6 ms·

Arrivo weren't really a vacuum system, at least for the last year or so. But the thing is that electrified rail networks doesn't address the quadratically incr

Arrivo weren't really a vacuum system, at least for the last year or so. But the thing is that electrified rail networks doesn't address the quadratically increasing losses from drag at high speeds. There's a reason you don't see railroads operating at airline speeds: drag at sea level is a killer. In fact, at high enough speeds, the energy of air travel is actually LOWER than that of a sea level train.\ Altitude gives you a lot of efficiency. The idea of the vacuum train is to bring that efficiency down to sea level. And I think it's a good idea, but a real engineering challenge. In principle, you can keep a vacuum pretty easily. Vacuum tubes remain sealed and evacuated for decades without energy consumption, for instance. It's just at the interfaces you have to worry about leakage, and there it's a matter of careful sealing. It's possible to get really good at it. The International Space Station is full of interfaces (and thermal cycling every 90 minutes) and would quickly run out of air if we didn't know how to maintain a vacuum well at interfaces.

mpweiher 8y ago
> drag at sea level is a killer. Yes. Apparently when jet turbines came along they were discounted as ever being useful for commercial/passenger airplanes because they were so incredibly inefficient. I mean, really incredibly inefficient. What they didn't take into account is that the turbines allow you to fly at much, much higher altitudes. The reduced drag there more than makes up for the lower efficiency. And gets you a smoother ride and higher speeds as well. Modern turbofan engines are much more efficient, but that's basically because they really are turbo-props with enclosed propellers, though we call them "high bypass turbofans". And of course if jets have to drop to a lower altitude, for example because their cabin has become depressurised, range is drastically reduced.
- Farradfahren 8y ago
  Are there no ways to get around this? We managed to carvitation for torpedos?
- pfdietz 8y ago
  They're turboprops, but they're turboprops that don't have the speed limit imposed by the need to keep propeller blade tips from exceeding the speed of sound.
netcan 8y ago
Key point: at high speed. If want to go 1000km in 3-4 hrs then you are the kind of problem hyperloop might solve.
- pedrosorio 8y ago
  You can do 1305km in 4h30 today: https://en.m.wikipedia.org/wiki/Beijing–Shanghai_high-speed_railway https://en.m.wikipedia.org/wiki/Beijing–Shanghai_high-speed_...
macspoofing 8y ago
>In principle, you can keep a vacuum pretty easily. Keeping a vacuum over a length of hundreds of km is pretty hard, and in fact, has never been done.
- rblatz 8y ago
  But it has been done at a length of 26.7km, for the LHC.
  - Retric 8y ago
    We also maintain very high pressure pipelines over even longer distances. So, that part is really not a huge leap. High vacuum like the LHC would be hard, but that’s vast overkill. Even the equivalent of just 100,000 feet would be enough for super sonic trains.
    - solarkraft 8y ago
      You're making a good point, but: What's the effect of leakage in both systems? And don't you need a bit larger pipes for a hyperloop? Other than that I do think the tech is applicable.
      - Retric 8y ago
        It’s mostly a question of cost. High pressure systems are only economic if they transport far more material than they leak, but some minor leaks are fairly trivial. If you talking coarse aka 7,600 micron aka 7.6 torr aka 1% atmospheric pressure you gain most of the value moving a train through an evacuated tube while still being able to use cheap and very fast pump systems to deal is lots of slow leaks. Making that kind of a vaccum tube even easier to maintain. The LHC however deals with high vacuume becase they need particles to travel hundreds of miles without encountering any atmospheric particles. That would let trains reach orbital velocity without issue, but would be horrifically expensive. Basicly 100% to 1% vacuume is considered rough/coarse and it cheap. 1% to 1 micron is the middle ground which is increasingly difficult but still not that bad. Under 1 micron aka High vacuume is expensive and mostly the realm of science experiments. https://www.hydraulicspneumatics.com/200/TechZone/Vacuum/Article/False/6460/TechZone-Vacuum https://www.hydraulicspneumatics.com/200/TechZone/Vacuum/Art...

mpweiher 8y ago

> drag at sea level is a killer. Yes. Apparently when jet turbines came along they were discounted as ever being useful for commercial/passenger airplanes because they were so incredibly inefficient. I mean, really incredibly inefficient. What they didn't take into account is that the turbines allow you to fly at much, much higher altitudes. The reduced drag there more than makes up for the lower efficiency. And gets you a smoother ride and higher speeds as well. Modern turbofan engines are much more efficient, but that's basically because they really are turbo-props with enclosed propellers, though we call them "high bypass turbofans". And of course if jets have to drop to a lower altitude, for example because their cabin has become depressurised, range is drastically reduced.

Farradfahren 8y ago
Are there no ways to get around this? We managed to carvitation for torpedos?
pfdietz 8y ago
They're turboprops, but they're turboprops that don't have the speed limit imposed by the need to keep propeller blade tips from exceeding the speed of sound.

netcan 8y ago

Key point: at high speed. If want to go 1000km in 3-4 hrs then you are the kind of problem hyperloop might solve.

pedrosorio 8y ago
You can do 1305km in 4h30 today: https://en.m.wikipedia.org/wiki/Beijing–Shanghai_high-speed_railway https://en.m.wikipedia.org/wiki/Beijing–Shanghai_high-speed_...

macspoofing 8y ago

>In principle, you can keep a vacuum pretty easily. Keeping a vacuum over a length of hundreds of km is pretty hard, and in fact, has never been done.

rblatz 8y ago
But it has been done at a length of 26.7km, for the LHC.
- Retric 8y ago
  We also maintain very high pressure pipelines over even longer distances. So, that part is really not a huge leap. High vacuum like the LHC would be hard, but that’s vast overkill. Even the equivalent of just 100,000 feet would be enough for super sonic trains.
  - solarkraft 8y ago
    You're making a good point, but: What's the effect of leakage in both systems? And don't you need a bit larger pipes for a hyperloop? Other than that I do think the tech is applicable.
    - Retric 8y ago
      It’s mostly a question of cost. High pressure systems are only economic if they transport far more material than they leak, but some minor leaks are fairly trivial. If you talking coarse aka 7,600 micron aka 7.6 torr aka 1% atmospheric pressure you gain most of the value moving a train through an evacuated tube while still being able to use cheap and very fast pump systems to deal is lots of slow leaks. Making that kind of a vaccum tube even easier to maintain. The LHC however deals with high vacuume becase they need particles to travel hundreds of miles without encountering any atmospheric particles. That would let trains reach orbital velocity without issue, but would be horrifically expensive. Basicly 100% to 1% vacuume is considered rough/coarse and it cheap. 1% to 1 micron is the middle ground which is increasingly difficult but still not that bad. Under 1 micron aka High vacuume is expensive and mostly the realm of science experiments. https://www.hydraulicspneumatics.com/200/TechZone/Vacuum/Article/False/6460/TechZone-Vacuum https://www.hydraulicspneumatics.com/200/TechZone/Vacuum/Art...