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Author Topic: Why are land vehicles so small?  (Read 405 times)
Shadow Of The Tower
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« on: January 01, 2017, 04:48:25 am »

 Relative to water going ships I mean. The largest ever land vehicles are equal to rather modest boats in size and capacity.

Why are there no landships? Nothing that even comes close to a small naval destroyer or frigate in size that can move on land.

Why are there no sand crawlers traversing the sahara  or research vessels with a crew of a hundred plying the antarctic wastes? Why where there no mobile fortresses crawling across france in WWII?

Is there a fundamental engineering reason you can't scale up a large mining truck or tracked vehicle to the size of a small ship?

Yes, I know about over land trains and ultra heavy tanks but none of those are even close to the size of a moderately large ship.

Is it just that nobody saw the need? or are they impossible with normal material science?
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« Reply #1 on: January 01, 2017, 06:08:20 am »

i Think a Lot of Folks are Afraid that Designers might go "Star Wars" instead of Victorian with the Design or Think of Landships because Many world War I Tanks were called Landships,or More Likely that Landship sounds like something from a Sci-Fi Role Playing Game called "Days of Empire"where Landships are a Major Type of Armoured Vehicle. Hope this Helps.
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von Corax
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« Reply #2 on: January 01, 2017, 08:26:09 am »

Water conforms to the hull of a ship, supporting it over its entire length and width. A land surface will not conform in this fashion, which means that either the landship's undercarriage must conform to the land surface (which becomes exponentially more complex as the vehicle grows) or the landship's frame must support itself over a long span, which increases the weight of the frame. Note that mine haul trucks universally have an almost comically short wheelbase relative to overall size.

One must also consider the mechanical strength of the ground. The German Bagger excavators use a large number of crawler assemblies to minimize ground pressure, while NASA's crawler-transporters rely on a specially-built crawlerway with four-foot foundations to support their weight. Even the aforementioned haul trucks require engineered roads for use. Compare the Russian Imperial Tsar tank whose prototype was abandoned in situ after becoming mired in soft ground.

TL/DNR: There are numerous engineering considerations which render progressively-larger land vehicles progressively less practical except in very specific applications.
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« Reply #3 on: January 01, 2017, 08:42:45 am »

Relative to water going ships I mean. The largest ever land vehicles are equal to rather modest boats in size and capacity.

Why are there no landships? Nothing that even comes close to a small naval destroyer or frigate in size that can move on land.

Why are there no sand crawlers traversing the sahara  or research vessels with a crew of a hundred plying the antarctic wastes? Why where there no mobile fortresses crawling across france in WWII?

Is there a fundamental engineering reason you can't scale up a large mining truck or tracked vehicle to the size of a small ship?

Yes, I know about over land trains and ultra heavy tanks but none of those are even close to the size of a moderately large ship.

Is it just that nobody saw the need? or are they impossible with normal material science?

Material science has a lot to do with it. The key words are material density, load concentration, bending moments,flexing moments, modulus of elasticity, Euler stability, maximum and ultimate tensile /compressive strengths, sheer strength. torsional flexibility and strength, stress concentration and stress flow. Added to that you need to consider dynamic bending of structures, resonance modes of cantilevers, beams, columns, and in the case of true Giants, the coupling of flexural behavior and aerodynamics, formally speaking the subject of aeroelasticity,  relevant in cases like the Tacoma Narrows bridge's resonant oscillations in the wind.

The name of the game for a ship is to generate buoyancy by creating a relatively thin walled structure,  like a pressure vessel (ie  Low density body) which will be uniformily supported with an even distribution over the entire hull/envelope by the water  or atmospheric pressure.  In contrast land giants are more akin to static structures; more dense and with highly concentrated loads on the wheels or tracks. The interaction with the ground becomes a huge problem. The structure of land giants is more akin to building bridges or towers, but lacking the benefits of a foundation underground. And for horizontally oriented structures, you need to span large distances with space frames. The stronger the frame needs to be to remain rigid, the heavier the structure will be. For vertical structures, the Euler Stability,vis a vis the buckling strength of columns becomes an issue, like for example a standing rocket -  you don't want it to flex and buckle in the middle while you're moving it horizontally.

