SP5103 Wrote:
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> Sorry, overlooked you showed it as a 3.2% grade in
> your first post.
>
> Video is interesting because something is really
> wrong here.
>
> EMD doesn't show specs for a P4 on their website,
> but show a standard SD70Ace is rated at 155,000
> pounds continuous tractive effort. Assuming a P4
> would be 2/3 that, it should be about 103,350 cte
> at about 37% adhesion (assuming it is ballasted
> heavy) which should be within its capability at 10
> mph. A 3GS21B at 1950 hp should be generating
> about 58,500 pounds TE at 10 mph and need about
> 23% adhesion.
>
> With both P4s and the genset the tractive effort
> at 10 mph should be about 265,200 pounds. 3.2% is
> 64 pounds/ton resistance plus add some for normal
> rolling resistance and a little curvature say 70
> pounds/ton resistance. 265,200/70 = 3,790 tons
> less the engines at 560 tons (ballasted heavy)
> leaves about 3,200 tons theoretical tonnage rating
> (22 loads at 143 tons).
>
> From the video of the train you can see the second
> cut has several (6?) empty flats being used as
> spacers for overhanging loads. Assuming all loads
> are at 143 tons and the empties at 30 tons, the
> train should have only been about 3,600 tons - a
> little more than what the guesstimated tonnage
> rating should be. I estimate the trailing tonnage
> on the first cut of 10 loads to not exceed 1,430
> tons and the second cut at 2,200 tons which
> assumes there aren't any 263k cars.
>
> Note that on both cuts, the #2100 has all three
> engines running. (Is it my imagination or is the
> NRE unit with green and clean engines generating
> more visible exhaust aka particulates than the
> dirty ole EMDs?) On a 3GS this typically indicates
> that the throttle is in Run 6 or better. In Run 6
> (75%) the consist still should have been capable
> of pulling about 2,280 trailing tons up the hill
> at 10 mph.
>
> Looking at it another way the 10 loads of the
> first cut should be no more than 1,430 trailing
> tons plus 560 tons for the power is no more than
> 2,000 tons total @ 70 pounds/ton resistance
> requires 140,000 pounds tractive effort. At 10 mph
> you would need about 4,700 hp on a conventional DC
> consist. So why are three engines with 10,500+
> potential struggling to move the first cut that a
> pair of GP39-2s could theoretically handle?
>
> I'm impressed - by how poor the engines are
> pulling. The leaves and low joints are probably
> causing the P4's to derate to keep their feet.
> Even derating to 25% adhesion the P4s should be
> very capable of 67,000 pounds tractive effort
> which 67k+67k+58.5k = 192,500/70 = 2,750-560 =
> 2,190 trailing tons or 15 loads at 143 tons.
>
> I don't see where the P4s are worth 2 cents in
> this application.

I agree..or maybe I've missed something in my 50+ years railroading?

Always was taught that weight on powered axles and the availability of as many HEAVILY LOADED POWERED axles was what moves trains. At the speed they are limited to a bunch of horsepower on six axles with only four of them powered running on steep grades with jointed rail, Washington rain and leaves makes no sense. Why they would want two less motors in long wheelbase trucks under these conditions is beyond me!

The reason that slugs are so popular is that they put four to six more heavily weighted MOTORIZED axles to work utilizing the excess power output of the "mother". In my book, a pair of GP39's each mated to a slug would give twice as many powered axles with less curve resistance and wheel wear.

But then...what do I know?

Dick Samuels
O P R