Deleted
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Post by Deleted on Aug 24, 2014 15:46:48 GMT
I have recently being reading the Ministry of Transport reports on a few collisions that have occured, the most recent being the collision of a ballast train and a staff train at Neasden in 1969.
One of the things that crop up over and over is drivers who attempted or may have attempted to reverse the motors as a last resort to avoid the crash. I am wondering if this was ever part of their training?
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rincew1nd
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Post by rincew1nd on Aug 24, 2014 17:03:43 GMT
Completely off-topic, but putting moving the reversing lever into centre or reverse is how you slow a road steam engine or keep it under control descending a hill.
Rheostatic braking is effectively this isn't it?
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Post by domh245 on Aug 24, 2014 17:17:03 GMT
My understanding of Rheostatic braking is that you are disconnecting the motor from the source and then reconnecting it across a resistor, using the motor as a generator to remove kinetic energy from the wheel and convert it into heat energy, I suppose it is similar in that you are taking the energy that is there are wasting it to slow yourself down. As for the OP, I suspect that it isn't part of the training. You would more likely get taught what to do if an incident happened, but in terms of accident mitigation, you would just get told - slam the brake on. I suspect the reason that they don't get told to reverse the motors is because it is probably pretty bad for the motors to have the field change across them, and would probably destroy the motors, and quite possibly harm the passengers, although if you are heading towards another train closing at 40mph ruining the motors probably won't be your biggest concern...
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Post by Deleted on Aug 24, 2014 17:20:40 GMT
Do we really think reversing the motors on a tube train would help? At any kind of speed I can't imagine you'd have enough traction, you'd probably just end up skating along. You might mutilate the wheels, or just spin them, but I can't see it slowing you down more than braking. What do you think?
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Colin
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Post by Colin on Aug 25, 2014 1:33:36 GMT
I can confirm that this isn't something we train.
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class411
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Post by class411 on Aug 25, 2014 7:12:31 GMT
Do we really think reversing the motors on a tube train would help? At any kind of speed I can't imagine you'd have enough traction, you'd probably just end up skating along. You might mutilate the wheels, or just spin them, but I can't see it slowing you down more than braking. What do you think? I agree. One would hope that the braking system is designed to be able to brake to just before the point where the wheels would start to slip on dry rails. In which case, adding any extra retarding force through the wheels would be counter-productive. As a supplementary question; does the latest stock have anti lock braking systems? I would imagine these could be useful, particularly when the wrong type of leaves are on the track. |
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Post by tjw on Aug 25, 2014 7:50:29 GMT
I suspect that in the days of wooden or similar brake blocks, and steam locomotives, putting the locomotive into reverse could stop a train in a shorter distance than using brakes alone. There seem to be plenty of accident accounts of this method being used, but I have seen no scientific discussion as to how effective this is. The idea of putting a train into reverse comes from past practice.
If antilock brakes work as they should, and wheel slip is to be avoided, putting a modern electric train into reverse would not be a such a good idea. Rheostatic brakes should add a retarding force to the motored wheels that should gradually slow the train without wheel slip.
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Post by Deleted on Aug 25, 2014 9:01:19 GMT
I would have thought on older DC motored stock cutting the power and hard breaking even locking the wheels would be preferable to going into reverse as you end up with a lot of slipping and erratic behaviour at the wheel rail interface which could actually make the situation worse!
XF
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Post by Deleted on Aug 25, 2014 12:38:02 GMT
As a supplementary question; does the latest stock have anti lock braking systems? I would imagine these could be useful, particularly when the wrong type of leaves are on the track. Well there's WSP (Wheel Slide Protection). I remember watching an old British Rail video on driving during low adhesion conditions which talked about WSP - link. I'm pretty sure the S stock has it and quite possibly other new stock on LU. |
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Post by Deleted on Aug 25, 2014 19:09:49 GMT
As a supplementary question; does the latest stock have anti lock braking systems? I would imagine these could be useful, particularly when the wrong type of leaves are on the track. Well there's WSP (Wheel Slide Protection). I remember watching an old British Rail video on driving during low adhesion conditions which talked about WSP - link. I'm pretty sure the S stock has it and quite possibly other new stock on LU. You can hear it work on the 92ts very frequently, providing the ATO hasn't thrown a fit and thrown in the emergency anchors because it can't cope with the rain! It sounds like a load of frequent hisses as the train is braking and is the sound of the WSP system releasing small amounts of air from the brake cylinders to minimize any slide. 1992ts don't have 3 step disc brakes but this video explains the Wheel Slide Protection system. |
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Post by Deleted on Aug 26, 2014 22:26:04 GMT
I know that reversing of the motors is not taught and has not been in my time (passed Motors in 1988) but I have read reports of it being done from 1938, 1946 and 1969 and on another occasion from long ago but can't remember the date now. This is why I was wondering if it was ever taught in the early years of the Underground.
However, I have actually reversed the motors on a 72 stock by mistake. It was common practice when driving in wet conditions to put the reverser key into the "reverse position"; this would cut out the Rheostatic brake and stopped the wheels from locking up. I was approaching the home stick in the pouring rain, at Edgware (or possibly High Barnett, I can't remember now) which was on; as I neared it, it cleared as expected and forgetting I was still in the reverse position I put the handle straight into "series". Well I can tell you I have never heard that noise from a train before. I instantly shut off and went to "Forward 1" and to my relief the motors were ok.
I don't think I ever reversed the key again. Incidentally if any one is wondering the Deadman was fully operational when the selector key was in the reverse position.
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Post by jacko1 on Sept 2, 2014 22:11:47 GMT
although on the mainline,i,by mistake, put the reverser on a br class 302 on the lts,into reverse(as then,there was no ssf(you could put the reverser into neautral,and the dsd was inactive).I knocked it into reverse while struggling with my bag,and there was a almighty bang.i looked out o the cab window,only to see plumes of black smoke coming frok the 3 motor coaches(12 car train).the guard buzzed me up and told me his van was full of smoke§. I managed to limp at about 20mph into east ham.i expected to be disciplined as all the traction motors were wrecked,but luck was on my side as a fitter found and blamed a fault in the wiring between jumpers cables and blamed that! I never did own up to say it was my fault I had reversed it by accident! taught me a lesson to never again put it in neautral!
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Post by rheostar on Sept 3, 2014 6:28:42 GMT
Putting the motors into reverse is certainly not taught to T/Ops on LU. Back in 1981 I did my motors on 38 stock and it was never mentioned.
I only know of one instance when a Piccadilly line T/Op tried it on '73 stock 'just to see what would happen' coming into Wood Green westbound . Apparently, there was an almighty bang and left the train with several damaged motors.
If there was going to be a collision, the natural reaction would be to drop the handle and probably leg it through the J door.
When the '73 stock first came out it was fitted with a form of ABS called 'slip slide'. It didn't work and was removed before all the stock had been delivered.
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roythebus
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Post by roythebus on Sept 16, 2014 14:15:38 GMT
The train that hit the stationary train at the Clapham crash was found with the reverser in the reverse position according to the Railway Inspectorate Report.
A contributor I know on here used to occasionally stop COP stock using reverse!
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Post by james66526 on Sept 26, 2014 20:33:15 GMT
Used to drive Battery locomotives. At low speed, you could definately stop a loco pretty quickly by putting the key into reverse and opening up a couple of notches. The issue with this at high speed with a collision imminent is the driver will inevitably have already made an emergency brake application which would prevent them from taking power anyway.
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