GWR Class 800

[hassaanhc]

FirstGroup have taken this to extremes, though. There has been more and more padding added to GW schedules over the years to take account of this. Crawling into and out of platforms at 10mph is simply not needed.

Interesting to note that SWR are now exhibiting similar driving characteristics with an increasing number of trains being driven like the driver is a frightened old woman going to the shops.

Probably at depots like Bristol I expect can't imagine anywhere else?

I first started travelling between Southall and Paddington semi-regularly in 2014, and until the end of 2015 it seemed quite common to see drivers of both GWR and HC services slow right to a crawl before entering platforms at stations they were stopping at, which usually lost a minute per stop. Things started to improve in 2016, probably helped by big reduction in fatalities on the line. And since the 387s have come the drivers seem very confident with the braking, sometimes slowing down a bit later than with the DMUs and generally entering platforms at greater speeds. And to me it seems that DMU timings are still being used, as I've seen no time lost when a 165 has covered a stopper, and 387s usually arrive early at stations which helps recover slight late running (often caused by passengers at Ealing Broadway/Southall not using the full length of the train )

 

[Railperf]

Surely the IEPs still have a full service retardation rate of 9%g but presumably with enhanced emergency braking (12%g) which the HSTs don't have. If so I don't how the service braking is better other than perhaps more positive application and release.

I'm not sure what the official figures are - but in practice - we are not yet seeing any major reduction in stopping times or distances to reflect that. I cannot imagine that the TOC or network rail will ever base the timetable on full service braking rates for safety reasons.

London Underground trains for example can use close to their full service braking rate in the dry tunnel sections, but once in the open, the braking rates for trains with ATO drops back to between 5 and 6% G so that the stopping times and distances (and subsequently the timetable) can be maintained in wet or dry weather.
This article in Rail magazine seems to indicate that the TOC's and Network Rail are looking at ways to improve braking particularly in the wet...

https://www.railmagazine.com/news/network/rssb-variable-rate-sanders-can-halve-braking-distances

 

[SaveECRewards]

VTEC have Tweeted they've had some Azumas arrive from Japan yesterday. Does anyone know why these ones weren't assembled in the UK?

 

[hexagon789]

I'm not sure what the official figures are - but in practice - we are not yet seeing any major reduction in stopping times or distances to reflect that. I cannot imagine that the TOC or network rail will ever base the timetable on full service braking rates for safety reasons.

London Underground trains for example can use close to their full service braking rate in the dry tunnel sections, but once in the open, the braking rates for trains with ATO drops back to between 5 and 6% G so that the stopping times and distances (and subsequently the timetable) can be maintained in wet or dry weather.
This article in Rail magazine seems to indicate that the TOC's and Network Rail are looking at ways to improve braking particularly in the wet...

https://www.railmagazine.com/news/network/rssb-variable-rate-sanders-can-halve-braking-distances

Interesting, but I agree with you agree that it's unlikely timetables will ever be based on using full service braking rates. It would be asking for too much really.

 

[59CosG95]

800034 entered service yesterday I believe. Only 001-004, 007, 019, 032, 035 & 036 are left of the /0s to enter service.

 

[swt_passenger]

VTEC have Tweeted they've had some Azumas arrive from Japan yesterday. Does anyone know why these ones weren't assembled in the UK?

The UK plant wasn’t sized to cope with the whole subsequent Hitachi order book. I expect it is down to Hitachi where they actually build individual units, and initial plans will have changed resulting from additional orders by GW, TPE, Scotrail etc...

 

[800001]

The UK plant wasn’t sized to cope with the whole subsequent Hitachi order book. I expect it is down to Hitachi where they actually build individual units, and initial plans will have changed resulting from additional orders by GW, TPE, Scotrail etc...

These are pre-series trains which were always going to be fully assembled in Japan.
They are 800201 and 800202, 5 car bu-modes, and are going to be used for training vtec staff.

 

[snowball]

The current Railway Magazine has an article on Class 800 performance, including a statement that mode switching on the move originally tended to involve about 1 minute of coasting, now reduced to about 30 seconds as the drivers have got more used to it.

