Prototype information for the modeler

 Hello I'm back regarding the EMD F7 + F9 diesel locos,

I noticed that some model train manufacturers offer the "B" unit in complement with the main loco; now my question is: Where these units added by the railway companies to increase the towing power of the main unit when they where used as freight locos or just because they where adding more pasenger cars with the FP 7 + 9 models ?

Thank you,

 Serge

The very first B unit was part of the very first freight diesel offered by EMD.  That model was the FT and it was connected to the A unit by a drawbar so it was a permanent connection.  Railroads had very large concerns that the unions might demand a crew in every engine so initial engine A & B  units were often the same number with an a or b suffix also.  The first F3 engines on the Pennsylvania were helpers for horseshoe curve out of Altoona PA.  They consisted of an ABA set to get sufficient horsepower.  The Chicago Great Western which ran west and north of Chicago ran trains toward the end of its existence with as many as fifteen F units in any order.  Most of the F units ranged from 1200hp for the FT up to around 1800HP for the later models.  These numbers may be off a little but they illustrate that EMD was aware early on that the railroads wanted more Horsepower in the engines and EMD made a lot of money for nearly fifty years by coming out with increasingly higher horsepower engines that replaced three current diesels with two new ones equal to the horsepower of the three. B units eventually fell out of favor because they required switching them so they didn't lead the consist.  The original idea was railroads could save some money by not having the cab.  So the first answer is yes to increased Hp for freights.  Every division has a ruling grade that dictates how mush an engine can pull up that grade.  Every engine has a tonnage chart that allows the person assigning power to determine how many engines a particular train requires to pull that grade.  The big dilema is do you assign only so many cars to a set of engines and run a second train or do you increase the number of cars and engines to pull it or have helpers on that grade? Each railroad does it differently.  Passenger trains are pretty static in the US as far as make up.  The only time cars get switched out is when they need repair.  Many years ago sleepers were often set out along a route so passengers could spend the night in the car and exit at their stop in the morning.  But once again the consist was a set amount of cars leaving the origination city.  The one exception is mail and express that was usually carried on the secondary all stops trains and not the limited or name trains like the 20th century or the Broadway Limiteds.  For many years on the Pennsylvania there were assigned engines to the Broadway Limited and I suspect that may have been the case on other railroads.  The FP7 & 9 engines came along fairly late in the history of passenger operations in the US.  I can only speak for the Pennsylvania but they were mostly used in freight service but with the steam heater they were back up power for passenger work if needed.  The only differenece between an F7 and an FP7 is that the FP7 is slightly longer, has a water tank for the steam boiler and a steam boiler for heating and cooling the passenger cars.  Generaly passenger trains are much lighter than freight trains in the US and would not need nearly the number of engines or horsepower a freight would.  If you model the ATSF for example they used matched sets of F units on their trains and took great pride in their appearance.  Theyb ran 2000 miles between Chicago and the mostly Los Angeles and crossed the ROcky Mountains.  To the best of my knowledge the matched sets of F units were adequate for the entire run with possibly the exception of Raton Pass which required helpers.

it became common practice on many railroads to "overpower" trains because of on the road failure of one or more units as age and deferred maintenance took their toll.

  been there-done that.

  PC used 3 or 4 big six axle units on 4000 ton trains out of E St Louis because it was almost a sure thing that one or two of them would throw craps before reaching Indianapolis.

  when they still had a fireman, he spent most of his time resetting ground relays.

ATSF started running a fifth f unit on their passenger trains out of Chicago for this very reason.  2000 miles is a long way to go hoping that one unit out of four would not fail.

grizlump

Unlike their E-unit sisters, cab units of the F series didn't have space for a steam generator (or at best a very small one). Railroads that used Fs as passenger engines instead of E units (usually railroads like Great Northern or Northern Pacific who found E units couldn't climb the mountain grades like the Fs could) had steam generators only in the B units. So, if you wanted to power say a 4-5 car local with an F3, you'd also need a B unit with the steam generator...even though the one F3 could easily pull the train itself.

That's one reason railroads bought EMD's FP engines, one FP could haul the 4-5 car train by itself since it had the power to do so and the steam generator too. Of course, other railroads bought the FPs because they added another steam generator to help heat the cars in harsh climates. In an A-B-B-A set of F units, only the Bs would have steam generators. With FP A units, you'd have four generators producing steam.

BTW Northern Pacific engines had to create so much steam heat in the winter in the Rockies and Plains that they had special baggage cars with water storage tanks running right behind the engines to provide enough water so the engines could produce enough steam.

 I thank you so much for all this valuable information, it was very much appreciated...

Serge

wjstix:

BTW Northern Pacific engines had to create so much steam heat in the winter in the Rockies and Plains that they had special baggage cars with water storage tanks running right behind the engines to provide enough water so the engines could produce enough steam.

One thing to add is that the water lines between the baggage car and the engines often froze up. Imagine trying to balance between an F unit and a baggage car, both covered in ice, using a lit fusee to thaw out the water line...while moving at 69 MPH on a -20F windy night.

wjstix:

Railroads that used Fs as passenger engines instead of E units (usually railroads like Great Northern or Northern Pacific who found E units couldn't climb the mountain grades like the Fs could) had steam generators only in the B units.