kcsivils Wrote:
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> Why were double headers used in some instances and
> mid-train helpers or pushers used in others?
>
> The skill sets to operate in each of these
> examples has to be different and in narrow gauge
> country I would imagine reasonably complex at
> times.
The placement of helpers in a train always depends on tonnage, curvature, gradient, etc. Using the D&RGW Narrow Gauge west from Alamosa as an example here's what they did, and why...
Westbound trains from Antonito over 1600 (?) tons had the helper cut into the train. The maximum length of trains was 70 cars, and many were in this range. The grade was 1.42% maximum with some miles of less and even a few that were dead flat. The trains had loads and empties mixed together, and placing the helper mid train kept in-train forces (slack action) to a minimum and reduced the strain on the head end cars With the train wrapped around the many reverse curves, another issue would be string lining the train around one of these. Also, the bridge over Cascade Creek was limited to only one large locomotive on it at a time, so having the engines separated meant they didn't have to stop there.
Eastward out of Chama, up the 4%, the helper was placed either ahead of the caboose or cut into the middle of the train if there were a considerable number of empty wooden cars in the train. If the tonnage exceeded what two engines could pull, the third engine was put on the point. Doing this again kept the in train forces stable. The lead engines did their share, the rear engine did its share. Somewhere in the middle the slack would ease in and out where the head end would not be pulling any more, and rear engine took up the slack. The third engine on the front did require the train to stop at Lobato Trestle and cut the lead helper off to cross ahead of the train.
Between Chama and Durango, the railroad was a roller coaster profile. There were many miles of 1.42% grade in each direction, as the railroad climbed up out of a valley then dropped down the other side, then climbed back out again. With this kind of railroad, you need the motive power on the front. With a helper in the middle, the slack would come in when drifting down hill, then come out again climbing up the other side. Even with the engines on the head end, they still ripped a few cars in half coming out of the sags. Double heading down steeper grades can be difficult with the extra weight of the second engine wanting to pull the train downhill - when using air brakes going downhill, the locomotives brakes are kept released, using the train brakes and keeping the engine rolling free keeps the train stretched out. The extra weight of the second just makes the train handling more difficult. In later years, they would double head eastward from Durango where the ruling grade was 2%. But westward trains would depart Chama with one locomotive, with the helper running ahead to Gato, where the longest stretch of 1.42% started. there were a couple of short stretches of uphill going west that one engine could surmount. At Gato, the helper would be added to the front for the up and down 1.42% run to the top of the last hill near Falfa. Here began a 2% down grade into Durango. After a fatal derailment on the hill with two engines coupled together, all doubleheaded trains stopped here and the helper was cut off and run ahead light into Durango with the train following.
One additional point to make: With VERY rare exceptions, additional locomotives are never added to trains going down hill for "braking power" Steam locomotives do not have dynamic brakes. They roll free down grades, and the air brakes on the train control the speed.
