A (weighty) question for train drivers
Discussion
As a daily commuter up and down the Cambridge/Stansted Greater Anglia line, I’ve always wondered how noticeable the difference is from the drivers seat when the train is full of passengers at rush hour vs. a practically empty train at quieter times of the day.
I’m not meaning dealing with bags trapped in doors etc. but acceleration and braking.
Several passengers and a boot full of luggage has a noticeable impact on the dynamics of even large cars - is it the same for a train?
I’m not meaning dealing with bags trapped in doors etc. but acceleration and braking.
Several passengers and a boot full of luggage has a noticeable impact on the dynamics of even large cars - is it the same for a train?
Trains have Levelling and Compensator Valves on the (air) suspension. The Levelling Valve keeps the train at the correct high depending on load, the Compensator Valve lets more air into the brake cylinders for a given brake demand so that the braking curve remains constant. It s basically a rod attached to the Levelling system that opens a vavle letting more air into the brake. If you ve ever got off a busy train and heard air hissing out that s this system doing its job, dumping excess air out of the suspension to maintain the correct high for the train. Modern trains have the same stuff except it s all sensors and computers rather than mechanical, often with Dynamic braking rather than mechanical.
Most stuff I ve driven you can t really feel the differed between full and empty. Ride, braking and performance pretty much remain the same. Push/pull loco stock there was a big difference depending on whether you were driving from the DVT or loco. You could really feel the weight of the loco pushing you when driving from the DVT.
Older DMUs used to struggle a bit loaded up. 142s were terrible. I drove one so full the suspension was on the bump stops. The horrific ride on those units amplified several fold.
Most stuff I ve driven you can t really feel the differed between full and empty. Ride, braking and performance pretty much remain the same. Push/pull loco stock there was a big difference depending on whether you were driving from the DVT or loco. You could really feel the weight of the loco pushing you when driving from the DVT.
Older DMUs used to struggle a bit loaded up. 142s were terrible. I drove one so full the suspension was on the bump stops. The horrific ride on those units amplified several fold.
You can't really tell. It's occasionally noticed on the brakes more than the power. Football specials where you take an empty train and then stuff 200 people per vehicle on you might be able to tell but it's usually surprisingly small difference.
The main problem is that the units are quite variable. One that's had a couple of refreshed engines in will be noticeably faster than one with tired engines, likewise with the state of the brakes. That had a bigger effect on performance.
When driving electrics it's noticeable when there's another electric train in the section if they're both (or more) taking full power. The voltage drops a bit and you can tell it's a bit slower.
The main problem is that the units are quite variable. One that's had a couple of refreshed engines in will be noticeably faster than one with tired engines, likewise with the state of the brakes. That had a bigger effect on performance.
When driving electrics it's noticeable when there's another electric train in the section if they're both (or more) taking full power. The voltage drops a bit and you can tell it's a bit slower.
Great question and very interesting responses. Something I have also often wondered.
Completely understood on the automatic braking compensation , but I would have assumed acceleration would be massively hindered once ‘loaded’.
Working through some numbers for an extreme example, taking a 3 car ‘class 165’ for example, say 250 people getting on (let’s say, for a football special)….thats potentially 16 tonnes boarding! However, the total set weight is 111t empty (according to Google), so only a 14% ish increase.
Hence for a bigger train, in a normal pick up scenario, I can kind of see why the performance drop is negligible.
Completely understood on the automatic braking compensation , but I would have assumed acceleration would be massively hindered once ‘loaded’.
Working through some numbers for an extreme example, taking a 3 car ‘class 165’ for example, say 250 people getting on (let’s say, for a football special)….thats potentially 16 tonnes boarding! However, the total set weight is 111t empty (according to Google), so only a 14% ish increase.
Hence for a bigger train, in a normal pick up scenario, I can kind of see why the performance drop is negligible.
I drive 185 units. 50ish tonnes per car, 750hp per car. They can keep time and hit their maximum speed on two engines (I’ve even done a ton on one engine), that’s with 50T of dead weight being dragged along and up and over some pretty demanding gradients. You can feel the reduced performance in that case, but a few tonnes of SLF isn’t going to affect their performance too much if at all.
ChocolateFrog said:
You can't really tell. It's occasionally noticed on the brakes more than the power. Football specials where you take an empty train and then stuff 200 people per vehicle on you might be able to tell but it's usually surprisingly small difference.
The main problem is that the units are quite variable. One that's had a couple of refreshed engines in will be noticeably faster than one with tired engines, likewise with the state of the brakes. That had a bigger effect on performance.
When driving electrics it's noticeable when there's another electric train in the section if they're both (or more) taking full power. The voltage drops a bit and you can tell it's a bit slower.
New brakes used to be dicey until bedded in. We always used to leave the repair book open on the desk with the entry in for the relief to see in case we didn’t catch them to tell them when bringing a unit off shed that had just had new blocks.The main problem is that the units are quite variable. One that's had a couple of refreshed engines in will be noticeably faster than one with tired engines, likewise with the state of the brakes. That had a bigger effect on performance.
When driving electrics it's noticeable when there's another electric train in the section if they're both (or more) taking full power. The voltage drops a bit and you can tell it's a bit slower.
The 158 units in the 1589xx series were always better than the 1587xx despite having exactly the same running gear. Odd. Some put it down to the 1589xx units being “depot pets” having being allocated to the same depot since new where as the 1587xx had been abused all over the country before arriving at our TOC. Funny how even strange things like that can effect performance.
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