How fast dare they push an multiple unit with doors on the front?

[NightatLaira]

As far as I'm aware no multple unit with doors on the front exists on today's UK railway that will go past 100mph.

But having read the DFT's requirements for a 125mph+ proposal to replace the HST fleet I can't help feeling that head end power is 'off the cards'.

They're wanting the train to be splittable, but properly joinable as well (like a 158/desiro/electrostar etc - so how are they going to do this, and get it to fast also?

Is there a limit to how fast something with doors on the front can go? And what about the flatish front end? Don't you need a slanted front to go much beyond 110mph?

 

[Bevan Price]

Is there a limit to how fast something with doors on the front can go? And what about the flatish front end? Don't you need a slanted front to go much beyond 110mph?

Putting it simply - you don't need a slanted front, but having one is thought to reduce the front-end "wind" resistance, so that you need less energy to reach 110+ mph than with a flat front.

Bevan

 

[Clip]

As far as I'm aware no multple unit with doors on the front exists on today's UK railway that will go past 100mph.

But having read the DFT's requirements for a 125mph+ proposal to replace the HST fleet I can't help feeling that head end power is 'off the cards'.

They're wanting the train to be splittable, but properly joinable as well (like a 158/desiro/electrostar etc - so how are they going to do this, and get it to fast also?

Is there a limit to how fast something with doors on the front can go? And what about the flatish front end? Don't you need a slanted front to go much beyond 110mph?

Dont EMT join 2 of their together and split them? mind i have no idea of what speed they get up to but it is doable. though the need for 2 ticket inspectors would increase the cost of this

 

[ainsworth74]

Dont EMT join 2 of their together and split them?

The only 125mph stock that EMT have is 222s and HSTs neither of which have gangway connectors between units or sets. So the OP's point still stands that there is no 125mph stock with gangways, I can't see why it couldn't be done however.

 

[TEW]

Stock running above 100mph needs a certain amount of space between the passenger seats and the front of the train which makes having flat fronts very impractical.

 

[Domeyhead]

I suspect the front end's loss may be the back end's gain with corridor-joined units. Automotive research around 20 years ago noticed that a "streamlined" backend shape actually induces drag compared to a "flat" back that creates a large vortex which permits the object to proceed leaving its turbulence behind. This is why aircraft started putting a short upward spur on the end of aircraft wings to induce a vortex at the end of the wing. Eagles do this in nature by the way
Anyway, at Reading station every morning I observe a Cross Country class 220 with sloping "gofaster ends on platform 8 and over on platform 1 a good old SWT Alsthom class 458 with a very unnatractive front and back end and I reckon there is not much in it! (ie they would both break down side by side 100 yards outside the station)

 

[jopsuk]

The winglets thing is a bit more complicated than that to say the least- without winglets the very end of a wing essentially produces no lift.

The French run 125mph (200km/h) Corail services using rather blunt locos and no aerodynamic rear coach.

It is possible to design an efficient "aero" rear, however this will be a different shape from an efficient aero front. There's been some good recent research in Japan- the Fastech 360 was an interesting test bed. Umtoimately with high-speed units a trade off is made to allow bi-directional use.

 

[YesToHS2]

What was wrong with the 125mph 180s that were supposed to run on the GWML? I'm assuming tilt isn't an issue on the line so it's not as if a 221 style unit is required. If the plan is to replace the HSTs with more diesels it be be quite easily done surely. It seems a lot more straight forward than the WCML

 

[PaulLothian]

Class 380 has a sloping front (not very sloped, admittedly) and corridor connections. Don't know how much the aero-dynamics are a worry with its maximum speed.

 

[Lampshade]

A beefed up 444 could probably do 125 without too many problems.

 

[route:oxford]

Class 380 has a sloping front (not very sloped, admittedly) and corridor connections. Don't know how much the aero-dynamics are a worry with its maximum speed.

Isn't the plan to use 380 derived units at 125mph between Glasgow & Edinburgh?

 

[Electrostar]

According to Wikipedia, these flat-fronted Danish multiple units have a top speed of 112mph.

http://en.wikipedia.org/wiki/IR4

 

[ainsworth74]

What was wrong with the 125mph 180s that were supposed to run on the GWML?

They had truly terrible reliability when first introduced with FGW, so eventually FGW got fed up with them and replaced them with HSTs (I think) that First bought itself (much to the annoyance of DfT). It's only in the last few years that the 180s have actually been reasonably reliable.

 

[YesToHS2]

They had truly terrible reliability when first introduced with FGW, so eventually FGW got fed up with them and replaced them with HSTs (I think) that First bought itself (much to the annoyance of DfT). It's only in the last few years that the 180s have actually been reasonably reliable.

