and when going 3cells, maybe use a slightly smaller prop, a 9x4.7. I had something similar with a blade on 2 cells with an AXI 2208/34 , 10x4.7 prop, plane flew barely,
then I decreased the prop size to 9 x 4.7 and the enigine seemed to be much happier. Even on 2 cells the power was much better. On 3 cells it's of the scale.....

Winfried