RE: Low Wing Skimmer 400 w/not fly
The plane was most certainly stalling, probably from that near-irresistable urge to pull back desperately on the elevator stick when the plane is underpowered and/or isn't ready to fly. Chant to yourself, "The elevator is not the magic up stick! The elevator is not the magic up stick!" A plane needs power and airspeed to climb; up elevator bleeds off airspeed and consumes power. If you don't have enough of one or the other, or both, up elevator makes the plane go DOWN.
You definitely need more power. Heed Dr. Kiwi's words on this issue. More cells is like putting a bigger displacement engine in a car.