The limits of high-speed rail

[masraum]

Originally Posted by RWebb

Shanghai maglev is 270 mph now

https://en.wikipedia.org/wiki/Maglev

According to the article, the Japanese beat the French by 6kph (581kph vs 474.8kph) about a week before the French did it, but using maglev (the French did it with wheels or rails). In 2015 the Japanese hit 603kph with a maglev train.

The French were pretty sure that they could have hit 600 in their train, but that's getting awfully close to the speed at which the train would outrun the wave on the wire that fed it power (610kph) which would be bad.

That's something that I hadn't thought about which was interesting in the article, the need to keep the overhead power wire under high tension to keep it tight (no sag).

The key factor for very high speed circulation, however, is the mechanical response of the catenary. Its behavior is easy to understand picturing a finger pressing a guitar string. The finger represents the pantograph of a train. By moving longitudinally through the catenary applying a vertical force to ensure the continuity of the electrical contact, the pantograph creates a wave that moves in both directions along each span of automatic compensation of the mechanical tension of the catenary.

The frequency of the generated wave increases with mechanical stress — and for that reason the tighter strings of a guitar sound sharper. But if the finger is pushed along the string instead of just plucking it, the wave ceases to be static and moves at a speed proportional to the mechanical tension and inversely proportional to the mass per unit length of the string material [3].

This idealized scenario is altered by the existence of fixed masses in the overhead contact line, which are indispensable for its mechanical support. Droppers and registration arms, which allow the shape of the contact wire to be maintained by anchoring it to the messenger wire and to the masts respectively, induce reflected waves that alter the behaviour of the entire assembly. At high speeds, the dynamic interaction between the pantograph and the overhead contact line is further complicated by the Doppler effect, which shortens the waves in the direction of travel — while lengthening them in the opposite direction.

And then there's the fine line of wire size, power transmission and tension.

[wdfifteen]

I conclude from reading the OP that what is called "high speed rail" may not be worth the effort is a country populated the way the US is. The problems of going over about 180 mph don't seem to be worth the expense and effort. But 180 mph trains between relatively close cities (300 t0 500 miles apart) would have been welcome when I was traveling all the time.
A question:
Do those 400 mph trains use the wheels for braking or do they have some kind of brake shoe that drops down and contacts the track?

[tcar]

Originally Posted by wdfifteen

....Do those 400 mph trains use the wheels for braking or do they have some kind of brake shoe that drops down and contacts the track?

They use dynamic braking... like regenerative braking on EV's to slow. Brakes the motors to brake the wheels.

They have disc brakes to finally stop the trains when they are slow.... say 10 mph.

[wdfifteen]

Originally Posted by tcar

They use dynamic braking... like regenerative braking on EV's to slow. Brakes the motors to brake the wheels.

I wondered about that, given the statement in the article, "The contact surface per wheel on the rail head is barely 250 mm², guaranteeing minimum frictional forces — the rolling resistance coefficient for steel on steel contact is, at its worst, 30 times lower than that of rubber on asphalt."

So with minimum friction between the wheel and the rail, it seems the ability to stop in an emergency using the wheels only (regardless of how they are retarded) would be limited.

[Sooner or later]

They take about a mile to stop.

[stuartj]

High speed rail is just awesome. Fast, comfortable, safe, fuss free. And delivers you, tyicallly centre to centre rather than to an airport a cab ride out of the city. Paris- Bordeaux, 500kms. A little over 2 hours, a glass of wine, internet, good food. From memory, 18 services per day. Pretty amazing.

Travelling into Madrid a few months ago.

[island911]

" And delivers you, tyicallly centre to centre rather than to an airport a cab ride out of the city. "

That's the best plus of roads (rail or paved)

I think that we need more VTOL aircraft. Let's make runways a thing of the past. ..along with choo-choo trains; which are essentially REALLY long runways. I mean over a mile to stop? shessh!.

[tcar]

And NO TSA (or equivalent) with trains....

[berettafan]

Comfortable and fun way to travel.

[rcooled]

Originally Posted by stuartj

High speed rail...Fast, comfortable, safe, fuss free. Paris- Bordeaux, 500kms. A little over 2 hours, a glass of wine, internet, good food. Pretty amazing.

Yes, travelling overland at 300km/h is quite an experience. It's especially interesting when another train passes going in the opposite direction. It's just a quick blur outside the window, and then it's gone

[stuartj]

Originally Posted by rcooled

Yes, travelling overland at 300km/h is quite an experience. It's especially interesting when another train passes going in the opposite direction. It's just a quick blur outside the window, and then it's gone

I remember the first time with the train displaying 200+ on the bulkhead, comfy chair, glass of wine....thinking that the last time I travelled this fast terrestially I was strapped in, helmeted, ****ting bricks....

[varmint]

Originally Posted by wdfifteen

I don't think we can judge rail travel by what it is, we need to think about what it could be.

A fine attitude to have when spending your own money.

[WolfeMacleod]

Originally Posted by varmint

A fine attitude to have when spending your own money.

We're sorry you don't like nice things.