Ok.. so I had my instructor take (or try to take up) my Gremlin today. It balances properly at 1.7" back from the LE (upside down, tank empty). I've got a Fox .29RC with a 9x4 Master Airscrew prop.

I launched it underhand, it travelled three or so meters and then nosed down into the grass at about a 30-40 degree angle. Twice. Breaking props both times.

I'm at a loss as to why. I set the elevons to 3/8" travel up and down. With this sort of behavior, is it likely that the CoG is too far forward? Or maybe I don't have enough elevator travel. Or maybe my motor is too puny?

thanks for any help,
Stefan