Double Headed 'toasters'

[Ryan]

It's closer to 20, but that isn't what shotgun7 was asking about. The fact you've got 2 locomotives doesn't change the max length because of the HEP issue (unless it's one at each end of the train and you're running a split bus, but that's way outside the scope of this thread).

 

[stonesfan]

Alright, somebody needs to set me straight on this once and for all: Why is it that electric locomotives require so much more horsepower to move a much smaller train? If two Dash-9s (a combined 8800 hp) can handle a 100+ car long manifest over rolling terrain, why is 8000hp just barely cutting it to move 11 heavyweight cars in the NEC? Just another basic concept I haven't been able to grasp yet, since I know next to nothing about electrics.

Having just read a similair article in a journal, I'll try and explain!

There is adhesion to bear in mind, the fact electrics are usually lighter means they simply don't get the grip on the rails that a heavier diesel does. Plus 2 diesels means twice as many wheels to provide adhesion to get that heavy train moving. And bear in mind that electrics tend to be geared for higher running speeds than diesels meaning their tractive effort to pull a heavy load from a stand may not be as high as a diesel. A 7000hp 125mph geared electric could really struggle to shift a freight train from standing. However, a 4000hp 75mph geared diesel would have a higher tractive effort and probably get it moving better.

However, I don't know whether you have any specialist electric freight locos in the USA, but we have a 7000hp Co-Co (12 driving wheels) heavy electric loco designed purely for freight, and I tell you what, these locos would probably drag the entire amfleet inventory up the Penn incline in the blink of an eyelid!!! There are even more powerfull freight only electric locos in places like South Africa and Russia.......

 

[Shotgun7]

Alright, somebody needs to set me straight on this once and for all: Why is it that electric locomotives require so much more horsepower to move a much smaller train? If two Dash-9s (a combined 8800 hp) can handle a 100+ car long manifest over rolling terrain, why is 8000hp just barely cutting it to move 11 heavyweight cars in the NEC? Just another basic concept I haven't been able to grasp yet, since I know next to nothing about electrics.

Having just read a similair article in a journal, I'll try and explain!

There is adhesion to bear in mind, the fact electrics are usually lighter means they simply don't get the grip on the rails that a heavier diesel does. Plus 2 diesels means twice as many wheels to provide adhesion to get that heavy train moving. And bear in mind that electrics tend to be geared for higher running speeds than diesels meaning their tractive effort to pull a heavy load from a stand may not be as high as a diesel. A 7000hp 125mph geared electric could really struggle to shift a freight train from standing. However, a 4000hp 75mph geared diesel would have a higher tractive effort and probably get it moving better.

However, I don't know whether you have any specialist electric freight locos in the USA, but we have a 7000hp Co-Co (12 driving wheels) heavy electric loco designed purely for freight, and I tell you what, these locos would probably drag the entire amfleet inventory up the Penn incline in the blink of an eyelid!!! There are even more powerfull freight only electric locos in places like South Africa and Russia.......

Wow... if only I could get this much detailed info so fast for everything in life!

 

[AlanB]

Hokie pretty much hit the nail on the head. It's not that it takes more power to do it, it's just how quickly you want to accomplish what you're trying to do. You can get an 8 car set up to 110 MPH with a single diesel. But if you put an electric powered train on a parallel track the electric train will be at 110 MPH much faster than the diesel powered set.

Hmm... I still recall hearing that you can only put about 15 cars together before you start having HEP issues.

ALC,

You're sort of confusing two different issues. Yes, there is a finite length to just how long the consist can be because of HEP. However, that length has nothing to do with how powerful the locomotive is and the question originally asked here. The electric engines are more powerful simply because Amtrak wants get up and go, plus you need more power for faster speeds. That's why the electrics are more powerful than freight diesels or even passenger diesels.

Yes, taking HEP off any engine reduces its motive power, which is one reason that freight engines can haul a bit more than a passenger engine. Gearing of the engines also has a lot to do with it. IIRC, taking HEP off of a P42 reduces its 4,200 horses to something like 3,800 HP. One reason that most Amtrak LD trains do need at least two locomotives, especially if there are any big hills.

Turning to the HEP car limitation, there is no hard and fast rule as too just how many cars can be chained together on one engine's HEP. One has to factor in what type of car, diner's pull more power than coaches do for example. And bi-level cars pull more power than their single level counterparts. But the Auto Train manages close to 20 cars before they start pushing the limits of the cables. So in theory with single level cars, one should be able to reach at least 30 cars, maybe more depending on type.

On the other hand, pulling 30 cars with even one HHP (8,000 HP) the most powerful Amtrak engine around, would still be an interesting exercise. While I suspect that it probably could still move the consist overall, performance would be terrible. By the time it got up to track speed after leaving Newark it would probably be halfway to Trenton and would have missed the Metropark stop.

 

[ALC Rail Writer]

Hm fair enough.

 

[DET63]

It's closer to 20, but that isn't what shotgun7 was asking about. The fact you've got 2 locomotives doesn't change the max length because of the HEP issue (unless it's one at each end of the train and you're running a split bus, but that's way outside the scope of this thread).

A "split bus" sounds like what someone who's bought a train ticket wants to see when forced to ride a Thruway or Greyhound instead for a significant part of the trip.

 

[stonesfan]

A classic example of 'tractive effort' would be this:

A small class 08 diesel shunter with just 350hp (top speed 15mph) on tap could actually take 12 coach train from standing to 10 mph in less than 12 seconds.

A class 67 express diesel loco with 3200hp (top speed 125mph) would probably take about 16 seconds to get to 10 mph with the same load. Of course this loco would come into its own once it got above 40mph.

Again I've used our own examples as I'm probably not qualified to quote exact figures from your own locomotives.

But I would say, stuff like you see on your heavy freights will have some serious tractive effort given the gearing and HP available........