Hi Julien,
Having instructed in Diamond aircraft for years, I think they are in that location for three purposes. They offer some buffet over the aileron for pilot's stall indicator purposes. They guarantee aileron effectiveness right up to the stall by converting a laminar boundary layer into a turbulent boundary layer. They modify the spin characteristics of the aircraft to make it still a good spinner, but consistent and safely so.
Cheers, O8
Last edited by Oktas8; 12th Nov 2012 at 07:22.