[dr_lew]

Indeed. I once got into a discussion with someone who challenged by assertion that I could build a plane with NO airfoil at all, just a plank with an angle of attack of about 55 and it would fly.

This is a contradiction in terms, since "a plank with an angle of attack of about 55" is no other thing than an airfoil, however inefficient.

[John Valentine]

Dr. Lew, not to quibble, but an “airfoil” is presumed to have one of a number of quintessentially teardrop, although not necessarily symmetrical, shape. A catalog (obviously incomplete) of such shapes was once published as “Theory of Wing Sections - Including a Summary of Airfoil Data”. (Dover, 1949)

Nowhere in this volume is a rectangular or “plank” section described or presented as an airfoil, nor was data thought to be important enough to publish.

You may be alone as describing a “plank” section as an airfoil and I may be alone (although I suspect that I am not) in proving that it can function as one.