On Wednesday, 26 October 2016 21:20:09 UTC+3, Eric Greenwell wrote:
Schleicher uses two layers of zig-zag tape just in front of the NACA
inlets that pressurize the control surface blowholes. A single layer is
not thick enough to trip the laminar flow that far back on the airfoil.

Ok. Blow holes seems amazingly expensive and complicated construction when compared to simple tape. I have very hard time believing that Waibel, Heide et al. did this without any benefits. I have to confess that I have more believe in their collective aerodynamic wisdom than this groups', no doubt impressive it might also be.