QUOTE: Originally posted by uzurpator Oh my... Power sets the rate of which work is performed. 2000 hp loco will need 1/2 of time to do the same job that 1000 hp loco would do. Also - if we disregard adhesion limit - 2000 hp loco willl pull twice the tonnage of 1000 hp loco. The problem lies in the fact that adhesion is limited - mostly by locomotive mass and efficency of wheel slip control systems. So - gp38 (2000 hp) with 55000 lb of TE is at its adhesion limit. gp40 (3000 lb) could theoreticlly do 82500 lb TE, but adhesion will limit it to about 55000 lb... So pretty much 1000 hp is not used. hence the idea of slugs - the "extra" 1000 hp at slow speed is sent to the slug thus increasing TE to 110000 lb.
"No soup for you!" - Yev Kassem (from Seinfeld)
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
QUOTE: Originally posted by BR1116 So if you have a 14000hp electric that only weighs 200,000lbs and can only provide 85000 TE, vs a 3000hp diesel electric that weighs 400,000 and can provide 100,000 TE, the Diesel could move a heavier train, but the electic would go faster and climb a steeper hill? Just to be clear... or am I confused..
QUOTE: Originally posted by oltmannd QUOTE: Originally posted by dharmon Okay, I think I'm good on the general horsepower vs. tractive effort concept (starting power vs speed) but now I have a couple of questions: 1. I was on the GATX leasing site. The GP38s are listed as2000 HP, weigh 250K average, and have a TE of 58K/lbs @ 10 MPH. The GP40s show as 3000 HP units, weighing 257K average, but have a lower TE at 55.4K/lbs @ 10 mph. Both show to have the same traction motors. I was under the impression that the greater weight would give a greater TE, but in this case it seems it doesn't. Similiar but less. Why would this be? 2. In Gabe's thread about reduced horsepower in rebuilds, one of the members mentioned that a shortline may not need the additional 1000 HP of a GP40 when a GP38 with essentially the same TE would suffice. Makes sense to me. Now that being said.....St Lawrence and Atlantic uses GP40s as mothers for their RM1 RoadMATES. Many of the pictures I have seen show two mother / slug units in consist (4 units total) in the lead. My understanding is that about 25 mph after the train gets rolling, the slugs get shut down......extra tractive effort to start the train, then HP from the 2 GP40 mothers take over once its going.....so I guess the question would be why GP40s instead of GP38s as mothers? Is the extra 1000 HP what is needed to pull the train once in motion or is it also needed to generate the extra juice for the the slug or both? Dan Answer to #1 Normally, the TE rating specified is for the thermal limit the traction motors, so, regardless of weight, you'd have the TE rating at minimum continuous speed. For an EMD four axle, with 62:15 gears and D77 motors, that would be 55,000#. To find the minimum continuous speed (MCS), use the formula: TE (lbf) x speed (mph)/308 = HP For 2000 HP you get 11.2 mph For 3000 HP, you get 16.8 mph But, if you want to run a GP38 with a GP40 and get the max TE out of the consist, you have to "throttle back" the GP40 at speeds below 16.8 mph. EMD offers electronics that does this for you automatically such that the MCS for a GP40 would be about 11 mph. The weight of the loco will determine what adhesion is needed to get that force to the rail. For a 250,000# GP38 to get 55,000# to the rail, it would require 22% adhesion. This is achievable under good conditions, but the "all weather" rating for IDAC/WS10 EMDs, is more like 18%, so you'd only be able to count on 45,000# TE day in and day out. Answer to question #2: A GP38 and a slug will move the same tonnage as a GP40 and a slug. You could repower a locomotive with a Ford Power Stroke diesel @ 200 hp or so and still move the same tonnage. But, how slow do you want to go? 50% more HP = 50% more speed. You want to go up your max grade at 11 mph or 8 mph? The difference might be significant with respect to your operations.
