True, but they were not terribly heavy for their sizes, and dihedral effect is dihedral effect, regardless of size. It's more a question of proportion and geometry than size that determines roll stability. As I mentioned, just a consideration--wasn't really trying to persuade.

Comparing wing area loadings between aircraft of different sizes is completely meaningless. A meaningful comparison of flight performance between similar airplanes of different sizes requires exponents at the least.

Here is a comparison using area loading between: a 1/6 scale Cub at about 5 ft^2 wing area and weighing 7 lbs - 1.4 lb/ft^2.

and

a full-scale Piper Cub at 179 ft^2 and 1100 lb: 6.14 lb/ft^2.

To get close to the right “scale” weight, you can use the cube root of the wing loading of the prototype times the wing area of the model: (1100/179)^(1/3) = 1.83. Then: 1.83 * 5 = 9.16 lb, which is heavy for a 1/6 scale Cub, but not surprising, since we are trying to get the “scale” weight.

For the “scale” hp, we can get in the ballpark by using the linear scale as an exponent: 65^(1/6) = 2.01 hp, which is probably about what you would need on our 9 lb Cub for scale performance. Most models Cubs are kites anyway.



Now a 33% scale model of a 340 hp, 1600 lb Edge, with 106.2 ft^2 wing area and a 25.17 ft wing span:

(1600/106.2)^(1/3) = 2.47. 2.47 * 11.8 (wing area of the 1/3 scale model) = 29.14 lb. Heavy for prime 3D performance, but this is for approximately “scale” performance.

For the hp: 340^(1/3) = 6.98 hp. A little doggy for a 33% Edge, but again, probably about “scale” climb performance, and if we didn’t need to accelerate straight up from a dead stop on a hot day, (like the full-scale one can’t), it would be adequate. Considering that the Edge's max sustained climb rate is 3700 ft/min (42 mph, or about 20% of it's cruise speed), and a typical model Edge climbs at probably 80% or 90% of it's cruise speed, these predictions pass the "reasonable" test.

Going the other way, if the full-scale Edge was to have performance similar to our model with say, 14 hp at 25 lb, it would have to weigh 1009 lb, and have over 2700 hp! I don't know if this relationship holds up to such extremes when horsepower is converted to thrust.

We could also have used the formulas for power required, but since we are doing ratios instead, we can skip all that.

I know this can be improved upon, and it doesn’t do anything to predict scale speed, if there is such a thing that can be meaningfully expressed. It deals primarily with scaling down of power and weight for scale climb performance, and scale inertial properties vs. lift. This method doesn’t get into aerodynamic theory; it’s basically just curve fitting. It does provide a somewhat meaningful rough first approximation comparison between different size aircraft, and shows the folly of comparing wing area loadings between different size models, or between models and their prototypes.