Hi all,
Very interesting stuff so far about one of our (my brother Will's and mine) favorite locomotives! Here's some information from the operating manual for BL2 locomotives which sheds some light on EMD's intentions for their creation.
First off, the manual itself is actually a completely standard contemporary F3 manual, with an added multi-page insert at the end. The reason for this is, as the insert states, that a "BL2 locomotive is essentially an F3 locomotive rearranged to be especially suitable for branch line service. With the exceptions listed below the F3 and BL2 locomotives are functionally the same."
(This eliminates any questions about the BL2's mechanical reliability or capability, and one has only to look at the information available about the F3's performance to qualify that. Performance clearly wasn't the problem, not from a mechanical standpoint anyway.)
Certainly the visibility was worse on the BL2 than "road switchers", and the unique and very different control stand arangement on the BL2's actually probably compounded the problem. Briefly, it places the throttle and in fact just about everything a bit farther away from the engineer than on F3's. I've read of engineers using pipes to extend the throttle handle length so as to make it more reachable when looking out the side window, or when turned around. Better visibility than an F3 for sure, but not as good as a "true" "road switcher".
But other mechanical differences in the BL2 show EMD's intent more clearly. They made mechanical, electrical, and control changes which depart from F3 "road freight locomotive" standard equipment, and in these changes lie the majority of the differences from the F3.
First, the throttle had no escapement mechanism, and could be opened as rapidly as desired. This was useful for switching service, and many switchers had like arrangement, especially if they had air throttles!!
Automatic transition was NOT standard on the BL2, but when provided it was WITHOUT the forestalling feature currently in use on the F3's. I would hazard to guess that the design engineers realized that it was unlikely that BL2's would regularly encounter conditions where the forestalling feature would be useful, and so simplified the design by omitting that. Also, the BL2 used a through cable type relay system for back transition, which would later become standard on road engines (F3).
A "load regulator control" (LRC) switch was provided on the control island which had two positions, namely ROAD and SWITCHING. In ROAD position, the locomotive's load regulating system behaved as a current, contemporary F3 using modified maximum field starting. With the switch in SWITCHING, a shunt was inserted bypassing the load regulator, providing more rapid starting of the locomotive. (This essentially ties excitation to throttle position, within certain limits. NOT throttle response, but not standard load regulator control either) This, as the manual states, is more desirable for switching service, and the same kind of thing could indeed be found on switchers. This is a very important difference from F3's, and was EMD's first use of such a system on a locomotive intended to be regularly capable of road service. This is also the genesis of the very similar load regulating/control system used on the locomotive which would successfully address the shortcomings of the BL2, namely the GP7.
There are still a few other minor differences, but those are the major ones. Clearly, we see that EMD felt that the mechanical changes they made were the major needs in a locomotive fit for branch line service. It should be noted that nearly all these mechanical features caried over to the GP7, or were improved for it, and that the GP7 is more BL2 than F7 in some ways. What the GP7 did too was fix the visibility problems of the BL2, which could not have been done in any carbody style unit.
-David A. Davis