 

[jyte]

The current Railway Magazine has an article on Class 800 performance, including a statement that mode switching on the move originally tended to involve about 1 minute of coasting, now reduced to about 30 seconds as the drivers have got more used to it.

1 minute to 30 seconds is pretty impressive. I imagine they could probably shave more off that too.

Every second counts

 

[hexagon789]

The current Railway Magazine has an article on Class 800 performance, including a statement that mode switching on the move originally tended to involve about 1 minute of coasting, now reduced to about 30 seconds as the drivers have got more used to it.

Yes, I remember reading that. That was also the source that stated that the 800s could only manage about 118 mph in Diesel Mode on the level.

 

[jyte]

Yes, I remember reading that. That was also the source that stated that the 800s could only manage about 118 mph in Diesel Mode on the level.

The 118mph thing was first reported in an issue of rail a few months ago now.

 

[hexagon789]

The 118mph thing was first reported in an issue of rail a few months ago now.

I see, must've missed that article. It does seem a bit ridiculous that they can only manage 118.

 

[JN114]

I see, must've missed that article. It does seem a bit ridiculous that they can only manage 118.

It’s because it is tripe. I’ve been on diesel power IETs doing more than 118; downhill, uphill, level; in a corner. They take a while to get there; but they’ll do 125 while on GU power. Unless these so-called reports are from people actually in the driving cab observing the position of the power brake controller and speedometer reading they can’t say that the 118 recorded is the max speed; or the driver has reduced power to meet schedule; or whatever.

 

[hexagon789]

It’s because it is tripe. I’ve been on diesel power IETs doing more than 118; downhill, uphill, level; in a corner. They take a while to get there; but they’ll do 125 while on GU power. Unless these so-called reports are from people actually in the driving cab observing the position of the power brake controller and speedometer reading they can’t say that the 118 recorded is the max speed; or the driver has reduced power to meet schedule; or whatever.

Well I can appreciate that, I have no idea myself but I've seen it mentioned on several publications by different authors.

 

[Wilts Wanderer]

I have a GPS phone app that displays current speed. All evidence I’ve recorded so far points to a balancing speed of about 118mph on the level, on diesel mode.

What is also interesting is that running from Swindon to Didcot, the train seems to reach 119-120, whereas from Didcot-Swindon the natural maximum seems to be about 114-115mph. When you consider that the gradient is about 1:600 falling towards London, it shows how marginal the change in conditions have to be to have a material impact on performance. I imagine a strong headwind will have a similar impact, or a tailwind would give a boost!

It’s no different to HSTs. A crush loaded peak departure from London will perform differently to an empty set on Sunday morning. I’ve spoken to drivers who have told me just that.

 

[hexagon789]

I have a GPS phone app that displays current speed. All evidence I’ve recorded so far points to a balancing speed of about 118mph on the level, on diesel mode.

What is also interesting is that running from Swindon to Didcot, the train seems to reach 119-120, whereas from Didcot-Swindon the natural maximum seems to be about 114-115mph. When you consider that the gradient is about 1:600 falling towards London, it shows how marginal the change in conditions have to be to have a material impact on performance. I imagine a strong headwind will have a similar impact, or a tailwind would give a boost!

It’s no different to HSTs. A crush loaded peak departure from London will perform differently to an empty set on Sunday morning. I’ve spoken to drivers who have told me just that.

All the published reports I've read suggest a balancing speed of 118 on the level.

Yes, the fact that such a slight gradient so greatly affects maximum speed is quite interesting.

 

[Wilts Wanderer]

It’s to do with the inverse square relationship between power and acceleration. To get from 100mph to 125mph (an increase of 25%) you require double (200%) the power input compared to going from 0-100mph. This is why a 2+8 HST running on one power car will balance at about 100-105, whereas a normal configuration will eventually sit at about 128mph.

So in a similar manner, if you increase the resistance to acceleration even a little, in the highest speed ranges, the impact on required power is more noticeable than you would think. This is also why there is a legitimate view that HS2 aiming for 225mph rather than a more standard 200mph is an unnecessary expense, as it greatly increases the energy requirement.

