Patrick,

The airfoil of the YMF is a slightly mocified Clark Y. You are correct, in that the cross section is a little chubby when compared to a true Clark Y. The wing that you are planning on for the aerobatic version won't be scale, since no Waco that I am aware of ever used a symmetrical airfoil. Wonder how one would operate with a Laminar Airflow airfoil?

You can be a Brother too if you wish (a little blatant campaigning there)

Bill, AMA 4720
WACO Brotherhood #1