Here's another way to look at the effect of wing loading relative to larger airplanes:

When we fly a model, our perception of speed comes down to how many "fuselage-lengths-per-second" it appears to travel. So if you take two models, one 24" long and one 48" long, but traveling at the same speed, the bigger model only appears to be going half as fast. And, you can let the bigger model get twice as far away before it seems too far out to control easily. You can check this out for youself by watching a large airliner come in to land. They seem to fly impossibly slow compared to a model.

In addition to the visual size effect, there is the damping effect. If we go back to the two models, one 24" and the other 48", both at the same wing loading, the larger model will be more heavily damped in all axes by the air that flows around it. Thus, the model is visually and physically easier to fly.

Now, how much heavier does the 48" airplane have to be in order to fly at the same "fuselage-lengths-per-second" as the smaller airplane? It works out that you have to increase the weight (and thus wing loading) by the square of the scale ratio in order to make the twice as large airplane fly twice as fast. So the 48" airplane would have to be: 2 squared, or 4 times as heavy to appear to fly at the same speed.

Am I discounting Reynold Number effects? Definitely not. The higher Rn is pure icing on the cake for making larger models fly better.

To cite some personal experience on this scaling business, here is an experiment that I was involved in back in the late 1960's: I was working on an unmanned flight test vehicle at Edwards AFB which would be flown by a pilot in a ground based cockpit, much like the Predator drones of today. The only problem was that we didn't have forward looking TV in those days and so the decision was made to transfer control to a regular RC pilot for the landing. Somehow I was appointed the RC landing pilot.

Since this was a very expensive test article, we did not enter into the enterprise carelessly. One of the preparatory exercises was to evaluate my ability to percieve height, speed, turning radius, etc. of a faster and larger aircraft while standing at the planned landing site. I positioned myself alongside one of the drylake runways with a communications radio. Then an airplane was flown into my vicinity from which I directed the pilot in turning and power adjustments to guide him down to my planned touchdown spot. I did this with a B-52, an F-111, and an OV-10 in order to evaluate a range of aircraft sizes and wing loadings. You don't even want to think about the wing loading of an F-111, by the way. Anyhow, the result was that all three of the evaluation aircraft could be easily be "flown" to the planned touchdown spot, including the flare. In all cases, a typical sport/pattern model seemed faster than the big airplanes.

Did the test program work out? Yes, but we only got to make one flight with the final vehicle before we lost our launch aircraft. We had borrowed an SH-3 helicopter from NASA Houston for our launcher and somehow they wanted it back for final water rescue training of some guys who planned to go to the moon.

Dick Fischer