4 ms·

Passengers are much more sensitive to vertical acceleration than horizontal. Repeated 1g swings from -0.5 to 0.5 g would make this thing a vomit comet. Would be

Passengers are much more sensitive to vertical acceleration than horizontal. Repeated 1g swings from -0.5 to 0.5 g would make this thing a vomit comet. Would be interesting to see this analysis done with normal limits for high speed rail design, instead of Elon's chosen 0.5g limit. Edit: HS2 in Britain, for instance, is being designed with a maximum of around 0.01g vertical acceleration. If Elon's has figured out how to get passengers to handle 50x that much, he could save them a lot of money.

morsch 13y ago
Vertical acceleration refers to acceleration in the direction of the tracks, right? Some other figures I could find: Shinkansen: 2.6 km/h/s = 0.07g ICE (German HSR): 0.5 m/s2 = 0.05g S-Bahn (metro transport): 1 m/s2 = 0.1g Makes sense that metro transport has higher acceleration, as high speed rail spends a lot of time "cruising" at certain speeds, while metro transport is basically always either accelerating or decelerating. I'd guess subways also feature relatively high g-forces. Also interesting: http://en.wikipedia.org/wiki/Orders_of_magnitude_%28acceleration%29 http://en.wikipedia.org/wiki/Orders_of_magnitude_%28accelera...
- lmm 13y ago
  Vertical as in up-down. You're much more comfortable accelerating forwards-backwards or left-right.
  - cma 13y ago
    Then change the orientation of the seats? Without a reference frame you can't tell.
    - modoc 13y ago
      Gravity?
      - dspeyer 13y ago
        Include that in the calculations. There's a certain absolute sideways g-force (decreasable by slowing or straightening), and a certain absolute downwards gravity. These add up to a single total force. So long as the magnitude is at least 1g, there exists a seat orientation such that the passenger feels 1g toward the seat and something on the back. How much you can spin the seat without those movements causing problems is an open question. Airplanes are an encouraging precedent. They often make quite sharp turns at extremely high velocity, but tilt into them such that there's almost no perceived lateral acceleration.
    - jotm 13y ago
      You'd still be going up (from the Earth's surface) and down (towards the Earth)...
  - ak217 13y ago
    Is there a source for left/right acceleration being more comfortable than down? My subjective/uneducated guess would actually be that acceleration is most comfortable in the order of: forwards, up, backwards, left/right, down.
- JonFish85 13y ago
  My understanding of his/her comment was that vertical acceleration is "up & down" (perpendicular to the earth).
  - mcguire 13y ago
    I believe specifically, perpendicular to the passenger's horizontal reference frame.
    - IvyMike 13y ago
      Are you saying that laying down on a roller coaster would make it less nauseating? Admittedly I have not tried it but I don't think that would work.
      - gaius 13y ago
        It would, but not for the reason you think: lying on your back activates the mechanism you still have from when you were a baby that stopped you getting motion sickness when you were being carried by your mother. We advise people suffering from seasickness that one thing they can do is lie on their backs, and it often is enough by itself.
        bashinator 13y ago
        That would also be one reason why motion sickness in microgravity is so pernicious.