QUOTE: Originally posted by dharmon Okay, I think I'm good on the general horsepower vs. tractive effort concept (starting power vs speed) but now I have a couple of questions: 1. I was on the GATX leasing site. The GP38s are listed as2000 HP, weigh 250K average, and have a TE of 58K/lbs @ 10 MPH. The GP40s show as 3000 HP units, weighing 257K average, but have a lower TE at 55.4K/lbs @ 10 mph. Both show to have the same traction motors. I was under the impression that the greater weight would give a greater TE, but in this case it seems it doesn't. Similiar but less. Why would this be? 2. In Gabe's thread about reduced horsepower in rebuilds, one of the members mentioned that a shortline may not need the additional 1000 HP of a GP40 when a GP38 with essentially the same TE would suffice. Makes sense to me. Now that being said.....St Lawrence and Atlantic uses GP40s as mothers for their RM1 RoadMATES. Many of the pictures I have seen show two mother / slug units in consist (4 units total) in the lead. My understanding is that about 25 mph after the train gets rolling, the slugs get shut down......extra tractive effort to start the train, then HP from the 2 GP40 mothers take over once its going.....so I guess the question would be why GP40s instead of GP38s as mothers? Is the extra 1000 HP what is needed to pull the train once in motion or is it also needed to generate the extra juice for the the slug or both? Dan
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QUOTE: Originally posted by CSSHEGEWISCH Slugs are inherently low-speed motive power, and are often used with a high-horsepower road unit to get the extra tractive effort at low speeds out of the extra horsepower that otherwise could not be used due to adhesion limits. A GP40/slug set would be roughly equivalent to 2 GP7's. Notice that most road slugs are paired with GP40's (CSX and PAL) and SCL's MATE's were paired with U36B's. CSX road slugs and perhaps others are equipped with fuel tanks to supply extra fuel to the mother unit.
QUOTE: Originally posted by adrianspeeder I thought the Geep 40 was turboed and the 38 wasnt, so yards and such want a 38 not to deal with turbo problems. Adrianspeeder
QUOTE: Originally posted by Randy Stahl QUOTE: Originally posted by dharmon QUOTE: Originally posted by HighIron2003ar A slug is a desiel with no prime mover, just the traction motors with perhaps more weight added, it would need a mother unit to feed it. What I was getting at was.. Does the extra 1000 HP of the GP40 make it more advantageous because that HP is going to support the slug's tractive effort (ie powering it) without affecting it's own tractive effort or does that extra 1000 HP over the GP38 let it move the train at say 40 mph vice 20 mph once it gets moving and the slugs shut down? Why would they choose the GP40 as a mother for the RM1s vice a GP38? With a GP-38 it may not get up to 20 mph very fast if at all. Remember that you must divide the current output from the main generator by 8 instead of 4. The AR-10 is a constant kilowatt machine. After 20 mph the slug really isn't needed anymore . Time to go into parellell and really get going. The GP -38 is not a low speed locomotive at all. On the Milw we used them for short fast trains. As far as I know, for a while now railroad wheels are all made from the same thing, steel. Randy
QUOTE: Originally posted by dharmon QUOTE: Originally posted by HighIron2003ar A slug is a desiel with no prime mover, just the traction motors with perhaps more weight added, it would need a mother unit to feed it. What I was getting at was.. Does the extra 1000 HP of the GP40 make it more advantageous because that HP is going to support the slug's tractive effort (ie powering it) without affecting it's own tractive effort or does that extra 1000 HP over the GP38 let it move the train at say 40 mph vice 20 mph once it gets moving and the slugs shut down? Why would they choose the GP40 as a mother for the RM1s vice a GP38?
QUOTE: Originally posted by HighIron2003ar A slug is a desiel with no prime mover, just the traction motors with perhaps more weight added, it would need a mother unit to feed it.
QUOTE: Originally posted by daveklepper Different gear ratios would explain the difference. The higher tractive effort results from a gear ratio that has the wheels turning slower for given speed of rotation of the motors.
QUOTE: Originally posted by martin.knoepfel another question as to slugs. wouldn't it make sense to equip them with an extra-large fuel-tank, to avoid refuelling-stops? the larger tank can occupy the space under the empty hood. of course, you need a flexible pipe-connection between mother and slug.
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