davebradwell wrote:...I doubt if you could measure the effect uneven weight distribution has on haulage, Will. Apparently it does make a difference on the prototype, where once the first wheel slips there's enough inertia to knock the legs from under the others but I've never noticed it in 4mm scale where the greatest haulage is generated by turning the controller to full and spinning the wheels... (quoted out of order) Perhaps there just isn't enough weight in our models for them to behave like the full size.
Not convinced. The adhesion available from our chassis derives from the coefficient of friction between wheel and rail. The calculation is based on a linear equation so the implications are not affected by scaling and won’t differ between model and prototype. The static version of the coefficient of friction, which applies when the wheels aren't slipping, is significantly higher than the kinetic variety that applies when they are (0.6 as against 0.4), and it is this fact that leads to a slipping chassis having less adhesion,
see this post to have it spelled out in detail.
...If I jacked up the springs on the leading axle of the 4-4-0 to pinch some weight from the bogie (and the trailing axle) I would expect it to pull more and I've done it on a 4-6-0 which was reluctant to pull the required 10 coaches up a 1 in 100 so a little weight transfer from the bogie was required.
Given the very real difficulties there are in judging exactly what the spring rate is for a individually adjusted spring, I don't see how you can know what the weight distribution actually was before or after such an adjustment. Clearly you achieved an improvement, but I don't think you can claim to know why it worked. The advantage of CSBs being that you do have some control of what the weight distribution actually is, and that is exactly why I prefer them to individually adjusted springs. We may need to agree to differ on this one until such time as we have available to us an accurate single axle weigh bridge that works in 4mm scale. This being a very tricky problem to solve as the late lamented Don Rowland demonstrated.
Don't the world's freight locos now use a 3rd type of friction when the wheel is just starting to slip in order to get massive loads under way?
My understanding, and I could be wrong, is that what modern locos do is to monitor each wheel/axle individually for slip and reduce the power to that axle so it stops slipping. That way they deliver the maximum available adhesion and take fully into account not just the weight on a particular axle but also the condition of the track under each wheel.