Ken,
Is your question focused on model trains or prototype operation? In model train operation, one locomotive can often handle 20-30 good rolling cars. However, in prototype operation, on the Q, you would never see just one locomotive on a road freight train. Several other posters have responded concerning the criteria that railroads use to determine motive power requirements for a train. The first is the ability to move the specific train over the ruling grade en route. Locomotives in the Q days, had short time ratings for their traction motors. Depending on the gear ratio, the minimum continuous rating would be around 12 mph. Generally, RRs didn't like to have trains operating below the minimum continuos speed, so power was assigned accordingly based on the least capable locomotive in the consist so that the train would go over the ruling grade at or above the minimum continuous speed. The second factor in assigning locomotives to a specific train is train priority or how fast do they want to get the train over the road. High priority trains were assigned more horsepower per trailing ton. A train like the CD (Chicago - Denver freight) or the CGI (Chicago - Grand Island) were priority trains and would have greater amounts of horsepower assigned. When the SD24s arrived on the Q, they were usually assigned to the priority trains in four unit sets, primarily for speed, not tonnage. Bulk commodities like coal, grain or sand, were usually operated at lower speeds, but because they were quite heavy, they too, would have multiple diesel units assigned to provide sufficient tractive effort to get over the ruling grade.
Look at the Q's early diesel operations. Their first freight units were four unit drawbar connected FT's rated at 5400 hp for the consist. When the F2s came along after WWII, their were coupled to pairs of FTs that had been separated into two unit consists. Ten four unit FT consists became 20 three unit FT / F2 consists rated at 4050 hp. I believe this was done because the lower hp requirements more closely matched some of their train requirements of the day (late 1940s). In other words, the four unit FT consist was more hp and tractive effort than they needed for some trains. Later, they bought four unit F3 consists and subsequently broke some of those up into three unit consists with the addition of an F7 A unit. The three unit F3 / F7 consists were rated at 4500 as opposed to a four unit F3 consist at 6000 hp. When the Q bought F7s, they were all in three unit consists except for those single units coupled to the two unit F3s.
GP7 and GP9s were purchased for secondary service and generally operated as single units until later years when road freights required more power. Then, it was common to see a GP7 coupled in the middle of a four unit F3 consist. SD7 and 9s were also mainly used as single units, but where heavier tonnage existed, they were often used in multiple unit consists. Such consists were used to replace Qs 2-10-4 steam locomotives in the southern Illinois coal fields where high tractive effort was required. They also worked such lines as the Ottawa branch in multiple units on silica sand trains.
With the arrival of the SD24s and U25B and C units, the horsepower race was on and the Q was no exception to that business idea. From that time on, three and four unit consists were the norm. At first the higher hp units were sold as three units replacing four units for a cost savings, but it didn't take the RRs long to realize the full benefit of higher hp for speed. At that time, the RRs also realized that even heavy bulk commodity trains that normally ran slow, had to go faster to keep from delaying faster priority trains, particularly on single track RRs. So, even the heavier trains were powered higher.
If you intent is to model the prototype, you may want to put two or three locomotives on your 30 car train even though it doesn't need that much power. Obviously, with three or four units, the Q would be running an 80 - 100 car train.
Bill Barber Gravois Mills, MO
Tue Nov 18, 2014 1:03 pm (PST) . Posted by:I admit I am not the most knowledgable about diesel operation on mainline trains. In mainline usage how many "motors" were typically used on a train? What got me thinking is I recently got two of the U25c's. Now recently they have been bringing in engines with two different numbers. So on a typical train are two engines enough, would one do or do you need to mix in other engines?
Tonight I am planning on using the two U25c's to pull a long coal train (33 cars) at the club and plan to use the two new engines.
Ken Martin
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Posted by: William Barber <clipperw@gmail.com>
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