jecorbett.....I imagine it was quite a bit trickier in the steam era with an engineer in each loco and coordinating the speed of all of them......
In model railroading, this is a seldom-used opportunity ideally suited to DCC operation - multiple steam locomotives on a train, each controlled by its own engineer. No reason, of course, that you couldn't add an mu'd set of diesels, too, controlled by another operator.
Wayne
When the SP was putting trains over Tehachapi with cab-forwards, they used six, two on the point, two 40% of train length back and 2 80% of train length back. The load per pair agrees with more recent SP practice, but less calculation since all pairs were equal.
On my prototype, freights that needed it got a rear end pusher from Agematsu to Kiso-Fukushima. The few steam passenger runs heavy enough to need help took the helper in front of the road loco. Adding and removing that helper was no problem, since those trains were scheduled to stop at both stations.
On the other hand, I have been aboard a passenger train [Up (eastbound,) west of Hiroshima] with a tall-drivered 4-6-4 on the point and an extra-heavy 2-8-2 pushing. The ride in my car wasn't bad...
Chuck (Modeling Central Japan in September, 1964 - with helpers)
dehusman The position of the helpers is determined by the tonnage and the force on the drawbars. Rear end helpers are the most common since they are the easiest to attach and remove, plus they reduce drawbar forces. Head end helpers increase drawbar forces since all the strain is put on the car behind the engine. Mid train helpers are used when the drawbar forces on the rear helper are too large. I have seen pictures of steam era coal trains with a couple engines on the head end, 3 or four midtrain and another three or four on the rear. The simplest description of how they operate with rear helpers, the rear engine shoves as hard as it can and then the lead engine pulls enough to control the speed and move the train.
The position of the helpers is determined by the tonnage and the force on the drawbars. Rear end helpers are the most common since they are the easiest to attach and remove, plus they reduce drawbar forces. Head end helpers increase drawbar forces since all the strain is put on the car behind the engine. Mid train helpers are used when the drawbar forces on the rear helper are too large.
I have seen pictures of steam era coal trains with a couple engines on the head end, 3 or four midtrain and another three or four on the rear.
The simplest description of how they operate with rear helpers, the rear engine shoves as hard as it can and then the lead engine pulls enough to control the speed and move the train.
I should have made clear I was more interested in steam and tranistion era helpers. Although the physics are the same, loco control is not. I have no idea what a DPU is although I'm going to take a wild guess that it is a midtrain or rear pusher being controlled remotely by the engineer in the lead unit.
I imagine it was quite a bit trickier in the steam era with an engineer in each loco and coordinating the speed of all of them.
I've seen a number of videos and still pictures of multiple steam helpers throughout the consist and I believe it was a coal drag. I've also seen steamers leading a multiple diesel lashup. I'm guessing the steamer was the helper.
Dave H. Painted side goes up. My website : wnbranch.com
Mid-train helpers are usually employed on long trains running in mountainous regions; the helpers in the middle aid in going up the grade. It might have a DPU in the rear, but trains with locos on the front and DPUs on the rear with no DPUs in the middle are usually found on more flat terrain.
jeffhergert Here's instructions for placement of helpers from the SP. http://espee.railfan.net/helper.html Jeff
Here's instructions for placement of helpers from the SP.
http://espee.railfan.net/helper.html
Jeff
Nothing complicated about that formula.
Doug
May your flanges always stay BETWEEN the rails
The UP frequently runs mid-train DPUs on Cajon and Tehachapi, but you can also find them on the rear. BNSF runs DPUs on the rear of heavy stack trains.
Mid train helpers(most likely DPU's not helpers) improve train handling by balancing out tractive effort, reducing draft gear strain and bunching of the pushed cars, and also balance and reduce braking times. when an engineer makes a reduction in a train with just headend power the reduction has to travel the full length of the train before the tail cars start braking. With rear helpers/DPU's , the reduction in the trainline moves aft from the headend and forward from the rearreducing the reduction signal travel time. With mid train helpers/DPU's, the braking is further balanced as the reduction signal travels forward and aft from the mid train power, resulting in the brakes applying more quickly and evenly along the entire length of the train.
ACY Passenger trains were rarely pushed from the rear. I understand this is to avoid the rough buff and draft forces, which create a concertina effect in the train, resulting in a rough ride. This isn't universal practice, however. SR used rear end helpers on Saluda grade. This may have been to relieve extreme stress on the draft gear on that extremely steep grade. Once off the grade, a rear end helper (at least in steam days) had to be removed because you don't want excessive buff and draft in a train running at higher speed ranges. A train requiring a second engine would run as a doubleheader if it were dispatched from a major terminal and carded to run the entire distance to the next significant terminal. Freight trains were generally pushed from the rear to avoid strain on the couplers and draft gear. Efficient attachment and removal of the helper can be a factor. If the helper engine can be attached behind the caboose, it is sometimes possible to remove it on the fly, making it unnecessary to stop the train. Some State laws required helpers to be attached ahead of the caboose, complicating the attachment/removal process. Ohio's caboose law banned the use of helpers behind occupied cabooses. B&O got around that by attaching the helper behind the caboose and requiring all rear end train crew members to ride the helper. This meant that the helper couldn't cut off on the fly in Ohio because the crew wouldn't be able to get back on the caboose. There are probably other factors as well. Tom
Passenger trains were rarely pushed from the rear. I understand this is to avoid the rough buff and draft forces, which create a concertina effect in the train, resulting in a rough ride. This isn't universal practice, however. SR used rear end helpers on Saluda grade. This may have been to relieve extreme stress on the draft gear on that extremely steep grade.
Once off the grade, a rear end helper (at least in steam days) had to be removed because you don't want excessive buff and draft in a train running at higher speed ranges.
A train requiring a second engine would run as a doubleheader if it were dispatched from a major terminal and carded to run the entire distance to the next significant terminal.
Freight trains were generally pushed from the rear to avoid strain on the couplers and draft gear.
Efficient attachment and removal of the helper can be a factor. If the helper engine can be attached behind the caboose, it is sometimes possible to remove it on the fly, making it unnecessary to stop the train. Some State laws required helpers to be attached ahead of the caboose, complicating the attachment/removal process. Ohio's caboose law banned the use of helpers behind occupied cabooses. B&O got around that by attaching the helper behind the caboose and requiring all rear end train crew members to ride the helper. This meant that the helper couldn't cut off on the fly in Ohio because the crew wouldn't be able to get back on the caboose.
There are probably other factors as well.
Tom
Any thoughts on the reasons for mid-train helpers?
Helper engines of course have been placed just about anywhere in a train. They sometimes doublehead. Sometimes mid-train. Sometimes pushing from the rear. Sometimes a combination of the above. My question is what factors dictated whether to doublehead the helpers, place them mid-train, or pushers on the rear?