SalmonBug,
This is so evident that I didn't mentioned it
I simply wanted to make it clearer about the setup... The more servos you have for a given set of functions (to some extent), the safer you fly, generally speaking. Sorry if it was pointless.
a rudder who can manage the roll control in case of aileron servo failure
I bet you assume your wing has a fairly good amount of dihedral, otherwise rudder seems to have only a marginal outcome on aircraft roll (enough for a controlled crash ? can't say...). To my mind, it is all the more impossible to control the roll of your aircraft with rudder only as your ailerons have gone farther form the neutral position (and are stuck [:@] there). I've never experienced any servo failure [8D], so I can't say more, but I guess they seldom get back to neutral before failing... In a few words, my feeling is that, if you lose both ailerons, be prepared to rekit your aircraft
(or perhaps should I take some piloting lessons
?). What about your rudder equipped / no dihedral Wonder, SalmonBug ?