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GWR "Castle" HSTs 16/01/2020 at 21:11 #122892
DaveHarries
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Hi,

I have established, for the purposes of making headway with my Exeter timetable and thanks to a forum post, which of the trains are booked to be worked by "Mini HSTs". I have them provisionally set as HST speed class too.

1. I used the length calculator and 2x 43s + 4x Mk3 coaches came in at 127m with a top speed of 125mph. Would that be correct?
2. What setting for the acceleration / brake rate for these units?
3. In terms of description are they 4-car Class 43 or 4-car Class 255? I believe I am right in thinking that these Mini HSTs were once referred to as either 254s or 255s.

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Dave

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GWR "Castle" HSTs 16/01/2020 at 21:26 #122893
Stephen Fulcher
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I believe they are restricted to a slower speed due to lower brake force with half the coaches.
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GWR "Castle" HSTs 16/01/2020 at 21:36 #122894
Steamer
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Stephen Fulcher in post 122893 said:
I believe they are restricted to a slower speed due to lower brake force with half the coaches.
100mph, as I understand it. I don't think there are any sections with a higher speed limit than this in the Exeter area anyway though?

Dave Harries said:
3. In terms of description are they 4-car Class 43 or 4-car Class 255? I believe I am right in thinking that these Mini HSTs were once referred to as either 254s or 255s.
"4-car Class 43" is definitely wrong; I don't know about 25x numbers. I think "HST (2+4)" would also be acceptable.

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GWR "Castle" HSTs 16/01/2020 at 21:39 #122895
Peter Bennet
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Do they run anywhere that's has 125mph provision?
Presumably, Class 43s were designed to work in 8/9 carriage formations so I think short-form trains have issues with braking which tends to require lower speeds.

Twice the power and half the weight (or something like that).

Peter

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GWR "Castle" HSTs 16/01/2020 at 22:05 #122896
Albert
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Motive power is not relevant for braking - what matters is the brake force instead. Many locos (I know for sure that this is the case on Cl. 66) have only one brake pad per wheel, whereas coaches and freight wagons have two per wheel. As such the ratio of brake force to weight is significantly lower for a loco than for a full train, and this limits such locos to 60 mph when running on their own.

Cl. 43 appears to have disc brakes instead, at every wheel, so it might well be able to brake properly on its own. Also, two class 43's and 4 carriages is in no way equal to a loco train. It means 24 axles with disc brakes for a ~275 tonne train or 40 axles with disc brakes for a ~410 tonne train, which means the ratio of brake force to weight decreases by just over 10%.

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Last edited: 16/01/2020 at 22:07 by Albert
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GWR "Castle" HSTs 16/01/2020 at 22:29 #122897
pedroathome
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The only section greater than 100MPH I believe is between Uphill Junction and Highbridge areas on Bristol PSB (Just south of Weston SM), which I believe is 110MPH. There again, stopping at all stations, how achievable this speed is, I wouldn't know

Class 43 though is the good old fashioned BR(WR) warship class. Definitely not the HST power cars (This comment should keep JamesN happy)

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GWR "Castle" HSTs 16/01/2020 at 23:00 #122898
Albert
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Thanks for the correction I can see on some pictures though that those had 2 brake pads per wheel, so neither should they have any problems running at top speed with a low number of carriages.
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GWR "Castle" HSTs 16/01/2020 at 23:11 #122900
jc92
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Most of the 2015/19 timetables are expressed as HST 2+x where X is the number of coaches. I think this is the best option so the signaller knows how long the set is.
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GWR "Castle" HSTs 16/01/2020 at 23:22 #122901
JamesN
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The castle sets are officially recorded as Class 255 (or 257 for slam-door variant), and in 2+4 guise are permitted to run at the full 125mph if in full working order. That drops to 100 if formed 2+3, but we haven’t had one of them for a while.
Last edited: 16/01/2020 at 23:22 by JamesN
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GWR "Castle" HSTs 16/01/2020 at 23:24 #122902
DaveHarries
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Thanks all for your replies. Best settings, as I see it, would be Train Length 110m @ 125mph; speed class HST. Others as default. (HST 2+8 given as 220m on one of the Hereford timetables and 219m on an Exeter TT).

