breezinup posted:Dominic Mazoch posted:If one can find an old SP employee timetable of the 1970's, look in the back. There were serveral formulas about where to place helpers. At that time the electronic controls for the remotes were not as robust as today's. Plus there were no AC traction motors on diesels.
History of another period.
My guess there are like formulas for today if DPU units are placed on a train.
I would guess that computers and algorithms might be used now to calculate the most efficient placement of engines for each individual train, based on a number of variables, such as load tonnage, distribution of load tonnage, power of the individual diesels to be used, route travelled including factors such as grades encountered enroute, speed requirements and achievement of optimum fuel economy.
It has traditionally not been quite that sophisticated. In the early days of remote consists, the remote consist of the same horsepower was placed behind approximately 67% of the train's total tonnage. That way the two consists were Balanced in what they were moving, and the radio signal was more reliable than when the remote was just ahead of the caboose.
When I left railroad employment in 2007, there was a formula in the Special Instructions, for figuring in-train placement of remote consists that was designed to balance in-train forces and avoid buckling the train by shoving against blocks of empties with loads ahead of them. The formula had to be re-figured every time the train set out or picked up cars, and was not popular as a result. Mostly, these days, I see mid-train remotes only in mountain grade territory on unit trains consisting of cars of similar weight.
With trains of intermodal equipment that need to begin and end their trips in yards, mid-train helpers are placed so as to be accessible to the hostling crew who will take the engine to the service area.