Same problems with the 175s, based around the same design. The 175s now though are thought to be amongst the most comfortable medium distance train currently serving in the UK, so I read. They only had a few minor problems, air con not working, brakes failures, doors jamming, small things lol. All fixed now though. I was just wondering if they are less efficient than HSTs or there are other problems with fast DMUs in general , if network rail aren't going to electrify the whole route the only other option is new high speed DMUs.

 

[rail-britain]

Isn't the plan to use 380 derived units at 125mph between Glasgow & Edinburgh?

Yes, that is the plan but the units will not have end corridors connections; internal gangways only
The units are expected to be five cars in length

 

[PaulLothian]

Yes, that is the plan but the units will not have end corridors connections; internal gangways only
The units are expected to be five cars in length

Which may reduce the likelihood of unexpected short formations turning up in rush hours!

 

[me123]

Yes, that is the plan but the units will not have end corridors connections; internal gangways only
The units are expected to be five cars in length

5 carriages? Does that mean that 10 carriage trains will be operating, or will they be limited to 5? Because 5 will be a reduction on what's currently available (ie 6 carriages in the rush hour if all goes to plan). And 10 would be too long for Queen Street I would have thought.

 

[Kneedown]

Trust me on this, from a Drivers point of view you definitely don't want 125mph units with gangways.
What with all the draughts and whistlin and water ingress they're terrible when you get to 60mph.
15X's been in service since the mid to late 80's now, and no ones ever been able to come up with a reliable seal on the gangway doors.

 

[jopsuk]

Those Danish-built units though are a rather different prospect for the drivers I'd have thought- look at the huge pins used to secure the large central door.
The Japanese meanwhile seem to go for what Alsthom didn't really get right with the 458- full retractable gangways with outer doors that seal over.

 

[CosherB]

Automotive research around 20 years ago noticed that a "streamlined" backend shape actually induces drag compared to a "flat" back that creates a large vortex which permits the object to proceed leaving its turbulence behind. This is why aircraft started putting a short upward spur on the end of aircraft wings to induce a vortex at the end of the wing. Eagles do this in nature by the way

Not quite. Any flat backed or flat fronted vehicle will produce prodigious amounts of drag compared to one that tapers at the ends. There aren't any flat backed or flat fronted aeroplanes for that reason. If a shape is producing a lot of turbulance, then it's also producing a lot of drag. Take a look at the flat back of an estate car that's not been washed recently - it will be filthy with road grime that gets sucked up from below because of this turbulence.

And winglets are ther to reduce the drag at the wingtips - the induced drag. A wing in flight has higher pressure air beneath it than above it, which is what produces the lift the keeps the aeroplane in the air. At the tip, the high pressure air from under the wing slips around the tip to the low pressure area above the wing. As the aeroplane is moving forwards, the result is a vortex of air trailing off each wingtip. Watch an aeroplane landing on a damp day and these vortices can be seen as vapour trails off each tip; as the high pressure air reduces its pressure as it rounds the tip, it can, if saturated, no longer hold as much water in saturation and the excess condenses out into visible vapour.

The pressure difference above and below the wing is far greater when landing because the wing is at a higher angle of attack (angle between the wing and the airflow) in order to generate enogh lift for flight at the much lower speed of landing than of cruise (indicated airspeed in cruise, about 300 knots. On the landing approach, about 120 knots).

A winglet doesn't eliminate wing tip vortices, but it greatly reduces their intensity and therefore their drag on the aeroplane.

 

[O L Leigh]

Trust me on this, from a Drivers point of view you definitely don't want 125mph units with gangways.
What with all the draughts and whistlin and water ingress they're terrible when you get to 60mph.
15X's been in service since the mid to late 80's now, and no ones ever been able to come up with a reliable seal on the gangway doors.

Agreed. Try a Cl150 cab (identical in all major respects to a Cl317) at 90mph.

We've had gangway doors taped up with masking tape, some with strips of self-adhesive foam like you get at B&Q and some with the gaps plugged with handfuls of newspaper or even that blue paper roll you get in messroom toilets. And then there are the ones they don't bother with at all which have gaps so big you can see daylight even without having to crouch down to see it and let in so much air that they overwhelm both heaters. One thing is certain, you NEVER put your bag on the floor. When it rains it's not a case of if water will come in but when and in what quantities.

O L Leigh

 

[CarterUSM]

With the 380's , apparently there isn't a hint of a draught coming through the gangway end. Though perhaps that'll change after a few years of use!

