BMatthews

There's another issue here as well. If this is to be a purely practical plane to carry a given load to do some job and you want it to do so with the least power used so you can fly for longer then you're far better off to design the model from scratch. Things like what is a good chord to achieve a reasonable reynolds number for the small one will result in a larger chord than you need for the double size. At that point you're better off to increase the chord only slightly and use the higher efficiency of the higher aspect ratio along with the moderate area increase to achieve your increase in efficiency. But as soon as you do this you find you need to alter the fuselage and stabilizer as well. And since you don't want to slavishly copy the internal structure of the smaller model in any event you may as well just given in to the reality of the situation and start afresh.