Indeed; they are built in sheeted foam. Wings are breaking due to poor wood quality combined with low density foam. According to the analysis we made, the cracks begun in the leading edge (yes, leading edge) near the servos bays and once the flutter begun the crack traveled directly to the wing root where the aileron begins. I shall remark that the trailing edge where the aileron is hinged (and this is a design failure) does not continues from one wing to another.
In my opinion, the plane can be good (I can't afirm this since the three flight I saw finished so soon...) but better material shall be used for construction and wing structural design must be revised.