https://github.com/ptrbortolotti/SONATA/blob/9f037d7dd78ea9b19698596f828138cae99da539/SONATA/classAirfoil.py#L197-L216
This interpolation approach of airfoils can result in non-monotonic thickness across the length of the blade (especially transitioning from circle sections at the root to airfoils). Would recommend defining interpolated airfoil coordinates at every section of interest in input yaml file to ensure that interpolation does not cause weird behavior.