Is high horsepower per axle really neccessary or even better for high speed work(60 to 75 MPH)

[ericsp]

You all might find this thread interesting.

http://www.trains.com/community/forum/topic.asp?page=2&TOPIC_ID=19048

[Anonymous]

Simple college dynamics ... work = force x distance, power ( as in horse power) = work per unit time. If you want to go more distance in a given time you are doing more work per unit time,so you need more power, thus higher horsepower. Axles, friction coefficient and weight on an axles yield traction, thus a need for 6 axles while speed (provided you have the traction) depends on horsepower. Hence the U23C and SD39, relatively little horse power but 6 axles, thus good for lugging, not speed and the GP60M, only 4 axles but high horsepower, good for speed but not lugging. Horsepower and traction are both handy for acceleration since force = mass x acceleration, work = force x distance and power = work per unit time. Classic example was the use of FM Trainmasters for the SF commuters. Required was both highspeed (2400 HP) and frequent acceleration (2400 HP and CC trucks). You knew college had to be good for something!!!!!

[Anonymous]

Overmod,

Thanx again fro the quick reply!

My question centered around pre 1990's motive power philosophy. Mostly GP40's in the east and SD40's in west for high speed work . But also what was the facination that Santa Fe and SP had for the GP60 and B40-8 for their premium hotshots and CSX and Conrail had for the B40-8 for the same kind of work hot TOFC hotshots.

I know with advent of the C40-8 and more importantly the Dash9-44CW, which incidently has about the same HP per axle as the GP40-2, the super high HP C-C locomotive have pretty much won the day kind of like old Espee of the late 60's and 70's which elevated the SD45 as do everything locomotive. Dragging freight over Donner Pass to speeding the Blue Streak at 70 MPH on the Sunset Route. All that with fewer cylinders, much better fuel consumption, super wheel slip control and more efficient DC electrical transmission.

But out there is the Union Pacific and to a greater extent CSXT giving the AC6000CW the old college try for high speed intermodal and mechandise work. A bridge too far or the wave of the future???

PS, I remember how C-C trucks of the past were not very good for high speed work. When I was is high school I remember how the then new fangled E60CP destroyed the track at 100 MPH prolonging the career of the GG1 even longer than anyone had expected!! So are GE's Hi-Ad "inline roller skate" truck track better at 75+ MPH than the old Adirondack trucks?????

[Overmod]

Horsepower per axle, per se, is somewhat immaterial; in fact, the more the horsepower per axle, generally the larger the size, weight, and rotational inertia of the motor -- none of which are good things for high speed.

The point of B trucks, historically, is that they weighed less and could be designed to have better suspension and track better than C trucks. That's still true of extremely-high-speed designs. It's not true for 'standard' B trucks vs. good radial-steering C trucks (HTCR-II being a good starting place) -- especially radial C trucks with good secondary suspension to the locomotive carbody, and progressive lateral compliance.

For all intents and purposes, the advantages of the B-trucked locomotives translate as suspension advantages, not traction-motor or "horsepower" advantages -- and they all more or less derive from lower mass and lower costs associated with that.

You don't "feed the traction motors the full 3000hp" below a certain critical speed... as others have already noted. You don't get 'more' benefits out of the 3000hp above a certain range of speeds... as others have already noted. Acceleration is a function of effective TE (which favors more axles) and weight (which favors fewer) -- you can't answer that one 'absolutely' without knowing the profile, the train, etc. etc. etc.

Now, for "3000 hp" the answer is probably going to be B-B locomotives, because 3000hp is ridiculously small by 'high-horsepower' standards. When you get up to the B40, P42, etc. categories, the only reason you get away with that kind of power at all is because modern wheelslip systems significantly derate the amount of power that would otherwise go into amazing slip with most kinds of trailing resistance "economically justified for speeds under 79mph" -- the net effect of which is slower acceleration due to lower effective adhesion (the same result as noted above).

There are more electrical losses associated with more traction motors -- so at high speed it may be more efficient to run fewer motors. However, as soon as you get into high amperage conditions or heat restrictions (as in tunnels) you start to hit hourly and even instantaneous rating limits -- oops, where's my big savings? Again, you couldn't coherently answer this sort of question without knowing specifics.

