There have been several threads here recently about small 1/2A models for sport and/or training. One that caught my eye many years ago and still want to build for a yet too young grandson to fly is a thing called the Dainty Dolphin, October 1959, American Modeler. 20 inch wing span, 100 square inches. Plans show a McCoy Diesel, but any of the Wasp, Hornet, Atwood and Cox engines would do. I would think even a Cox .020 Baby Bee would work for a very docile airplane. It is so homely, it is almost cute.
Keith