Look at the land crawler used to transport the Space Shuttle into launch position.  There is a giant crawler for you.

It's a losing battle, and you will definitely encounter material strength limits. Even with unobtanium, the weld joints or riveted joints on acute angled surfaces are the weakest part of a structure. Assuming a perfect weld, every corner is a point for load concentration, which means stressses are much higher at those corners. That is why the Romans invented arches. (read my second post below). And in real life weld joints, bolts and rivets are usually much weaker than the the surrounding material. The rivet joints are what set a limit to the height of the Eiffel Tower.

Don't forget the ground becomes part of the structure in a way.  I guess you can always mount the Eiffel Tower on wheels if you wanted to, but the wheels or tracks would dig into the land and become useless without some special arrangement.

Another obstacle for the crawler is inertia and bending moments. On the massive scales you're talking about, the inertia is ridiculously enormous. Usually the bigger, the slower you will have to travel, because the dynamics of the structure become a serious problem (flexibility, bending, rotation, turning, etc.).  Also, even if the structure had an infinite maximum strength, or it was infinitely rigid, starting and stopping something like a train might clue you in to the acceleration challenge involved in just trying to set the vehicle in motion or stop it. Easier in air or water where you have plenty of space and where you are floating. In the open ocean or the atmosphere, precise manouvres in tight spaces such as roads is not a concern at all.  Another is that climbing and descending mountains is also very difficult to do.  There is no buoyancy to play with, like in airships, and the terrain is seldom perfectly flat like in the ocean.

Yes. There are obstacles.
« Last Edit: January 01, 2017, 09:42:32 am by J. Wilhelm » Logged

Drew P
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« Reply #4 on: January 01, 2017, 09:11:39 am »

Well, that was easy.
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« Reply #5 on: January 01, 2017, 09:40:31 am »

Actually I should correct myself. The Roman Arch thing is really because the shape re-directs the flow of internal stresses inside the structure, in such a way that all stresses are compressive everywhere in the arch... So that's a poor example for stress concentration. It's a good example however of how you can limit and control stresses; in the case of stone, the tensile strength is very low, but the compressive strength is high.  By using the arch you distribute the stresses in such a way that you never get a tensile stress in the arch.  It's all compressive.


A better explanation of stress concentration for metal structures is the example of the DeHavilland Comet aircraft accidents.  Tensile forces tend to "accumulate" right at the corner of acute angles and cracks tend to develop at those corners.  That is the reason the DeHavilland Comet aircraft experienced catastrophic failures early on. The passenger window frames were rectangular and developed cracks at the corners, leading to sudden "explosive" crack propagation and cabin decompression, after the crack expanded to a certain size.

In modern airliners the window corners are rounded to more evenly distribute the stresses, and prevent cracks at the corners . The strongest window shape is actually round, like a porthole.

Bottom line is that corners in structures are weak points. Even a right angle weld must be terminated with a nice fillet buildup at the joint to "round" the corner.
« Last Edit: January 01, 2017, 09:53:51 am by J. Wilhelm » Logged
Shadow Of The Tower
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« Reply #6 on: January 01, 2017, 11:50:02 am »

These seem to be some valid points but, just playing around with numbers here for sake of a thought experiment:

Consider something like a Sturgeon class destroyer of the late 19th century with a weight of 300 tons and dimensions of 20x200 feet, large enough to carry fifty men and associated armaments, quarters, equipment, fuel, etc.

Then consider a Liebherr T 282B haul truck with carry capacity of 363 tons and size of roughly 20x50

It does not seem unreasonable to me that a vehicle of say 25x100 feet long could be constructed with about same amount of useable space as the destroyer ship and the same approximate weight of a loaded Liebherr dump truck, for total vehicle of about 1,000 tons.

If it was a six wheel vehicle unsupported spans would not substantially different than that of the Leibherr dump truck and the actual loading per wheel would be reduced by about 50%.

