Z, most likely the ailerons are lightly built stick and covering and perhaps not able to handle much speed. If you have already experienced a lot of flutter most likely they are are damaged internally with small fractures here and there. I would recommend building new rons and making them much stiffer than stock. That coupled with decent servos and linkages should solve your problems. Also make sure your servo mounts are very solid. All the aboe is useless if your servo mount structure is flimsy.