Trying to make sense of the observation. The fabric folds into the aileron cut out and has been glued to a rib. The 150mm cut runs along the rib and the material covering the wing above the cut has curled. The material is obviously under tension. The rib is sharp. Mechanical flexing of the wing in flight and the sharp edge of the rib will have contributed to the cut. My question above goes to how sensitive fabric is to temperature changes. I recollect a LAME once telling me that putting my homebuilt tube and fabric covered aircraft into the sun would tighten the fabric. The temperature change in the hangar can change from -10 to 20 in a matter of a few hours. A differential of 30 degrees. Over time, could temperature variations contribute to the fabric failure?