 

[JamesRowden]

It’s to do with the inverse square relationship between power and acceleration. To get from 100mph to 125mph (an increase of 25%) you require double (200%) the power input compared to going from 0-100mph. This is why a 2+8 HST running on one power car will balance at about 100-105, whereas a normal configuration will eventually sit at about 128mph.

So in a similar manner, if you increase the resistance to acceleration even a little, in the highest speed ranges, the impact on required power is more noticeable than you would think. This is also why there is a legitimate view that HS2 aiming for 225mph rather than a more standard 200mph is an unnecessary expense, as it greatly increases the energy requirement.

It's actually a cube root relationship between top speed and output power if air resistance is the dominant resistance at top speed. This because differentiating 'Work = Force integrated by displacement' with respect to time produces 'power = force x velocity'. And for air resistance the force is proportional to the square of speed. So at top speed (where the forces are equal) 'power / speed = drag_coefficient x speed x speed'. Leading to 'speed = cube_root(power/drag_coefficient)'

 

[hexagon789]

It’s to do with the inverse square relationship between power and acceleration. To get from 100mph to 125mph (an increase of 25%) you require double (200%) the power input compared to going from 0-100mph. This is why a 2+8 HST running on one power car will balance at about 100-105, whereas a normal configuration will eventually sit at about 128mph.

I think 128 is simply where the limited kicks in, not where the installed power will get you.

 

[absolutelymilk]

It's actually a cube root relationship between top speed and output power if air resistance is the dominant resistance at top speed. This because differentiating 'Work = Force integrated by displacement' with respect to time produces 'power = force x velocity'. And for air resistance the force is proportional to the square of speed. So at top speed (where the forces are equal) 'power / speed = drag_coefficient x speed x speed'. Leading to 'speed = cube_root(power/drag_coefficient)'

I think this has been noted on another thread, but note that of course energy required only goes as the square of speed because the power has to be applied for a shorter time if you are at higher speed, and energy = power x time.

 

[D1009]

Very interesting posts, which possibly explain the reasoning for not having the full power available at the higher speeds.

 

[hexagon789]

Very interesting posts, which possibly explain the reasoning for not having the full power available at the higher speeds.

Sightly off-topic, but the APT-P was designed with just enough power for 155 mph + 5% for reasons of efficiency and sure enough it's record was 162 nearly 5% over 155 mph.

 

[43096]

I think 128 is simply where the limited kicks in, not where the installed power will get you.

Correct. On GWR power cars the ATP will also kick in to prevent overspeed.

 

[hexagon789]

Correct. On GWR power cars the ATP will also kick in to prevent overspeed.

Forgot about that, though won't it technically only "warble" at 128? If it wasn't for the limiter you could get up to 131 before "intervention" braking with ATP.

 

[jyte]

I'm pretty sure the traction motors in an HST cut out at 128.

 

[hexagon789]

I'm pretty sure the traction motors in an HST cut out at 128.

I thought the limiter simply reverted the engine to idle and the driver would have to put the power controller to the OFF position, wait until speed dropped to 125 or less and then re-apply power. That's how I always understood it anyway, happy to be corrected on that.

 

[jyte]

I thought the limiter simply reverted the engine to idle and the driver would have to put the power controller to the OFF position, wait until speed dropped to 125 or less and then re-apply power. That's how I always understood it anyway, happy to be corrected on that.

Nope that's correct, I committed a technical inexactitude.

 

[hexagon789]

Nope that's correct, I committed a technical inexactitude.

No worries, I've lost count of the times I've done the same!

 

[PHILIPE]

Short of 800s this morning. 3 trains ex Swansea/Carmarthen and a Taunton to Paddington formed 5 Cars vice 10. GWR - More than usual undergoing repair.

 

[hexagon789]

Short of 800s this morning. 3 trains ex Swansea/Carmarthen and a Taunton to Paddington formed 5 Cars vice 10. GWR - More than usual undergoing repair.

Any particular issue?