I'd like to know if Otto's challenger had turbulators on the airfoil (it appears that it did - looking at an old photo) - I've emailed and called - no response. Does anyone out there know?

Thanks

I get the impression he had sheeted the wing but several layers of trim tape to turbulate the wing. True turbulators require a hard difference of about 0.010" on a surface. The stringers on an open frame wing (no LE sheeting) don't qualify.

thanks - that's how it looked to me - why don't stringers qualify?

Because for many cases they don't stick up far enough to trip the airflow into a true turbulent boundry layer.