 

[The Decapod]

And what about the flatish front end? Don't you need a slanted front to go much beyond 110mph?

A French electric loco "BB 9004" hauled 3 carriages at 205 mph (331 kph) on test in 1955 - that loco had a flat-ish front end, if somewhat rounded off in plan view.

See: http://www.railpictures.net/viewphoto.php?id=217349

 

[Kneedown]

And then there are the ones they don't bother with at all which have gaps so big you can see daylight even without having to crouch down to see it

O L Leigh

You know you've got one of them when you hit a pigeon and the feathers end up in the cab swishing around your head!
--- old post above --- --- new post below ---

With the 380's , apparently there isn't a hint of a draught coming through the gangway end. Though perhaps that'll change after a few years of use!

Give it 6 months

 

[NightatLaira]

I really do despair with the DfT sometimes...

I've got nothing against EMUs or DMUs, but it's a ludicrous waste of resources to order a bulk batch of 5 car units, with no external gangways and then have the 2 of these units joined together therefore needing two sets of separated crews to run a service that could otherwise have served by one team on a fully joined 8,9 or 10 car service.

If multiple units with external gangway doors can't be made water and airtight then maybe we should have a return to loco-hauled and some nice new mk5 coaching stock that's easily splittable?

I'll just about tolerate these 2x5car or 2x4car diagrams at the moment because of lack of available stock, in the same way that I tolerate Virgin running diesels under the wires to a certain extent. But to make these sorts of decisions for the future in the full knowledge that you're ordering something inappropriate just seems to me to be insanity!

 

[Aictos]

Agreed. Try a Cl150 cab (identical in all major respects to a Cl317) at 90mph.

We've had gangway doors taped up with masking tape, some with strips of self-adhesive foam like you get at B&Q and some with the gaps plugged with handfuls of newspaper or even that blue paper roll you get in messroom toilets. And then there are the ones they don't bother with at all which have gaps so big you can see daylight even without having to crouch down to see it and let in so much air that they overwhelm both heaters. One thing is certain, you NEVER put your bag on the floor. When it rains it's not a case of if water will come in but when and in what quantities.

O L Leigh

The 313s used by FCC are like that, when it rains the vestibule area by the cab can and does get very wet, you certainly don't want to place your bag on the floor.

 

[TGV]

Regarding the "flat rear end" discussion - the earlier post is incorrect. The flat rear facing end of any vehicle creates a HUGE amount of pressure drag - more so than the leading end which may be contrary to many peoples thoughts. The sloping of the leading end of a train is more for wind noise and comfort than actual aero resistance, although it will have an effect there too. The trailing end of a vehicle generally has more of an effect on drag than the leading end.

However with the narrow top speed ranges that most trains travel in (90-125mph) and the fact even a modest EMU these days has around 2000hp or more, the flat front makes very little difference to power consumption for a given speed. The cross-sectional (or "frontal") area makes a large difference and in this respect, most trains are very similar being built to the same loading gauge (or within a few inches of each other anyway). The two main factors are pressure drag (due to the geometry of the front and particularly rear end, and the area exposed to flow) and skin-friction drag - that's the shear forces of the air as it "rubs" over the sides, roof and undersides of the train. Skin friction drag will increase as the length of the train is increased. Also increased on rolling stock with under-frame equipment exposed instead of streamlined like Mk3, Mk4, Eurostar carriages etc... However the pressure drag will be less affected.

The fastest I know of a gangwayed front end train going was that 3rd rail world speed record between Farnborough and Basingstoke where they got some EMU up to 108mph. That's not to say something somewhere else has been faster, just that it's the fastest I can think of right now.

 

[moonrakerz]

What was wrong with the 125mph 180s that were supposed to run on the GWML?

Apart from the reliability problems, the 180s just show the complete lack of understanding of the people who bought these things.

The HSTs already running on this route were not big enough and had already been increased from 2 +7 to 2 + 8. So the master stroke was to buy 5 car units. These could then be joined into 10 car trains at peak times - Yeah !
Because there was no gangway between the 2 halves of the the train it was impossible to move around the train. The result was that half the train was even more crowded than ever and half the train was nearly empty - this ratio, and location of the overcrowding, was variable, depending on the weather and the locations of the platform access at the stopping points of the train.
Apart from which; they were noisy, they looked cheap and "plasticky" inside - but they did ride well - on the odd occasion that they managed to get up to line speed.

 

[CosherB]

....So Northern have them. 125mph trains used on local stoppers Hazel Grove to Preston! :roll:

 

[MCR247]

Better than them running empty at 125 from Doncaster - London all day.