I THOUGHT the instruction manual said where the CG is suposed to be. If not, however, 1/3 of the way back from the leading edge f the wing is usually a pretty safe typical 'starting point' for nearly anything that flies.

In either case, if the plane still wants to nose dive, WHEREVER it's currently balanced is likely too far back, and should be moved foreward, which is done by moving the weight back a bit...ether by moving the battery back (I know they don't have much room, but do what you can) or by adding a bit of weight to the tail section.

As for landing quickly, in my experience these birds tend to drop pretty quickly when power is removed...one caution though...if there's much wind at all (a stiff breeze will do it) when you point the aircraft into the wind to land, it WILL tend to float for a while.