Acela - 150mph rated, but again add around 10-15% for top speed. I believe there was a test run where they got it up to 168mph but don't quote me on that.

I'm not sure which Talgo the Amtrak ones are based on, but some diesel models are rated at 125mph, though I doubt the Amtrak ones can do that. Apparently the Amtrak Talgos are somewhat heavier than normal so the top speed might be reduced somewhat.

There is a more or less optimum range of rotational speeds of the motor and the rotational speed of the wheels is determined there from by the gearing. In addition to this, there are issues of vibration and machiinery harmonics that come into play at higher speeds.

When the French did their 515 km/h (320 mph) run with the TGV on the TGV Atlantic line before opening, they shortened the train to increase the power to weight ratio, applied larger diameter wheels to the power units, do not know if they changed the gearing, but think they did, increased the voltage in the overhead line by about 10% above the normal 25 kV, and increased the tension in the line a lot, but how much I do not know. The 515 km/h speed was essentially the limit they could achieve within the length of track they felt safe to run on at above 300 km/h. In other words, if they had had more room, they probably could have gotten to a higher speed.

There is a natural frequency for the propogation of the wave of the train loading in the track and in the catenary. I do not know what this speed is, but it should be calculable. It is above the 515 km/h speed achieved. It is thought that this wave speed may form a limit, and even if not, it will change the nature of the solution.

A more ultimate limit would be the speed of sound. 320 mph is approaching half way there. The faster the train moves, the more aerodynamic noise there is. That is the reason the noise reduction of a maglev is mostly imaginary. At higher speeds a large component of train noise is aerodynamics. If the speed of sound is exceeded, there is a continuous sonic boom. That is why the SST was only allowed to exceed the speed of sound while over the ocean.

We are building a 300 km/h railway which is very little more than a finese of the normal railway. Tunnel sizes and other clearances are larger than needed to simply pass the trains due to aerodynamic considerations. The spirals have a variable rate of change to avoid the jerk on entry and exit of the spiral that is essentially unnoticible at 60 to 80 mph, and the high speed turnouts (up to 100 mph) have spirals in the switch points and beyond the frogs. All main line frogs are swing nose. Vertical curves are very long to minimize the vertical acceleration effects. There are no road crossings at grade at all. The bridges have a continuous half height noise wall.

how does that help?

At this time, you can not put a diesel with enough horses in the engine within the weight limit to economically run at high speeds. With high speed you are trying hard to reduce weight. With freight the weight of the train that you can start and move at low speed depends upon the weight on powered axles.

Generally freight trains are powered from something under one horsepower per ton up to around 2 hp/ton for high priority freight. Passenger trains, US style are normally between 5 and 10 hp per ton. The TGV's, ICE's and Shinkansens are usually powered above 20 hp/ton, with of course a lot of attention paid to aerodynamics to reduce rolling resistance, since aerodynamics is the biggest part of train resistance at high speeds. Now, think of a normal modern 4400 hp diesel on six axles weighing in at about 214 tons. That only gives you 20.56 hp/ton with no train what so ever, and of course the high speed aerodynamics would be terrible. Therefore, if you run without carrying your sorce of power on your back, you can run faster.

The basic formula of acceleration explains it.

F = ma, or Force equals mass times acceleration. Reshuffle that and you have

a = F/m, or the amount of acceleration you can get equals Force divided by mass.

Since you have to have some accelerating force to maintain any speed, the less weight you are dragging around the better off you are. I know that sounds contrary to basic physices, but it is true since we are not in a frictionless universe. You must have enough accelerating force to balance the train's rolling resistance to maintain any given speed.

quote:

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Originally posted by EmpireBuilder:
Am I correctly understanding that even under identical track conditions, the Acela is an inferior train in terms of speed when compared to the TGV or ICE?

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I believe that is correct. The Acela is a very heavy train (relative to other high speed trainsets) for a variety of reasons - I think the primary one is that the Federal Railroad Administration has numerous crash safety requirements that most foreign countries don't have, which makes the train heavier. 167/168mph sounds about right for the maximum speed achieved with an Acela. It'll never go faster than that, even under ideal track conditions.

In one word: No.

The speeds you suggested, assuming you are using the usual SI notation where m/s is meters per second are:

299 m/s = 669 mph = mach 0.9
792 m/s = 1772 mph = mach 2.4
458 m/s = 1025 mph = mach 1.4

Why did you pick such odd numbers?

Ordinary wheel on rail will not work because you can not apply enough power through the wheels at this speed to overcome the aerodynamic resistance. Aerodynamic resistance increases at the square of speed. I have been told that when you get near or above the speed of sound, there is a V^3 factor, as well, but I really know nothing about that. V^2 is enough. At some point, even with all axles powered, the aerodynamic resistance will pass the power that can be put into the rails through the wheels, even with all axles powered.

Also, for your higher numbers, getting above the speed of sound for something on the ground is totally impractical. Remember, the SST was allowed to exceed the speed of sound only when well out to sea, never over land. One word: NOISE, LOUD NOISE, OK, that's two words.

What is the maximum you can reach with an ordinary railway? As tests and demonstrations, probably somewhere around 400 mph on level track. If you can throw in a nice long downgrade, you can go faster, but no matter how much power you have you are not getting a lot faster than this, and it will take a power plant of about 100 hp/ton to get this fast. Since you want reliablility, you can not go beyond the practical wet rail adhesion, which will be much less, and this says that your maximum will be somewhere around 300 mph.

Anytime you get much above 100 mph, it becomes very difficult to get an alignment straight enough to run it consistently. Remember our old V^2 friend. To double the speed, requires a 4 times larger minimum curve radius. To triple it requires 9 times, so if you want to run 300 mph you get this: At 100 mph you want 1 degree or less curve, that is radius 5730 feet or larger. At 300 mph, this means the minimum curve should be on the order of 52,000 feet, or a 0d06m40s degree of curve. You have to use very large vertical curves, as well. No sudden changes of grade, or you get than sinking feeling.

If we go to maglev or something that does not require adhesion, we still have the curve considerations. Airplanes do not worry about this because they can rotate to a much larger angle than would be practical with any guideway, and since they are up in the are, they do not worry about terrain features and other considerations that constrain alignment.

Oh, and if you think the discussion above is on the order of those that said in 1903 that flight was impossible, or whatever idiot in 1820 said that travel ove 20 mph was impossilbe because people could not breathe, most of what I told above is extrapolation from experimentially derived information. (I suspect the 20 mph story has nothing to do with scientific knowledge as it stood in 1820, anyway. Probably some dolt with his mouth in gear while his brain was turned off. Anybody who had ever been to sea or stood out in a high wind knew good and well that breathing was quite possible when facing a wind of well over any 20 mph, whether the issue had come up in 1820 or 1020 or even BC something or other.)

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I just assumed (which makes a you-know-what out of "u" and "me") that she or is it he was just coming up with three silly 3-digit numbers, not one silly number. I figure the best way to deal with asinine sarcasm a lot of times is to act as if it were not there. After all, if they do not get a rise out of you, they have failed in their redicilous mission.

Since my brain's default mode is the English system, even after 14 years of working in metric units, I still have light as 186,000 miles per second, so the number did not ring a bell.