Every day on the way to work, at some point, I drive alongside a freight train. The varying lengths of any given train seem to dictate how many locomotives are propelling it along the rails. It is not rare to see a train with two or three, sometimes even four locomotives. Multiple locomotive trains are frequently arranged with the first facing forward(obviously), the second facing to the rear of the train, the third facing forward and the fourth facing the rear again. I imagine the shape of locomotives makes this adviseable and efficient. My question is, are locomotives #2 and #4 keeping pace of the others in reverse? Does this only seem strange to me because I happen to be driving alongside in a vehicle that couldn’t dream of such forward/reverse gear parity? Or, are these backward-facing locomotives just along for the ride, and the two facing forward are doing all the work?
I don’t know whether #2 and #4 are working or are just along for the ride but I do know that electric motors, such as those that drive both electric and diesel locomotives, work just as well in either direction.
Even a steam powered locomotive should work just as fine in reverse…it’s powered by the pressure in the piston chamber, and since the piston just goes in and out, all it takes is the initial motion to move the wheel backwards…then each push and pull of the piston will accelerate the wheel in whatever direction is wants to go. Your car engine could go just as fast in reverse if it wanted to…but they only build the transmission to have one reverse gear, and 4 or 5 forward gears. If they built a 9 speed transmission with 4 reverse gears, you’d be flying in reverse. The engine shouldn’t care what way the gears are moving. In short, it’s just the way the transmission’s built…the engine keeps running exactly the same whether it’s in reverse or forward. (and trains, to my knowledge, don’t have different gears…but I could be wrong on that.)
Jman
Frieght locomotives have diesel engines, but these are used only to generate electricity for the electric motors, which turn the wheels. Electric motors work just as well in reverse as forward. I’m not sure why they alternately reverse some of the locomotives - it might be for convenience, so that the cabs of the locomotives are close together.
As others have said, most electric motors work equally well in both directions. There is usually just a fixed set of gears between the motor and the wheels - no ‘transmission’ in the sense of variable gear ratio mechanism. (Though I hear the motor has several connections to the windings, making it possible to connect parts of it in series or parallel optimal for the speed).
Since only the front locomotive has crew members aboard (usually 2, engineer and conductor) it doesn’t matter which way the other locomotives are pointing. I think they just keep the locomotives in groups of two or three, facing away from each other. That way, you can add the group to the train and the front locomotive will always be facing the correct way. Or maybe they just find one locomotive pointing the correct way and put that in front; and add others as needed, not caring which way those are pointing. I wonder if they ever find themselves with a yard full of locomotives all facing the wrong way, though…
By the way, there are two types of steam engines - tank engines and tender engines. Tender engines have a separate car that carries the water and coal, and don’t run backwards very well - it’s unstable to push the tender in front of the locomotive. Tank engines have the tank on the main locomotive frame, and run backwards just fine.
Most railroads have run their diesel locomotives “short nose forward”, but a few, especially Norfolk & Western and Southern (now a part of CSX) ran in the other direction because they believed it provided a little extra protection to a crew in the case of a collision.
How they are arranged is usually a matter of chance, although for a “turn” (a local freight that goes out and returns on the same route) the locos on the ends usually pointed in the “correct” directions.
Most major yards have either a turntable or a wye (a sort of triangle formed from three turnouts, which looks more like a capital delta) that is intended for turning locos.
How many there are can vary. The goal is to have just enough power to move the train, but this is the real world. For example, if the units are old, and prone to breakdowns, and there are extras available, one or two may be included but not even operating until needed. Or, there may be an power imbalance in the system, and several extra idle units will be added solely to get them where they are really needed.
Sorry raoulortega, but under threat of the railfan police, I must correct you - the Norfolk and Western RR and the Southern RR merged to form the (new) Norfolk Southern in the 80s. Nothing at all to do with their competitor CSX.
And in fact, Conrail was just split up and absorbed by CSX and Norfolk Southern.
I knew that.
I plead brain freeze.
My SWAG is that they alternate directions because that’s the way they were pointed when they stuck 'em together; why turn 'em around?
And yes, the diesel engine is only a generator for electric motors. I’ve worked near a railroad station…when they start moving, it sounds exactly the same as when one strikes an arc on a self-powered arc welder: the sudden power draw causes the generating engine to triple its speed. (chug-chug-chug-BWAAAHHHH…)