Running cab first - Classes 20 and 91

[TimboM]

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.

I don't think it's related to the pantograph, but simply a cost/energy-saving measure in that running with the un-aerodynamic flat/slab end first takes up a fair bit more juice to hit 125mph (or 140mph) than the aerodynamic end first, so the environmental (and cost) conscious designers/BR put the 110mph limit on it.

Also, the flat end was intended to be used for overnight sleepers/freight etc. - such services wouldn't need to run at anything above 110mph (if that), so didn't need to be set up for anything more.

Re. the pantograph - I guess it could be a plausible reason, but as pointed out it's in the opposite direction when propelling and still 'exposed' to significant airflow atop the train. Also, if you look at any 100mph+ electric locos (e.g. a 90) the pantograph is whichever way round it is when the loco's coupled up and doesn't result in any speed limitation AFAIK.

 

[randyrippley]

The class 20s weren't designed in isolation. They were one of a group of similar English Electric designs built for service around the world. The immediate precursors were the New Zealand DE class built in 1951-52
https://en.wikipedia.org/wiki/New_Zealand_DE_class_locomotive
Later, around 1958 Western Australia got the F class
https://en.wikipedia.org/wiki/MRWA_F_class

Conceptually they were grown-up versions of the class 8 shunters with bigger EE engines and bogies replacing the 0-6-0 drive. Locally in Australia EE built similar designs, some with improved visibility.
While for Portugal the enhanced loading gauge allowed EE to raise the cab for the Class 1400, giving better visibility both ways
https://en.wikipedia.org/wiki/CP_Class_1400

Essentially the height of the nose/body is a direct result of standardising on the EE SVT / CSVT range of vertical engines. If instead Paxmans had become standard then UK locomotive design may have gone down a different path

 

[fowler9]

I don't think it's related to the pantograph, but simply a cost/energy-saving measure in that running with the un-aerodynamic flat/slab end first takes up a fair bit more juice to hit 125mph (or 140mph) than the aerodynamic end first, so the environmental (and cost) conscious designers/BR put the 110mph limit on it.

Also, the flat end was intended to be used for overnight sleepers/freight etc. - such services wouldn't need to run at anything above 110mph (if that), so didn't need to be set up for anything more.

Re. the pantograph - I guess it could be a plausible reason, but as pointed out it's in the opposite direction when propelling and still 'exposed' to significant airflow atop the train. Also, if you look at any 100mph+ electric locos (e.g. a 90) the pantograph is whichever way round it is when the loco's coupled up and doesn't result in any speed limitation AFAIK.

True, my thinking was though that pretty much all UK electric locos are/were limited to 110 and was wondering if this was down to airflow disruption over the pantograph. Are Class 90's allowed over 110 on the ECML?

 

[LA50041]

True, my thinking was though that pretty much all UK electric locos are/were limited to 110 and was wondering if this was down to airflow disruption over the pantograph. Are Class 90's allowed over 110 on the ECML?

Class 90 110mph max are they not?

 

[fowler9]

Class 90 110mph max are they not?

My thinking was that they are not physically limited to 110. More that they aren't allowed to go over 110 for other reasons. A Pendolino could go 125 with the front pantograph up but it isn't done.

 

[LA50041]

My thinking was that they are not physically limited to 110. More that they aren't allowed to go over 110 for other reasons. A Pendolino could go 125 with the front pantograph up but it isn't done.

You're not really comparing apples with apples there.

Pendolinos are permitted to run in service at 125mph, a class 90 is not permitted to run above 110 without regearing and modification to the brakes

 

[fowler9]

You're not really comparing apples with apples there.

Pendolinos are permitted to run in service at 125mph, a class 90 is not permitted to run above 110 without regearing and modification to the brakes

I get your point but are Pendolinos permitted to run at 125 using the forward pantograph? It isn't how they normally operate. I ask because I don't know, not being awkward.