I balanced the model at 5.5" just inside were the wing and fairing join. I used a Great Planes CG Machine. The fact that I had to add so much weight does not surprise me since the RCS 140 is the lightest gas engines I know of. I will however recheck the balance before I remove any weight and will inform you here.

I do have an OS 160 twin 4 stroke which I used on an 84" ARF Spacewalker. The model weighted around 11 lbs and was nicely powered, maybe somewhat overpowered but not enought to make me think that a model of almost twice the weight would fly comfortably. However, I have not tried it in the Staggerwing so Dick Pettit's opinion on this should be a more informed one besides the fact that he probably has build 10 times more airplanes than I have.