Am I off base with any of this? Because it seems to me that such a vehicle should be feasible.

Granted, this is still equivalent to a small naval vessel but it would still be something that in capability and crew would could be called a landship could it not?
« Last Edit: January 01, 2017, 11:53:56 am by Shadow Of The Tower » Logged
Cora Courcelle
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« Reply #7 on: January 01, 2017, 08:05:23 pm »

Why are there no landships?

I would hazard a guess that you have never tried negotiating an English country road .....
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« Reply #8 on: January 01, 2017, 09:50:37 pm »

Where will drive giant vehicles? In careers they already have. Where else?

Let them not need a giant of the road. But where they can safely leave their giant footprints?

Well, in principle, a train, it is not so small.
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« Reply #9 on: January 01, 2017, 11:32:37 pm »

My Good Tower-

It is grand to see you here again!

Your question is an interesting topic, and was explored at one time in the "Bolo" novels written by  Keith Laumer in the 1960's

He first imagined the AI Superheavy Armored Tank in the short story "Combat Unit" in 1960, later expanded the concept into a series
of "Bolo" novels, and particularly explored the idea of the AI achieving sufficient self-awareness to be considered a living partner by his
human commander.  I highly recommend the series!

Here is an excerpt from the wiki article:

https://en.wikipedia.org/wiki/Bolo_(tank)
----------------------------------------
"Bolos as envisioned by Laumer in his future history military SF are described as automated superheavy tanks.
What they have in common—besides enormous firepower—is:

1) their overly large size:
       the Bolo Mark I is described as weighing 150 tons,
       the Mark II 300 tons
       while the much more advanced Mark XXXIII, considered a standard model in the series, weighs 32,000 tons.

In comparison, the largest superheavy tanks of the real world weighed around 100 tons and were never tested in combat.
The enormous Bolos are even described as tank-carriers themselves.

2)  their increasingly complex AI:
      Where first models are controlled by programming intended to reduce the need for a human crew, later models
      mimic human thought patterns, feature strong AIs and finally Psychotronic circuitry, enabling self-awareness,
      strategic planning and decision-making, and even conscience.

3) minimized human crew, often consisting only of a single human commander who can either directly control all aspects
    of his unit thanks to an advanced interface, or who communicates with his unit, giving it instructions to carry out."
----------------------------------------

One aspect of the Bolo Supertanks is the complete destruction of any terrain they crawl over, and the resulting collateral damage to buildings, fences, etc.

For a domestic application, one needs roads, and The limit, as our Russian Friend Morozow pointed out, is with the roadway.
Leveling, paving, and maintaining a roadbed ( even if only with rock, sand, and gravel ) wide enough and strong enough for a
Land Behemoth is the problem!

As Morozow also points out, We already have Land Behemoths, called Railway Trains, which can carry far more than the destroyer example - thousands of tons and hundreds of troops.

Here are two military examples:
Russian Civil War of 1919


Modern, Slovakia


And during WWII "everyone" discovered the limitations of railways - they only go where they already are. Thus the great minds of the times
developed superhighways such as the Autobahn, and the U.S. Interstate system - both were literally funded by the federal level governments as "strategic necessities for defense of the state", and the convenience to citizens and commerce was a side benefit.

And now we swing back to Behemoth Airships - the best of all solutions, as they require much less infrastructure!

But wait, they are limited by wind and weather conditions and load limits -  an airship that could lift and deliver , only 10 tons :
for example, the Zeppelin Hindenburg, with it's dead weight, crew, fuel, etc. weighed in at
Dead weight    118,000kg  or 260,145 lbs. and could manage a Payload for passengers, mail, freight
w/ hydrogen    9,560 kg or 21,076 lbs.

Inflated with hydrogen, Hindenburg was able to carry 21,076 lbs of payload ( only 10 tons).
if the ship had been inflated with helium it could not have made the flight at all, it would have been
34,000 pounds overweight ( due to the lesser buoyancy of helium).

The airship also could not deal with ground winds or bad weather when trying to make deliveries.

