In 1984 while touring the EMD factory at LaGrange, the Company showed us a Burlington Northern unit (I’m pretty sure it was an SD40-2) with a very interesting wheel arrangement.
Underneath the engine cab was a conventional 3-axle powered truck, but the backside of the unit had something different. Underneath the frame was a span bolster and connected to said span bolster were two, two-axle, powered trucks. Equipped with a total of 7-axles, this locomotive looked mighty weird.
Now remember too that BN had been exploiting its newly constructed Orin Subdivision (“The Main Street of the Powder River Basin”) for just a very short while, so perhaps this was an experiment to get more tractive effort or slow speed lugging power out of a 3,000-hp locomotive. Maybe the railroad was feeling out EMD about having them develop a better locomotive for unit coal train service using conventional technology.
Beyond this prototype I never saw any mention of this unit, or any discussion about its design. I don’t recall either Trains Magazine or the trade press ever publishing anything about it. So, que pasa?
Does anyone have any more details about this unique locomotive?
The unit was BN SDP45 6599 as a radial truck experiment. This was done in January 1985. A Second (yes, second) unit, Santa Fe GP50 3180 was modified for the same reasons in December of 1984, and was later remodified for testing of a new radial truck design, in Febuary of 1986. BN’s unit was stored at West Burlington in May 1986. Where they went afterwords is a mystery to me.
Source: The Contemporay Diesel Spotter’s Guide 2nd Edition By Louis A. Marie Printed in 1995
Notice the silver truck replaced the four axle one
NRE facility Mount Vernon IL - 11/98 - {Dan Bohannon Photo} - experimental SDP45 that was equipped with a four axle rear truck by EMD, removed in photo
I think this creature has been mentioned on the forum before. Type the number in the search function and see what comes up.
If I remember correctly, one of the traction motors on the lead truck was cut out while the unit had the four-axle truck, so it was still six powered axles.
So if only 6 axels were powered at once the only purpose would be to lessen the axel loading i.e. less weight per axel? With 7 axels carring the weight I would think it would have less pulling power than with 6? Less weight on each axel.
On some South American narrow-gauge lines (in Brazin I think) I have seen modified standard SD and GP units with two two-axle sets (AKA net eight axles). They look very interesting. Seeing eight narrow-gauge axles on a standard SD-40.
Was the experiment to test a mechanism for the current 3 axle units like what came out on the SD70 or was EMD thinking about reviving the D-D combination. Would a D-D combination be more helpful today now that you are seeing HP in the 4000+ range. Is wheelslip an issue, or the lack of the ability to get the power down due to wheelslip control?