Why did the class 91s need a flat cab for freight operations?

[ProbablyIdiot]

Hello,
I know that the class 91s were designed to be used as freight locos when they weren't doing passenger service (even though it never ended up happening) - but I've always wondered why dd they need a specifically made flat cab for freight operations. I know aerodynamics isn't needed on a freight loco, but surely if you just already had an aerodynamic cab, it wouldn't be an issue?

 

[yorkie]

Hello,
I know that the class 91s were designed to be used as freight locos when they weren't doing passenger service (even though it never ended up happening) - but I've always wondered why dd they need a specifically made flat cab for freight operations. I know aerodynamics isn't needed on a freight loco, but surely if you just already had an aerodynamic cab, it wouldn't be an issue?

Are you sure it was stated that they "needed a flat cab for freight operations", and if so, where was this stated please?

Surely it's more the other way round, i.e. you would only expect one cab to be aerodynamic unless there was a very good reason for both to be?

 

[Alfonso]

The flat cab isn't needed to make it more aerodynamic when going flat cab first but to make it more aerodynamic when going pointy end first as it eliminates the area of turbulence you'd otherwise have between the back cab and the carriages. It's similar to the way modern articulated trucks have a relatively small gap between the tractor unit and the trailer

 

[ProbablyIdiot]

Are you sure it was stated that they "needed a flat cab for freight operations", and if so, where was this stated please?

Surely it's more the other way round, i.e. you would only expect one cab to be aerodynamic unless there was a very good reason for both to be?

The asymmetric body style is streamlined at one end to allow high speed operation with the fixed sets of Mark 4 coaches in push-pull operation. An additional requirement of the design was that they could operate as normal locomotives. This led to a second cab being incorporated into the 'flat end'.

British Rail Class 91 - Trains

train.spottingworld.com

 

[edwin_m]

Also, if the second cab had been aerodynamic, it would have needed more length for the sloping front so the cab would have been further in from the end of the loco. Thus the loco might have needed to be longer and heavier to contain all the traction equipment.

 

[yorkie]

British Rail Class 91 - Trains

train.spottingworld.com

Your post is empty/blank, but the source you cite doesn't say what your opening post says (unless I've misunderstood what you are asking exactly).

 

[Snow1964]

Not so much a flat cab, but simply a cab both ends, which had been policy for electric locos for decades.

When the decision was made in mid 1980s to electrify ECML, there was assumption that part of the operations would be similar to West Coast with the locos working some freight/parcels/sleeper overnight. A better question might be why did the thinking change around 1990 before they went into service.

 

[DarloRich]

If you didn't have a flat end you would have a class 89......

 

[Ashley Hill]

Perhaps InterCity didnt want the pride of the East coast seen pulling freight in a streamlined manner . Or possibly saving the cost of two streamlined cabs.

 

[norbitonflyer]

Perhaps InterCity didnt want the pride of the East coast seen pulling freight in a streamlined manner .

They would have been able to haul freight from either end. As others have observed, the assymetric design was for aesthetic and aerodynamic reasons - avoiding having a wedge-shaped gap between the loco and first carriage, as you have for example with a Class 68 or class 90.

 

[Shimbleshanks]

Hello,
I know that the class 91s were designed to be used as freight locos when they weren't doing passenger service (even though it never ended up happening) - but I've always wondered why dd they need a specifically made flat cab for freight operations. I know aerodynamics isn't needed on a freight loco, but surely if you just already had an aerodynamic cab, it wouldn't be an issue?

It possibly didn't happen for freight but I do remember arriving from Hull at Kings Cross in the late 1980s or 1990s to find a class 91 attached to our train 'flat side first'. So the flat cabs were used to some extent.

 

[61653 HTAFC]

It possibly didn't happen for freight but I do remember arriving from Hull at Kings Cross in the late 1980s or 1990s to find a class 91 attached to our train 'flat side first'. So the flat cabs were used to some extent.

It definitely happened on occasion. Recall being on a Leeds to London run in GNER days which ground to a halt north of Peterborough. After sitting for what was probably ten minutes but felt much longer, the guard came on the PA system to say there's a fault with the cab at the front, so we're bringing a spare round from the back! Moments later our 91 trundled past "backwards" and within another ten minutes we were on our way.
Getting to the Cross and walking down to see our backwards 91 alongside the Class 89 with its own rake in reverse formation, makes me wish camera phones had been invented a few years earlier, as it would have been an unusual sight even then.

