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Mortal Engines

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Re: Mortal Engines
Post by Joat42   » Thu Dec 13, 2018 4:52 am

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Dilandu wrote:..snip..
P.S. Another possibility, actually, is a flying one... build inside of mile-sized concrete tensegrity sphere. The old "Cloud Nine" design, envisioned by Fuller; the volume-to-weight ratio of the sphere is so great, that even a relatively small heating of air inside (say, one degree, provided by nuclear reactor) would allow it to float in air. And, since its tensegrity structure, it become stronger with size increased, thus allowing a simple concrete to be used.

If the sphere is made with the right materials you could have a vacuum in it instead to dramatically increase lift. No point in using primitive technology like heating or cooling a gas.

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Re: Mortal Engines
Post by Dilandu   » Thu Dec 13, 2018 10:56 am

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Joat42 wrote:If the sphere is made with the right materials you could have a vacuum in it instead to dramatically increase lift. No point in using primitive technology like heating or cooling a gas.


Considering that the idea is to have a city inside the sphere, the vacuum solution didn't seems to be particularly attractive. Not to mention the stress of having such difference in pressure and problems with the repairs in case of cracks.
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- Who would won in battle between strawman Liberal-Democrat and strawman Conservative-Republican?
- Scarecrow from Oz; he was strawman before it became political.

P.S. - And he have Russian twin, to watch his back)
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Re: Mortal Engines
Post by Joat42   » Thu Dec 13, 2018 5:10 pm

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Dilandu wrote:
Joat42 wrote:If the sphere is made with the right materials you could have a vacuum in it instead to dramatically increase lift. No point in using primitive technology like heating or cooling a gas.


Considering that the idea is to have a city inside the sphere, the vacuum solution didn't seems to be particularly attractive. Not to mention the stress of having such difference in pressure and problems with the repairs in case of cracks.

Ah, who cares about the little things like breathing when you can soar into the great blue yonder... ;)

---
Jack of all trades and destructive tinkerer.


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Re: Mortal Engines
Post by Michael Everett   » Thu Dec 13, 2018 5:37 pm

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In the HP fanfic Make A Wish, a couple of the secondary characters (the Doctor* and Henchgirl) build a zeppelin that uses a vacuum instead of helium for lift.
Not only does it work, it works well enough to become their roving base of operations and from a purely physics-based viewpoint, it is technically feasible.
In my opinion, the best way of doing it, though, would be to create a closed cylinder of helium cells and then evacuate the air from the enclosed area, thus getting the advantage of the relative lift/volume ratio while providing a protective barrier around the vacuum (two layers of fabric for anything to pierce is more than twice as hard than a single layer due to the energy loss in the initial penetration).

*No,not the one in the Tardis.
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Re: Mortal Engines
Post by Imaginos1892   » Thu Dec 13, 2018 7:31 pm

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Michael Everett wrote:In the HP fanfic Make A Wish, a couple of the secondary characters (the Doctor and Henchgirl) build a zeppelin that uses a vacuum instead of helium for lift.

Not only does it work, it works well enough to become their roving base of operations and from a purely physics-based viewpoint, it is technically feasible.

Uuuhhh… no. It's not.

I've done some calculations for a zeppelin in one of my stories. Total surface area for a 485,000 cubic meter zeppelin comes out to over 48,000 square meters, making total atmospheric pressure at sea level just over 500,000 metric tons. What is the lift chamber to be made out of? Bear in mind that gross lift available at sea level is less than 600 metric tons.

To contain a vacuum, the lift chamber has to be proportionally much stronger than a 55 gallon steel barrel. I've seen atmospheric pressure crush several of those barrels with only a partial vacuum inside on Mythbusters.

Those barrels weigh over 18 kilograms, and displace about 266 grams of air at sea level. Even if the barrel could hold a perfect vacuum, that's less than 1.5% of the lift needed to make it float.

There is no way to make a container that is strong enough to withstand that much pressure, light enough to float in air at Standard Temperature and Pressure, and large enough to provide a useful amount of additional lift. The forces involved would require construction materials at least three orders of magnitude stronger than anything we know of.

There are online calculators that can provide most of those answers. If only more writers could take the trouble to look a few things up, do a little math, and not put insanely stupid things in their stories.
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Re: Mortal Engines
Post by Annachie   » Sat Dec 15, 2018 7:52 pm

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True.

But then sometimes it's the insanely stupid that makes the story. :)

From a story teller perspective though, most readers would not know that such a zeplin was that undoable, or would think that it's reasonable for "mad scientist" tech.
Fantasy/SF can bog down in too much realism, especially as it's internal consistancy that really matters.
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Re: Mortal Engines
Post by Imaginos1892   » Sun Dec 16, 2018 1:35 am

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Annachie wrote:Fantasy/SF can bog down in too much realism, especially as it's internal consistancy that really matters.

I like for stories to be consistent with the laws of physics, too. It's especially painful when authors ignore those laws so blatantly, and when it's so easy to avoid by doing a little thinking, looking a few things up and working through some simple math.

I know something about the power of pressure. I worked for a company that makes underwater equipment, some of it rated to FOD (Full Ocean Depth, 11,000 meters). Pressure down there is 1,100 atmospheres, 111 megapascals, or over 16,000 PSI. I've seen thick titanium housings crushed like beer cans.

The notion that a chamber over 200 meters long and weighing less than the air it displaces could withstand sea-level atmospheric pressure with a vacuum inside…is insanely stupid. NOT in a good way.
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Re: Mortal Engines
Post by isaac_newton   » Mon Dec 17, 2018 5:53 am

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Annachie wrote:True.

But then sometimes it's the insanely stupid that makes the story. :)

From a story teller perspective though, most readers would not know that such a zeplin was that undoable, or would think that it's reasonable for "mad scientist" tech.
Fantasy/SF can bog down in too much realism, especially as it's internal consistancy that really matters.


I'm with you on this :-)
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Re: Mortal Engines
Post by Michael Everett   » Mon Dec 17, 2018 10:34 am

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Early box office figures indicate that the film is... not a total success. Not yet a flop, but it isn't going to rival Star Wars IV's opening.
Guess I'm waiting for the home release...
And I doubt there'll be a sequel...
~~~~~~

I can't write anywhere near as well as Weber
But I try nonetheless, And even do my own artwork.

(Now on Twitter)and mentioned by RFC!
Animal Crossing Dreams at 6E00-00F5-2891
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Re: Mortal Engines
Post by Dilandu   » Tue Dec 18, 2018 12:26 pm

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Michael Everett wrote:Early box office figures indicate that the film is... not a total success. Not yet a flop, but it isn't going to rival Star Wars IV's opening.
Guess I'm waiting for the home release...
And I doubt there'll be a sequel...


A pity (albeit predictable); the book series is good.

Well, maybe someone would try the animated adaptation? It actually could work much better as animation...
------------------------------

- Who would won in battle between strawman Liberal-Democrat and strawman Conservative-Republican?
- Scarecrow from Oz; he was strawman before it became political.

P.S. - And he have Russian twin, to watch his back)
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