One of the most difficult decisions one must make when trying to create a scale model of an iconic plane, is how much to deviate from the original.
Ideally, everything should be exactly to scale. But this will often result in a plane that is difficult -if not impossible- to fly.
For the CL-415 this is most obvious in the tail section: The two vertical fins in the horizontal stabeliser are slightly angled and will force the plane to the right. This was apparently done to compensate for the increase in engine power in the design upgrade from CL-215 to CL-415.
To me, this will lead to an unacceptable flight performance in the model. Placing them straight and have the propellors counter rotate to remove the tendency to “turn left” seems like a no-brainer.
Two smaller issues are the non-symmetrical wings and horizontal stabilizer. As you may have noticed, the wing and stabilizer are not the same on the left and right side. The difference is not big, but it is there. Again, this would not fly well on a model, hence on the model both sides of stabilizer and wing will be symmetrical.
But the biggest worry is the main wing. Or rather the wing load. The total wing area is approximately 100 dm2 when designed to scale. To get a realistic flight experience the wing load should be as low as possible. If build as lightly as possible, I estimate that the total weight would be around 6-7kg mark. That gives a wing load of 60..70 gr/dm2. Which is not all that bad, but does not leave much room to the upside. Especially if the landing gear should be fully operational, or when a water load/drop mechanism must be added. A model this size should be able to drop upwards of 1 litre, which would of course add another kg (or more) to the flying weight. Adding these extra’s would easily bring the model to 8-9kg range, and hence a wingload of 80..90 gr/dm2.
It will fly with that wingload, only I would expect that the scale flying impression will be negatively impacted. The rule of thumb is that the stall speed is srq(21 * gr/dm2), which translates for 60gr/dm2 to a stall speed of 35km/h and for 90gr/dm2 a whopping 43km/h. Take-off is of course above the stall speed, and a takeoff at 50 or 60kmh is not really “scale look”. Even 35km/h is pushing the limits of scale feeling.
I am thus contemplating to increase the wing area by 10% to get some “elbow room”. This would mean adding 15 mm to the leading edge and 25mm to the trailing edge of the wing. Adding this area would bring the wing load for an 8kg flying weight back down to approximately 75 gr/dm2 and the stall speed to 40km/h for a fully loaded model.
This would have the added optical advantage that the wings would seem less “flimsy”. Very often when a real plane is build to exact scale, the wings end up looking flimsy, “to thin/small”.
Also, there is room to do this, it would not impact the fuselage very much, and in fact it would be easy to make this reversible. In other words I could start with implementing a scale version, and if it becomes necessary simply upgrade to a larger wing. For this to work, I have to size the fuselage/wing coupling for the slightly larger wing. This should not create any problems.