They are controlled by a bus system that passes along the entire rake of vehicles.
Pushing or pulling doesn't matter, because the final drive is via a traction motor, there's no direct drive, and the trains can still run with either power car having failed, be it pushing, or pulling.
Here's an intersting question though. Although these trains will do more than 125 mph, just suppose for a moment that the train's top speed at full performance was actually 125mph. What would the train's top speed be if one power car fails?
a) still 125 mph, but the train would accelerate slower
b) 62.5 mph
c) 80mph
d) 100 mph
If you can, please include some logic with your answer!, if not, just post a, b, c, or d.
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It obviously isn't b, as there isn't a linear relationship between power and speed - owing to the influence of drag which goes as the square of the speed.
We cannot possibly make a choice, logically (which is how we are invited to tackle this problem), between c and d. Accordingly the answer must be a.
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Thanks NC.
Having been on half-power trains a number of times, I think it's d (100) - doesn't seem to make a lot of difference, but they do apologise for the delay. Although I suppose that might just be down to taking longer to get up to speed.
And I guess it also depend on how much faster than 125 they can go, and whether the driver is allowed to 'overstretch' the single power unit. Perhaps it is 125 after all.
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make a choice logically (which is how we are invited to tackle this problem) between c and d. Accordingly the answer must be a.
Surely not.
If it takes say, 1000bhp to propel the train at 125mph and the train's power is reduced to 500bhp, then the maximum speed must be reduced. By how much? I don't know, there are factors such as wind resistance and friction.
I don't have the maths to make the calculation, but my best guess is that the new maximum speed would be around 100mph or d.
Edited by drbe on 04/09/2008 at 11:38
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>>By how much? I don't know, there are factors such as wind resistance and friction.
Accordingly, without further information (and a computer model...) we cannot make a logical choice between 80 and 100.
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>>Accordingly, without further information
Some basic physics will get you to the right answer!
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It requires 1000BHP to hit 125 mph consistently uphill into the face of a gale with 500 people on board.
500BHP will still get it to 125 mph, downhill tail wind and empty
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I would say 100mph.
Top speed is a product of the power divided by the resistance. The resistance is proportional to the speed squared, so the relationship between the power and speed is cubic.
If the power is reduced by half then the speed is reduced by the cube route of 2, which is approximately 1.25.
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Pass stackman a banana! Not only for the right answer, but getting the underlying logic too!
As rolling resistance between tyre and rail on a train is quite low, and especially at speed, the predominant drag is aerodynamic drag, for which the drag force is proportional to speed squared, and the drag power, speed cubed.
In theory, these trains could top out at about 150, and in practice, they are limited to about 132mph.
As AE says, the margin between the theoretical top speed of 150, and the rated 125mph is to allow for gradients, and for weather, particularly, headwinds.
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...but at 125mph (on the level), how much power is in reserve? If the units are running at say 80%, what can one unit do at 100%, assuming it was allowed to?
EDIT posted before reading NC's answer
Edited by Focus {P} on 04/09/2008 at 12:05
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*goes to hide in corner with large pointy hat with a large D *
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The interesting thing about this calc is that it does carry across to cars at motorway speeds.
Half of the power demanded, and hence half of the fuel being burnt is for the last 20% or so of the speed you're doing.
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NC- following on from my last post which arrived just after your answer, does the 100mph assume the single engine is running at the same power as it would in 'normal' operation at 125mph (eg. 80%), or has the driver had to turn up the wick a bit (eg. 100%)?
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The 100 mph assumes that the pair of engines would only just make 125 mph - i.e., a simplifying assumption.
In practice, 100mph isn't too far from the truth for one power car, because not only is top speed reduced, but, the acceleration at any given speed is halved - so, even though the train could theoretically do about 117 mph with only one power unit, there aren't stretches of track un-interrupted by hills or stations long enough for it to get there.
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These are remarkable trains, still providing some of the fastest services in the country over 30 years after they were introduced. The BR mk3 coach which forms the passenger accom is still the most comfortable and best riding stock on NR metals. It's also a vary good place to be if you have to have a rail accident (I would have been in the Colwich crash in 1986 had family illness not delayed a trip to the Potteries for a week).
The 125 still retains the world record for a diesel, a little over 140mph somewhere near Thirsk. Under normal conditions they will comfortably maintain 125 up Stoke bank (the steam loco Mallard attained her record in the opposite direction) so there is lots in reserve.
I'm sure I've read somewhere that they're limited to 115 when running on one power car, though that was in rapidly dissapearing version with the original Paxman Vallenta engines - they're mostly on MTU power now. The lost time when running on one power car is more down to slower starts etc than any loss in top speed.
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Some info on Wikipedia; 'The HST strikes back' is interesting.
en.wikipedia.org/wiki/InterCity_125
Production stopped in 1982, making the youngest over 25 years old.
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>>These are remarkable trains, ...
I couldn't agree more - they are my absolute favourite way to travel, fast, quiet, and comfortable.
There are some dull dull people making decisions for the railway. After the clear success of the HST, they foist beastly, noisy, smelly, cramped, mean Voyagers and Meridians onto us.
Among the highlights of my career so far was instrumenting up 43060, County of Leicestershire, and then taking strain and dynamic data on a test run on a glorious summer day from Leeds Neville Hill depot to Darlington and back - a full HST rake, going at full pelt with just a handfull of depot staff and engineers on board. It was one of those (all too rare) days where I would have worked for free!
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I live on Merseyside where, for most of the day, the extensive electric trains service is operated by three-car units.
However, for the morning and peak periods and/or some of the longer routes, a number of trains are made up of two three-car units coupled together and the drivers and guards man them exactly as for the three-car units (i.e at the end of each journey a driver walks from his cab to the rear of the train to start the return trip, whilst the guard takes the opposite direction).
In fact this manning setup was also used on the previous fleet of electric trains, which were operated for a period of 40 years (from 1938 onwards); as far as I know, the only replacements most of the electric units required during this period of service were new bushes!
I do recall that the current trains originally caused problems when first going into service as the drivers discovered they couldn't always stop the train at a station as intended and had to reverse back to the platform...:-)
Re mainline trains. I recently travelled the modest distance from South Parkway to Liverpool Lime Street on a Birmingham to Liverpool lunchtime train.
Apart from arriving exactly on time, the train provided a smooth, quiet and extremely comfortable short trip; I was even impressed with the excellent, large sized toilet which was similar in some ways to those modern, 20p a time public street loos.
Edited by Stuartli on 05/09/2008 at 17:35
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