h a l f b a k e r yExtruded? Are you sure?
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A honking great railgun propels the train out of the station. The train, now so much the lighter because it doesn't have motors and other self-propulsion wherewithall, shoots forth, a gleaming bullet of freight and passengers, and coasts gently into the next station. Banked track ensures that little
or no speed is lost on the corners and if the next station is too far away, booster guns at regular intervals down the line can top up the train with momentum. The force needed to propel the train to the next station (a science as old as rollercoasters) is be calculated by weighing the train, either by axle sensors or a weigh-station embedded into each launcher.
If some catastrophe was to occur (as surely it would if implemented on Britain's rail network), then one could simply reverse the railgun's polarity, "Star Trek"-style (and no, mentioning the Trek does not WIBNI-fy the idea), and rapidly decelerate the train.
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An interesting notion, but would only be possible if you completely redesigned all of the track layout. Many trains, quite sensibly, share a single piece of track, and often have to stop and wait at red lights. However, I could see this being used for shuttle type services once we have mastered all of the superconductor / magnets / frictionless pallava though. |
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Have a croissant to mop up that spilt coffee. |
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1. The tremendous acceleration at the beginning would squash all the passengers. |
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2. Frictional losses (rolling resistance, air resistance) are proportional to speed, which means you have to launch them *really really fast* for them to get there at all, wasting a lot of energy. |
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3. Rail lines are designed for a certain speed, and you'd have to build very special and expensive rail lines to deal with trains leaving the station at 1000kph, even though the average speed will still be the usual 80kph. |
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4. You're not saving anything. The main losses are due to friction, not mass, so putting the engine on the train really does make sense. Otherwise you'd be a lot better off with a high-speed cable car or something. |
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Mentioning Star Trek doesn't un-WIBNI-fy the idea, either. |
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[sild] It could be reasonably argued that the removal of signals and points would vastly enhance the safety of the rail network. |
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[Egnor] Your comments give much food for thought. |
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I see two solutions to the admittedly serious drawback (1): |
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(a) Reduce the acceleration to bearable levels, for example those experienced on a passenger jet. This would, however, mean an improbably long railgun barrel. |
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(b) Restrict the system to freight trains only. Since the train will be coasting on a suitably banked track, no driver will be necessary, and you can then fling the blighters as hard as you like. |
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To the frictional issues, I have no response, save to suggest the railgun locomotive as a possible form of mass transit on some far-future lunar colony. |
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[bristolz] I was just trying to partially naysayer-proof the idea. |
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Actually reducing the weight on the car reduces the normal force, of which friction is a percentage. It makes sense to make the car lighter. It will reduce losses to friction. |
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I'm not sure that reversing the polarity of a railgun changes the direction it fires the slug though. |
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So horribly, horribly baked. Which is a slight black mark against the author, and a laughable one against the annotators who said it was impossible. |
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Again, I reference the Skytrain line in Vancouver. It uses linear propulsion, which is the same thing as a railgun, but not as rash. Starting out, it uses one phase to obtain the most "torque". Then, as it accelerates, it switches to other phases to compensate for the increased speed and less power needed. It gives the train a unique sounds, something akin to a Zorg Guardian changing gears. |
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It almost sounds mechanical, as with an engine. But it isn't. It's all linear magnetics. Like a railgun. |
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And so, let me get this straight, [rapid transit] . . . the Skytrain line you reference is only powered momentarily at the start of its journey by an external magnetic system, coasting to the destination with the occasional assistance of magnetic boosters also external to the vehicle? |
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I think you jumped the track. |
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No one was objecting to linear magnetics but rather to the ballistic nature of the idea and the changes in infrastructure neccessary to accomodate the incredible speed and acceleration needed to fulfill the model as proposed. Nowhere did anyone proclaim the idea impossible they just thought it a terrible plan. I agree, it's not so good as proposed. If that's laughable, well, I guess I'm funny. |
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[rt] Would it be what you call rapid transit or is the average speed below that of a normal train? <g> |
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and how does the train company pay for this immense power usage? and electronics on the train would fry.
high guass levels hurt people (supposedly). people would have to drink from pouches with valves due to regular boosts from track. this Vancouver thing is more like it! |
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How about using linear motors to help accelerate the train from the station and linear generators to slow the train at the next stop. On relatively flat terrain this would allow the trains to get by with smaller, lighter motors sufficient for cruise speed. |
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