How powerful were Modernization Era Diesel-Electrics and Hydraulics?

[Sun Chariot]

55,000lbs all round, but the 44s were 72,000lbs as delivered until regearing reduced that figure.

DerbySulzers also quotes the Continuous TE for each class. My grey cells can't remember the relationship between Max TE at Rail, versus Continuous TE. Are you able to enlighten? Thanks

Continuous Tractive Effort (Class 44): 41,000lbs (and after re-gearing 29,100lbs) at 23.2mph.
Continuous Tractive Effort (Class 45): 30,000lbs at 25mph.
Continuous Tractive Effort (Class 46): 31,600lbs at 23.3mph

 

[hexagon789]

DerbySulzers also quotes the Continuous TE for each class. My grey cells can't remember the relationship between Max TE at Rail, versus Continuous TE. Are you able to enlighten? Thanks

Continuous Tractive Effort (Class 44): 41,000lbs (and after re-gearing 29,100lbs) at 23.2mph.
Continuous Tractive Effort (Class 45): 30,000lbs at 25mph.
Continuous Tractive Effort (Class 46): 31,600lbs at 23.3mph

Relationship in what way, sorry?

I take it you mean something other than simply the difference between the two?

 

[Sun Chariot]

Relationship in what way, sorry?

I take it you mean something other than simply the difference between the two?

Max TE at Rail, I always assumed is when the loco first starts to move its train. Is that correct?
I understand that TE drops away from Max, as a loco's speed increases.
However, I'm unclear of why Continuous TE gets quoted at a specific speed. I'm also unclear how Continuous TE behaves, as each field divert kicks in (e.g. on the 45).
In my days as a passenger on 45-hauled BR services, I do not recall any sudden surge in "pulling power", through the train's speed range.
Does my non-technical babble make sense?

 

[Richard Scott]

Max TE at Rail, I always assumed is when the loco first starts to move its train. Is that correct?
I understand that TE drops away from Max, as a loco's speed increases.
However, I'm unclear of why Continuous TE gets quoted at a specific speed. I'm also unclear how Continuous TE behaves, as each field divert kicks in (e.g. on the 45).
In my days as a passenger on 45-hauled BR services, I do not recall any sudden surge in "pulling power", through the train's speed range.
Does my non-technical babble make sense?

Continuous is max power at rail and occurs at a specific speed which will have a corresponding tractive effort. Likely occurs at the lowest speed that maximum power is available.

 

[Deepgreen]

That TE figure seems steep. DerbySulzers site quotes:
Maximum Tractive Effort at rail (Class 45/46): 55,000lbs

class 44 class 45 class 46 details

Echoed by the info on Wikipedia.

Thanks - I must have been thinking of the 44s as delivered (as pointed out by 'hexagon789').

Max TE at Rail, I always assumed is when the loco first starts to move its train. Is that correct?
I understand that TE drops away from Max, as a loco's speed increases.
However, I'm unclear of why Continuous TE gets quoted at a specific speed. I'm also unclear how Continuous TE behaves, as each field divert kicks in (e.g. on the 45).
In my days as a passenger on 45-hauled BR services, I do not recall any sudden surge in "pulling power", through the train's speed range.
Does my non-technical babble make sense?

Yes, broadly max. TE is usually around starting. I think Continuous TE is quoted at a particular speed just to give a realistic picture of performance in service. I don't think it varies as long as engine power remains constant at a particular speed. Mine is also a somewhat non-technical understanding! Very crudely, I consider TE as the ability to accelerate (with a set load), which obviously drops away with speed.

 

[hexagon789]

Max TE at Rail, I always assumed is when the loco first starts to move its train. Is that correct?
I understand that TE drops away from Max, as a loco's speed increases.
However, I'm unclear of why Continuous TE gets quoted at a specific speed. I'm also unclear how Continuous TE behaves, as each field divert kicks in (e.g. on the 45).
In my days as a passenger on 45-hauled BR services, I do not recall any sudden surge in "pulling power", through the train's speed range.
Does my non-technical babble make sense?

I understand what you mean now, I just wanted to be sure I had the right idea.

@Richard Scott and @Deepgreen have explained that though, so I'll leave it there.

 

[ac6000cw]

As an illustration, the TE versus speed graph for a class 66 (from Steve Brown's Rail Technical website) - with a US SD40-2 for comparison:



The 'maximum starting TE' is basically a function of axle weight and rail head condition (potentially with sanding) - the 'adhesion' - combined with the maximum allowable current through the motors (the current generates the axle torque) and how good the wheelslip control is at exploiting the available adhesion. But limitations of the DC motors and the other electrical equipment mean that it can't be sustained without damage for long periods of time. AFAIK EMD specify a 'minimum continuous speed' below which operation at very high tractive effort is time-limited. The vertical blue dotted line marks the 'continuous rating' speed.

Modern AC motor traction drives don't have the same limitations at low speeds, so can safely generate very high tractive efforts for long periods of time - meaning if you don't care how slowly you climb long gradients you can haul more weight per loco.

For comparison, this is for a class 60 (note the lower 'continuous rating' speed and higher starting TE, due to lower gearing and better wheelslip control):



Meanwhile, back in history, this is a set of curves for a class 44, both original and revised gearing (the whole cl. 44/45/46 set are here - https://www.railtechnical.com/class-44-45-46-diesel-electric ):

 

[Sun Chariot]

Thanks all. Yes, that makes far more sense to me now.