i put a carbon spar in my zagi, backfilled the hole with foam and "Spackle" (the readymix lightweight polyfiller, then used some x-weave tape in strategic places (refer to yourzagi.com)..., light sand then spray with spray on adhesive 3m77 or carpet adhesive etc, ironed on profilm, start from the centre and work outwards. in retrospect it was a lot of effort for what tunred out to be a dissapointing model, it needs quite a decent wind at my local hill to stay up, and setting it up well is critical. unlike all my other models, it never really behaves itself and goes where its told. i shouldve bought a wing from phoenix model products instead, but at least i dont mind if it hits a tree, fencepost, or if i reverse over it in the car park the Xit is a better wing than the zagi as its all EPP, the zagi only has an EPP leading edge the rest is cheapo polystyrene! Try to build it light, mount the servos quite far forwards and youll need less lead to balance it.