Hi Gianluca,

either measure your servo's angle of rotation so that you are sure, or try the calculation again with 40 degrees of servo rotation. 40 degrees is fairly normal, 45 degrees is unusual unless you turn up the travel % in the transmitter. That should allow you to move the pushrod a bit further out on the servo arm.
It is not unusual to find that ailerons on the scale jets even at very high speeds only need very low power servos. Without doing proper calculations, people just assume you need very powerful servos. I still prefer to fit a lot more power than the calculation says, since the calculation can not deal with flutter and while a small, low power servo can move the ailerons, I don't want it to be overcome by flutter that a bigger servo could resist.
Harry