I think the 'effective real-world answers' to your question conform to this general assessment: the NS Northeast Corridor experimental train 25A (and essentially all the surviving electric locomotives) used B trucks; however, essentially all modern high-speed road power for general service since about the mid-Nineties has used C trucks... but doesn't run much above 74mph for perfectly logical economic reasons, and is more flexible -- in general service -- than an equivalent locomotive with four rather than six powered axles.

(I might add that imho the future of very-high-speed freight locomotives will involve more, rather than fewer, powered axles, but that has little to do with perceived horsepower per unit...)

[Anonymous]

Gentlemen,

My original question centered on whether having a high HP per axle rating like 750 HP per axle of the GP40-2 all the the way the the whopping 1000 HP per axle of the B40-8 is more advantagous for sustained high speed as opposed to the relatively low 500 HP per xale rating of the SD40-2 and C30-7 which is the the same HP per axle of the lowly GP38-2.

In other words IS FEEDING JUST FOUR TRACTION MOTORS THE FULL 3000 HP IS BETTER FOR ACCELERATION AND/OR MAINTAINING SPEED THAN FEEDING THE THE SAME 3000 HP ACROSS SIX TRACTION MOTORS ???

Or is the ONLY advantage of such high horsepower B-B's such as the GP60 and the B40-8 have in high speed work is that they typically weigh 60 to 70 tons less than their C-C counterparts ????

[Anonymous]

My understanding of the U.P. Fast Forties and Centenials is they were used for early premium TOFC M&E trains(Super-Van and South Seatle Special) to compete with the Sante-Fe Super-C and SP Starpacer. Both UP routes were longer so they either had to go faster or loose the business. According to the LA&SL book by John Signor the Centenials had 59:88 gearing for an 83 mph top speed. A common configuration for the L.A. - Chicago trains was 2 Centenials with 1 Fast Forty and there are numerous pictures of that configuration as well as 3 Centenials. They were used on other Hotshot trains as well.

[kevarc]

Fuel and maintanence costs where a big factor in regearing them also.

[Overmod]

Let me add just a touch to the excellent explanation so far, and address Colin's original question a bit at the same time.

You'd want the added hp per unit for high-speed sustained service. I think Colin has been looking specifically at the UP "Fast Forties" with respect to high-speed gearing; one of the points here was to keep critical traction-motor rotational speed in line for locomotives that would spend considerable time at high rpm. I have always been interested that UP built so many of these, then ran them for so short a time in high-speed trim. With the traffic drop after 1980 (and before the MOP-UP merger) I think they regeared just about all the converted SD40s within a couple of years -- and, perhaps more significantly, never up-geared them again even when traffic picked up. What this indicates to me is a confirmation of what Mark has said in earlier posts: the top speed realistically achieved by standard-geared SDs is plenty fast to get the job done, and the added TE achievable from the lower gearing is, of course, significant.

It's been mentioned before that some AC traction motor designs aren't rotational-speed-limited in the same way that brush-equipped and/or wound-rotor traction motors are. That makes the relative effect of higher gear ratios on AC-motor locomotives somewhat less important (and I suspect that common gearsets, wheel sizes, etc. may become important in some cases, although I am aware of the special (larger) wheel sizes on some modern AC locomotives)

[Junctionfan]

Thankyou for your answer. That also answers other questions I was going to ask.

[Junctionfan]

How much merit do the SD90ACs (6000 hp) versus the SD90/43MAC (4400 hp) or like wise the AC6000CW and the same thing de-rated to 4400 hp?

If something requires 10,000 hp , which is better; 2 6000 hp or 3 4400 hp locomotives for either flat or graded hauls?

[Anonymous]

Is high horsepower per axle really neccessary or even better for high speed work(60 to 75 MPH)??

In the recent past the western RR's like the ATSF, BN and UP used high geared C-C like (59:18) F45, SD45-2, Fast Forty SD40-2 and (60:17) SD40 and SD40-2's for high speed work like TOFC/COFC and perishable produce reefers.

But the eastern RR's such as NYC, SCL and B&O relied HP B-B's like the GP40 and the U36B which had a horsepower per axle rating of 750 HP and 900 HP respectively.

So why the western RR's use 3000 HP C-C unit for high speed work even though they have the 500 HP per axle rating of GP38???