DPU locomotive

how does this engine get controlled from the lead locomotive? i don't see any cables or anything between the cars. And just why are they only on coal trains, is it something to do with weight?

I could be wrong, and corrections are welcome, but I think they are remote controled (via radio signals). That is why you see so many antennas on the roof of a locomotive. As far as using them on coal trains, yes I think is simply has to do with the weight. Using DPUs reduces the amount of stress on (mainly) the front few couplers. I have actually seen pictures of coal trains that have pulled the coupler and draw-bar clean off the first car, and it was just hanging there, still attached to the last locomotive. Here is an example http://www.railpictures.net/viewphoto.php?id=71078

Kevin B. wrote:I could be wrong, and corrections are welcome, but I think they are remote controled (via radio signals).

This is definitely the case. RF-controlled distributed power is one of the success stories of modern railroading.

Kevin B. wrote:As far as using them on coal trains, yes I think is simply has to do with the weight. Using DPUs reduces the amount of stress on (mainly) the front few couplers.

Confirmed. Add to the this the huge amount of tractive effort that modern locomotives are able to transmit through couplers and the stress on them is increased dramatically. Adding power from behind keeps this within tolerances for draft forces.

Coupler knuckles are designed to give first, thus saving the coupler that's under extreme stress. Sudden and/or overwhelming forces can, however, result in the effects seen in Kevin's photo.

so that explains what those little white boxes on the cab roof are for.

Again, I think I'm right in telling you that most of the white boxes you are talking about are GPS antennas. They are used to track where a train is.

Now, I could be wrong, but judging from the placement of the "white box" in that photo, isn't that the air conditioning unit sitting on top of the cab? It looks to be about the right size for that.

Komachi wrote:Now, I could be wrong, but judging from the placement of the "white box" in that photo, isn't that the air conditioning unit sitting on top of the cab? It looks to be about the right size for that.

yeah, it kind of resembles the AC units on the BNSF (ex SF) B40-8's, although I thought the air conditioners on the SD75's were located right behind the conductor's rear window, i reall dont know, there was some topic on that a few months back... oh wait, here it is http://www.railroad.net/forums/viewtopic.php?t=4074

I think the antennae are both GPS and radio...I mean the box is big enough, right?

OK, here is a Dash 9 with the box antenna and two "skate" antennae. http://www.railpictures.net/viewphoto.php?id=65950 Most of the newer locomotives seem to have the boxes, and most older ones have the skates...I have no idea why this one has both. Whatever it is it ain't the air conditioning...

One of the biggest advantages of DPU has do with braking.
The remote unit charges and vents the brake pipe just like the controlling locomotive so the brakes are applied and released from both ends of the train rather from the head end only. Much better control of slack and shorter stopping time. Have you noticed that you dont hear much about electrically controled air braking systems since DPU came along?

Funny, it seems the only railroad i have seen so far using DPU's is Union Pacific. The only other local railroads here in southern illinois besides UP (such as BNSF and Illinois Central) that haul coal don't use them. Is this a west coast thing?

DPUs are mostly used in hilly/mountainous regions. That's why you wouldn't see them in IL, Chris. UP is odd though, they use them here in flat Illinois on coal trains.

I've seen BNSF using DPUs on the Thayer Sub on the way to Memphis from the Ozarks.

I saw an empty coal going through McCook, NE on Nov. 14 that was a DPU. Two Motors. One on the point and one on the rear.

BNSF uses DPU on all the loaded coal trains I've seen, but the empties are sent back to the mine with all units up front (and some isolated). They're also used on grain trains, taconite trains, and other heavy unit trains.

The purpose of the white domes on the roof of the cabs is to prevent water from leaking in. With all the antennaes that modern locomotives have water leakage has become a major problem. The easiest solution was to cover them all under one housing. Hence the white domes.

Stuart