Elon's hyperloop under construction:

Originally posted by twhitehead
Once again. Musk is not designing it!

No but he has the last say on what design is used.

Originally posted by sonhouse
No but he has the last say on what design is used.

No, he doesn't. The main company supposedly developing the idea, Hyperloop One has no direct ties to Musk whatsoever. He is not a shareholder, board member or engineer in that company.

https://en.wikipedia.org/wiki/Hyperloop_One

Originally posted by twhitehead
No, he doesn't. The main company supposedly developing the idea, Hyperloop One has no direct ties to Musk whatsoever. He is not a shareholder, board member or engineer in that company.

https://en.wikipedia.org/wiki/Hyperloop_One

Why do they associate it with Musk then? He has no money in it?

Originally posted by twhitehead
This perhaps?
[youtube]RNFesa01llk[/youtube]

arr that was it.

Originally posted by sonhouse
Why do they associate it with Musk then? He has no money in it?

Musk popularized it and helped get it in the news. He did recently get involved in a competition for students to design a car that would go inside the tube. Not a genuine engineering challenge really but more of student games. And the student designs failed really badly.
The reason he gets associated with it in every single news article is because he makes great headlines.
I know that there is a lot of talk about fake news these days, but there is also the phenomenon of sensationalism in news which isn't new, but is surprisingly under recognized.

Originally posted by humy
arr that was it.

He has some excellent points, but he doesn't conclusively show it can't be done. But the fact that Hyperloop One has raised many millions of dollars and is talking to various parties about actual contracts to build a real track but are yet to publicly test the key engineering challenges is of concern. My own view is that it will most likely prove too complex to be viable. More streamlined high-speed trains would probably be a far better investment. Possibly with improvements to maglev technology.

Originally posted by twhitehead
He has some excellent points, but he doesn't conclusively show it can't be done. But the fact that Hyperloop One has raised many millions of dollars and is talking to various parties about actual contracts to build a real track but are yet to publicly test the key engineering challenges is of concern. My own view is that it will most likely prove too comp ...[text shortened]... ains would probably be a far better investment. Possibly with improvements to maglev technology.

I wonder if a design based on a half buried hyperloop would be cheaper and more reliable? Half the steel and half buried half the stress on the frame. Less support structure and such. The bottom half could just be a concrete hemicircle with support rods buried in the facing piece.

Originally posted by sonhouse
Musk usually does what he says he does. His space exploits are well known, doing something NASA, ROSCOSMOS, ESA, the French, and the rest never did, a rocket that lands itself safely.

What I wonder is just how much of a vacuum they will be aiming for. I work with vacuum tech all the time, roughing pumps, cryo pumps, diffusion pumps, titanium sublimation ...[text shortened]... ewtons? Sounds like it would fly apart for sure.

Probably too much for any kind of real use.

The hoop stress is density times velocity squared. Assuming a radius of 80 cm, then v = 320 m/s, this gives a specific tensile strength required of 102 kJ/kg. The specific tensile strength of high strength steel is given on the Wikipedia page for flywheels as 100-200 kJ/kg, composites are stronger, so the bearing would not fly apart unless it was made of cast iron or some other weak material.

Originally posted by DeepThought
The hoop stress is density times velocity squared. Assuming a radius of 80 cm, then v = 320 m/s, this gives a specific tensile strength required of 102 kJ/kg. The specific tensile strength of high strength steel is given on the Wikipedia page for flywheels as 100-200 kJ/kg, composites are stronger, so the bearing would not fly apart unless it was made of cast iron or some other weak material.

I think we already ruled out physical wheel bearings. Much more likely would be magnetic bearings. I already have experience with those, I had several turbo-molecular vacuum pumps, they had magnetic bearings and rotated depending on the size, from 30,000 to 60,000 RPM. They look internally a bit like a jet engine and they work about the same except for the fuel combustion deal😉

Right now, I am contemplating replacing our Brooks/CTI "Onboard 8" cryopump with a turbo but it has to run in horizontal position, don't know if they can do that, the bearings might only work in vertical orientation.

One thing about tubo pumps, when they fail, it is spectacular! I had several on the ion implanters I used to work on and when something with that kind of mass breaks down (the vanes crack and fail which causes a catastrophic cascade of flying blades and the transfer of momentum to the body of the pump is something to behold🙂 It twists around about 30 degrees and destroys the mounts and vane debris ends up in very unlikely places scattered about the ion implanter guts, the pump is a pile of broken blades inside after that🙂

Originally posted by sonhouse
I wonder if a design based on a half buried hyperloop would be cheaper and more reliable? Half the steel and half buried half the stress on the frame. Less support structure and such. The bottom half could just be a concrete hemicircle with support rods buried in the facing piece.

It could probably be buried for most of its full length. There are a number of advantages to doing so including more even temperatures, and fewer right of way issues. The reason railways are not underground except for in cities, is they are much larger and aren't naturally in a tube already so the tunneling is far too expensive.

But the overground/underground question is meaningless until the more serious questions are resolved - especially those surrounding the vacuum.

Originally posted by sonhouse
Much more likely would be magnetic bearings. I already have experience with those,

Not the same thing at all - just like the air bearings you mentioned.
There is a massive difference between holding a rotating shaft in place and holding a moving train above the tracks.

Originally posted by twhitehead
Not the same thing at all - just like the air bearings you mentioned.
There is a massive difference between holding a rotating shaft in place and holding a moving train above the tracks.

Sure but it is already a known technology, nothing new about that at all.

Maglev trains:

http://science.howstuffworks.com/transport/engines-equipment/maglev-train.htm

Originally posted by sonhouse
Sure but it is already a known technology, nothing new about that at all.

Yes, I know. So are liner motors (which maglevs use too). Yet Hyperloop One decided to do a large scale linear motor as their only technology demonstration so far.

Originally posted by twhitehead
Yes, I know. So are liner motors (which maglevs use too). Yet Hyperloop One decided to do a large scale linear motor as their only technology demonstration so far.

Never saw a liner motor🙂

I wonder when they will ever have a demo? Like you say, it might be just another scam, like the cold fusion scam.

Originally posted by sonhouse
I think we already ruled out physical wheel bearings. Much more likely would be magnetic bearings. I already have experience with those, I had several turbo-molecular vacuum pumps, they had magnetic bearings and rotated depending on the size, from 30,000 to 60,000 RPM. They look internally a bit like a jet engine and they work about the same except for the ...[text shortened]... scattered about the ion implanter guts, the pump is a pile of broken blades inside after that🙂

I had a look at the Wikipedia page about the hyperloop thing and it said they were looking at some sort of magnetic levitation. The problem with the project is that they are trying to build some sort of mass transportation system, but it's more like Concorde. Tony Benn, for perfectly laudable reasons made travel on Concorde as cheap as possible; the problem was that people expected it to be expensive and so it was underbooked. After Lord King took control over British Airways he increased the price of seats to what people expected them to be, improved the service on board to match the price, and it was full from then on. So I think with this, if they get it to work, they'll have problems getting people to travel on it. If they make it cheap then people will think something is wrong with it, and if they make it expensive then it's difficult to fit into "the holiday of a lifetime". The toughest problem for them may turn out to be getting the fare right. Roughly speaking, I think the market they need to try to compete with is the Orient Express.

Regarding your last paragraph, that sounds a little like uncontained engine failure in a turbofan and truly dangerous. I hope the room is empty of people while these things are running!