Electroliner 1935 https://runllalpacarun.files.wordpress.com/2011/01/pushmepullyou1.jpg These make me think of some RR executives. All talk and full of it. No place to put a diaper.
https://runllalpacarun.files.wordpress.com/2011/01/pushmepullyou1.jpg
These make me think of some RR executives. All talk and full of it. No place to put a diaper.
Must be a "Two L" Llama.
Norm
Pretty sure that "Pusha-me, Pulla-you" or similar was a photo caption in Trains back in the 1960's or 70's, and most likely for a loco on both ends as tree68 describes, or a commuter cab-car configuration, etc.
- Paul North.
Mac- Thanks for the explanation. It sounds like the smartest cat around has to be the engineer trying to coordidate the DP power from the front end of a mile long train.
Thanks to Chris / CopCarSS for my avatar.
Deggesty Mowgli (which means "frog") was raised by the wolves, a bear (Baloo), a snake (Kaa), and a panther (I disremember his name). In time, he saw to it that Shere Khan was killed.
Mowgli (which means "frog") was raised by the wolves, a bear (Baloo), a snake (Kaa), and a panther (I disremember his name). In time, he saw to it that Shere Khan was killed.
Never read the books, but I know Bagheera the panther because my sister's kids named one of their black kittens Bagheera and he really did look like a panther when he grew up. I say "kids" but they are all well into their fifties now, making their uncle feel even older than dirt.
You can't have the DP units in dynamics while the head end is in power. The system won't allow it, so the manual says. The only way it could happen, and it has to me, is if there is communication loss with the DP.
You can have the DP in power while the head end is in dynamics.
Jeff
Murphy Siding Jeff- If you're on flat ground, do the DP's and the lead power have to be in the same power notch? It's my non-railroad brain that compares this to automobiles. If you're in the lead pulling in 4th gear, and I'm in the back pushing in 1st gear, eventually aren't you dragging me to go faster?
Jeff- If you're on flat ground, do the DP's and the lead power have to be in the same power notch? It's my non-railroad brain that compares this to automobiles. If you're in the lead pulling in 4th gear, and I'm in the back pushing in 1st gear, eventually aren't you dragging me to go faster?
I'm not Jeff, but...
It's already been noted that sometimes the DP is run in Notch 1 just so it's carrying its own weight.
A locomotive not contributing is just another "boxcar." Our holiday trains have a locomotive at each end, mainly so a loco is in the lead and we don't have to do a 12 mile push move. The trailing locomotive is in idle on the way back, as it's mostly downhill. The lead locomotive can handle it, and the trailing loco is simply another car.
On the way north, however, we have about 3 miles where the lead loco can't maintain track speed by itself, and the trailing loco (at the other end of the train) has to function as a pusher.
As has been noted, the DP/pushers are effectively shortening the lead loco's train. Depending on how the power is split, you may have a situation where the lead loco is actually pulling only 2/3 of the train, while the DP/pusher is shoving the other 1/3. Mid-train DP will be pushing some, and pulling some.
I recall reading that in steam days, a pusher loco would start shoving before the lead loco started pulling. The throttle was advanced (gently) until the loco stalled. That bunched up as much of the train as possible before the head end began to pull.
You'll also note that before we reached the point where almost all locomotives were the same HP, you saw some interesting mixes of power in the same consist, from switchers to high-HP six-axle units. As long as they can be MU'd, and can handle the speed of the train, they can be in the mix - they simply contribute what they are able.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
This discussion is a very good lesson in the Law of physics.
Cannonball
Y6bs evergreen in my mind
Murphy Siding Jeff- If you're on flat ground, do the DP's and the lead power have to be in the same power notch? It's my non-rilroad brain that compares this to automobiles. If you're in the lead pulling in 4th gear, and I'm in the back pushing in 1st gear, eventually aren't you dragging me to go faster?
Jeff- If you're on flat ground, do the DP's and the lead power have to be in the same power notch? It's my non-rilroad brain that compares this to automobiles. If you're in the lead pulling in 4th gear, and I'm in the back pushing in 1st gear, eventually aren't you dragging me to go faster?
Murphy,
I will take a stab at this and invite Jeff to confirm or deny. The DPU and head end power can be in the same or different notches AT ANY TIME. Profile is irrelevant to that independent fact.
There is no gear, it is all throttle notch which converts directly to amps in the traction motor, which converts directly to pull or dynamic brake effort.
An automobile is one vehicle that occupies say 15 feet. A train is 100 vehicles that occupies say 5,000 feet. Your rock train will be shorter, a TOFC train longer holding number of cars constant.
Railroad profiles are seldom flat. Curves add resistance to motion. Slack and slack action is a major consideration and DPU operation will always involve a "node".
Resistance to motion in journals is equal to about .2% grade, or 4 pounds per ton. Grade adds 20 pounds per ton per percent. Curves also add resistance. Air resistance varies as the square of velocity, but at low speeds is negligible. Excess draft will break knuckes or stringline a train on a sharp curve. Excess compression will shove wheel flange over the rail on a curve, or roll a rail. Both excesses must be avoided. Our assumed 100 car train is 100 individual vehicles, not a single mass like an auto.
If train is operating on flat straight track it needs 4#/ton tractive effort to maintain speed. A 100 car loaded rock train at 131 tons per car needs 52,400# of TE to maintain speed. Want faster, need more throttle. In steady pulling condition entire train will be stretched out, with successively less pull at each set of couplers as each car absorbs 524 pounds of force.
Things get more interesting where the grade changes. Assume head end enters a 1% upgrade. Now each car needs 2620 pounds of TE for the hill plus the 524 to keep going at steady speed. Obvious solution is more power, increase throttle notches as more and more of train enters the hill.
