Re: Helper Engines Placement

First criteria is weight of pulling power of one engine. If it can't handle the train a second is required. On the C&TS, the Chama-Cumbres portion usually had a rear pusher since it was easier to get off the train at Cumbres that from the middle. It was not doubleheaded on this section normally since the Lobato trestle was not strong enough for two engines coupled together on it(the same span of the trestle) at the same time. However it was strong enough to handle two-engines on the trestle, as long as there were 5 cars between them. In 1993 we did a midtrain helper with engine 5 cars back midtrain of a 15 car train.
On the Antonito side, mid-train helpers were normally used if the weight of the train was such that they wanted to spread the drawbar weight out more so that a train wasn't pulled off the rails on all those curves in the gorge someplace. Thus a 70 car train was better off with an engine halfway back versus on the rear or doubleheading. Am sure other more qualified guys can shed further light on this question.
One of the appeals of D&RGW mountain railroading for the fan in my estimation was all the of these multiple engine configurations on freights in the old days.
Steamingly,
Greg Scholl