F-unit basics

[upjake]

Today I saw a pair of C.N. D9-44CWs (or similar to this) and it got me thinking about F units and how they operated. 

My question is two-fold.  I am not too familiar with M.U. development and operation so please bear with me.  First, did the lead F3 or F7A always have full control of the trailing F7B 'boosters' and any other additional A units behind? 

Second, depending of course on how long a train was, did all F units in a typical train lash-up (say an F7A-B-A set on a train) remain running throughout the trip or were some just added to trains as emergency back-up power only?  I guess you could ask the same thing about today's back-to-back diesel operations as well.

[cx500]

upjake

Today I saw a pair of C.N. D9-44CWs (or similar to this) and it got me thinking about F units and how they operated. 

My question is two-fold.  I am not too familiar with M.U. development and operation so please bear with me.  First, did the lead F3 or F7A always have full control of the trailing F7B 'boosters' and any other additional A units behind? 

Second, depending of course on how long a train was, did all F units in a typical train lash-up (say an F7A-B-A set on a train) remain running throughout the trip or were some just added to trains as emergency back-up power only?  I guess you could ask the same thing about today's back-to-back diesel operations as well.

 

The quick answer is that the lead unit would control all the units behind, which might include B-units, other A-units and road switchers, and usually all would remain running throughout the trip.  But to say "always" (or "never") is unwise - there always seems to be an exception that happened at least once.  Of course in helper districts there would be two separate crews and their respective power sets would not normally be MU'd together.

From time to time you would probably have units deadheading, home for repair, or just being repositioned, and these might be hauled dead.  Another complication is that not all railroads had MU connections in the nose of an A-unit, so if there were more than 2 A-units a second engine crew would be required to run the additional one.  This obviously would usually be avoided, except in case of emergency, and many railroads later added nose MU if it wasn't there already.

John

[JonathanS]

If the lead unit lacked a certain feature, say dynamic brakes or manual transition, then that feature could not be controlled on any of the following units.

[rrboomer]

This link might answer most of your questions:

http://www.railway-technical.com/us-musp.shtml

[ndbprr]

 

Don't lose sight of the fact that early F units ranged from 1350 to 1750 HP.  EMD marketed engines for almost forty years based on replacing three units with two of equal HP.  I would look for pictures of the Chicago Great Western (CGW).  They ran trains with as many as 9-12 F units.  It didn't make one iota of difference to the engines if an A unit followed a B unit or the direction of any in the lash up.  The only concern early on was that the unions would demand a crew in each one as on steam.  That is the reason for drawbarring some engines or identical numbers followed by a letter. Needless to say that concern was unfounded in reality.

[Wdlgln005]

 I understand as built many early E or F units had no MU connections on the front end. At some point the units were modified to have the feature added.

On the FT, some units were intended to run as AB with a drawbar connecting the units. Trains may have been smaller then, if on some roads a ABBA set provided too much power while a single AB was too small. How much things have changed over 60+ years!