I used a ryobi 31cc on a 14lb bandito grande. It was a 82"ws and I think the cord was about 15". Comes to about 1200+ sq". The engine flew with a 18x6 master airscrew at about 6700 rpm. At that weight with that engine, it had very lively performance. Not 3d but was a ton of fun for general aerobatics.
Edwin