Angus, thanks for your post! Now we have a confirmation that even on modern pattern differrentials are still needed to reach good roll capabilities.

Just for curiosity, how much do you use on your Sinergy?

These day I'm thinking again and again to the problem, and I have noticed an intersting thing that someone in the thread has mis-understood. That is: both on airplanes with top wing and on airplanes with low wing aileron differentials are needed in the same direction (I mean, less downward than upward). Interesting!

The only case where differentials are needed in opposite direction (more down than up) seems to be the top-hinge aileron case...

To me this thought seems to go against the thesis of wing-thrust line difference: in fact, in top-wing planes the wing is in the top of propeller wash, in low-wing planes the wash goes on the top of the wing... so it seems that this explaination is also wrong???

Thank you all for your replies... but it seems we need an aero expert here! Several days ago I posted the question to George Hicks, on his forum... but it seems George is away from a computer!!! I will post a message in case of a reply...