By contrast, a flatbed Freight Truck, which can easily navigate even rural roads in nearly any weather
short of a Monsoon or Hurricane, has a Weight Capacity of 48,000 lbs or 24 tons.

Finally there is competition from the Lockheed C-130 Hercules which can deliver a similar load of 45,000 lb and can deliver
nearly anywhere. The C-130 is Capable of using unprepared runways for takeoffs and landings; Lockheed demoed
that it could take off and land from an aircraft carrier, and the C130 is even used to do "air drops" of cargo
from only 50 feet , such as  the humanitarian food drops to Ethiopia, Somalia, and more recently Haiti.

so, that's why no monster landships outside of strip mines, rocket launchers, and fiction  Cry

yhs
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« Reply #10 on: January 01, 2017, 11:40:45 pm »

These seem to be some valid points but, just playing around with numbers here for sake of a thought experiment:

Consider something like a Sturgeon class destroyer of the late 19th century with a weight of 300 tons and dimensions of 20x200 feet, large enough to carry fifty men and associated armaments, quarters, equipment, fuel, etc.

Then consider a Liebherr T 282B haul truck with carry capacity of 363 tons and size of roughly 20x50

It does not seem unreasonable to me that a vehicle of say 25x100 feet long could be constructed with about same amount of useable space as the destroyer ship and the same approximate weight of a loaded Liebherr dump truck, for total vehicle of about 1,000 tons.

If it was a six wheel vehicle unsupported spans would not substantially different than that of the Leibherr dump truck and the actual loading per wheel would be reduced by about 50%.

Am I off base with any of this? Because it seems to me that such a vehicle should be feasible.

Granted, this is still equivalent to a small naval vessel but it would still be something that in capability and crew would could be called a landship could it not?


Where will drive giant vehicles? In careers they already have. Where else?

Let them not need a giant of the road. But where they can safely leave their giant footprints?

Well, in principle, a train, it is not so small.

If you build horizontally, you may scale (roughly) the same as Mr. Shadow of the Tower suggests, with mass proportional to the horizontal area covered by the vehicle (For a train it scales with the length).

But multiplying the size of a vehicle as it grows in all 3 dimensions is much more difficult, because the mass scales as the volume of the vehicle. Perhaps a giant space frame in the shape of a Tetrahedral Pyramid made of trusses (triangular elements), preferably a Fractal structure.

Also note a train is divided with flexible joints, not just to turn but also to climb on hills, etc. Therefore it is much easier to build a horizontal land crawler subdivided in flexible segments.

Outside of that building the "3-D" structure, poses major problems, already outlined above. I guess a train is the easiest land giant to build.
« Last Edit: January 01, 2017, 11:43:56 pm by J. Wilhelm » Logged
RJBowman
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« Reply #11 on: January 02, 2017, 12:51:50 am »

There is a story that has long been in circulation, probably apocryphal, that the size of the NASA Space Shuttle's booster rockets was limited to what could be carried to the launch site on existing railways. The size of those railways was based roughly on the width of carriages in the early 19th century, and the width of carriages was based roughly on the width of two horses. Some versions of the story claim that the standard goes all the way back to Roman chariots.

The point being that the reason that we don't have land behemoths one hundred feet wide is that they would require roads one hundred feet wide. The expense of building roads for the non-standard vehicle would be prohibitive.

There are a few exceptions; special purpose off-road vehicles, assembled on site, for use in a confined area. They tend to be specialized for use in mining or earth moving. Examples:
http://gizmodo.com/5824170/the-single-largest-land-vehicle-on-earth
http://jalopnik.com/5934614/the-ten-biggest-land-vehicles-ever-built/
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« Reply #12 on: January 02, 2017, 04:38:23 am »

There is a story that has long been in circulation, probably apocryphal, that the size of the NASA Space Shuttle's booster rockets was limited to what could be carried to the launch site on existing railways. The size of those railways was based roughly on the width of carriages in the early 19th century, and the width of carriages was based roughly on the width of two horses. Some versions of the story claim that the standard goes all the way back to Roman chariots.

