Can someone cite a source for the claim that there is a study for a maglev train between Philadelphia's International Airport and the Urban Core?

The distinction between maglev trains and coilguns for launching payloads into space seems an artificial one, as both use linear induction motors to provide acceleration (a coilgun is only the motor part, with passive stabilization). --Christopher Thomas 03:34, 23 Mar 2005 (UTC)

The introduction to this entry states that maglev vehicles can travel at extremely high speeds (404 mph) with "resonable" energy consumption because there is no contact between the vehicle and the track. In fact, wheel friction was never the issue. Rather, the problem is air friction, which goes up geometrically -- thus, any train running at those kinds of speeds would not have "reasonable" energy consumption (i.e. would not be commercially viable).

Furthermore, the claim that maglev allows for far faster speeds than what is possible conventional rail is debateable as TGV's have run as fast as 320mph under test conditions.

Emccaughrin

Furthermore, the claim that maglev allows for far faster speeds than what is possible conventional rail is debateable - No, it isn't, at least not in the near future. All conventional high speed rail in existence is electric. Running electric trains faster than 350 km/h is considered commercially unfeasible, because friction between the pantograph and overhead wire is so great that the wires need to be replaced after just a few runs. Maglev doesn't have that problem because it's contactless and it is already proven to run commercially at 430 km/h, not just under lab conditions. Combustion engine-powered high speed rail might achieve that, but a diesel high speed train has never been built commercially because of the enourmous weight of the engine or gas turbine required. Klafubra 09:49, 26 September 2005 (UTC)[reply]

First, I'm going to give yet another ObPedanticNote about the difference between polynomial and exponential progressions. Exponential progressions are "geometric". The relation between speed and energy consumption for objects moving through air is cubic (a polynomial relation). Secondly, as conventional passenger aircraft (which fly just below Mach 1) demonstrate, the energy requirements of subsonic high-speed movement through air are low enough that such speeds are still cost-effective for commercial passenger travel. Thus, I question the appropriateness of the "not reasonable" label. Thirdly, unless your train's internal mechanisms are frictionless, you'd better believe there's energy loss going on. The modes that I can think of offhand have quadratic (second-power) energy to speed relations, but the coefficients are considerably larger than those for air resistance, so the speed at which they balance is significant. --Christopher Thomas 16:25, 4 Apr 2005 (UTC)

The commercial aircraft comparison is not applicable as they do not fly at Mach 1 at ground level. Air density is considerably lower at 30,000 feet. -EM

The commercial aircraft comparison is applicable, as both the force required per unit cross-sectional craft area and the energy required are still far larger than any train built to date. Commercial jetliners typically travel in excess of 900 km/hour. At 30,000 feet, the usual aircraft cruising altitude, air has about a third the density it does at sea level (0.4 kg/m^3, vs. 1.2 kg/m^3). See density of air for calculations. Given a cubic rate of energy change with speed, a sea level craft would expend the same energy travelling cube_root(1/3) * 900km/h, or about 620 km/h. The world speed record for a wheeled train is 515 km/h, and for a magnetic levitation train 581 km/h (high-speed rail). Proposed operating speeds for maglev trains are typically below 500 km/h (about half the energy requirements of aircraft-speed-equivalent trains, or (500/620)^3).

You are correct in noting that the increase in speed is not _free_ - plane tickets cost more than low-speed rail tickets - but the whole idea behind high-speed rail and maglev systems is that customers will pay a premium to be able to travel a given distance more quickly. Also note that, due to increased speed, the energy required per unit _distance_ only goes up quadratically, not cubically. --Christopher Thomas 23:48, 4 Apr 2005 (UTC)

"Proposed operating speeds for maglev trains are typically below 500 km/h." Not to nitpick, but this is a lot less than 404mph (I interpret "reasonable" as commercially viable). -EM

The 650km/h (404 mph) figure cited in the article is close enough to the 620 km/h figure I cite above for the energy requirements to be very close to those for aircraft. My figures for aircraft are actually a conservative underestimate - 940 km/h is a typical figure for commercial aircraft (example: boeing 747), which yields almost exactly 650 km/h as an equivalent ground speed. I am also skeptical of seeing a maglev with routine operating speeds over 500 km/h in service any time soon. High speed rail trains are capable of over 500 km/h, but are more typically run at closer to 300 km/h.--Christopher Thomas 01:30, 5 Apr 2005 (UTC)

Well, the real world doesn't always obey back-of-the-envelope calculations. It could be rather expensive for a train operator to sustain 400mph up 4% grades, or brake/accelerate @400mph when going through curves. And while the airplane analogy might work as a rough, first-order approximation, such an analysis doesn't consider things like ground turbulance, which could be considerable. Also, HSR trains are considerably longer than a plane -- granted that improves the seats per frontal area value, but what effect does that have on overall drag? As mentioned, there are no commercial proposals to build 400mph Maglev's, thus the "reasonable" claim seems more like 'Popular Mechanics' type fodder. -EM

Going up a 4% grade requires little power consumption compared to plowing through air at 650 km/h. It's very easy to calculate exactly how much energy it takes. You're going at about 180 m/s, which means you're going _up_ at about 7 m/s. This requires 70 W/kg. By comparison, you need something along the lines of 5 MW/m^2 of frontal area to push through the air (there's a coefficient that reduces this for streamlined objects, but it'll be in the same ballpark). As for ground turbulence, part of the _point_ of maglev is that it decouples the train from much of that. For systems that are more sensitive to precision alignment, like the German system tested many years back, the track is made smooth enough for variations to be negligeable. For other systems, like the Japanese one, these constraints are relaxed due to a larger gap between the track coils and the train. As for train length, as long as the linkages between cars are sufficiently streamlined, the body of the train contributes far less to power consumption than breaking the train into two pieces would, for the same amount of cargo. There will of course be a limit to what can be pulled by one engine, but you have the same kinds of limits for conventional trains. As for your "popular science" epithet, please provide numbers to back up any claims you choose to make. I interpret lower running speeds as being selected simply because it's more cost-effective to use them (an airplane ticket costs enough that commuters may not want to use a train with the same ticket price). This is an economics issue, not a technical one.--Christopher Thomas 15:35, 5 Apr 2005 (UTC)

Where HSR competes against air, rail ticket prices are basically identical to air (aside from special promotional offers). You can verify this yourself by visiting any one of expedia.com, sncf.com, eurostar.com, etc (I just did this a few minutes ago for London-Paris and Paris-Nice). Thus, your ticket economics interpretation is not valid.

While it might be technically feasible to run a 400mph train, it would not be economical to do so. Hence, I stand by my claim that the energy cost would not be "reasonable" because there is no credible business plan that could justify the added cost. -EM

Your initial claim was that it was not technically feasible. Now you claim that it isn't ecomomically feasible. Please provide economic data from maglev trains proposed and currently running to back up your claim. So far, I'm seeing lots of opinion, but not much backing it up.--Christopher Thomas 19:09, 7 Apr 2005 (UTC)

Anon addition moved to the talk page until citations are provided. It would also have to be rewritten for narrative viewpoint. --Christopher Thomas 29 June 2005 15:53 (UTC)

MagLev might be built accross the Atlantic, but this would cost billions, maybe even trillions. It would go from New York to England and England to New York, in Record time of just 54 minutes, and at the speed of roughly 8000kmph which is faster than a bullet! Of course, air in the way would slow it down so in order to get to that collosal speed you would first of all have too make a vacuum. Though expensive, it is theoretically possible and if many different countries contribute to it, it could work.