Originally Posted by PeterVRC
...I decide on 2.5mm ply faces.....
That should be more than enough Pete. Seeing that the entire model is made of the same foam, thinner will have less strength, like the LE of the tailerons at the tip. But the foam does twist, just not enough to be concerned about. So the ply is more than enough added assurance flat slotted or just about any which way to add it.
I don't recall but where did you place the servo arm with respect to the full span of the LEF. I usually add the arm at what ever happens to be the surfaces MAC. Since it tapers the horn mounted a 3rd of the span from the root. Yours may be different since its a few inches short of the full span but you likely know what I mean.
Any new numbers on the CS70/12? Motor/Batt/Amps/thrust/RPM/Efflux.... Been meaning to ask Mark/ExtremeRC what he thinks of them. My guess is they are optimized for thrust not speed with similar drive trains applied.