Originally Posted by
CristianTabush
I have an observation on this, which has always intrigued me. While the laws of Physics remain the same, I think the application might change a bit. I think where things get tricky is that Surface area increases ^2 and volume increases ^3.
That's the crux of the problem if one desires to get data from a scale model and accurately apply it to a full-scale model (or vice-versa).
Originally Posted by
CristianTabush
One example that stuck in my brain was the effect of down force at the slower speeds affected our cars.
Aerodynamics is one of the disciplines where scale models are used since large wind tunnels are expensive, but getting useful data that extrapolates back to 1:1 scale is difficult because the air itself isn't scaled; i.e. the distance between molecules doesn't shrink by a factor of 10 for a 1/10 scale model if the tests are run at normal atmospheric pressure and temperature. The general goal is to run the scale model in the wind tunnel at the same Reynolds number if one wants reasonable data to use on the full-scale vehicle. This value is dependent on many factors such as density and viscosity of the medium, and velocity. Also, the equations that describe aerodynamics well are wildly non-linear, which adds to the fun.
Aerodynamicists in both the aviation and automotive industry constantly yearn for ever-larger wind tunnels so that they can more accurately predict what will happen on the actual vehicle.
Small models are actually less aerodynamically efficient than one might guess, because they operate at lower Reynolds numbers. Small model airplanes don't generate lift as readily as real airplanes, and small model cars don't generate downforce as readily (though it can still be substantial). Imagine how good these things would stick to the track if the air were 10 times thicker!