Hi Levanter,
I am the Isabella designer. It is nice to see someone does build the model.
To overcome potential nose heaviness, you could have extended the fuselage length a bit. But I think that a standard 4 cell RC pack far back in the cockpit will be sufficient to get the CoG right.
I deliberately designed the wing spar further back and well below the airfoil outer shape. I am always dissatisfied when the main spar and semi spars protrude into the airfoil. Air does not like to flow around sharp corners. I believe that some US designers favor wings with visible spars and semi spars at the very critical first 30% of the airfoil. By having the big recess the iron on film cannot attach to any spar, thus making the airfoil perfect according to its design specifications. Of course, the airfoil at the middle section between two wing ribs is slightly different from the airfoil exactly on the ribs, but again, I have rather a slightly different airfoil than a sharp edge. The Isabella wing provides a very smooth shape, which air really loves.
Designers in the 30s actually measured and specified the airfoils that were created by the wing covering hanging down between the ribs.
I used the same design methodology also on my glider Carina, which is a very nice flier with a MH30 airfoil.
The Isabella wing gets very strong as soon as iron on film is applied. On the other hand, beefing it up a bit is not a bad idea, if modelers decide to put in some extra power. My Isabella was first powered by a 2S power application and later with an Enya Quicky 09. The plane was not used for aerobatics.
I get lots of requests for bringing Isabella as a CNC kit to the market. In fact my Kadett is a smaller version of Isabella when you compare the wings.
Keep up the good work!
Cheers,
Marco