The way that the coal naturally falls into an enclosure (like a tender) is known as the angle of repose. I suppose that, at times, the top of the coal pile was "manually trimmed" with a shovel by whomever was in charge of the chute!
I also would be interested in knowing how well the model runs, especially speed at a "standard" voltage, say 12 VDC. Also, what voltage is the engine designed for...or can use? I suppose that with a sound system better operation might be at 18 volts?
