I am in the process of designing a wing for a 4M scale Schweizer 1-35. I need some advice in the airfoil selection for this sailplane. The AR is 20 and the wing has a taper ratio of .43. I've calculated the Re at root is approx 300K+, midwing is 150K-200K, and the tip is around 100K. For the approximate weight of this sailplane model, the CL is 0.4 at normal crusing speed. I've chosen the airfoils for the root and midwing section but still perplexed of how to select the tip airfoil. The family of airfoils is the HQ in which the root is HQ3512 and the mid wing is HQ3012. However, the HQ drag polars do not look very good at low Re's.

Through literature search, I found that some German scale sailplanes use high Clmax airfoils the tips. Tip airfoils have greater t/c than even at the root. I think this aids handling, turning for such large models especially closer to the ground. Scale flying characteristics seem to be the drivers rather than pure efficiency. I also looked at the Algea 3M wing. The tip airfoil has lower lower drag than the root at low Re but it also has lower Clmax. This is opposite to the scale saiplane in which this design seeks for the ultimate thermalling efficiency.

The rationale for low drag polar is high AR wing has high skin friction drag thus the airfoils should be optimized along the span. However, high AR wing can be proned to tip stalling in high bank turns. Therefore, high Clmax airfoil should be used in the tip section with the expense in additional drag.

The question is should I choose a tip airfoil for the low Re drag polar characteristic or should I choose to go with high Clmax? How should I resolve this compromise? Thanks.