Elad:

Common measure is wing area to displacement. Haven't bothered to plot it, but an 0.049 wants about 250 sq", going up to a 0.60 arount 800, a 1.20 goes well at 1200 sq" area, and so forth. This is just a rough guide, nothing set in stone. A 1/2A racer might have only 120-140 sq' while the BTE "Super Flying King" has two square miles of wing area and a 2.3 cubic inch engine recommended. Two miles? Well, maybe a slight exaggeration, but it's huge.

Whatever sort of plane you want. look at kit and ARF planes of the sort you want for the engine size you want to use, this will give you numbers to start from.

Bill.