Running cab first - Classes 20 and 91

[lparris]

Hi,
Does a class 20 run cab first or bonnet first?

Thanks

 

[AlterEgo]

Hi,
Does a class 20 run cab first or bonnet first?

Thanks

It can run either way. It is more common to see them cab end first.

 

[MichaelWells]

Both. Two Driving Desks in the same cab on the left hand side in the direction of travel, normally paired with a second one so there is an unobsturcted view from the cab end

 

[Supercoss]

Both, although usually with a mate, cabs at outer end
https://www.youtube.com/watch?v=05ioz7ASvJc

most useful locomotive

 

[daikilo]

Hi,
Does a class 20 run cab first or bonnet first?

Thanks

Either, although in general they now run as pairs with the cabs at the "outer" ends or with another loco (say a 37) again with the cab at the outer end.

 

[KingDaveRa]

Does anybody know why they were designed with the single cab? Was it just to improve driver acceptance at the time of converting to diesel from steam? Besides shunters, they're a bit of an anomaly.

 

[70014IronDuke]

Does anybody know why they were designed with the single cab? Was it just to improve driver acceptance at the time of converting to diesel from steam? Besides shunters, they're a bit of an anomaly.

money, weight, money.

back in the day they were not such an anomaly - see the D82xx, D84xx etc.

 

[Spartacus]

Compared to the steam locos they replaced the nose front view was still in most cases better than a boiler first view, and it many cases that was the BEST view available on a steam loco, on the 20 it was the worst.

 

[jopsuk]

money, weight, money.

back in the day they were not such an anomaly - see the D82xx, D84xx etc.

... two prototype/pilot classes that were regarded as unsuccesful and withdrawn fairly quickly. Class 20 was the only long serving mainline locomotive of this configuration in the UK

 

[SpacePhoenix]

Did the 20s ever have a reduced maximum speed when running bonnet end first?

 

[D1009]

Did the 20s ever have a reduced maximum speed when running bonnet end first?

No...

 

[DelW]

I remember reading or hearing many years ago that ex-steam drivers, used to a large lump of loco in front of their cab, felt vulnerable in diesels with only some sheet metal and glass as protection from any obstruction on the line, and so felt happier in a class 20 or similar running bonnet forward. The photos that I have seen suggest that it was much more common in the early days than it was after diesels became established.

 

[MarlowDonkey]

Does anybody know why they were designed with the single cab?

It was and is, an established American style. Their version would have a cab higher than the rest of the bodywork.

 

[DelW]

It was and is, an established American style. Their version would have a cab higher than the rest of the bodywork.

Indeed, and in the early days of road-switchers (single-cab units) there, many (most?) of them ran long hood first, with most railroads later changing to run short hood first. IIRC, Norfolk & Western and its successors were about the last big stronghold of long hood first running.

 

[D365]

Did the 20s ever have a reduced maximum speed when running bonnet end first?

Why would that be?

 

[rebmcr]

Why would that be?

91s have a restriction when blunt-end-first, so it's a reasonable query.

 

[D365]

91s have a restriction when blunt-end-first, so it's a reasonable query.

Both ends of a Class 20 are rather blunt, if either end was going to have a restriction surely it would be the cab as that's a greater surface area.

 

[43096]

Both ends of a Class 20 are rather blunt, if either end was going to have a restriction surely it would be the cab as that's a greater surface area.

Other way round with a 20, surely, as the issue is visibility from the cab.

 

[CosherB]

91s have a restriction when blunt-end-first, so it's a reasonable query.

That's because of the aerodynamics of the pantograph's knuckle creating excessive uplift force on the OLE, limiting speed to 110mph - neither issue will trouble a 20!

 

[D365]

Other way round with a 20, surely, as the issue is visibility from the cab.

Which isn't any worse than the visibility from a steam locomotive, I am told.

 

[LA50041]

That's because of the aerodynamics of the pantograph's knuckle creating excessive uplift force on the OLE, limiting speed to 110mph - neither issue will trouble a 20!

Sorry if this is a dumb question, but How does that not have the same effect when the 91 is propelling as surely the knuckle of the pantograph is still under the same force?

 

[4973]

I remember reading or hearing many years ago that ex-steam drivers, used to a large lump of loco in front of their cab, felt vulnerable in diesels with only some sheet metal and glass as protection from any obstruction on the line, and so felt happier in a class 20 or similar running bonnet forward. The photos that I have seen suggest that it was much more common in the early days than it was after diesels became established.

Part of the reason it was more common in mixed steam/diesel days was the risk of meeting a kettle over water troughs. If the kettle's fireman didn't wind the scoop up soon enough and 'swilled out' lumps of coal (potentially quite large) could be washed off the tender. If the positions of the respective locos were just so the lump would then come straight in the windscreen of the diesel.

I once read that in some areas diesel crews automatically ducked below the control panel if they met a kettle on troughs.

 

[birchesgreen]

Seeing as they are 60 years old this year does anyone know if there are going to be any "official" events celebrating that? I guess some preserved railways will but NR?

 

[matt]

Seeing as they are 60 years old this year does anyone know if there are going to be any "official" events celebrating that? I guess some preserved railways will but NR?

The Wensleydale are holding a class 20 gala from the 14th to 17th September

 

[D1009]

Seeing as they are 60 years old this year does anyone know if there are going to be any "official" events celebrating that? I guess some preserved railways will but NR?

In recent years I don't remember any events on the national network to celebrate anniversaries of introduction of particular classes, other than the HSTs, which are a special case.

 

[D6975]

Sorry if this is a dumb question, but How does that not have the same effect when the 91 is propelling as surely the knuckle of the pantograph is still under the same force?

No, in one direction the airflow produces a downward force on one half of the pantograph arm and an upward force on the other half. When running in the other direction these forces are reversed, so the forces operating on the various parts of the pantograph are different in each direction.

 

[LA50041]

No, in one direction the airflow produces a downward force on one half of the pantograph arm and an upward force on the other half. When running in the other direction these forces are reversed, so the forces operating on the various parts of the pantograph are different in each direction.

But the pantograph would be the same way around and under the same forces if running blunt first as if propelling - but there is no speed restriction on a propelling 91

 

[fowler9]

But the pantograph would be the same way around and under the same forces if running blunt first as if propelling - but there is no speed restriction on a propelling 91

I would guess that when propelling the Pantograph end of the 91 has an entire train changing the airflow. If blunt end first with nothing in front of it the airflow would be completely different.

 

[RichmondCommu]

Seeing as they are 60 years old this year does anyone know if there are going to be any "official" events celebrating that? I guess some preserved railways will but NR?

How about a run to Skegness like the old days?

 

[KingDaveRa]

I remember reading or hearing many years ago that ex-steam drivers, used to a large lump of loco in front of their cab, felt vulnerable in diesels with only some sheet metal and glass as protection from any obstruction on the line, and so felt happier in a class 20 or similar running bonnet forward. The photos that I have seen suggest that it was much more common in the early days than it was after diesels became established.

That does sound quite plausible. I imagine there's savings on the fact it's a single cab with two sets of controls in as well.