Terry Bendall wrote:I don't see how this can apply since the mass of the model is not scaled down from the prototype. As the model engineering fraternity have found with things like steam ports, you cannot scale nature.
The mass is scaled down OK but it's the weight that is not. You see as I said earlier you can't scale time and therefore you can't scale gravity.
If you want to reproduce the dynamic effects on our models you have to run them approximately 8 (8.72 actualy) times faster. So if you wish to reproduce the dynamics of Mallard doing its record breaking run of 126mph then you have to run the model at 1000mph. You then realise what an achievement the actual Mallard run was.
Of course we don’t want to do that because what we are interested in doing is essentially modelling the static dimensions. We must therefore accept that we need to find methods which enable us to allow the model to move and stay on the track. RTR manufacturers do that by employing deeper flanges etc. We do it by introducing non-scale springing and of course weighing up our models with lead (which is an attempt to correct the mass/weight mismatch).
The bottom line is that you can't have linear fidelity and dynamic fidelity at the same time.