Class 91: Why do they have a lower top speed blunt end first?

[greyman42]

Why do Class 91 sets have a slower maximum speed when blunt end running ?

 

[gazthomas]

Why do Class 91 sets have a slower maximum speed when blunt end running ?

Reduced crash protection and more air resistance I would guess.

 

[BestWestern]

Is it technically possible to drive them a full belt from the slab end?

 

[D365]

Is it technically possible to drive them a full belt from the slab end?

Yes, I can't remember exactly how the wind resistance effect changes though.

 

[coppercapped]

Yes, I can't remember exactly how the wind resistance effect changes though.

What goes around, comes around...

I remember that the same question was asked when the locomotives first came out. IIRC the answer then was that they could do, as they have enough power to overcome the increase in air resistance, but as the pantograph is nearer the 'blunt' end of the roof the air flow eddies off the 'blunt' end are such that it finds it more difficult to remain in contact with the overhead.

 

[91104]

They must have been cleared for 125mph blunt end first once upon a time as I remember one of my first jobs when I started as an apprentice at Bounds Green in 1991 was to change the max speed stickers in the cabs from 125mph to 110mph in the no 2 cab and from 140mph to 125mph in no 1 cab.

 

[AnonymousUser1]

Yes, I can't remember exactly how the wind resistance effect changes though.

it;s not only blunt end first, the slope of the cl 91 'sharp' end ( and that of the class 43 sharp end ) is steeper than a class 90 or even the 89 - meanign there is a turbulent ari thing going on betwee nthe trailing sloped cab and the the TO(E) - be even worse if you were hauling sharp cab to DVT cab

 

[goblinuser]

They must have been cleared for 125mph blunt end first once upon a time as I remember one of my first jobs when I started as an apprentice at Bounds Green in 1991 was to change the max speed stickers in the cabs from 125mph to 110mph in the no 2 cab and from 140mph to 125mph in no 1 cab.

Interesting the rear speed was reduced from 125 to 110 alongside forgetting about 140mph operation altogether.

 

[jopsuk]

Not all 125mph locos are particularly obviously aero- eg the French BB22200 locos, which can do 200km/h hauling standard corail type coaches with no aero coach on the rear.

 

[Prestige15]

Not all 125mph locos are particularly obviously aero- eg the French BB22200 locos, which can do 200km/h hauling standard corail type coaches with no aero coach on the rear.

So does American's Amtrack

 

[TimboM]

I'm sure this question cropped up on another thread somewhere not too long ago...

I don't think the pantograph aerodynamics is the key reason - it evidently was designed to go 125 mph blunt end first and also the pantograph travels both ways every day in normal service and subject to all sorts of different turbulences and forces depending on direction of travel, wind direction/speed, OHLE tension etc. etc. 91010 also famously achieved 161.7 mph on test ('sharp' end first admittedly) so the pans should really be able to cope.

I suspect it's for efficiency reasons in that it could go 125 mph blunt end but doesn't ever really need to, and with the aerodynamics of the "slab" the power draw is that much higher, so to reduce electricity loads/costs they're restricted to 110mph.

 

[FOH]

I got a tour once and the guy conducting it said it was due to the extreme suction effect on passed platforms and there was no reason for special trackside signage since the chances of it being used were minimal

 

[hexagon789]

I was told that the 110 mph limit on blunt-end first running was due to excessive wind noise around the cab making it difficult for drivers to hear the AWS and DSD.

 

[noddingdonkey]

If the loco hypothetically was slab end first but the consist was driven from the DVT at the other end, would it be limited to 110mph?

 

[AnonymousUser1]

If the loco hypothetically was slab end first but the consist was driven from the DVT at the other end, would it be limited to 110mph?

ifit;s the wind noise / vibration arguement , quite possibly, but it would depend what the official book of words said , as after all when coupled to a mk4 rake + DVT they run at 125 mph bluent end first but not blunt end exposed ...

 

[TimboM]

If the loco hypothetically was slab end first but the consist was driven from the DVT at the other end, would it be limited to 110mph?

Not as hypothetical as you may think... https://flic.kr/p/HwME4y (not mine)

I've no idea how fast it was permitted to go...!

 

[SpacePhoenix]

What would be the most common/likely reason for a 91 being blunt end first rather then "pointed" end first?

 

[Ianno87]

What would be the most common/likely reason for a 91 being blunt end first rather then "pointed" end first?

Normally either:
-when some sort of failure means the loco (or a loco) has to be placed on the London end of the train to 'pull' the train towards London conventionally, such as with a dead loco on the back or a TDM failure (with no means of turning the loco around), or
-occasionally, if some sort of failure only affecting the pointy end cab (e.g. AWS, air conditioning) so the loco is placed on the country end, but the other way around. Although there aren't many places that this can be done (Gateshead triangle?) so this scenario is rare.

 

[507 001]

Normally either:
-when some sort of failure means the loco (or a loco) has to be placed on the London end of the train to 'pull' the train towards London conventionally, such as with a dead loco on the back or a TDM failure (with no means of turning the loco around), or
-occasionally, if some sort of failure only affecting the pointy end cab (e.g. AWS, air conditioning) so the loco is placed on the country end, but the other way around. Although there aren't many places that this can be done (Gateshead triangle?) so this scenario is rare.

