

Autodesk's Idea to Knit the Hyperloop Out of Carbon Fiber - bcn
http://www.businessweek.com/articles/2013-10-31/autodesks-idea-to-knit-the-hyperloop-out-of-carbon-fiber

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pudquick
I think one thing they missed here is pointed out by this statement in the
article:

 _" [...] in less than two years, and, says Brandt, require fewer support
pylons. “Elon’s estimate calls for about $2.6 billion for concrete, but we’d
get that down to more like $1.5 billion,” he says."_

The pylons aren't purely for lifting the steel, they're also for distributing
the weight of the Hyperloop cars. If anything, an equal length of carbon fiber
tube would be more flexible (not less) than the same length as steel and would
potentially require the same number _or more_ of pylons.

The air that these cars float over does not negate gravity or the effect of
their weight on the tunnel that they travel through.

All that being said, it looks like our current carbon fiber pre-preg
([http://en.wikipedia.org/wiki/Pre-preg](http://en.wikipedia.org/wiki/Pre-
preg)) production is currently able to handle a construction project like
this. According to Wolfram Alpha, a cylinder 9 feet in diameter from Los
Angeles to San Francisco would have a surface area of approximately 52 million
square feet.

According to the book "Boeing 787 Dreamliner" by Mark Wagner and Guy Norris,
in 2007 Boeing actually expanded the capacity of carbon fiber plants they had
access to in France, Japan, and the US from 125 million square feet per year
to 363 million square feet per year. I would hope that 6 years later we would
be able to produce 52 million square feet.

~~~
bradleyland
I have a few questions stemming from ignorance. These aren't meant to me
rhetorical in any way. I'm just curious how my understanding is incorrect.

I was under the impression that carbon fiber was "stronger" than steel. I
understand that stronger doesn't always mean more rigid, but I was also under
the impression that carbon fiber could be woven in different ways to offer
greater rigidity on a desired axis. Is it possible to construct carbon fiber
in a way that is more rigid than steel?

Couldn't they also increase the amount of material used, or does that not
increase rigidity? I'm thinking something like 8-ply vs 6-ply, or something
like that. I'm speaking entirely from a layman's view, so I'm curious why
increasing the number of plies wouldn't work.

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MechSkep
This is interesting because they could potentially avoid the thermal expansion
problem that would otherwise sink the hyperloop. Carbon fiber has a negative
coefficient of thermal expansion in its axial direction, and you can pair it
with a metal to get a net zero expansion structure.

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Maarten88
That is a really good idea. But I wonder if carbon fiber wouldn't be very
expensive for a static structure like that. Why not use much less expensive
glass fiber? Compared to steel it would still be much stronger, lighter and be
manufactured in one piece, without welds.

~~~
tinco
Perhaps glass fiber is not rigid enough? Also, I think the only reason carbon
fiber is so expensive is the manufacturing cost, if you're paying for the
machines anyway, perhaps the cost isn't that much higher.

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clebio
>> There are machines that can churn out limited qualities of the braided
carbon fiber.

I'm guessing that's a typo and they meant limited _quantities_, but I'm
honestly not sure (not snark).

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bkev
Reminds me of the carbon fiber loom Toyota came up with for making the Lexus
LFA.

[http://youtu.be/AScfESzQzIQ](http://youtu.be/AScfESzQzIQ)

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Swannie
[http://www.buzzfeed.com/autodesk/a-new-look-at-the-high-
spee...](http://www.buzzfeed.com/autodesk/a-new-look-at-the-high-speed-
hyperloop-b3y4) From Aug 30th with some cool images and a like to the YouTube
CGI:
[http://www.youtube.com/watch?v=mV7lbDcaCo4](http://www.youtube.com/watch?v=mV7lbDcaCo4)

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ericcumbee
I'm not sure there is that much production capability for Carbon Fiber. Back
in 2011 Audi attributed the delay in the Debut of the Audi R18 LMP as being
due to the global shortage of Carbon Fiber caused by the 787 Dreamliner
program(Not to be confused with the Mazda 787B).

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brei
This makes the Hyperloop concept feel vastly more feasible. And manufacturing
carbon fiber at those scales will open up all kinds of new
infrastructure/architecture possibilities. The biggest question on my mind is:
how does one continuously infuse/cure epoxy?

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crazytony
Hmmm. I'd have to see this run through an earthquake model. It seems to me
that having them stacked/connected vertically would cause problems during an
earthquake.

Think about those coffee stirrer straws that look like a figure 8 (it's a
single straw pinched in the middle): if you hold one between your fingers the
range of movement left/right is easy but an up/down movement is quite
difficult (and if you push hard enough the straw buckles).

There's usually significant vertical and horizontal displacement during an
earthquake. My thinking is that Elon's original design would fare better.

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brianbreslin
How easy is it to repair?

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ye
Building the structure is the least of the Hyperloop's problem.

How about supporting near-vacuum on such a large scale?

How about dealing with earthquakes, erosion, landshifts, where even a small
shift in a section of a tunnel would mean instant death for the travelers.

How about obtaining the land rights to build it between SF and LA?

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plam
Regarding ground changes, we can look to current bullet-train rail systems.
Nobody has ever died on a bullet train in Japan due to earthquakes. I saw on a
documentary that Japan feed seismic sensor data into train control centers
where any dangerous seismic event would trigger automatic stopping of the
trains.

~~~
ye
I never said it's impossible, I think it's a much bigger problem than building
a machine to build the tunnel walls.

~~~
ricardobeat
How is it a bigger problem if it has already been solved today?

The original paper attempts to deal with all of these problems, pressure,
safety, land rights, it's a very interesting read.

~~~
ye
First of all, it hasn't been solved in the US, and not for these speeds, which
are at least double of the fastest bullet train in the world.

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berntb
How are the safety aspects with steel or carbon fibers, considering that it
will be close to roads and lots of people will have close access?

Could the (near) vacuum be compromised by any idiot with a hunting rifle and
bullets optimized for piercing body armour? (At a minimum repairs and off time
for a day or more.)

Can a kg of explosives put shrapnel through it and create a big crash? What is
the safety distance for one of those Iranian self-fusing penetrators used in
Iraq?

~~~
nawitus
A bullet hole probably doesn't matter much. Air will be leaking inside
anywhere and air has to be pumped out all the time in any case.

I think you can create a big train crash with a kg of explosives, so that
scenario is already possible.

~~~
timmy-turner
Also, railways are not really meant to be safe against attackers with physical
access to it (so basically anyone). For example, the sensors/switches on a
railway that cause a train to perform an emergency halt if the train driver
misses a stop signal can be modified by anyone near it - no encryption, no
locks (source:
[https://www.youtube.com/watch?v=xwaKYZfgY8k](https://www.youtube.com/watch?v=xwaKYZfgY8k)
\- only in German though).

You don't even need explosives, a simple wedge welded on a rail would be
enough. In the end, I don't think it is economically feasible to secure a
railway against that (as well as any other kind of track). You have to make
sure that nobody does stupid things like these.