The point being that the reason that we don't have land behemoths one hundred feet wide is that they would require roads one hundred feet wide. The expense of building roads for the non-standard vehicle would be prohibitive.

There are a few exceptions; special purpose off-road vehicles, assembled on site, for use in a confined area. They tend to be specialized for use in mining or earth moving. Examples:
http://gizmodo.com/5824170/the-single-largest-land-vehicle-on-earth
http://jalopnik.com/5934614/the-ten-biggest-land-vehicles-ever-built/




Well on that second link, here is a two-dimensional scalable horizontal structure:

Quote

8.) Scheuerle SPMT

What it does: One self-propelled modular transporter is nowhere near the largest vehicle in the world. It is a low, flat platform with dozens of computer controlled wheels that can move independently from each other.

Each SPMT, however, can be connected to another. They can clamp together like Voltron, becoming unbelievably massive and able to carry the heaviest loads of any land vehicle. This includes a 14,350 ton offshore oil platform.

Dimensions: As big as you want it to be.


And here's a one-dimensional one:

Quote
7.) LeTourneau TC-497 Overland Train

What it does: The amazingly paranoid US government of the 1950s had the Texan company LeTourneau design these wheeled land trains, which could operate without the need for railway lines. This would presumably help us when the Ruskies nuked our train tracks.

Dimensions: The cab was over 30 feet tall and the whole train stretched 570 feet long. It had 54 wheel drive.
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« Reply #13 on: January 03, 2017, 08:48:25 am »

I think it depends a lot on the terrain. A forrest has a lot of obstacles, but a fairly stable ground. A desert has few obstacles, but loose ground. Both need specific wheels/legs. Unless you make it super large, like a moving city. The bigger the vehicle get, the more strenght must be added to keep the vehicle together.
If I would have to create a land-ship, I would go for a BELAZ-75710 dump truck, or rather a few of these, linked together with flexible joints. Imagine 4 or 5 BELAZ-75710´s back to back, like a giant caterpillar!

But then... It needs feul, lots of feul. One dunp truck would have to be equipped with a huge fuel tank, providing fuel to all trucks. One can not just pull over to the nearest gasstation and fill it up, so you have to think of an alternative. Lets say, one of the trucks will be equipped with an oil refinery, a mobile pump jack.

So in theory, it is probably possible. But why? What is the purpuse of that machine? Every vehicle has it's own function and terrain to conquer.
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« Reply #14 on: January 03, 2017, 09:03:39 am »

Rumor has it they did consider modifying the LeTorneau "engine" to use a miniature nuclear reactor.... In order to avoid obstacles, each segment had steerable wheels which would receive exact instructions from the engine to avoid a given obstacle - it was a giant caterpillar, basically.

Overland Train - LeTourneau - World’s Longest Off Road Vehicle


« Last Edit: January 03, 2017, 09:13:04 am by J. Wilhelm » Logged
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« Reply #15 on: January 03, 2017, 03:40:30 pm »

Asside from whether the ground can take such a heavy load, or whether the machine can navigate varying landscape....

How are you going to get the mega-landship to Antarctica?  Gonna need a bigger boat. 

How are you going to assemble this mega-landship in Antarctica?  It's too cold to be working out there on anything fiddly.

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« Reply #16 on: January 07, 2017, 01:23:58 pm »

Correct me if I'm wrong, but don't hovercraft become more efficient the larger they get, because the mass held up goes up by the square of the radius, whilst the leakage goes up in direct proportion (the air leaks at the edge, and the pressure difference is constant, so the rate of leakage should be proportional to the length of the edge)?

