's as much you only need displace <x>/6 volume.
-- FlyingToaster, Apr 25 2012

I take your point [FT] about displacement and buoyancy and the lifting capacities of gasses floating on mediums of different densities. But I wasn't using hydrogen or helium to fill my airships to float on sulphur hexahydrate but was using plain old air. Your 6x gain might well hold true if I used one of the conventional lifting gasses over the 6x heavier medium of SF6.

I also reassesed some of my own assumptions after I read the linked article which claims a much diminished lifting performance gain of only 13% for hydrogen over helium despite air H weighing 1/14th the weight of air while He is doubly heavy at 1/7th of air. That is even allowing for the diatomic nature of hydrogen molecules.
-- AusCan531, Apr 25 2012

ah right right; I had thought of that but got distracted by something shiny. Call it 5x then eh ? H2 and He are an effective weight of zero so the weight displacement is (1 - 0) volume's worth of air. SF6 is 6x the weight of air so, using air to fill, it's (6-1)'s volume's worth of air.
-- FlyingToaster, Apr 25 2012

//lifting performance gain of only 13% for hydrogen over helium//

That statement annoys me every time I see it. It's highly misleading, because it ignores the mass of the airship. In terms of _payload_, hydrogen gives a better advantage than that.

//SF6 is 6x the weight of air so, using air to fill, it's (6-1)'s volume's worth of air//

Not quite. You're forgetting that there's only (about) 1/6 as much air. The actual displacement of an air-in-SF6 craft will in fact be close to 1/6 that of a helium-in-air craft, for a given payload. Possibly even better, because the structure could be lighter, following the cube-square law.
-- spidermother, Apr 25 2012

//hydrogen gives a better advantage than that// Even though I'm in the use-hydrogen-not-helium camp, those numbers are about right.

While H2 only weighs half as much as He, the important figure is how much weight is being displaced for an equal volume of air. So, using N2 (mol.wt. 28) to represent air, for every volume <x>...

A vacuum will displace (28-0)/28 of the weight, ie: all of it.
H2 will displace (28-2)/28: 13/14ths of the weight.
He will displace (28-4)/28: 6/7ths of the weight.

Of course since we're using SF6, displaced by "N2"... <calculating... calculating...>

(146 - 28)/28: roughly 4.2x the equivalent mass of air.

(note at this point that SF6 is 5.2x the density of N2)
-- FlyingToaster, Apr 25 2012

Yes, the numbers are correct, but their application is still misleading. It's the gross mass, rather than the payload, that can be 1.13 times as great with hydrogen compared with helium. For instance, if the payload and the vehicle are of equal mass, then the advantage with hydrogen is not 1.13, but 1.26 - in other words, in that example, hydrogen is 1.26 times as 'good' as helium.
-- spidermother, Apr 25 2012

huh? no. That would be compared to a vacuum.

Even if you had a vehicle that weighed literally nothing, so all the lifting is on the payload, then you would get basically 1.26/1.13 or roughly 13% better.

AhI see, you're saying that there's extra volume available to lift the payload, so that a vehicle that was perfectly balanced with Helium and could lift nothing, could lift 13% more of its mass, which is *all* payload, for an increase of infinity%. Got it.
-- FlyingToaster, Apr 25 2012

//That would be compared to a vacuum.// Not at all. I'm merely assuming that the dead weight of the vessel (structure, engines, gas bladders, etc.) is approximately constant, so the increased payload is proportionally greater than the increased 'lifting power' (a vague term, which is partly responsible for this confusion) of hydrogen over helium.

[edit] Get it? //Got it.// Good.
-- spidermother, Apr 25 2012

Displaced mass = density * volume of the surrounding fluid. Vehicle mass = (density * volume of lifting gas) + structural mass + payload. Vehicle mass = displaced mass for neutral buoyancy.

Even that is a slight simplification, as it ignores changes in density due to the pressure gradient, but it will give good answers, as opposed to any simple comparison of gas densities, which is as meaningless in isolation as trying to predict the top speeds of two vehicles based solely on cylinder displacement.
-- spidermother, Apr 25 2012

Missed the bit where the airship has to be designed with a 13% increase in structural integrity. :)
-- FlyingToaster, Apr 25 2012

//Reality gets more complicated// <ahem>. As I said.
-- AusCan531, Apr 25 2012

//Reality gets more complicated//

-- Alterother, Apr 25 2012

random, halfbakery