2 locomotives pulling a load ( Couple 2-10-2's )

[ta152h0]

When you have two locomotives pulling ( and assuming they are both capable of the same traction force ) what is more efficient / the front one pulling harder of the aft one pushing harder ?

[jettrainfan]

Um.... are we talking about back engines or double headed? I would say let the back engine in either way stay to a close, slower speed. If the front is having problems the the back will help. For fun, do it the same way. I have done this and if you make it go faster than the front,well lets say "clean up on track 1!!!
If they still need power speed both up with the back still slightly slower. Hope this helps! Need anything else i should reply soon

[ta152h0]

Double header. Both locomotives in front of the train. it would be a similar engineering problem as the slightly offset gearing on a double axle of a semi tractor. I am guessing the aft locomotive pushes harder than the lead locomotive pulls, otherwise it would just be another railcar load. Right ?

[jward]

i would say they are both pulling about the same, as long as neither one's wheels are slipping.

for proof, the real railroads rate locomotives by tonnage pulled over any particular route. the tonnage ratings are added together to determine what a particular consist is capable of pulling. think of it like a giant game of tug of war. everybody pulls on the rope and the force they exert on the rope is added together......so it follows that identical locomotives should exert roughly equal force.

[Yampa Bob]

I prefer both locomotives to be closely matched in speed. For my small layout, I place the two locos halfway around the track from each other and run them at full throttle. I figure if it takes 8-10 laps for one to catch the other, they are matched close enough.

I put the slightly faster loco in the lead, so the loco couplers are lightly extended. It is highly unlikely that the load will be equally shared between the two locos.

[Jim Banner]

If you are double heading for looks, then you can keep it simple and use a dummy.  If you are double heading because a single locomotive does not have enough traction to pull the train, then speed matching is relatively unimportant as long as the two locomotives together can pull the train without either one spinning its wheels.  It does not matter if one locomotive is taking 90% of the load and the other only 10% - neither one will be overloaded as long as the locomotives have never had extra weight added to them and you keep them lubricated.

As far as pushing or pulling is concerned, when you are double heading with locomotives that cannot move the load alone, then they must both be pulling, even if the second locomotive runs faster than the first when they are running light.  The trouble starts when conditions are such that the second locomotive can pull the train by itself, such as going down hill.  Then the second locomotive may start pushing the first, exacerbating any surging problems.  Cycling the couplers between pull and push can cause them to uncouple, letting the lead locomotive run away when the train reaches the next hill.  It can help to turn on BEMF control in the second locomotive but turn it off in the lead locomotive.  This can force the second locomotive to brake the train while the lead locomotive pulls it down the hills.  A bit like stretch braking, except the stretch occurs between the two locomotives instead of within the train.

Matching draw bar pull is not a concern for the full size railroads and it has never been a concern on any of my model railroads.  If a particular train is a little bit too heavy for one large locomotive, all I need to add is a second, small locomotive capable of pulling that extra little bit.  In this case, if the large locomotive draws 3/4 amp at maximum load and the smaller locomotive draws 1/4 amp pulling that extra little bit, then the two together draw 1 amp, indicating that they are both working. 

The difference between what I do and what Bob does is that Bob is working to minimize the loads on both locomotives that together are pulling a train that either one could pull by itself.  This is an excellent way to minimize wear on both locomotives when you use two powered locomotives to double head for show.  I add locomotives as required to get the train over the humps.  Sometimes miscalculating the number of units at the point leads to a stalled train and a pusher has to be sent out.  In extreme cases, the train will have to double a hill (there goes the schedule) or a couple of mid train locomotives have to be cut in.  I am working to keep the trains running, even if it means running the locomotives at full load.  Both ways of running can be fun.

Jim   

[uncbob]

My 2 Bachman 2-8-0s are just about identical in speed

I  doublehead once in a while  with a 20 car coal train--just cause it looks neat--one can pull the load all by its lonesome