Anyway, hovercraft don't suffer from the limitations of axle loading, because there are no axles to load, and as the weight is distributed over the entire ground, they don't have to worry about sinking into it (except when they stop and switch off the engine - you're going to want some large pads which can be put down to distribute the weight). The biggest problem I see for a hovership would be uneven ground, though even then, a large ship should be a few metres off the ground in flight. I don't think it would be such a problem on the ice fields, though.
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« Reply #17 on: January 07, 2017, 08:17:31 pm »

There was much controversy as to whether a hovercraft was an aircraft, a boat or a land vehicle; in the words of Sir Christopher Cockerell, the British engineer who developed the concept into a workable vehicle in the 1950s:-

 .... "the navy said it was a plane not a boat; the air force said it was a boat not a plane; and the army was 'plain not interested'."

(from https://en.wikipedia.org/wiki/Hovercraft )

The Wikipedia article gives a pretty good history and technical description. Hovercraft, or air cushion vehicles, have been used for everything from sport to short-sea passenger carriers to military landing craft and patrol operations, and vary in size from that of a personal watercraft to a small seagoing ship, probably up to about Navy corvette sized. They are probably the only real genuine all-terrain vehicle, capable of navigating everything from a regular road to deserts, swamps, fields, ice, and of course the open sea.

Athanor.
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« Reply #18 on: January 07, 2017, 09:27:41 pm »

Which comes in very handy when delivering goods in Alaska.

If you want to build a landship, I think a hovercraft is the way to go (hmmm, the ending of Mortal Engines...), and the main reason I can see for making one would be providing haulage services in places like Alaska. Though it might also do for a mobile base in the polar regions. Or as a ferry for places where bits of land keep getting in the way.

But my own personal interest lies more in building automated hovertrains as a cheap(er) transit option, on raised guideways that can travel above streets, buildings, fields, and forests without interfering with what's below.
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Shadow Of The Tower
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« Reply #19 on: January 11, 2017, 12:19:45 pm »

As for the why....what I was thinking was for transporting people during long journeys through inhospitable terrain. Something ship sized could have crew quarters, galleys, etc for keeping people fed and rested in a land environment where pitching tents would be unfeasible or undesirable and where living in tiny rooms in conventionally sized vehicles would be too cramped over long term periods.

And for hovercraft that was something I was going to bring up, some of the large military hover craft really do approach proper ship proportions, of course they are even more limited than most land vehicles in that they cannot handle steep or very uneven terrain.

I don't know why but I've always found something really appealing about the idea of traveling overland in something large enough to have multiple rooms etc.  and mega land vehicles are a staple of sci-fi and steampunk stories but are totally lacking in the real world even though they seem far more practical than spaceships, airships etc.
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« Reply #20 on: January 11, 2017, 02:07:45 pm »

.....

I don't know why but I've always found something really appealing about the idea of traveling overland in something large enough to have multiple rooms etc.  and mega land vehicles are a staple of sci-fi and steampunk stories but are totally lacking in the real world even though they seem far more practical than spaceships, airships etc.


And now you can make the journey. Across Eurasia by train. In a separate compartment, even with a personal shower.

The question is the price.
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« Reply #21 on: January 11, 2017, 06:35:59 pm »

I don't know why but I've always found something really appealing about the idea of traveling overland in something large enough to have multiple rooms etc........ 

An old British type double decker bus allows you to do this very simply!
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« Reply #22 on: January 11, 2017, 06:55:47 pm »

Winnebago or 18-wheeler with custom trailer.
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« Reply #23 on: January 11, 2017, 08:26:48 pm »



There was a thread on BG  a while back about a fantastical  mobile city on  a platform.  It created much discussion on the  pros, cons and feasibility of such a  development.
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« Reply #24 on: January 11, 2017, 08:30:52 pm »

But they're not exactly big enough for a ballroom, are they, trains and trucks...

A ship sized hovercraft would hover at least a couple of meters off of the ground. When in flight, perhaps it could transition to flying in ground effect? Well, it depends on how fast you want to travel - there is probably little point at 40-60 mph.

The pressure would be distributed evenly across the ground, but you would want large landing pads I think that you could put down when stationary, so you can switch the engines off and not sink.

Again, the only thing I can think it would be used for would be in places such as Alaska, to provide cheaper shipping to isolated communities. Perhaps it could also offer an overnight sleeper service for passengers. Or cruises.
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