Thought I would share a little trick I came up with to quickly and accurately test for CG on Foam Planes during Pre-Flight checks and initial setup up.
I measure back from leading edge on the wing on the underside after the plane is assembled very close to fuselage and mark it with a felt tip marker.
Than I take to Daisy or Crossman BB's and push them into the foam on the Marks I made the CG with until they are about half way sunk into the foam wing. Pop them out, put a drop of glue in the indentation and put the BB's back in for permanent balance point.
It makes a No Brainer CG check that only requires FEEL with your fingers. Want to get really accurate? Drill a indentation in the BB's and use a couple of nails to balance on and fine tune with battery position or lead tape if needed.