The friction co-efficient of gravel when in contact with a cast wheel intended for a track is going to be less than f*ck all, so i'd be surprised if it would stop at all locked wheels or not!!
Tim..
It's not friction with the wheel that stops them, it's displacement of the gravel as the wheels sink into it (and presumably gravel-on-gravel friction)
It all comes down to heat in the end anyway, so I guess Branston's hot air is just his attempt to help.
He did seem in a bit of a pickle...
|!>>I thought trains had "dead man handle" brakes so they came on if the |!>>driver |!>>let go of the handle anyway. |!>
|!> They do, but you get more useful retardation if you apply the brakes |!> gradually and try to avoid the wheels locking up. This is particularly |!> important after a derailment, as a still-rolling derailed train is |!> _much_ safer than a derailed toboggan. It's quite likely that the driver |!> _did_ behave in a selfless and heroic manner to try and stop the train |!> sliding, which isn't recogised by Branson talking rubbish about |!> "steering" |!>
|!> I don't know what happens if the emergency system on a Pendolino comes |!> into effect. They're disk braked, so a full application would lock the |!> wheels instantly. They're also fairly modern and sophisticated, so maybe |!> they still keep the anti-lock system effective, even in such a case. |! |!The friction co-efficient of gravel when in contact with a cast wheel |!intended for a track is going to be less than f*ck all, so i'd be surprised |!if it would stop at all locked wheels or not!!
Yes but the wheels flinging gravel around and digging trenches in it is quite effective as braking. Think about gravel escape roads at the bottom/middle of a hill, which are quite common in hilly areas.
Agree about the design but they haven't lost a train. They've already said they will repair it and put it back into service.
Martin
|!>> wrote: |!>> >Sir Richard Branson yesterday declared the driver of his crashed Virgin |!>> >train to be a hero for staying at his post and continuing to 'steer' the |!>> >train. |!>>
|!>> >Am I missing something? I was always under the impression that trains |!>> >didn't |!>> >have steering wheels, and that their direction was determined by the |!>> >track |!>> >and points. Further, that when they leave the track their trajectory is |!>> >determined purely by Newton's Laws of Motion - not by anything which the |!>> >driver might do. |!>>
|!>> >Is this not correct? |!>>
|!>> I think that this was more to do with having to give ze press |!>> conference with little or no preparation. |!>>
|!>> Normsilly he is quite articulate and smooth during interviews, but |!>> looking at the video clip of the news interview it was a very |!>> different story - lots of Umms and pauses and in some cases even |!>> conjecturing which is probably unwise in his position. |!>>
|!>> Perhaps he was genuinely upset or possibly jetlagged after traveling |!>> back from his holiday, who knows. |!>>
|!>> Either way, I don't think I'd set any store by what was said. |!>>
|!>> It will be interesting to see if there are now calls to take Notwork |!>> Rail back into private ownership. |!>
|!> This train of his seemed to work very well considering there is no |!> call for restraining straps or even for passengers to remain seated at |!> all times. |!>
|!> Once in the ballast the stopping effect is greatly increased I would |!> have thought. And the ability to hold sway seems to have dealt well |!> with any wave of whiplashing traversing the train. |!>
|!> All told, a win for the design for the loss of one train. |! |!Agree about the design but they haven't lost a train. They've already said |!they will repair it and put it back into service.
They said *heavy* repair which sound to me like strip it down completely, inspect everything and build it back together again.
Quite. The fact that it remained largely intact is quite impressive.
A wonderful era, but not just at the bottom. An effective demonstration of how an economy should be run.
As for Branson, I am no particular fan, although it is some achievement by any stretch of the imagination to have achieved the brand value that Virgin has and to maintain that for more than a generation.
So does this mean repair, replace or improve something or everything?
I'm not sure that I completely follow this line of argument....
On a car, the only effective difference between fully locked wheels and ones just on the edge of locking is whether you retain steering or not. As already pointed out, steering is not a consideration for trains.
Colin Bignell
No, the "stopping power" of a locked wheel is much less than that of a rolling one. So not only do you retain steering you also stop quicker.
Though I doubt this locked/rolling is particulary relevant in the case of derailed train. As has already been pointed out it'll be the "gravel trap" effect of a few hundred tonnes of train ploughing a course through the ballast or track side trees/bushes/furniture that stops it.
I do have a slight problem with calling ballast "gravel" though. Ballast is generally rough crushed stone in lumps around the 2" size. Gravel, to me, tops out at less than inch.
The Metropolitan Police did a series of experiments that showed that the difference between the stopping distance of a locked wheel and a rolling one is minimal. The locked wheel is marginally better on a dry road. The rolling wheel performs slightly better on a wet one. However, the differences would not be significant in an emergency stop.
Colin Bignell
Not a foot lb?
Remind me not to drive with you, if you believe that.
Given the appalling driving standards of the plods that doesn't surprise me. No doubt they used a cross ply tyre on a transit van to prove their point.
The locked wheel is marginally better on a dry road.
The experience of every racing driver is that this is utter bollocks.
The rolling
Oh dear.
On 25 Feb 2007 12:23:06 GMT someone who may be "Bob Eager" wrote this:-
Also incorrect. Assuming the driver applied then using the normal controls the brakes would remain applied unless the driver operated the controls to reduce the application.
If one of the various emergency brake application systems activated/was activated by the driver then the brakes would have remained activated until the system was reset.
On Sun, 25 Feb 2007 15:19:58 +0000 someone who may be Andy Dingley wrote this:-
Wheelslide prevention equipment was introduced on trains starting in the early 1970s. Just about all passenger trains are now fitted with it and most have been for some decades.
So why have car makers spent loads of dosh on developing systems that prevent wheels locking and why are such systems pretty much standard fit on all new cars?
That statement would require qualification. It *might* be the case with certain high grip road surfaces in perfect condition, but for all intents and purposes is wrong. If it were correct, there'd be no need for either traction control or ABS - and yes I do know ABS allows you to steer during heavy braking, but in the vast majority of cases an emergency stop doesn't require this. But it doesn't explain why traction control helps - a spinning wheel is the same in principle when starting off as a locked one when braking.
Not quite! Because of the action of the differential, if one driving wheel is on a frictionless surface, you can't get any torque to the other driving wheel(s). By applying braking to the spinning wheel, you *can* then get torque to the other wheels.
ABS, on the other hand, seeks to maximise the stopping power of each wheel individually, and is less influenced by what the other wheels are doing. Having said that, it's a total joke to suggest that preventing the wheels from locking doesn't reduce stopping distance significantly (for cars, that is).
To return to the original topic(!), I doubt whether all this stuff about ABS on cars has much relevance to what a train does when it's pursuing a cross-country path!
There is a certain percentage of slip that gives the best grip..at least on a racing tyre. Too much overheats the tyre and lubricates the track with molten rubber..too little is underheating the tyre..
To be fair thats more about controllability in steering that ultimate braking performance.
very few road cars have the ability to lock their wheels at much over
40mph in the dry anyway..HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.