Hello Oistein,
Hello All,

I have only a little data, from watching airplanes that whistle with aileron deflection, but I think we can gather a better picture, here.
These planes generally feel like they need different amounts of aileron differential depending on whether they are loaded in positive G, negative G, or in a vertical, right?
The amount of aileron throw that is being used matters too, right?
I have also heard some say that there are differences in vertical up and down lines, right?
I suspect that there may be a pitch trim difference between the up and down lines that really makes this the difference between positively loaded, and truly unloaded.

Can you correlate the change in behaviour to the presence, or lack, of an audible whistle?
That sound energy has to come from somewhere, and it must come from the creation of drag.
It is, as you say, a non-linear effect.
An internal wiper seal may solve the issue.

best regards,
Dean Pappas