I've tried to search for this information on here but the results I get back are largely irrelevant so I apologize in advance if this has already been discussed.

I'm just wondering what the effects are on a plane if the CG is too far forward or if the CG is too far back...

I recently lost a GWS plane to "porpoising" even though I had checked all of the recommended specs for servo center, throw and CG.

It would just continually climb up then dive in a cycle that got increasingly more severe until it finally head-butted the ground.

Any info is appreciated.