How much 'deadweight' does a loco on drag cause?

[NightatLaira]

This question occurred to me the other day when I was considering how much ‘drag’ a loco on ‘drag’ caused to its towing loco?

Take for instance the following sceanarios:

A failed 90 at the head of 8 coach rake of mk3s being thunderbirded by a 67 or similar. How many more coaches worth of weight would the failed 90 be exerting upon the total load of the haul. Would it be simply the loco’s weight or would there be additional resistance from the driving bogies? I don’t know how electric locos motors work – can they be ‘put into neutral’ like a car on tow or do they remain in gear acting like a sort of passive dynamo?

And would they be any differences in the nature of a haul with say a failed diesel being thunderbirded by another diesel?

Or other locos for instance: 47, 57, 90, 91, 87, 86?

 

[sprinterguy]

This question occurred to me the other day when I was considering how much ‘drag’ a loco on ‘drag’ caused to its towing loco?

This has been discussed and answers mused at on here before:
http://www.railforums.co.uk/showthread.php?t=33692

Minds more knowledgable than mine have ascertained that the traction motors on a dragged electric loco or unit will cause some residual drag. I can only assume that the amount of extra drag that this creates is reasonably small. Otherwise, I would assume that given the much larger total number of traction motors present on a nine carriage Pendolino, in comparison to a single class 90 and carriage rake, would mean that it would be incredibly difficult to get a Pendo drag moving due to the cumulative drag effects of all the traction motors in comparison to a loco and stock formation if it was a larger force.

 

[mumrar]

This has been discussed and answers mused at on here before:
http://www.railforums.co.uk/showthread.php?t=33692

Minds more knowledgable than mine have ascertained that the traction motors on a dragged electric loco or unit will cause some residual drag. I can only assume that the amount of extra drag that this creates is reasonably small. Otherwise, I would assume that given the much larger total number of traction motors present on a nine carriage Pendolino, in comparison to a single class 90 and carriage rake, would mean that it would be incredibly difficult to get a Pendo drag moving due to the cumulative drag effects of all the traction motors in comparison to a loco and stock formation if it was a larger force.

Whilst a Pendo has more traction motors than a 90, they are smaller and so have less resistance per motor, as I'd guess.

 

[NightatLaira]

This has been discussed and answers mused at on here before:
http://www.railforums.co.uk/showthread.php?t=33692

So it has! My apologies - note to moderators: feel free to merge this topic with that one.

 

[Jordy]

I won't merge the threads but will lock this one - please use the other thread.