 

[norbitonflyer]

Saw them running flat end forward occasionally. Most likely reasons would be
-problem with control signals between DVT and loco
-problem with DVT cab (eg broken windscreen or AWS fault
- rake facing the wrong way - for example if it has been to Leeds via Temple Hirst, or Newcastle via the High Level bridge, and subsequently swapped locos with another rake.
The first two examples would see the loco coupled to the DVT, pointy noses together. The third would see the loco coupled to the "correct" end of the rake, but back to front.

Were they subject to a lower speed limit when running "bunker first"?

 

[GW43125]

Were they subject to a lower speed limit when running "bunker first"?

110mph.

 

[Western Lord]

The Class 91 was never intended for freight. They are high speed passenger locomotives and are geared as such. The blunt end was, as has been mentioned above, for aerodynamic reasons when running with rakes of Mk. 4 coaches. It was originally intended that they would be used on sleeper trains (before they all migrated to the WCML) and in this use they would have operated as normal locomotives with either end leading.

 

[themiller]

The 91s were designed to power mk4 coaches in push-pull mode. The locos were intended to work these trains at 225kph (140mph) which led to their streamlined leading cab. They were also intended to haul overnight freight which is why they were always at the country end at Kings Cross. Freight trains don’t need the streamlined cabs so the second one was flat fronted to minimise turbulence between loco and coaches which is why, on the rare occasions that they ran flat end first on passenger trains, they were limited to 100mph.

 

[sjpowermac]

Hello,
I know that the class 91s were designed to be used as freight locos when they weren't doing passenger service (even though it never ended up happening) - but I've always wondered why dd they need a specifically made flat cab for freight operations. I know aerodynamics isn't needed on a freight loco, but surely if you just already had an aerodynamic cab, it wouldn't be an issue?

Hello and welcome to the forum.

From the article that you quoted, I think you are possibly referring to this part:

This led to a second cab being incorporated into the 'flat end'.

If there were not the requirement to be able to haul freight, then it is possible that the Class 91s might have been constructed in a similar way to the HST power cars and without a second cab.

As others have commented, the blunt end of the Class 91 is for aerodynamic reasons, so that it’s more ‘flush’ to the Mk4 coaches (I won’t pretend to understand fully the science of aerodynamics!).

In the time between the Class 91s being specified and their entry into service, the organisation of railways in Britain had changed quite a bit.

Whereas previously it was usual practice for a loco to haul passenger trains during the day and freight or mail at night, with ‘Sectorisation’ of the railways ‘InterCity’ was separated from the freight companies, largely with each being responsible for their own locomotives.

In addition, the Class 91s were very intensively utilised on passenger workings and I don’t think there would have been time for them to be used on anything other than InterCity work.

In the end, there were very few instances of Class 91s working anything other than passenger trains. I was fortunate to see one once on a mail train (slab end leading).

It was fortunate though that the Class 91s did have two cabs. The loco/Driving Van Trailer communication system had problems in the early days, as did the cab air conditioning. It was not at all unusual to see Class 91s hauling Mk4 sets attached to the DVT or even on occasion with the ‘pointed’ end of the loco attached to the Mk4 coaches.

Freight trains don’t need the streamlined cabs so the second one was flat fronted to minimise turbulence between loco and coaches which is why, on the rare occasions that they ran flat end first on passenger trains, they were limited to 100mph.

A small point, but I think the speed limit was 110 mph when Class 91s operated blunt end forward with Mk4 stock.

 

[themiller]

For interest, there’s an episode of Equinox on YouTube about the class 91s called Running to Time charting their design through to introduction.

 

[norbitonflyer]

The 91s were designed to power mk4 coaches in push-pull mode. The locos were intended to work these trains at 225kph (140mph) which led to their streamlined leading cab. They were also intended to haul overnight freight which is why they were always at the country end at Kings Cross. Freight trains don’t need the streamlined cabs so the second one was flat fronted to minimise turbulence between loco and coaches which is why, on the rare occasions that they ran flat end first on passenger trains, they were limited to 100mph.

