Do you believe in "dirty" surface on a HLG wing by painting balsa wood instead of covering? Does it really save lift?

From : Don Stackhouse

Matthieu, the rough surface acts as a turbulator. Certain airfoils can benefit from turbulation of the boundary layer, particularly some of the older airfoils. Most of the newer airfoils have been designed to work fine without turbulation, although at hand-launch Reynolds numbers it's difficult in many cases to get the boundary layer to stay turbulent once it's been turbulated. In general, turbulation will improve the airfoils resistance to separation, but the extra drag exacts a small skin friction penalty for airfoils that are already sufficiently separation resistant. The benefits can be substantial for airfoils that need the extra energy in the boundary layer. The penalties are small (but not zero) for airfoils that don't need it. The net result you get will depend on your specific model and the way that you fly it.

Soartech 8 is a good place to start if you would like to study the issue of turbulation in more detail.

If one answer worked for all cases, our models would all look alike!

Don Stackhouse
DJ Aerotech