Dave

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GWR "Castle" HSTs 16/01/2020 at 23:28 #122903
JamesN
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17+4x23+17 = 126m

The power cars are much shorter than the trailers, so it’s not exactly half a 2+8. 110m would be too short.

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GWR "Castle" HSTs 17/01/2020 at 14:15 #122906
John 23
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Yes, they have disc brakes. Attached is my photo of a skip full of scrap brake pads taken a couple of years ago on a tour of Laira.


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GWR "Castle" HSTs 17/01/2020 at 15:42 #122907
postal
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DaveHarries in post 122902 said:
Best settings, as I see it, would be Train Length 110m
If you calculated the length correctly (give or take a metre) in your first post, why the change to a guesswork answer?

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GWR "Castle" HSTs 17/01/2020 at 18:06 #122909
lazzer
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I drove two 2+4 sets earlier this week, and can confirm that they accelerate like the proverbial waste material off a shovel ...

Their acceleration from a stand in full power is only marginally slower than a light loco in my opinion. Having driven 2+8 HSTs for many years, I feel that the braking capability is only slightly worse in a 2+4 set, if at all. You can certainly attack platforms with the same confidence that you could have in a full-length set.

As a matter of interest, on the sliding door sets (where a traction interlock light is provided in the cab) if you put the brake handle into initial (step one) when at a stand and with interlock broken, the train will automatically apply step 3 brake. You can only bring the brake back below step 2 when interlock is gained again. I assume this is some kind of safety feature that was specified when installing the interlock equipment.

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GWR "Castle" HSTs 17/01/2020 at 18:10 #122910
lazzer
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JamesN in post 122903 said:
17+4x23+17 = 126m

The power cars are much shorter than the trailers, so it’s not exactly half a 2+8. 110m would be too short.
As power cars are exactly 17.79m long, I would err on the side of caution and do (23m x 4) plus (18m x 2) = 128m.

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GWR "Castle" HSTs 17/01/2020 at 20:10 #122911
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Presumably, these short formed (2+4) HSTs still obey any HST and DMU speed differentials?
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GWR "Castle" HSTs 17/01/2020 at 20:27 #122912
lazzer
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JamesN in post 122901 said:
The castle sets are officially recorded as Class 255 (or 257 for slam-door variant), and in 2+4 guise are permitted to run at the full 125mph if in full working order. That drops to 100 if formed 2+3, but we haven’t had one of them for a while.
As stated in the Class 255 traction manual issued to drivers, the maximum speeds are as follow:

2 Power cars and 4 trailer vehicles - 100 mph
2 Power cars and 3 trailer vehicles - 90 mph
2 Power cars and 2 trailer vehicles - 75 mph

Also, provision is made to run the trains as "loco and coaches" (where the 36-way jumper cable between the rearmost coach and the rear power car disconnected, and the rear power car therefore does not power the train). In such cases the speeds would be:

Power car with 1, 2 or 3 vehicles (with the rear power car counting as one vehicle) - 75 mph where linespeed is 90 mph or above, and 60 mph where linespeed is 85 mph or below.

Power car with 4, 5 or 6 vehicles (with the rear power car counting as one vehicle) - 90 mph where linespeed is 100 mph or above, 80 mph where linespeed is 90 or 95 mph, and 75 mph where linespeed is 80 or 85 mph.

To answer a more recent question about obeying HST/DMU speeds - HSTs were always classed as MU trains for speed board purposes, and so far as I am concerned we can run at MU speeds where an MU speed is specifically stated (for example, going onto the single line at Largin between Liskeard and Bodmin Parkway the differential speed is "40 over MU 55". So we can go 55 once clear of the crossover onto the single line).

So far as I know, 2+4s can go at speeds specified as "HST" on speed boards, so long as they don't break the limits imposed by the tables above.

Last edited: 17/01/2020 at 20:37 by lazzer
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GWR "Castle" HSTs 18/01/2020 at 00:22 #122915
DaveHarries
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JamesN in post 122901 said:
The castle sets are officially recorded as Class 255 (or 257 for slam-door variant), and in 2+4 guise are permitted to run at the full 125mph if in full working order. That drops to 100 if formed 2+3, but we haven’t had one of them for a while.

Saw a 2+3 at Bristol Temple Meads on 10th January.
Dave

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