- brohee 13y ago
  I'm think vertical means bumps and dips, for which we really have little tolerance. I don't see i being much of an issue for hyperloop, as varying height of the pillars is pretty easy...
neltnerb 13y ago
Maybe he developed inertial dampers for spaceX?
wazoox 13y ago
Indeed. Apparently in commercial flights 0.5G is a targeted maximum in flight, rarely - if ever - reached: http://www.airliners.net/aviation-forums/tech_ops/read.main/130631/1/#0 http://www.airliners.net/aviation-forums/tech_ops/read.main/... However from the article chart, there would be more than 50 peaks at +/-0.5G in 35 minutes, that would definitely feel more like a huge roller coaster ride than anything else, so my bet is that it's just unbearable except for astronauts and fighter pilots.
- aetherson 13y ago
  Guys. The article has nothing at all to say about vertical acceleration. He's plotting left-right acceleration, not up-down. He says: "However, I only used this information for plotting. For this first study, the derived route is only 2-dimensional." And the graph's acceleration is noted as longitudinal and lateral. Not vertical at all. The word "vertical" appears nowhere in the article. All of the pictures show 2D diagrams of routes. I don't know where this sub-thread about vertical acceleration came from.
  - penrod 13y ago
    Quoting from the Hyperloop alpha paper: "To further reduce the inertial acceleration experienced by passengers, the capsule and/or tube will incorporate a mechanism that will allow a degree of ‘banking’." A banked turn transforms lateral acceleration into vertical within the passengers' frame of reference.
    - aetherson 13y ago
      Okay, sure. But that's not anything analyzed by the article at the top of this thread. And further: 1. Presumably, if lateral acceleration proves to be preferable to vertical acceleration, you just turn off the banking. 2. You control the precise amount of vertical acceleration by the size of the bank, so if there's some amount of vertical acceleration that's desired and some that isn't, you only bank hard enough for the desired acceleration. You also to at least some degree control the jerk (change in acceleration) so you can smoothly slide into the acceleration change as you bank slowly harder. 3. Importantly, this is only increased-acceleration in local "down," not decreased acceleration in local down. I don't have any scientific data to back this up, but it's the drops (ie, reduced vertical acceleration compared to gravity) that seem to nauseate people on roller coasters, not the climbs. But most importantly, I think that people were badly misinterpreting this article (not the original hyperloop paper) in thinking that its charts were about vertical rather than lateral and longitudinal acceleration.
PhasmaFelis 13y ago
What's the source for +/-0.5g vertical acceleration? Something in the design docs?
deleted 13y ago
[deleted]
xorblurb 13y ago
In a car max lateral acceleration is typically 0.3g for safety and 0.2g for comfort I think (and usually road design are even more conservatory). I think 0.5g lateral is way to high, especially if you can't look at the outside. People are gonna puke or going crazy from the discomfort. Probably < 0.1 might be a good target, maybe even < 0.05g Maybe the capsule should rotate during turns so that most lateral translation is translated to vertical (like in most trains at nominal speed).

