Bruce, 19% would be "terribly thick" for a model of a P-51, but not for a model of Burnelli's X-plane from the 1930s.

The Ford trimotor had a rather thick section, as did the inspiration for it, made by Fokker.

Have you noticed the section on some of the new 3-D ARFs? Very thick, symmetrical and teardrop shaped. I was taught that reflex should be up only, otherwise you get more drag without the benefit of increased stability.

Ah, airfoil theory, the sweet mystery of flight.
:spinnyeye