Most push-pull formations ran with the loco at the "country end" and the DBSO or DVT at the London end, to allow easy exchange of locomotives if required at the London terminus. This also meant passengers did not have to walk past the loco to reach the nearest carriage, and in the case of a DVT, the luggage van. An exception was the Norwich line - because the main depot was at Norwich, not London, they ran with the loco at the London end.

The Edinburgh/Glasgow class 47/7s were maintained at Eastfield (Glasgow) rather than Haymarket because there was an operating requirement to have the DBSO at the Glasgow end of the train - if I recall correctly there had to be a member of the crew in the rearmost veicle of a train climbing Cowlairs bank, which would not be the case if the DBSO was at the Edinburgh end (as both the guard and the driver would be in the leading vehicle)

 

[xotGD]

91s did operate parcels trains on a few occasions. Presumably blunt end first when heading southbound.

 

[507 001]

There was a booked working for 91s on a train originating IIRC from Hull in the early days. This was usually formed of mk2 stock.

 

[Spartacus]

One benefit of the slab end I've not seen mentioned elsewhere is that it makes coupling up at that end easier than it otherwise would be. Not a big issue with a 91, but still..

 

[D6975]

There was a booked working for 91s on a train originating IIRC from Hull in the early days. This was usually formed of mk2 stock.

Close - it was from Bradford. The stock was those re-seated high density seated ones.

 

[sprinterguy]

91s did operate parcels trains on a few occasions. Presumably blunt end first when heading southbound.

Photo of one such working in this old post here, there was at least one other working pictured in RAIL magazine around that time:

Can class 91s haul Freight Stock?

Or possibly a test run to prove that it could haul parcels vans.

www.railforums.co.uk

 

[Harpo]

A small point, but I think the speed limit was 110 mph when Class 91s operated blunt end forward with Mk4 stock.

Is that limit an absolute maximum speed when driven from that cab, or is it just because the loco is going to be at the same end as the DVT causing brake applications to propogate from one end of the train only and not both?

 

[themiller]

Is that limit an absolute maximum speed when driven from that cab, or is it just because the loco is going to be at the same end as the DVT causing brake applications to propogate from one end of the train only and not both?

Wasn’t it because of the lower crashworthiness of the blunt end?

 

[hexagon789]

Is that limit an absolute maximum speed when driven from that cab, or is it just because the loco is going to be at the same end as the DVT causing brake applications to propogate from one end of the train only and not both?

Wasn’t it because of the lower crashworthiness of the blunt end?

Excessive wind noise was the reason I always heard.

Certainly, when the non-aerodynamic cab leads, the airflow produces a very high pitch shrill whistling sound, not unlike some EMUs like 319s do at speed but more intense and irritating.

 

[sjpowermac]

Close - it was from Bradford. The stock was those re-seated high density seated ones.

There was also a working from Hull as the OP mentioned. 1A24 15:30 Hull-London Kings Cross, booked a Class 47 Hull to Doncaster, with the Class 91 working forward, slab end leading, formed of Mk2 stock. It was certainly diagrammed in the Summer of 1989, but I’m not sure how long it lasted for.

 

[D6700]

There was also a working from Hull as the OP mentioned. 1A24 15:30 Hull-London Kings Cross, booked a Class 47 Hull to Doncaster, with the Class 91 working forward, slab end leading, formed of Mk2 stock. It was certainly diagrammed in the Summer of 1989, but I’m not sure how long it lasted for.

I also recall a York to London Kings Cross on Sunday afternoons, with a 91 blunt end leading with commuter Mk2's. 15:15 rings a bell, but may well be wrong. I couldn't put a date on it, though.

 

[sjpowermac]

I also recall a York to London Kings Cross on Sunday afternoons, with a 91 blunt end leading with commuter Mk2's. 15:15 rings a bell, but may well be wrong. I couldn't put a date on it, though.

Yes, I remember that. If I recall correctly it usually used what is now platform 10 at York. I think that came a little bit later, once electrification to York was completed. I guess it made sense to dispense with the need to use a Class 47.

There’s a picture here showing a Class 91 with Mk2 stock working 1450 York London King’s Cross, dated 13.01.1991

91023 Colton 130191 img1102-0491mb-a

13th January 1991 91023 heads away from Colton Junction blunt end first with 14:50 York - Kings Cross. When the Class 91 was specified it was expected that they would see regular use blunt end first on slower nighttime traffic where the increased aerodynamic resistance is not as critical. Some...

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