Gianluca, I have put your numbers through the metric version of spreasheet and get similar result to you. I use servo rotation 40 degrees which gives a servo arm of 0.5cm and a torque requirement of 0.7kgcm, which is tiny. That is very similar to the results I get for my own models. You either have to use a longer horn on the aileron so that you can move the pushrod further out the servo arm, or reduce the travels in your transmitter for example at 30 degrees of servo rotation the servo arm still only needs 0.6cm and torque required goes up to 1.1kgcm. If you can get the aileron horn up from 2.2 to 3.5 it helps a lot.

Harry