Is there anywhere online where I can get running data on GWR locomotives? I'm about to buy some decoders to fit to my n gauge steam locos and would like to set realistic running values into the CVs. At the moment I have some kings, halls and a PD Marsh kit for a 9300 class as well as a 47 in First Great Western livery (perhaps I'll leave that one off the layout for now!!).
I guess the top speeds are easy enough to find but can I calculate the acceleration from the traction effort, wheel diameter and weight or is that too simple?
Re: top speeds: What matters more than the loco's maximum speed are the actual speeds allowed on the lines to which the locos were assigned. These varied according to topography, and even more according to train type. Maximum allowable speeds were rarely anywhere near the actual top speeds the locos could achieve. Even top-link expresses ran at less than
60mph most of the time. Unfitted freights had a maximum speed in the
20mph range, and lower if the freight was a heavy one: a loaded coal train might run at not much above walking speed even on the main line.
Re: acceleration: if you want to use prototypical rates, you'd better have _long_ stretches between stopping points. Even a short suburban train would take a half mile (35ft) or more to reach top speed. A heavy express will take a mile or more. Braking takes longer distances: an express in full flight will take about a mile to stop in emergency braking mode, much longer in normal mode (ie, slow enough not to toss the passengers around inside the carriages.)
So: experiment with various values so that the acceleration and braking rates look reasonable on your layout. They will be swifter than if scaled from the prototype, but then we have to make compromises in other aspects of railway modelling, too.
Final point: it may be better to adjust CVs so that all locos run at the same speed at a given controller setting, so that switching between engines won't require relearning controller use. But that's more a matter of personal taste.
It's important to distinguish between design speeds and maximum speeds. Perfect balancing of a steanm locomotive's drivers through all its speed range is impossible. Thus, a steam locomotive's counterweights were designed to provide the best balancing of the drive wheels at the maximum speed range that the loco would be operated in most of the time.
So, a steam loco might be capable of 80 to 100mph, but would be balanced for 60 to 80mph, because it was intended to run at that speed. The occasional record-attempting run aside, locomotives normally did not run above their design speed. Note, also, that if the designed maximum speed was 80mph, time-table timings would be based on a lower speed, so that the driver could push his loco when making up time and still stay within a safe range.
That's why operating speeds of locomotives matter more than maximum speeds when setting up a speed table.
Yes I had assumed that Wolf was referring to balancing the reciprocating forces since rotational irregularities can be adjusted for all speeds assuming perfect bearings. It had not occurred to me before that reciprocating imbalances varied with speed.