ISTR that there was a requirement for push pull trains to run Loco first if there is snow on the ground. The idea being that if the entire train passes before the Loco, disturbed snow might be pulled into the Traction motor Blowers.

 

[Ianno87]

ISTR that there was a requirement for push pull trains to run Loco first if there is snow on the ground. The idea being that if the entire train passes before the Loco, disturbed snow might be pulled into the Traction motor Blowers.

WCML Mk3 sets heading over Shap/Beattock *had* to be loco-led in Winter months, as I recall; though I think that was more to with the risk of a 'lightweight' DVT leading the train derailing by hitting a snow drift/strong gust of wind.

 

[61653 HTAFC]

What would be the most common/likely reason for a 91 being blunt end first rather then "pointed" end first?

As others have said, usually a fault on the DVT when heading south. My one time behind a blunt 91 was due to a speedo defect on the DVT. Sat at Peterborough for 15mins while they decided whether to cancel, in the end 91023 (as-was) ran round and hauled south.

Do those snow rules still apply? I don't recall noticing it in recent snowfall periods.

 

[DarloRich]

What would be the most common/likely reason for a 91 being blunt end first rather then "pointed" end first?

it ( or the DVT) is broken somehow or the loco working light.

My only time blunt end first was when a DVT failed at Doncaster on Kings Cross service and the 91 was unhooked and run round to carry on south. Very exciting!

PS i wonder what the ride quality is like running quickly slab end first?

 

[alexl92]

What would be the most common/likely reason for a 91 being blunt end first rather then "pointed" end first?

Not relevant anymore but when built it was envisaged that they'd be used ECML expresses during the day and parcels traffic overnight; when running southbound on the parcels traffic, the loco wouldn't have been turned so it would have run blunt end first for that.

As we are on the topic, does anyone know if there's a particular reason why the sets face north, with the loco on the country end? Or is that 'just how it is'?

 

[Roast Veg]

As we are on the topic, does anyone know if there's a particular reason why the sets face north, with the loco on the country end? Or is that 'just how it is'?

It guarantees that first class is always in the same location, as the location of the DVT is fixed.

 

[AnonymousUser1]

What would be the most common/likely reason for a 91 being blunt end first rather then "pointed" end first?

instrument failure in pointy cab ,

wiper failure in pointy cab ,

horns or lights failed at pointy cab

winscreen / cab side window / door window broken in pointy cab

DVT failure for similar reasons or the 'remote' control of loco from the DVT play ing meaning it;s easier to just run the loco round the rake and if the loco isn;t turned it'll be blunt end first

 

[HSTEd]

As we are on the topic, does anyone know if there's a particular reason why the sets face north, with the loco on the country end? Or is that 'just how it is'?

As I understand it is just a tradition that first emerged once push pull operation started on the WCML.

Except at Crown Point [Norwich] where the loco I believe is on the south end of the set because of the position of the depot

 

[jopsuk]

Not relevant anymore but when built it was envisaged that they'd be used ECML expresses during the day and parcels traffic overnight; when running southbound on the parcels traffic, the loco wouldn't have been turned so it would have run blunt end first for that.

As we are on the topic, does anyone know if there's a particular reason why the sets face north, with the loco on the country end? Or is that 'just how it is'?

out of London, on the intercity operators, 1st class is at the London end. Keeps the noisy loco away from 1st and away from the buffer stops in London. The GEML went against that due to issues with the depot at the Norwich end.

 

[Ianno87]

As I understand it is just a tradition that first emerged once push pull operation started on the WCML.

Except at Crown Point [Norwich] where the loco I believe is on the south end of the set because of the position of the depot

Correct, so in the 91s' case, the loco can be released if necessary at Kings Cross to reach Bounds Green depot (WCML sets were the same at Euston to reaches Willesden).

 

[robbeech]

I'm not sure about the whole "efficiency" thing of 125mph running blunt end first. One would think that if a loco was able to (and permitted to) run at 125mph blunt end first then in order to not lose additional time the TOC would expect this to happen, after all, it's possible that a failed DVT at a station along the ECML might be able to run around and reattach in less than an hours delay which may or may not keep the overall delay down if it can (perhaps with reduced acceleration due to different aerodynamics) run at 125mph. So if this is not the case i would guess (and it is a guess) that the reason for reduced speed will be one of the other reasons stated.

One question i have always had in my head about this is the freight operations they were planning on doing with these. In my mind, i see the advantages of the second cab at the blunt end, but i don't see the reasoning behind using that end to haul freight, or the sleeper, or something else, regardless of the lower required speed. they're the same gearing each way (much much too high for heavy freight we can surely agree) so was it just because of the lack of turning ability at various stations?

 

[najaB]

...but i don't see the reasoning behind using that end to haul freight, or the sleeper, or something else, regardless of the lower required speed. they're the same gearing each way (much much too high for heavy freight we can surely agree) so was it just because of the lack of turning ability at various stations?

I don't think the idea was they would *only* haul sleepers/freight blunt end first, but rather that since they wouldn't be doing 140mph there was no need to make both ends aerodynamically efficient.