RE: What is cubic wing loading????
Actually, the 1.5 power thing is based on some valid stuff. The idea is to calculate the weight spread over the volume of the wing instead of the area. So, to truely calculate the volume loading of a plane, you take (wingspan) * (average area of a wing rib).
But wing ribs are hard to measure for area.
However, if you make a base assumption that everyone is using pretty much the same airfoil with pretty much teh same thickness, then, and only then, you can compare two models of different sizes buy just raising the area to the 1.5power. So, if you want to compare two IMAC planes, it works. If you compare an IMAC to a Cub, it doesn't. Compre two cubs, and it works again.
If you take the time to compare two planes with the same wing area, but one has a 9% thick airfoil, and the other a 18% thick airfoil, you know that wing area loading isn't enough to predict things like low speed handling. But if you do something to factor in the airfoil thickness, you can get a better comparison. That something is volume loading using the acutal volume of the wing.
The 1.5 thing is an easy short hand for a special case, that's all. But it does work, for a quick and dirty number in it's intended limited scope.