They do use radio communication, but route knowledge will also pay a large part - so the driver of the assisting loco will know where to shut off power for a speed restriction or give assistance for a gradient etc.
Not sure about steam locos, but I recall diesels having a thing that shuts off power if the brake pipe pressure drops indicating a brake application. Otherwise it could be very hazardous if a train became divided, the brakes came on in both parts but the loco powering at the rear was enough for the portions to re-collide.
Most rear steam locos were banking for short distances and were not coupled, so that they could drop back at the summit. It was a simple process that saw the rear loco buffer up, whistle in readiness and set off. There was little finesse about power application coordination with the lead loco; just open the regulator and plug away until over the top, drop back, cross over to head back to the base of the climb and repeat!
Wasn't that the case too with diesels and The Lickey bankers?
And the Liège bankers in Belgium, those being for passenger trains. The process - as I remember it - was the banking loco would buffer up to the rear of the train in the platform. Dispatch would happen as normal, with the train loco just releasing the brakes. The banker would then power up and start the train moving up to around 20km/h or so before the train loco applied power.
That's the one. Not sure there is even a banker there now any more, with more horsepower on the trains.Is that the bonkers gradient climbing out of Liege towards Brussels? I reckon my Nightjet went up that at about 110mph last autumn, but then we were only 4 coaches hauled by an 8600hp electric loco
Not at Liège, no. The banking locos were not coupled to the train and dropped away before the summit at Ans.
Indeed so. Lickey was unusual in having more than one banker per train as a matter of course (along with Folkestone Harbour) and they would usually be coupled to each other but not to the train. Diesel bankers were less common but could be found mixed with steam. The Consett iron ore trains, for example, would often have mixed 9Fs and class 40s.
What was the gradient there?
Not sure - I’ve struggled to find a source for it. Anyone know?