Multiple Units

[oarb00]

When running multiple units, how does wheel size, gear ratio, engine type(4-cycle vs 2-cycle), and locomotive age affect performance? Does run 5 throttle position equate out to the same speed on all diesels in the consist? Also, I've heard that a consist is only as good as the best loco in it. Here in St. Paul MN, I live near pigs eye yard and often see SD-70ace's, ac4400's, and other modern types mu'd with GP-38's and SD-40-2 snoots. Sometimes even older switchers. Does this affect the performance of the more modern diesels?

[BigJim]

Maybe this is not the wording you want to read.

Think of a Tug-of-War contest where the people on each side range from child to adult. They each pull their own weight in order to achieve the desired goal.

[Randy Stahl]

 .........And I'm dead in consist .....

[daveklepper]

Compatibilty problems between different sizes, ages, and makes of locomotives has very little to do with differences in tractive effort or horsepower, and the analogy of a tug of war with people of different strengths on both sides applies.   What can be a problem, however, is different loading characteristics.   If one locomotives reacts quickly to moving from throttle 3 to throttle 7 and another in the consists reacts slowly, then just might possible result in an overload relay tripping on the quick one.   But even this problem can be mitigated by skillful train handling.

[oltmannd]

oarb00

When running multiple units, how does wheel size, gear ratio, engine type(4-cycle vs 2-cycle), and locomotive age affect performance? Does run 5 throttle position equate out to the same speed on all diesels in the consist? Also, I've heard that a consist is only as good as the best loco in it. Here in St. Paul MN, I live near pigs eye yard and often see SD-70ace's, ac4400's, and other modern types mu'd with GP-38's and SD-40-2 snoots. Sometimes even older switchers. Does this affect the performance of the more modern diesels?

The consist is only as good as the worst locomotive in it.

Each notch is a power setting (more or less). Put an SD70MAC in notch 5 and you will get about 1700 HP - at any speed. A GP38, about 1100 HP for notch 5. Moving along at 30 mph, this is no problem. Neither locomotive is near the max speed you can safely spin the traction motors nor near the point where the wheels will slip.

The biggest problem will be at low speeds. You come to a grade and put the throttle in notch 8. As the speed drops, the GP38 will be OK to about 11mph. Below that, one of two things will happen. It will start to slip beyond the ability of the wheelslip system to correct by cutting back the power, or the traction motor will start to overheat. The SD70MAC won't have any adhesion issues until the speed drops down to 7 or 8 mph, and even then, you can keep the throttle in notch 8 and the wheelslip system will take care of everything.

So, if you build a consist with a GP38 and an SD70MAC, you won't be able to take advantage of the SD70MACs low speed pulling ability. If you tried, you'd do some heavy damage to the GP38.

If you had a consist of two SD70MACs and a GP38, you'd be limited to fewer tons than if you had just the 2 MACs. (based on the pull you need to get up the steepest hill)

Sometimes you see some strange consists because you have to dispatch trains with the power you have on hand, not because it's such a great way to do business.

[THE.RR]

oarb00

 Here in St. Paul MN, I live near pigs eye yard and often see SD-70ace's, ac4400's, and other modern types mu'd with GP-38's and SD-40-2 snoots. Sometimes even older switchers. 

 

If your BNSF is like my BNSF (Tehachapi), those small GP's and SW's are not on line, just being hauled from the diesel shop back to their duty station (or vise versa).  Always interesting to see a GP30 / 35 / 38 or 2 in a consist going up the grade moviung between Barstow and what ever yard they serve in the Valley. 

Phil

[oarb00]

Thanks for the info. There are 4 tracks running through my back yard, all used by BNSF, CPR, UP, DM+E, and Twin Cities and Western. Occasionally all tracks will be occupied at once. This is a heavily traveled area. I see some interesting consists. I've even seen CPR locos in a BNSF consist and vice versa. One other question. Any idea why the railroads prefer GE's to EMD's in this area? They seem to out number EMD something like 4 to 1. Especially on the BNSF and CPR.

Thanks

[YoHo1975]

BNSF and CPR just generally prefer GE.

GEs are cheaper to buy up front than EMDs. EMDs are cheaper to maintain.

Also, a comment on Tehachapi. Back in the day, Santa Fe would dispatch all sorts of mixed up consists over the grade. I have a video of a personal favorite that had a Dash 9, a couple 45-2s, a GP20 and a GP30. All were clearly online and lugging.

[ndbprr]

trains are not like cars or trucks where you have infinite speed variations. The speed limit may be 50mph but that is the limit. My understanding is that a chart is consulted which allows the rr to decide how much power is needed for the train. Generally there is a streth of track that determines the hp per ton needed. So a train probably will be running slower than the speed limit as the next notch would cause it to speed over the limit. You takes the speed you gets.