Now assume head end enters 1% down grade. Now each car generates 2620 pounds of push, less 524 resistance, or roughly 1100 net pounds that wants to accellerate the train. Assume want to maintain current speed, so have to throttle down as ever more cars pass the grade break, and by time whole train is over it we need 110,000# of braking force to maintain speed. Odds are train has sufficient dynamic to hold train, if not need air brake.
Now consider bottom of hill go from 1% down to 1% up, as at Benson AZ. Absent DPU the standard method is to back off dynamic as approach bottom of the sag, and start increasing power at the bottom, going to run 8 fairly quickly.
Consider the node in this move. The node is the place in the train where couplers are in neither buff nor draft. Comming down the grade, there is no node, train is all in buff. Once the engine goes to run 1, it is pulling and there will be a node somewhere back in the train. Done just right the node will stay at the bottom of the sag so the run out from buff to draft is gentle. Probably will not happen that way since standard plan is to go to Run 8 quickly in attempt to outrun the rear end and keep speed for the hill.
Now think about doing this with DPU. The head units can pick up power more slowly, since they are not trying to outrun the rear end AND the rear units should stay in Dynamic until they are approaching the sag even though the lead units are probably in Run 8 when the DPU goes to power near the bottom of the sag.
Locomotive engineers have to think much farther ahead than do auto drivers. Their train is a series of separate vehicles and none of them can be subjected to excess forces without undesireable consequences, or VERY undesirable consequences.
Mac
A further note: is there something aboout the name "Paul,"which kept them from getting a full education?
Johnny
Yes, Paul, if you never read, or had read to you, the Jungle Books, which are primarily about an Indian baby who was taken from his family by a tiger, Shere Khan, who had to give his prey up to Akela, the head of a wolf pack. Mowgli (which means "frog") was raised by the wolves, a bear (Baloo), a snake (Kaa), and a panther (I disremember his name). In time, he saw to it that Shere Khan was killed.
As I recall, the Doctor Dolittle series was written by Hugh Lofting. While I read some of Kipling's work, I must have missed the Mowgli. Some of these guys are trying to get us off topic by talking about DPU's.
_____________
"A stranger's just a friend you ain't met yet." --- Dave Gardner
If the track levelled out, those DP units may not have been working as hard. DP's can be operated independently from the head end, but I doubt they were just in idle. I would think the engineer at least had them in notch one to help move themselves.
Right now, all of our empty grain and coal trains with DP are restricted to running the DP now higher than notch 4. We can use them in full dynamics, but not in power (higher than 4) for fuel conservation. That's better than what they first tried out, running the DP in notch 1 on the empties.
Paul_D_North_Jr https://en.wikipedia.org/wiki/List_of_Doctor_Dolittle_characters#The_pushmi-pullyu I had thought it was in something written by Rudyard Kipling . . . - Paul North.
https://en.wikipedia.org/wiki/List_of_Doctor_Dolittle_characters#The_pushmi-pullyu
I had thought it was in something written by Rudyard Kipling . . .
Modeling BNSF and Milwaukee Road in SW Wisconsin
Murphy Siding The Dakota & Iowa runs Distributed Power on their rock trains running through our area. Last night I watched a train head south out of town up what appears to the naked eye as a slight incline. The two old Geeps on the tail were working loud and hard to push the loaded train. Several miles down the road, I encountered the same train cruising through the corn fields at about 45 m.p.h.The DP units were silent. I thought that DP power was active all the time, not just for hills, that the back engines pushed half the cars while the front engines pulled half the cars. With the exception of the little incline near my house, I believe the entire 80 or so miles to Sioux City, Iowa runs downhill for the loaded rock trains. Would that mean that the DP units are on the train to work that little mile long incline, but are just deadweight for most all of the other 160 mile round trip? Through Sioux Falls, the loaded rock trains do go down a BIG hill for about a mile. Would the DP units be on the train to help with braking as well?
The Dakota & Iowa runs Distributed Power on their rock trains running through our area. Last night I watched a train head south out of town up what appears to the naked eye as a slight incline. The two old Geeps on the tail were working loud and hard to push the loaded train. Several miles down the road, I encountered the same train cruising through the corn fields at about 45 m.p.h.The DP units were silent. I thought that DP power was active all the time, not just for hills, that the back engines pushed half the cars while the front engines pulled half the cars. With the exception of the little incline near my house, I believe the entire 80 or so miles to Sioux City, Iowa runs downhill for the loaded rock trains. Would that mean that the DP units are on the train to work that little mile long incline, but are just deadweight for most all of the other 160 mile round trip?
Through Sioux Falls, the loaded rock trains do go down a BIG hill for about a mile. Would the DP units be on the train to help with braking as well?
DP is under the control of the Engineer. If he needs power from the distributed units in addition to the controling power - he uses his DP controls to command the power from the units, when no longer needed he returns the to idle. He can also command Dynamic Braking from the DP units when required.
Never too old to have a happy childhood!
The Dakota & Iowa runs Distributed Power on their rock trains running through our area. Last night I watched a train head south out of town up what appears to the naked eye as a slight incline. The two old Geeps on the tail were working loud and hard to push the loaded train. Several miles down the road, I encountered the same train cruising through the corn fields at about 45 m.p.h.The DP units were silent. I thought that DP power was active all the time, not just for hills, that the back engines pushed half the cars while the front engines pulled half the cars. With the exception of the little incline near my house, I believe the entire 80 or so miles to Sioux City, Iowa runs downhill for the loaded rock trains. Would that mean that the DP units are on the train to work that little mile long incline, but are just deadweight for most all of the other 160 mile round trip? Through Sioux Falls, the loaded rock trains do go down a BIG hill for about a mile. Would the DP units be on the train to help with braking as well?
Our community is FREE to join. To participate you must either login or register for an account.