morsch 13y ago

Vertical acceleration refers to acceleration in the direction of the tracks, right? Some other figures I could find: Shinkansen: 2.6 km/h/s = 0.07g ICE (German HSR): 0.5 m/s2 = 0.05g S-Bahn (metro transport): 1 m/s2 = 0.1g Makes sense that metro transport has higher acceleration, as high speed rail spends a lot of time "cruising" at certain speeds, while metro transport is basically always either accelerating or decelerating. I'd guess subways also feature relatively high g-forces. Also interesting: http://en.wikipedia.org/wiki/Orders_of_magnitude_%28acceleration%29 http://en.wikipedia.org/wiki/Orders_of_magnitude_%28accelera...

lmm 13y ago
Vertical as in up-down. You're much more comfortable accelerating forwards-backwards or left-right.
- cma 13y ago
  Then change the orientation of the seats? Without a reference frame you can't tell.
  - modoc 13y ago
    Gravity?
    - dspeyer 13y ago
      Include that in the calculations. There's a certain absolute sideways g-force (decreasable by slowing or straightening), and a certain absolute downwards gravity. These add up to a single total force. So long as the magnitude is at least 1g, there exists a seat orientation such that the passenger feels 1g toward the seat and something on the back. How much you can spin the seat without those movements causing problems is an open question. Airplanes are an encouraging precedent. They often make quite sharp turns at extremely high velocity, but tilt into them such that there's almost no perceived lateral acceleration.
  - jotm 13y ago
    You'd still be going up (from the Earth's surface) and down (towards the Earth)...
- ak217 13y ago
  Is there a source for left/right acceleration being more comfortable than down? My subjective/uneducated guess would actually be that acceleration is most comfortable in the order of: forwards, up, backwards, left/right, down.
JonFish85 13y ago
My understanding of his/her comment was that vertical acceleration is "up & down" (perpendicular to the earth).
- mcguire 13y ago
  I believe specifically, perpendicular to the passenger's horizontal reference frame.
  - IvyMike 13y ago
    Are you saying that laying down on a roller coaster would make it less nauseating? Admittedly I have not tried it but I don't think that would work.
    - gaius 13y ago
      It would, but not for the reason you think: lying on your back activates the mechanism you still have from when you were a baby that stopped you getting motion sickness when you were being carried by your mother. We advise people suffering from seasickness that one thing they can do is lie on their backs, and it often is enough by itself.
      - bashinator 13y ago
        That would also be one reason why motion sickness in microgravity is so pernicious.
brohee 13y ago
I'm think vertical means bumps and dips, for which we really have little tolerance. I don't see i being much of an issue for hyperloop, as varying height of the pillars is pretty easy...

neltnerb 13y ago

Maybe he developed inertial dampers for spaceX?

wazoox 13y ago

Indeed. Apparently in commercial flights 0.5G is a targeted maximum in flight, rarely - if ever - reached: http://www.airliners.net/aviation-forums/tech_ops/read.main/130631/1/#0 http://www.airliners.net/aviation-forums/tech_ops/read.main/... However from the article chart, there would be more than 50 peaks at +/-0.5G in 35 minutes, that would definitely feel more like a huge roller coaster ride than anything else, so my bet is that it's just unbearable except for astronauts and fighter pilots.

aetherson 13y ago
Guys. The article has nothing at all to say about vertical acceleration. He's plotting left-right acceleration, not up-down. He says: "However, I only used this information for plotting. For this first study, the derived route is only 2-dimensional." And the graph's acceleration is noted as longitudinal and lateral. Not vertical at all. The word "vertical" appears nowhere in the article. All of the pictures show 2D diagrams of routes. I don't know where this sub-thread about vertical acceleration came from.
- penrod 13y ago
  Quoting from the Hyperloop alpha paper: "To further reduce the inertial acceleration experienced by passengers, the capsule and/or tube will incorporate a mechanism that will allow a degree of ‘banking’." A banked turn transforms lateral acceleration into vertical within the passengers' frame of reference.
  - aetherson 13y ago
    Okay, sure. But that's not anything analyzed by the article at the top of this thread. And further: 1. Presumably, if lateral acceleration proves to be preferable to vertical acceleration, you just turn off the banking. 2. You control the precise amount of vertical acceleration by the size of the bank, so if there's some amount of vertical acceleration that's desired and some that isn't, you only bank hard enough for the desired acceleration. You also to at least some degree control the jerk (change in acceleration) so you can smoothly slide into the acceleration change as you bank slowly harder. 3. Importantly, this is only increased-acceleration in local "down," not decreased acceleration in local down. I don't have any scientific data to back this up, but it's the drops (ie, reduced vertical acceleration compared to gravity) that seem to nauseate people on roller coasters, not the climbs. But most importantly, I think that people were badly misinterpreting this article (not the original hyperloop paper) in thinking that its charts were about vertical rather than lateral and longitudinal acceleration.

PhasmaFelis 13y ago

What's the source for +/-0.5g vertical acceleration? Something in the design docs?

deleted 13y ago

[deleted]

xorblurb 13y ago

In a car max lateral acceleration is typically 0.3g for safety and 0.2g for comfort I think (and usually road design are even more conservatory). I think 0.5g lateral is way to high, especially if you can't look at the outside. People are gonna puke or going crazy from the discomfort. Probably < 0.1 might be a good target, maybe even < 0.05g Maybe the capsule should rotate during turns so that most lateral translation is translated to vertical (like in most trains at nominal speed).